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习题练习:newnewnewnew



 作者: admin发布日期: 2024-10-29 15:04   总分: 109分  得分: _____________

答题人: 匿名未登录  开始时间: 10月29日 15:04  切换到: 整卷模式

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1#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Why does a child in a wagon seem to fall backward 0a/s5p; n rnktwhen you give the wagon a sharp pull for;/a 50nrpknt sward?
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2#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A box rests on the (frictionless) bed of a truck.kh.mkt2+v0iem 4rx ,w The truck driver starts the truck and accelerates forward. The box immediately starts to slide toward the rear of the truck bed. Discuss the motion of the box, in terms of Newton’s laws, as seen (a) by Mary standing on the ground beside the truck and (b) by Chris khir42, mt.e+kvmxw0who is riding on the truck


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3#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If the acceleration of an object is zero, are no forces acting on it? Expl ad4 vf3hx)b;0-g-ek9th)ciqn 8f uixain.
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4#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Only one force acts on an object.00 id8m +,fl4axldy xo(b-met Can the object have zero acceleration? Can it have zero veloc0x4e b- md+,iyo 0amfx8 ld(tlity? Explain.
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5#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When a golf ball is dropped to the pavement, iq,jc, zby,xr +emh :q,w8wpb3t bounces back up. (a) Is a force needed to mr y: ,+bq, ch,e3xwjbw8 ,mqpzake it bounce back up? (b) If so, what exerts the force?
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6#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If you walk along a log floating on a+pso6ol gv; h3ys.1ei lake, why does the log move in the opposite direcvso ; lipy h.+e1s6g3otion?
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7#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Why might your foot hurt if y wo r kh+f+ k4)7xbs4qiljw3eq2.p(c jou kick a heavy desk or a wall?
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8#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  When you are running and want to stop quickly, you must0x)dydbe 7l 92 ,iumne decelerate quickly. (a) What is the origin of the force that causes you to stop? (b) Estimad2m0yi ede n7)b,9l uxte (using your own experience) the maximum rate of deceleration of a person running at top speed to come to rest.    m/s$^2$

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9#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A stone hangs by a fine thread from the ceiling, and a s lbdv;is /x6t8ection of the same thread dangles from the bottom of the stone (Fig. 4–36). If a pxt8dil/v b;6serson gives a sharp pull on the dangling thread, where is the thread likely to break: below the stone or above it? What if the person gives a slow and steady pull? Explain your answers.

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10#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
The force of gravity on a 2-kg 2gb8xh zd kh0 a/jw9ll -5)wulrock is twice as great as that on a 1-kg rock. Why then doesn’t jx u 0h8la /2l)-lzhkdwg9w5 bthe heavier rock fall faster?
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11#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Would a spring scale carried to the Moon give accurate results if thejj1 r 8aauyxwl80.)q c scale had urlajwy)8 0cja.x1 8 qbeen calibrated (a) in pounds, or (b) in kilograms?
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12#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
You pull a box with a constant force across a fricey(+pm2nte;sig *zu7 tionless table using an attached rope held horizontally. If you now pull the rope with the same f ieg;usy+emz*n 7(p2t orce at an angle to the horizontal (with the box remaining flat on the table), does the acceleration of the box (a) remain the same, (b) increase, or (c) decrease? Explain.
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13#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When an object falls freely under the influence of gravity there i n :g xro.;knvaz3:0lks a net force mg exerted on it by the Earth. Yet by Newton’s third law the object exerts an equal and opposite force on the Earth. Wrvlnn0g;a.zok3 :x: k hy doesn’t the Earth move?
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14#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Compare the effort (or fc2* e1gd ;s8bma-sz;w er(c( mr5 imjuorce) needed to lift a 10-kg object when you are on the Moon with the force needed to lift it on Earth. Compare the fo5 rdezj(b;e*s as-81i2wu c (cm; rmmgrce needed to throw a 2-kg object horizontally with a given speed on the Moon and on Earth.
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15#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
According to Newton’s third law, each n;hx9 asgw. 09kl s v-dlg+z./0vnigqteam in a tug of war (Fig. 4–37) pulls with equal force on the other team. What, then, determines which team will win dgz;ixq.gvk /a . h0l gl+n9sn0-swv9?
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16#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A person exerts an upward force of 4iwk2) g hzwudd .:mn040 N to hold a bag of groceries. Describe the “reaction” force (Newton’s thirdu 0 knd4)dh .g2:wziwm law) by stating (a) its magnitude, (b) its direction, (c) on what object it is exerted, and (d) by what object it is exerted.
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17#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When you stand still on th9m9/dtt/1d 74uhnhq qnaki9uy ) nes +e ground, how large a force does the ground exert on you? Why doesn’t u q+7h99kn/4q9dsueytn/ d1 )t mah nithis force make you rise up into the air?
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18#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Whiplash sometimes results f33:ilfmm f iqr1fgh 4w87um4kus+ wm3rom an automobile accident when the victim’s car is struck violently from the rear. Explain why the head of the vic r4kum+ufm1l33s4g3qm fwi 8ih7w: mftim seems to be thrown backward in this situation. Is it really?
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19#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A heavy crate rests on the bed of a /w3/bda rzco(ht89 dzflatbed truck. When the truck accelerates, the crate remains wher/3 w/r aodc9bz8z hd(te it is on the truck, so it, too, accelerates. What force causes the crate to accelerate?
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20#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A block is given a push so that it slide 5,wwd:yackx gj+f7 7as up a ramp. After the block reaches its highest point, it slides back down but 7caf+xa djwg:y w 57,kthe magnitude of its acceleration is less on the descent than on the ascent. Why?
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21#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
What would your bathroom scale read if you weighed yourseeupft; z ly 2h5hp81l)lf on an inclined plane? Assume the mechanil1)thu5f8 y2h le;pz psm functions properly, even at an angle.
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22#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What force is needed to acn(v8cq c il/jl75 npc3celerate a child on a sled at 1.25m/s$^2$?   

