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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 backw6 i5 ol25d4+bo vvmee1fd0n vlard when you give the wagon a sharp pull55v 6fo0ddlmvevnb1+ lo4i 2 e forward?
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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 (fb ; 5g:1lyg.fflw07r l 0fa:1ddiyvafrictionless) bed of a truck. 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 w:7v:d0fb lf f;1wayl dflg1gi a50yr.ho 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 fo s i y.z;g4rdn,.it;srrces 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 acceleration?juqo1 :lnu b0ok(d:a : Can it have zero velocity? Explauo0 o1j: l(qb:: kdanuin.
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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 n+l4( b9sjoi3yb)5u2lm7v l dvf.ov lback up. (a) Is a force needed to make it bounce back up? (b) If so, what exerts tmv. f+v n3v5sdl)(obi 4by2ul9 joll7he 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 lake, why does the log move rph* d4 bo;(tiin the oppositepbo* 4th(ri ;d direction?
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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 uw j.fmotjq3b:(nz+t- l q q72a 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 must decelerate v2( o.)tjh uugr;4-px*eps wrquickly. (a) What is the origin of the force that causes you to stop? (b) Estimate (using your own experience) the maximum rate of deceleration of a person runninggx u o2t;*4wrhp(v pjrs-).ue 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 section iv96x 4zadcwra0ss: q45d i)p of the same thread dangles from 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? Explair a5pc 4vx:i9zais 0d4 dws6q)n 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 x2nkzq1/i(me*4ddou on a 2-kg rock is twice as great as that on a 1-kg rock. Why then doesn’t the heaviex 2u/d(m dez *qok1n4ir 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 the scf.1sk5u ovhq* ale had been calibrated (a) in pou.5koqf*v1hs unds, 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 fpbs ki-3dx9llw1 b wv1n2wr kcr98v43 orce 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 (dv1-b b2nl4w1 riw wrlkp3 9kx9v3cs8with 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 grav4 pdoz+s spb2rx9 )l2xou57 ojity there is a net force mg exerted on it by the Earth. Yet by Newton’s third law the objecx7zplssd+4 o9x b52ou j)o2rpt exerts an equal 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 (or force) needed to lift a 10-kg object when yo0+z wvgord7t6 u are on the Moon with the force needed to lift it on Earth. Compar 7owvgd0rz6t+e the force 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 te 5kw-b9b8edtfr,xgl8ps*d -aam in a tug of war (Fig. 4–37) pulls with equal force on the other team. What, then, determines which team will win-xs dbl*r p g-a 9,e5wdkf8t8b?
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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 40 N toe yx,rf2)( j5v ak+xmv hold a bag of groceries. Describe the “reaction” force (Newton’s third law) by stating (a) its magnitude, (b) its direction, (c) on what object it is exerted, and (d) by whatfjx(ma 2x)e vvrky5+, 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 l,n9wwikgt s 4*arge a force does the ground exert on yw4 *snwkgti, 9ou? Why doesn’t this 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 from l+rf4s,kv(wfan automobile accident when the victim’s car is struck violently from the rear. Explain why the head of the victim seems to be thrown backward fsr (l,wf4kv+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 i id)a41rlh48corew 4on the bed of a flatbed truck. When the truck accelerates, the crate remalw4e8hdc)i oia14rr 4ins where 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 slidebpn2 fa(su */es up a ramp. After the block reaches its highest point, it slides back down but the magnitude f*/ sau b2n(peof 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 your+-xti:lj g v-gself on an inclined plane? Assume the mevj lxg:-g t-+ichanism 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 acctn9*z/m-n v lbzy4cu,elerate 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 bike and rider at 2.30c*g (ous;,bx,e oonm 7$ \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 used to accelerate a 4n4j xt+qrbc)1t 7fhx960$-\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 a 4cthxxc k69 j0shsz,4 $76-\mathrm{kg}$ 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 1100-kgb +shq/ 5t*nt3*lq ocl car in 8.0 s if the car is travelingc lo/nqsb*lt5 *ht 3+q at 95km/h? -  

