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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 backwarc92 atr y33b8x7ndwwf d when you give the wagon a sharp pull forwx b8wra fn73c92t3 dwyard?
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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. Thh0 6g1fkucr ern )4biry )6yhhn):ju+e 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 Chri: rfyhjye bru)nu+cg1i0r6)k) h4n6hs who 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-tjp i6nvl5 ip/2gcn 9 object is zero, are no forces acting on it? Explain.
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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. Can the object have zero acceleration1-d(qblws,(aju ft(h ? Can it have zero velocity? Eh(u atq,lw - (jdf1(bsxplain.
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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, it bounces back up. (a) Is a forfi9st:i75/ fag4hd/ hmfnr*rr) h) tlce needed to make i)ighh45f*s :r da f)hlr/t9t fr/m 7nit 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 floafk )5euszkb ;0 z(g0+mb eq2epting on a lake, why does the log move in the opposite dfe pbq;(k0e520bgzmu+)zs keirection?
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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 you kick a heavy desk or a wa-nkk1k:a 3bj git- ;ghth c9+fll?
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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 quickc/jr7 fqm+hcd iq yb6gs/ w*kn(/w1:a ly, you must decelerate quickly. (a) What is the origin of the force that causes you to stop? (b) Estimate (using your own experience) the maximum rate o*fcwqcj1g b wysdanh6i+ / /mrk7q/(:f 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 froq nsu3s( f:l 0lkv2-wxm the ceiling, and a section of the same thread dangles fn2:3llqf k usw -x(0vsrom the bottom of the stone (Fig. 4–36). If a person 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 rock is twice as great5 ih4pd,5ztw m as that on a 1-kg rock. Why then doesn’t the heavier rpw55t, 4hmdi zock 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 theg( 13wqe 8pn xe/ivdm. scale had beenvq8(m/ix edw 31gen.p 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 forc ;fg3ahkkfxj3 y9/8lbe across a frictionless table using an attached rope held horizontally. If you now pull the rope with the same force at an angle to the horizontal (jay;98h3fg fklx/b 3k 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 iseigch1ij .45ag b(v6j a net force mg exerted on it by the Earth. Yet by Newton’s third law the object exerts an equa6.e j b154ih(cigjv gal and opposite force on the Earth. Why 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 (oc9up /3j-x)gcz),qrsyvek e:r force) needed to lift a 10-kg object when you are on the Moon with the force needed to lift it on Earth. Compare the fq ykc p,:ezvg ujxr-c)e)9 /s3orce 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 team in a tugv2*rd j/sx9ra of war (Fig. 4–37) pulls with equal force on the other team. What, then, determines which td j/ a2vr9*sxream will win?
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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 y4 0ql isg4bv. gb645nrjiq:zforce of 40 N to hold a bag of groceries. Describe the “reaction” force (Newton’s third law) by stating (a) its magnitude, (b) its direction, (c) on v5 bigrnbqsi4gjl:z404y6 q. 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 the ground, how laotg,)u*wlaas, 6j0g nrge a force does the ground exert on you? Why doesn’t this force make you n)atau lg0gs* w ,oj,6rise 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 from an automobile accident when the victim’s car is v:r knr lcs6tw(.svfs(v))v* struck violently from the rear. Explain why the head of the victim seems to ( klsrcr)vn*vss:( 6 . v)fvtwbe 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 flatbed truck. When the truck acceler6d0w) . q,vifehv9 1fk/vf mwwates, the crate remains where it is on the truck,.,0 vvfkw)f/iww1dq hfm 9v6e 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 thacd9 n gwfok-hxci.yz*n0)5u(t it slides up a ramp. After the block reaches its highest point, it slides back down but the magnitude of its acceleration is less on the descent than on the ascent. Whfn5 hi ( xczw.y*nc0u-o9kd )gy?
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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 yourself on an ind5zaf fqc0h;*+ wygf,clined plane? Assume the mechanism functions properly, even at 0 ;cff h5gwqay,*fdz+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 accelerate a c3 vr* i1a21vxdfad2qv hild 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 bike a 0dbi bi;cvv -wy-m ps3fs6s8s 4pb.(tnd 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 withstand if it is u0s4 y,sjqy ,nwsed 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 omu6 huiz1)gon6 l+,tbf a $76-\mathrm{kg}$ 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 requ (d(.:4wyx:nsytuck mired to stop an 1100-kg car in 8.0 s if the car is traveling at 95km/h :ywcsundy(4.:m( ktx? -  

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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-gra/v ypqgk+vbd6:+q+j cm pellet from rest to 125m/s over a6 c+ j:bq++gqvdvp/ ky distance of 0.800 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 v lj, eu2t/fpjdp3gwuf,zy q +/73f3c an acceleration of 2.tj 3q3wuf/y7+u3fp dg/2,e ,jzc pfvl5 $\mathrm{~m} / \mathrm{s}^{2}$ 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 coverc7 3t76av8cb;6f tz / pgy.vo1 wctgvu a 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 des2xw -o+fk ( d.vkk yz+obxa+b-igned so that the maximum acceleration is 0.0680 g . What are y b fk+ox2 .(dkw-+av-xbo+ kzthe maximum and minimum forces the motor should exert on the supporting 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 bathroom scale in a motionless elevator. 3vz eglo(h u.(v,omlrm o/1eg, st6v: When the elevator begins to move, the scale briefly reads only 0.75 of the person’s regular weight. Calculate the acceleration of the elevator, and find the direction of acceleratigze(o1 lv/ eom.(svm uhrvg:o ,6 3t,lon.     