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23#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A net force of 265 N accelerates a bikee8pa8:m* ot(i i6lt,hd,g tp a and rider at 2.30$ \mathrm{~m} / \mathrm{s}^{2}$ . What is the mass of the bike and rider together?   

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24#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  How much tension must a rope withstand0q*yg cb 6exk84ot ln0 if it is used to accelerate a 960$-\mathrm{kg} $ car horizontally along a frictionless surface at 1.20 $\mathrm{~m} / \mathrm{s}^{2}$ ?   

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25#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the weight of atkzy4a sc 15+r)zrld0xj k6 4s $76-\mathrm{kg}$ astronaut
(a) on Earth,   
(b) on the Moon $\left(g=1.7 \mathrm{~m} / \mathrm{s}^{2}\right)$ ,   
(c) on Mars $\left(g=3.7 \mathrm{~m} / \mathrm{s}^{2}\right)$,   
(d) in outer space traveling with constant velocity?   

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26#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 20.0-$\mathrm{kg}$ box rests on a table. (a) What is the weight of the box and the normal force acting on it?   
(b) A 10.0-$\mathrm{kg}$ box is placed on top of the 20.0-$\mathrm{kg}$ box, as shown in Fig. 4-38. Determine the normal force that the table exerts on the 20.0-$\mathrm{kg}$ box    and the normal force that the 20.0-$\mathrm{kg}$ box exerts on the 10.0-$\mathrm{kg}$ box.   



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27#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What average force is required to stop an 1e oubo/xby(qdak l55hv*y ,05100-kg car in 8.0 s if the car is traveling at 95km/hu /okbbqhvd0(l*y5 e ,y5a5ox ? -  

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28#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What average force is needed to accelerate a 7.00-gram pellet frmg4uov-zbo9o ,15 yozem,gl,om rest to 125m/s over a distance of 04om9g5byez ,l1 omug,oov-,z .800 m along the barrel of a rifle?   

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29#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A fisherman yanks a fish vertically out of the water with an ac(fcaf- 2he673r+( r3 6ukqfnnfmryd aceleration of 2.5 en-fuyn 2k dafrfr+h63(3 a76c(mrf q $\mathrm{~m} / \mathrm{s}^{2}$ using very light fishing line that has a breaking strength of 22 N . The fisherman unfortunately loses the fish as the line snaps. What can you say about the mass of the fish?
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30#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 0.140$-\mathrm{kg}$ baseball traveling 35.0 $\mathrm{~m} / \mathrm{s}$ strikes the catcher's mitt, which, in bringing the ball to rest, recoils backward 11.0 cm . What was the average force applied by the ball on the glove? -  

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31#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  How much tension musta rope withstand if it is used to accelerate a 1200-kg car vertically upward at0.8m/s$^2 ?   

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32#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A particular race car can cover a d ydf t-yy*x4+ n uw+2zjysg2u-a)b4k26peei quarter-mile track (402 $\mathrm{~m}$) in 6.40 s starting from a standstill. Assuming the acceleration is constant, how many " g 's" does the driver experience?    If the combined mass of the driver and race car is 485 kg , what horizontal force must the road exert on the tires?   

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33#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 12.0$-\mathrm{kg}$ bucket is lowered vertically by a rope in which there is 163 N of tension at a given instant.
What is the acceleration of the bucket? Is it up or down?     

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34#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An elevator (mass 4850 kg ) is to be designed so that thes 0.uyrh)e95gxq.c ksoc e59 g maximum acceleration is 0.0680 g . What are the maximum and minimum forces the motor should exert on the supp e50.gxkcs u y. shc9o)rge95qorting cable? max =    min =   

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35#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A 75$-\mathrm{kg}$ petty thief wants to escape from a third-story jail window. Unfortunately, a makeshift rope made of sheets tied together can support a mass of only 58 kg . How might the thief use this "rope" to escape? Give a quantitative answer.
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36#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A person stands on a bathrgf*9yogy 2djv h9sv 2z(.ysp.oom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.75 of the person’s regular weight. Calculate the acceleration of the yg9hys( 2ovjfvs9y..zg 2d*p elevator, and find the direction of acceleration.     

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37#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The cable supporting a 2125-k7qk7b;.n0uc w m dhc)hg elevator has a maximum strength of 21,750 N. What maximum upward acc0h knmq )c;77dhw. buceleration can it give the elevator without breaking?    ( two decimal places)

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38#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  (a) What is the acceleration of two falling sky divers (mass 132 kg inclunh(wa,tqk8b ,*z+fpf5m v g,wding parachute) when the upward force of air resistance is equal to one-fourth of their we, f(wfk8* +n,atwhqmz,gv bp5 ight?   
(b) After popping open the parachute, the divers descend leisurely to the ground at constant speed. What now is the force of air resistance on the sky divers and their parachute?    See Fig. 4–39.


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39#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A person jumps from the roof of a house 3.9-m high. When he strikes cw1x7pjm 093 y3i 1ffkp 1fkycthe ground below, he bends his knees so that his torso decelerates over an approximai0x3 y9wcp1f13f fjmpckky1 7 te distance of 0.70 m. If the mass of his torso (excluding legs) is 42 kg, find
(a) his velocity just before his feet strike the ground, and   
(b) the average force exerted on his torso by his legs during deceleration.   

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40#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A box weighing 77.0 N rests on a table. A aw(che7rf7:n rope tied to the box runs vertically upward over a pulley and a weight is hung from the other end (Fig. 4-40). Determine the force that the table exerts on the box if the weight hanging on the other si:7 wc re7fah(nde of the pulley weighs
(a) 30.0 N ,   
(b) 60.0 N ,   
(c) 90.0 N .   

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41#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Draw the free-body d2gwcfhk ) 1ov3pt4jj rm45q ,iiz a0*biagram for a basketball player
(a) just before leaving the ground on a jump, and
(b) while in the air. See Fig. 4–41.
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42#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Sketch the free-body diagram of a baseball (a) at the moment it is hitw tq 4egs6xai dv(fccng*8z,7ty t3u 6dl-d* + by the bat, and again (b) after it has dg8g-*d,*aicfw (zt+3tyc 6 udnqse xtl7v 46left the bat and is flying toward the outfield.
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43#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A 650-N force acts in a northwesterly direction. A sc lx w2bqt2:- u.fd 6(mfe4wkwecond 650-N force must be exerted in what direction so that the resultant of the two forces points westw .mcw txufe(:kbldw2 f2-6wq4 ard? Illustrate your answer with a vector diagram.
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44#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Arlene is to walk across a "high wire" strung horizont (ea5j-w 1w1fwq,tuszally between two buildings 10.0 m apart. The 1(1 uaw,-wqwt jzfs5esag in the rope when she is at the midpoint is 10.0$^{\circ}$ as shown in Fig. 4-42 . If her mass is 50.0 kg , what is the tension in the rope at this point?   



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45#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The two forces $\overrightarrow{\mathbf{F}}_{1}$ and $\overrightarrow{\mathbf{F}}_{2}$ shown in Fig. 4-43 $\mathrm{a}$ and b (looking down) act on a 27.0$-\mathrm{kg}$ object on a frictionless tabletop. If $ F_{1}=10.2 \mathrm{~N}$ and $ F_{2}=16.0 \mathrm{~N}$ , find the net force on the object and its acceleration for (a) and (b). (a) a =    at    $^{\circ}$;(b) a =    at    $^{\circ}$



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46#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  One 3.2-kg paint bucket is hanging by a massless cowl(f0xy*j +k8dkppzxy7 x8-vsf ebp;t +y q* 3rd from another 3.2$-\mathrm{kg}$ paint bucket, also hanging by a massless cord, as shown in Fig. 4-44.
(a) If the buckets are at rest, what is the tension in each cord? F1 =    F2 =    (The top rope is F1 and the bottom rope is F2)
(b) If the two buckets are pulled upward with an acceleration of 1.60 $\mathrm{~m} / \mathrm{s}^{2}$ by the upper cord, calculate the tension in each cord. F1 =    F2 =   




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47#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A person pushes a 14. sd+tv:mx*hm-0$-\mathrm{kg}$ lawn mower at constant speed with a force of F=88.0 $\mathrm{~N}$ directed along the handle, which is at an angle of 45.0$^{\circ} $ to the horizontal (Fig. 4-45).
(a) Draw the free-body diagram showing all forces acting on the mower. Calculate
(b) the horizontal friction force on the mower,   
(c) the normal force exerted vertically upward on the mower by the ground.   
(d) What force must the person exert on the lawn mower to accelerate it from rest to 1.5 $\mathrm{~m} / \mathrm{s} $ in 2.5 seconds, assuming the same friction force?   



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48#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Two snowcats tow a housing unit to a new loca, i9)/,i umfz gnyz)eation at McMurdo Base, Antarctica, as shown in Fig. 4-46. The n)9f/ izai,,m) yuezgsum of the forces $\overrightarrow{\mathbf{F}}_{\mathrm{A}}$ and $\overrightarrow{\mathbf{F}}_{\mathrm{B}} $ exerted on the unit by the horizontal cables is parallel to the line L , and $ F_{\mathrm{A}}=4500 \mathrm{~N} $. Determine $ F_{\mathrm{B}}$ and the magnitude of $ \overrightarrow{\mathbf{F}}_{\mathrm{A}}+\overrightarrow{\mathbf{F}}_{\mathrm{B}}$ .$F_B$ =    $\overrightarrow{\mathbf{F}}_{\mathrm{A}}+\overrightarrow{\mathbf{F}}_{\mathrm{B}}$ =   


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49#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A train locomotive is pulling two cars of the same mass behind it, f3p-.h c 8.tzdr s ;-o8 j2/blsdiealrFig. 4-47 . Determine the ratio of thea2 hdzrei d obj8 .c;8r-.tfpls l-3s/ tension in the coupling between the locomotive and the first car $\left(F_{\mathrm{T} 1}\right)$ , to that between the first car and the second car $\left(F_{\mathrm{T} 2}\right)$ , for any nonzero acceleration of the train.