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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-kg elevatura k p4,4*vgaor has a maximum strength of 21,750 N. What maxim*gkp v4a ,r4uaum upward acceleration 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 1e8yjny (jsb.,:ecq nfalling sky divers (mass 132 kg including parachute) when the upward force of air resistance is equal to oneqy, 1ny:n(jeej sb.8c-fourth of their weight?   
(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 hz0hdt 5vr-x ;n:gz:ykigh. When he strikes the ground below, he bends his knees so that his torso decekyzv0-xr:g5znt :;h d lerates over an approximate 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 rope tied to the box runs verticay53wqgh7jq)x5 yk-g+bo0fitj/i ( r wlly upward over ajq7rh 0i-t5/(wgjk3f+g)o iy ybqw 5x 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 side 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 diagram for a bpmrs8 7c;+ux q/;bpm0mn f3 xqasketball 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 i q0y: c( ol+2ij 6,a;duirsdrgs hit by the bat, and again (b) after it has left the bat and is 2uo0d jgq;s 6: i,ad+lr (yrciflying 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 northwesterikj//d qi4 h* h.w 5zvngrj,7rly direction. A second 650-N force must be exerted in what direction so that the resultant of the two forcern7i jidwzjv,*4/k/ hr.q h5gs points westward? 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 horizontaln2co6 27f(wiy pou4y8d 5nx coly between two buildings 10.0 m apart. The sacw75yn n 2cyou(2o8pox fi64 dg 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 +a+jel1d,ln;qc ih+l massless cord 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 1gyy)kjzj j6/l;j4:kf4.0$-\mathrm{kg}$ 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 n/. sn3 aokub7l:(vjsunit to a new location at McMurdo Base, Antarctica, as shown in Figu7k n.3nal ov (sjbs:/. 4-46. The sum 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 samex/q1jb-x /kw ud0 bm,q mass behind it, Fig. 4-47 . Determine the ratio o- wd q j/umqk,bxx0/1bf the 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 herself upward usini3je0;-(0nhsp6t htki bf 1gyg the bucket-pulley apparatus shown in Fig. 4-48. (a) How hard m 1bk(- e6n;fgyh ih300tsjitpust she 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 began, a q+*ln65 t 1z akdi i izdm8v0szc-s33o 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 block (0t xfyyso 49- bti)ft6mass $ 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 frictionl5:y4tv zwwe n.ess horizontal surface are in contact with each other, as shov ze45w w.ny:twn in Fig. 4-51. A 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 ini ,qljygefp:* 9tially 1.80 m above the ground, and the massless frictionless pulley is 4.8 m above the ground. What maximum height does9feg*,y lpj :q the lighter object reach after the system 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 a frictionless table are connecyh:ev u1f(9g td(2sqxj2b* nzted by a heavy cord of mass 1.0 kg . Calcj2* (nq1hzs:be2xf dv9(ytgu ulate 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 friction betwev 9jw9m-l98u gds(qg2cpta*sen 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 requi 3l(zaatjl 0-nred to start 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 accelerating at 0xao200e*m50dt kw*oy7k f lbx.20g. What minimum coefficient of static friction must exist bx *dty5 a*e02o0l k ofkxmwb07etween your 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 coefficient of stati;0mxf zv:r pg6c friction between the tires and the gropm; v:gfr0 6xzund 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 harpxi (elq9k 8t:d rubber and normal street pavement is about 0.8. On how steep a hill (maximum angle) can you leave t 8xip(:qk el9a 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 -67q4iuk05m3df gt+jco(v8hd ft fjeb s/u 13l4.80 $\mathrm{~m} / \mathrm{s}^{2}$ 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 romvzqsd( o52ep56yher.;1vk p2 bte v8ugh 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 contsz kim6uygx6 :lxx8hu0 10gc n-y :y,kte3mm(act with an asphalt surface have a very high coefficient of static frict:1yxuxc-ylzi h st 86km gkx,(mu m:g0036yenion.

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 fr/u u*d,ww0ero iction 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) how large a mass would bow2shsb s :vez+0 td5w:x A have to have to prevent any motion from occurrind2ssw:0 vhs t+ezw5 :bg? 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 8pe3jpxtpz1 0u2m5e macross the floor. How far will it go, given that the coefficient of kinetic friction is 0.20 and the push imparts an initiale2et8pzx3mpp 1j5u 0 m speed of 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 , are in(grmn+ :n xl;z contact and at rest on a horizontal surfl:ng nz(r+x;mace (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 cwn3 g 4m:,qonb0nu9:.qusyyxw(i;c heavy crate. The coefficient of static friction between the crate and the bed of the truck is 0.75. What is the maximum rate at which the driver can decelerate and still avoid having the crate slide against thw9yb3;oi. scmcuxg 40qnu: n: (yqnw ,e 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 pa8gp,1k mka/30w)iuewyw y-r a25t zlsrking your car in your driveway, which has an incline of k23/1ysle 5k apg8ur wwmtz0)i,a y-w12$^{\circ}$ . 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 a s497 *stq ykoqplide 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 a plane tilted at an:l;;s -t/xd :f(u, y0jsuxpp (tjciwt 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 initial spnf7h2e )j7rvqx3;li8l cmz-reed 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 reaches the top of the steepest hill with a speed of s/xi7 k6yw: q)jv2qkj 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 place against a r,k( nv: +snglzough wall by someone pushing on it with a force directed upwa ngvsz, l(kn:+rd 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 projectiles aslm3 )(g pwv :wk,qd0 p-mfnij9 they melt. Consider a chunlnw pqi j(3k:gpm)vf- md 0w,9k of snow at the ridge 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 mivnm 65zngvxc68y n (ndwe8*+qnimum stopping distance for an automobile traveling at speed v isqvvgendynn(86cwz8mn *x +65 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 ca/w .52ikyv chqr slides forward on the dash when the driver decelerat yikc.wvhq2/5 es 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 a 2 : xph()ov:t0qkke10nnjl spn initial speed $ 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 belt frobboze5gf0 i cx -5gt(7m 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 half 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 gbocfe5g57(z- xit0 bbox?   

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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 coefficient7 nc s jzv5).:vg7 w+c(f9pd.b vmxi8hdbk.xd 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 bico2p v*tfucw e)k9+,9 nbdx+v c;i9 dlwycle) can coast 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 eab -la; s/:xfsq(al8wb ch pulse approximately 20 sf:l /;w(ba -sxlbqa 8g of blood is accelerated from 0.25 $\mathrm{~m} / \mathrm{s}$ 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 crash if the deo.zi 17vq4 gg(mo/ro nceleration is no more than 30 " g 's." Calculate the formg/ roooz(i.gq 41v7n ce 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 produced by an earth( ed+/ ilde8tqxsr0 p(wp )q9squake is a , and if an object is going to "hold its place" on the ground,q9s/rq (d0(xpe idtse+) wp l8 show that the coefficient of static friction with the ground must be at 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 of an accident inv -*y:)5dqoumvlov(p b)0srqn olving 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 p - uq)d(0oqvsbory:n 5)lm*v friction between rubber and the 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 a4/5x 2;tgunjqqw5 yqm 1-in-4 hill (1-in-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 botto2y ;gq4j/uwt mqxq 55nm after traveling 55 m? (a) 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 and fallsns u8 ubd3a9u8bl fu :o:3v*-osdl5x f 55 m before ubns8a:lu: o39b8 x*vfud os5d-ulf3 reaching 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 bwc m:3; -dd6af,/ xk*lr)qndy y,kh eput enters a muddy stretch where the effective coefficient of friction is 0.60 6*krd; e maxnw,-q)clf, ky3dpyd:/h. 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 emerging?   

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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 redesign of a hilly po1; ygkpue :06qfwm.+ idd*td4h peg- nrtion 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 particular small car, with a mass of 1100 kg , caud n fg -;m*hged:tk+p0pdqe1.y4i6w n 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 k s j5vo2195y2 -dwicmax:-b icaq/lmphysics experiments, dangles her watch from a thin piece of string while the jetliner she is in takes off from JFK Airport (Fig. 4-58). She notices that the string makes an anglwi9-cm5q:jd21 y-som bki vlx a25c/ae 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, smb-mx) xxod :t17qi/ ewn+omut+:n(ael q2:there are to be several ramps connecting different lbit2/a+( ):mu1n xe+q-qxwemtsn:7x: doo m parts of the 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 to li y7awxz9m3yus 4a-ezs1zgg19 ft the piano (mass M ) using the pulley appar gzs7m9 ge4zusx1zwy- y a9a13atus shown 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 h9g /ww 5ib ;i fsqb;fv51rr4m 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 chil; +e3+bi*qy dtjbi -z r. tcq.ltq0n/ld-restraint chair, an engineer considers the following set ofl- bl/.c3td yie.b+ zr+0qi*qtqtnj ; conditions:
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 6dw9o 2+hdkx2*.uodce 03n ac m60 metric tons (660,000 $\mathrm{~kg}$) . 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, Bivf 2jjzm an)8l+wz v8t: u c4l1go+x4pll and Karen, use safety ropes of similar length. 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). (a) 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 roz4 n l+toc2 j+j upx l8a4fz1wm8)vgv:pe 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 boat is using a debe8qet2m2xpb5 up ny.45 r," 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 rtr +:f) ) wbxqft*mwpvd(p.fjy p(4 3zeach 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 together are ascending an ice field inclihl b7m9s 7jk.oned at 21. hl kjb7so.m790$^{\circ}$ 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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