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50#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A window washer pulls herselfy4,g+epen gmmf* 5.8iez xl7 b upward using the bucket-pulley apparatus shown in Fig. 4-48. (a) How hard must sg4z,+ie b8ye7lxf5penm*m. ghe pull downward to raise herself slowly at constant speed?   
(b) If she increases this force by 15 % , what will her acceleration be? The mass of the person plus the bucket is 65 kg .   




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51#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  At the instant a race 4r f i9xs z;ah * 51fwdotb9p6x9lq/lnbegan, a 65$-\mathrm{kg}$ sprinter exerted a force of 720 N on the starting block at a 22$^{\circ}$ angle with respect to the ground. (a) What was the horizontal acceleration of the sprinter?    (Keep one decimal place)
(b) If the force was exerted for 0.32 s , with what speed did the sprinter leave the starting block?    (Keep one decimal place)

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52#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Figure 4-49 shows a blot3-j7we:c vebb k.mtj54 c 5ynck (mass $ m_{1}$ ) on a smooth horizontal surface, connected by a thin cord that passes over a pulley to a second block $\left(m_{2}\right)$ , which hangs vertically. (a) Draw a free-body diagram for each block, showing the force of gravity on each, the force (tension) exerted by the cord, and any normal force. (b) Apply Newton's second law to find formulas for the acceleration of the system and for the tension in the cord. Ignore friction and the masses of the pulley and cord.
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53#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Three blocks on a frictionless horizontal surface are in contact with et0mz 7axwk+q 1ach other, as shown in Fig. 4-51. A kt 7qz0mwa x1+force $\overrightarrow{\mathbf{F}}$ is applied to block 1 (mass .$m_{1}$) .
(a) Draw a free-body diagram for each block. Determine
(b) the acceleration of the system (in terms of $m_{1}$, $m_{2}$ , and $ m_{3}$ ),
(c) the net force on each block,
(d) the force of contact that each block exerts on its neighbor.
(e) If $m_{1}=m_{2}=m_{3}=12.0 \mathrm{~kg}$ and $ F=96.0 \mathrm{~N}$ , give numerical answers to (b),(c) , and (d) . Do your answers make sense intuitively?

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54#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The two masses shown in Fig. 4-52 are each initially 1.8/1qmne5 ir)(sj lmr7n0 m above the ground, and the massless frictionless pulley is 4.8 m above the ground. What maximum height does the lighter object reach after the sysn rs)(j 1imlmqer5/n 7tem is released? [Hint: First determine the acceleration of the lighter mass and then its velocity at the moment the heavier one hits the ground. This is its "launch" speed. Assume it doesn't hit the pulley.]   





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55#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Suppose two boxes on o8bk) usoi)ba- 0;c9fh v;pyx+v1o he a frictionless table are connected by a heavy cord of mass 1.0 kg . Calculah0po +vu;xo-8y) );caik bhe1 sfvo 9bte the acceleration of each box and the tension at each end of the cord, using the free-body diagrams shown in Fig. 4-53. Assume $F_{\mathrm{P}}=40.0 \mathrm{~N}$ , and ignore sagging of the cord. Compare your results to Example 4-12 and Fig. 4-22.
(4-53)
(4-22)
(4-12)
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56#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If the coefficient of kinetic fritph8/h3tpsz6sia8 6h ction between a 35$-\mathrm{kg}$ crate and the floor is 0.30 , what horizontal force is required to move the crate at a steady speed across the floor? What horizontal force is required if $\mu_{\mathrm{k}}$ is zero?
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57#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A force of 48.0 N is required to 28cr )gj +zyll)5 al++xyo0dhcsp l 9estart a 5.0$-\mathrm{kg}$ box moving across a horizontal concrete floor. (a) What is the coefficient of static friction between the box and the floor?   
(b) If the 48.0$-\mathrm{N}$ force continues, the box accelerates at 0.70$ \mathrm{~m} / \mathrm{s}^{2}$ . What is the coefficient of kinetic friction?   

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58#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Suppose that you are standing on a train zsrf9mz6;dh7y8pnf ) vyx8 4oaccelerating at 0.20g. What minimum coefficient of static friction must exist between yof dhz zp 6n);om8svf48y7xy9r ur feet and the floor if you are not to slide?   

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59#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the maximum acceleration a car can undergo if the coefficientk90 tv .su 5u ayabnowb93r35m of static fricysumbn5b.5t 933a9v oa rk0u wtion between the tires and the ground is 0.80?   

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60#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The coefficient of static friction between hard rubber a1r9qnw.sfxx0so2 u )ma rxu/0nd normal street pavement is about 0.8. On how steep a ho 1fw.n0rmuu a2)x 0sq/9 rxxsill (maximum angle) can you leave a car parked?   $^{/circ}$

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61#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 15.0$-\mathrm{kg}$ box is released on a 32$^{\circ}$ incline and accelerates down the incline at 0.30 $\mathrm{~m} / \mathrm{s}^{2}$ . Find the friction force impeding its motion.    What is the coefficient of kinetic friction?   

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62#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A car can decelerate at -- eqr*e. iayvxcr0qgjq;a7a/jfr8.:3 qu 0wr 4.80 $\mathrm{~m} / \mathrm{s}^{2}$ without skidding when coming to rest on a level road. What would its deceleration be if the road were inclined at 13$^{\circ} $ uphill? Assume the same static friction coefficient.   

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63#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
(a) A box sits at rest on a rough9tiwb 8f9q3gy 30$^{\circ}$ inclined plane. Draw the free-body diagram, showing all the forces acting on the box.
(b) How would the diagram change if the box were sliding down the plane?
(c) How would it change if the box were sliding up the plane after an initial shove?
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64#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Drag-race tires in contact with an asphalt surface hz 94w6okp03 sqi)zxu om7fg1ag,n*orave a very high coefficient ofusi1o9gro)g7z fqwa* m kpn0 3ox4z 6, static friction.

Assuming a constant acceleration and no slipping of tires, estimate the coefficient of static friction needed for a drag racer to cover 1.0 km in 12 s , starting from rest.   

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65#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The coefficient of kinetic fricti3rkmj 6 n3-ftkvoi: 9ron for a $ 22-\mathrm{kg}$ bobsled on a track is 0.10 . What force is required to push it down a $6.0^{\circ}$ incline and achieve a speed of 60 $\mathrm{~km} / \mathrm{h}$ at the end of 75 m ?   

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66#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  For the system of Fig. 4-32 (Example 4-20) kt 9th (uv)ri0how large a mass would box A have to have to preru0)tkiv (ht 9vent any motion from occurring? Assume $\mu_{\mathrm{s}}=0.30$ .   




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67#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A box is given a push so that it slides across k*wth5nhr: o2l c9it4the floor. How far will it go, given that the coefficient of kinetic friction is 0.20 and the push imparts an initial speed ofcot k 4w*h2n l5h9i:tr 4.0 $\mathrm{~m} / \mathrm{s}$ ?   

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68#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Two crates, of mass 75 kg and 110 kg , a.e/h+ piz.cn8m iiqe b )eer;a-aa55n re in contact and at rest on a horizontal surface eec5) mbznn -pr qiaa8ae5 /e;+.ii.h(Fig. 4-54). A 620$-\mathrm{N}$ force is exerted on the 75$-\mathrm{kg}$ crate. If the coefficient of kinetic friction is 0.15 , calculate
(a) the acceleration of the system,   
(b) the force that each crate exerts on the other.   
(c) Repeat with the crates reversed.   

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69#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A flatbed truck is carrying a heavy crate. The coefficient of static frickpa.bz83m4yj tion between the crate and the bed of the truck is 0.75. What is the8bpykm.j4z a 3 maximum rate at which the driver can decelerate and still avoid having the crate slide against the cab of the truck?   

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70#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
On an icy day, you worry about parking your car in your driveway, which has an is -*oi 6bf,fg (uv.toanct( f,bu-ogf*i6vso a.line of 12$^{\circ}$ . Your neighbor's driveway has an incline of 9.0$^{\circ}$ , and the driveway across the street is at 6.0$^{\circ}$ . The coefficient of static friction between tire rubber and ice is 0.15 . Which driveway(s) will be safe to park in?
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71#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A child slides down 4f .b4amoqu9dh.qor) ru r .f+a slide with a 28$^{\circ}$ incline, and at the bottom her speed is precisely half what it would have been if the slide had been frictionless. Calculate the coefficient of kinetic friction between the slide and the child.   

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72#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The carton shown in Fig. 4-55 lies on :u4pqf ayqj:7l n:t( ma plane tilted at an angle $\theta=22.0^{\circ}$ to the horizontal, with $\mu_{\mathrm{k}}=0.12$ . (a) Determine the acceleration of the carton as it slides down the plane.   
(b) If the carton starts from rest 9.30 m up the plane from its base, what will be the carton's speed when it reaches the bottom of the incline?   

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73#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A carton is given an ini5azlms *jpv( 2l uiq)y +sv)8gtial speed of 3.0 $\mathrm{~m} / \mathrm{s}$ up the 22.0$^{\circ}$ plane shown in Fig. 4-55.
(a) How far up the plane will it go?   
(b) How much time elapses before it returns to its starting point? Ignore friction.   


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74#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A roller coaster reache0+y9biew7jgo k7nh mlet +80+af/ hsh s the top of the steepest hill with a speed of 6.0$ \mathrm{~km} / \mathrm{h}$ . It then descends the hill, which is at an average angle of 45$^{\circ}$ and is 45.0 m long. What will its speed be when it reaches the bottom? Assume $\mu_{\mathrm{k}}$=0.18    km/h

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75#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An 18.0$-\mathrm{kg}$ box is released on a 37.0$^{\circ}$ incline and accelerates down the incline at 0.270 $\mathrm{~m} / \mathrm{s}^{2}$ . Find the friction force impeding its motion.    How large is the coefficient of kinetic friction?   

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76#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A small box is held in 5m: dcbt:kqnw5pgu4k*qw 1 f3xm3p4t place against a rough wall by someone pushing on it with a for:5qwp b xf33tk4k*u m:wn dgm1 q4pt5cce directed upward at 28$^{\circ}$ above the horizontal. The coefficients of static and kinetic friction between the box and wall are 0.40 and 0.30 , respectively. The box slides down unless the applied force has magnitude 13
N. What is the mass of the box?   

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77#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Piles of snow on slippery roofs can become dangerous lgulnj rkjvk5r+( 2.2 projectiles as they melt. Consider a chunk of snow at the rivuk +l glr.r225jn(kjdge of a roof with a pitch of $ 30^{\circ}$ .
(a) What is the minimum value of the coefficient of static friction that will keep the snow from sliding down?   
(b) As the snow begins to melt, the coefficient of static friction decreases and the snow eventually slips. Assuming that the distance from the chunk to the edge of the roof is 5.0 m and the coefficient of kinetic friction is 0.20 , calculate the speed of the snow chunk when it slides off the roof.   
(c) If the edge of the roof is 10.0 m above ground, what is the speed of the snow when it hits the ground?   

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78#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
(a) Show that the minimum stopping distance for an automobile traveling at speednhw ala /wt+:vh *j(*a v *a/aahhjw*t :+l ( nvwis equal to $v^{2} / 2 \mu_{\mathrm{s}} g $, where $ \mu_{\mathrm{s}}$ is the coefficient of static friction between the tires and the road, and g is the acceleration of gravity.
(b) What is this distance for a 1200$-\mathrm{kg}$ car traveling 95 $\mathrm{~km} / \mathrm{h}$ if $\mu_{\mathrm{s}}=0.75$ ?
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79#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A coffee cup on the dashboard of a car slides forward on the dash when th -(szxa quud(,e drivera( x( zdquu,s- decelerates from 45 $\mathrm{~km} / \mathrm{h}$ to rest in 3.5 s or less, but not if he decelerates in a longer time. What is the coefficient of static friction between the cup and the dash?   

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80#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A small block of mass m is given an initial c(x96dftenv h*0m v (m.05jiocvi -grspeed $ v_{0} $ up a ramp inclined at angle $\theta $ to the horizontal. It travels a distance d up the ramp and comes to rest. Determine a formula for the coefficient of kinetic friction between block and ramp.
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81#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The $75-\mathrm{kg}$ climber in Fig. 4-56 is supported in the "chimney" by the friction forces exerted on his shoes and back. The static coefficients of friction between his shoes and the wall, and between his back and the wall, are 0.80 and 0.60 , respectively. What is the minimum normal force he must exert? Assume the walls are vertical and that friction forces are both at a maximum. Ignore his grip on the rope.   



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82#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Boxes are moved on a conveyor beltfp arbt).ll;2 from where they are filled to the packing station 11.0 m away. The belt is initially stationary and must finish with zero speed. The most rapid transit is accomplished if the belt accelerates for half the distance, then decelerates for the final hfl;p)rbl2 . atalf of the trip. If the coefficient of static friction between a box and the belt is 0.60, what is the minimum transit time for each box?   

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83#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A block (mass $m_{1}$ ) lying on a frictionless inclined plane is connected to a mass $ m_{2}$ by a massless cord passing over a pulley, as shown in Fig. 4-57. (a) Determine a formula for the acceleration of the system of the two blocks in terms of $ m_{1}$,$ m_{2}$,$ \theta $ and g . (b) What conditions apply to masses $m_{1}$ and $m_{2}$ for the acceleration to be in one direction (say, $m_{1}$ down the plane), or in the opposite direction?

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84#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Suppose the coefficie /, dd ygi+7aadanvhap36f joik02 9g3nt of kinetic friction between $m_{1}$ and the plane in Fig. 4-57 is $ \mu_{\mathrm{k}}=0.15$ , and that $m_{1}=m_{2}=2.7 \mathrm{~kg}$ . As $m_{2}$ moves down, determine the magnitude of the acceleration of $ m_{1}$ and $m_{2}$ , given $\theta=25$ ?   
(b) What smallest value of $\mu_{\mathrm{k}}$ will keep this system from accelerating?   



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85#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A bicyclist of mass 65 kg (including the bicycle) can coas;,egxz+yz1q wqc)t9y t down a 6.0$^{\circ} $ hill at a steady speed of 6.0 $\mathrm{~km} / \mathrm{h}$ because of air resistance. How much force must be applied to climb the hill at the same speed and same air resistance?   

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86#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  According to a simplified model of a mammalian heart, at each pulse appkmzo /;ipc3,h v:mv fmre9p3)h );ynp roximately 20 g of blood is accelerated from 0.2n9vh/3 h cm mp: )y ;zimf;e)ppvrok3,5 $\mathrm{~m} / \mathrm{s}$ to 0.35 $\mathrm{~m} / \mathrm{s}$ during a period of 0.10 s . What is the magnitude of the force exerted by the heart muscle?   

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87#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A person has a reasonable chance of surviving an automobile crassa761).zy5 oyox 31log l coq.lb iq*bh if the deceleration is no mxbgozc*qylo1 7. .1s )6lboyia5q o3 lore than 30 " g 's." Calculate the force on a 70$-\mathrm{kg}$ person undergoing this acceleration. What distance is traveled if the person is brought to rest at this rate from 100 $\mathrm{~km} / \mathrm{h}$ ?   

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88#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If the horizontal acceleration mj6pg 4rfs*jw17hb( al3;a t fproduced by an earthquake is a , and if an object is going to "hold its place" on the ground, show that the coefficient of static friction with the ground must be aj(a3w 6hlm f1gsptr*a 7f j4;bt least $\mu_{\mathrm{s}}=a / g$ . (b) The famous Loma Prieta earthquake that stopped the 1989 World Series produced ground accelerations of up to 4.0 $\mathrm{~m} / \mathrm{s}^{2}$ in the San Francisco Bay Area. Would a chair have started to slide on a linoleum floor with coefficient of static friction 0.25 ?
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89#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An 1150$-\mathrm{kg} $ car pulls a $450-\mathrm{kg} $ trailer. The car exerts a horizontal force of 3.8$ \times 10^{3} \mathrm{~N}$ against the ground in order to accelerate. What force does the car exert on the trailer? Assume an effective friction coefficient of 0.15 for the trailer.   

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90#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Police investigators, examining the scene ofv5tvazw .1u6b an accident involving two cars, measure 72-m-long skid marks of one of the cars, which nearly came to a stop before colliding. The coefficient of kinetic friction between rubber and theta6bvvw. u1z 5 pavement is about 0.80. Estimate the initial speed of that car assuming a level road.   

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91#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A car starts rolling down a 1-in-4 hill (1-i;s x fl+o j 8zw6gdi;t.68pcya vn,qq8n-4 means that for each 4 m traveled along the road, the elevation change is 1 m). How fast is it going when it reaches the bottom after traveling 55 m? (a)s.fjzvo ;yn ga+ l6w t 8dq;c,p88x6qi Ignore friction.   
(b) Assume an effective coefficient of friction equal to 0.10.   

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92#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 2.0-kg purse is dropped from the top of the Leaning Tower of Pisa an+56vunec 7+f xek0)hlmy w 4fmd falls 55 m before reachinmufv0+eh)l5cfxek+ w6 47nym g the ground with a speed of What was the average force of air resistance?   

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93#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A cyclist is coasting at a steady speed of 12m/s but enters a mud1py ls0w+3cd8jwaoivq07jd 8 dy stretch where the effective coefficient of friction is 0.60. Will the cyclist emerge from the muddy stretch without having to pedal if the mud lasts for 11 m? If so, what will be the speed upon emergingjwwo q 1s0pidd8a73 y8lv0j+c ?   

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94#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A city planner is working on the redesigucx bofi1v)) d-k( he5n of a hilly portion of a city. An important consideration is how steep the roads can be so that even low-powered cars can get up the hills without slowing down. A partbvo1dek(5xcfi ) )-huicular small car, with a mass of 1100 kg , can accelerate on a level road from rest to 21$ \mathrm{~m} / \mathrm{s}(75 \mathrm{~km} / \mathrm{h})$ in 14.0 s . Using these data, calculate the maximum steepness of a hill.    $^{\circ}$

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95#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Francesca, who likes physics experiments, dangles her watch from a tq1qq5t ;l1d:8)ok gstr k3 vvhhin piece of string while thed tkhg lt os)5v1 :3;qkqv8rq1 jetliner she is in takes off from JFK Airport (Fig. 4-58). She notices that the string makes an angle of 25$^{\circ}$ with respect to the vertical as the aircraft accelerates for takeoff, which takes about 18 s . Estimate the takeoff speed of the aircraft.   




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96#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 28.0$-\mathrm{kg}$ block is connected to an empty 1.35$-\mathrm{kg}$ bucket by a cord running over a frictionless pulley
(Fig. 4-59). The coefficient of static friction between the table and the block is 0.450 and the coefficient of kinetic friction between the table and the block is 0.320 . Sand is gradually added to the bucket until the system just begins to move. (a) Calculate the mass of sand added to the bucket.   
(b) Calculate the acceleration of the system.   


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97#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  In the design of a supermarket, there are to be severa)z) em+t qu1iul ramps connecting different parts of tuum q)t e)+i1zhe store.
Customers will have to push grocery carts up the ramps and it is obviously desirable that this not be too difficult. The engineer has done a survey and found that almost no one complains if the force directed up the ramp is no more than 20 N . Ignoring friction, at what maximum angle $\theta$ should the ramps be built, assuming a full $30-\mathrm{kg}$ grocery cart?    $^{\circ} $

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98#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
(a) What minimum force F is needed z3:gekfb9dbnh ;cg(3 72rtaato lift the piano (mass M ) using the pulley apparatus shown;h2zgfc3a kt:93d r e(ab gn7b in

Fig. 4-60? (b) Determine the tension in each section of rope: $F_{\mathrm{T} 1}, F_{\mathrm{T} 2}, F_{\mathrm{T} 3} $, and $ F_{\mathrm{T} 4}$ ,


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99#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A jet aircraft is accelerating at 9 nl4ynyh;uf : 3.5 $\mathrm{~m} / \mathrm{s}^{2}$ at an angle of 45$^{\circ} $ above the horizontal. What is the total force that the cockpit seat exerts on the 75$-\mathrm{kg} $ pilot?    N    $^{\circ} $

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100#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  In the design process for a child-restraint chair, an engineer conkg-odrm8y 7b f *;h lkmopz:l767gpj:siders the following set of condit-7mfoz7g p:h6 y:kl kjogml*b 7pd8r; ions:
A 12$-\mathrm{kg}$ child is riding in the chair, which is securely fastened to the seat of an automobile (Fig. 4-
61). Assume the automobile is involved in a head-on collision with another vehicle. The initial speed $v_{0}$ of the car is 45$ \mathrm{~km} / \mathrm{h}$ , and this speed is reduced to zero during the collision time of 0.20 s .

Assume a constant car deceleration during the collision and estimate the net horizontal force F that the straps of the restraint chair must exert on the child in order to keep her fixed to the chair. Treat the child as a particle and state any additional assumptions made during your analysis.   

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101#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 7650$-\mathrm{kg}$ helicopter accelerates upward at 0.80 $\mathrm{~m} / \mathrm{s}^{2}$ while lifting a 1250$-\mathrm{kg}$ frame at a construction site, Fig. 4-62.
(a) What is the lift force exerted by the air on the helicopter rotors?   
(b) What is the tension in the cable (ignore its mass) that connects the frame to the helicopter?   
(c) What force does the cable exert on the helicopter?   



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102#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A new high-speed 12-car Italian train has a mass of 660 metric tons (660,;sispk/: 1lm j000 $\mathrm{~kg}$) . It can exert a maximum force of 400 kN horizontally against the tracks, whereas at maximum velocity ( 300 $\mathrm{~km} / \mathrm{h}$) , it exerts a force of about 150 kN . Calculate (a) its maximum acceleration   
(b) estimate the force of air resistance at top speed.   

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103#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 65$-\mathrm{kg}$ ice skater coasts with no effort for 75 m until she stops. If the coefficient of kinetic friction between her skates and the ice is $\mu_{\mathrm{k}}=0.10$ , how fast was she moving at the start of her coast?   

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104#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Two rock climbers, Bill and Karen, use safety ropes of similar lengthbu8gid t2nq:2 ;opt b;. Karen's rope is more elastic, called a dynamic rope by climbers. Bill has a static rope, not recommended for safety purposes in pro climbing. Karen falls freely about 2.0 m and then the rope stops her over a distance of 1.0 m (Fig. 463). (aq8po2:;bu ; igdnb tt2) Estimate, assuming that the force is constant, how large a force she will feel from the rope. (Express the result in multiples of her weight.) (b) In a similar fall, Bill's rope stretches by 30 cm only. How many times his weight will the rope pull on him? Which climber is more likely to be hurt?
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105#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A fisherman in a boa /m+ gx6 +;+a7qhp nv8ht8xcgsr5r fnst is using a " 10-1 $\mathrm{~b}$ test" fishing line. This means that the line can exert a force of 45 N without breaking (1 $\mathrm{lb}=4.45 \mathrm{~N}$) . (a) How heavy a fish can the fisherman land if he pulls the fish up vertically at constant speed? (b) If he accelerates the fish upward at 2.0 $\mathrm{~m} / \mathrm{s}^{2}$ , what maximum weight fish can he land? (c) Is it possible to land a 15-lb trout on 10-1b test line? Why or why not?
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106#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An elevator in a tall building is allowed to reaco5jj,ydmaq ygp xw a/27 aa(,8h a maximum speed of 3.5 $\mathrm{~m} / \mathrm{s}$ going down. What must the tension be in the cable to stop this elevator over a distance of 2.6 m if the elevator has a mass of 1300 kg including occupants?   

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107#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Two boxes, $m_{1}$=1.0 $\mathrm{~kg}$ with a coefficient of kinetic friction of 0.10 , and $m_{2}=2.0 \mathrm{~kg}$ with a coefficient of 0.20 , are placed on a plane inclined at $ \theta=30$ ?
(a) What acceleration does each box experience? $a_1$ =    $a_2$ =   
(b) If a taut string is connected to the boxes (Fig. 4-64), with $ m_{2}$ initially farther down the slope, what is the acceleration of each box?
(c) If the initial configuration is reversed with $m_{1}$ starting lower with a taut string, what is the acceleration of each box?   





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108#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 75.0$-\mathrm{kg}$ person stands on a scale in an elevator. What does the scale read (in N and in kg ) when the elevator is
(a) at rest,   
(b) ascending at a constant speed of 3.0 $\mathrm{~m} / \mathrm{s}$ ,   
(c) falling at 3.0 $\mathrm{~m} / \mathrm{s}$ ,   
(d) accelerating upward at 3.0 $\mathrm{~m} / \mathrm{s}^{2}$ ,   
(e) accelerating downward at 3.0 $\mathrm{~m} / \mathrm{s}^{2}$ ?   

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109#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Three mountain climbers who are roped tog zej3+x,d +qjt4ueb)sether are ascending an ice field inclined+qe)sbx,j4j+ e3tz du at 21.0$^{\circ}$ to the horizontal. The last climber slips, pulling the second climber off his feet. The first climber is able to hold them both. If each climber has a mass of 75 kg , calculate the tension in each of the two sections of rope between the three climbers. Ignore friction between the ice and the fallen climbers.      

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