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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-gramv me 57mjmh /lk4gt-:l pellet from rest to 125m/s over a distance mlg:7h /4lm-m 5jet vkof 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 outyf6ld j/ls.ojhy 0)hi 1jct40 of the water with an acceleration of 2.5 0ts4ly.j /hj0jcy61ld fo)h i$\mathrm{~m} / \mathrm{s}^{2}$ 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 quarter-miu jt/kreb 27u9le 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 the max 8mv 8ci/gm u88fgk:. fxxbom,cs50d ximum acceleration is 0.0680 g . What are the m c08f:/. 8cxxkg dvomgus58xbi, fm8maximum 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(8 dgsi ez .i0amrk(8j bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads onli8 ezk jgdrs0(i(.am8y 0.75 of the person’s regular weight. Calculate the acceleration of the 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-kg elevator has a maximum strenr()p48v6c8 bfodm6qbxa4ck n gth of 21,750 N. What maximum upward accelb48r6vd(b kncoqpfxc )64ma 8eration 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 dish6c//s zpsu/c o;* xbvers (mass 132 kg including parachute) when the upward for/b;//cp s6ucs*sz ohxce of air resistance is equal to one-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 high. When hezw:i;+wa 6d s kvm6 qi4ze8e;p strikes the ground below, he bends his knees so that his torso decelerates over an approximate distance of 0.70 m. If the mass of his torso (excluding legs) is 4vz;z6 sa 6w4wi;p +mekd8ie:q2 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 vertically :(bc :c1 yg h rgppn3p0pq.dy(vz,9mkupward 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(dp q1ch0p, y: vyz:gpk9mgb3 n(c. rp 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 baskeii*b 5zrsj 9g7tball 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 xv7tqpws2q if d8 et-s- /z(m+baseball (a) at the moment it is hit by the bat, and again (b) after it has left the bat and is flying toward thewd2tq / i+s-smfzpx t qe-7v(8 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/t5w rz : ehxprzu(wt2 8zl2u0 northwesterly direction. A second 650-N force must be exerted in what direction so that the resultant of the two forces points westward? Illustrate your answer withzwzu p0z t2 8trhx2e/(5:wrul 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 horizontall,bcx9) ycct501o jmpey between two buildings 10.0 m apart. The sag in the rope when x tb1, jm5yoc pce0c9)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 ct k qb;ouysxg ky14gcsnh*.,+/ti*z / ord 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 1ki ha gqeczc6uemu..;+m ,f 3 5x+zag04.0$-\mathrm{kg}$ 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 hozcr2+*nl(ae cusing unit to a new location at McMurdo Base, Antarctica, as shown in Fig. 4-46.reac (*2zcl +n 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 same mass behind it, Fig4h492yox xcb xtnm 67nfx /ef(. 4-47 . Determine the rat m byxo h9txn47xf(n4cf/ e6x2io of 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 her19 m5*u5d,li*.ws*hgqh)ia z libdf rself upward using the bucket-pulley apparatus shown in Fig. 4-48. (a) How hard must she pull dlh)ridu zg.,*fb51l i59 i* adwhmsq*ownward 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 c lgem 4we ,8p2r),knkbegan, 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 block (mapl5csqjr)s4c ky (5m.hmrsie.g (w5 / ss $ 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 1)dsu8 5pief2f 2er,ng*ydhxhw.7mo with each other,172pmhy, inw8fo deg5)u*de. hr sx f2 as shown 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 .rcg)cf -su w2vfxml; 29 r4yxFig. 4-52 are each initially 1.80 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 syst2xc.x l r-;f9mvgyw 2f)r4usc em 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 adsb) b 9 5tz;ugk;p,gz frictionless table are connected by a heavy cord of mass 1.0 kg . Calculate the acceleration of each box and the tension at each end of the cord, using the free-body diagrams shown in Fig. 4-53. g 95p, )d;zz;sukbtbg 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 between-;lj86o7ij xx l .puqk 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 ttmvsu q;5(:lr o 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 accelecuy/p,+1cj 1+sa tcizzg v:a-rating at 0.20g. What minimum coefficient of static friction must exist be yvzcj+-+ cz acas/gt1,uip1:tween 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 coef:u5t-m(a c (*q(7rvuolqjc dp ficient of static friction between the a: c 7*(urul oqdq(ptvcm( 5j-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 and normal street pavem 1g t,r+jjq1lly b)0:ac ;xiigent is about 0.8. On how steep a hill (maximum angle) can you leave a car parkeaj; lciq)b+x:gr1gli0 t 1jy,d?   $^{/circ}$

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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 -4.:::lej mntvnqnxdj;m,i z m.::yq* s880 $\mathrm{~m} / \mathrm{s}^{2}$ 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 rougp6d:mavl 2k j+h 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 have a very high cooyayn0ocm3 6h p9*lg.efficient cgyon0o al6yh 3*m9 .pof 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 kinj*ji,m)mzw z v1 *kcg3etic friction 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 larg 3s:)g) aicyu 5z)ecxi3 /cbmfe a mass would box A have to ha)cimb xf)ecc 3g 5s zuiay3/:)ve to prevent 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 acrossoo2j2*b qz7,fv*hpn2u/huj q the floor. How far will it go, gi7 p2oq/hfn z2v*j*bhuo, j2qu ven that the coefficient of kinetic friction is 0.20 and the push imparts an initial 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 contact and at rj yjnoi :ka6)j :*ts-,o67d8x fylqxx est on a horizontal surtqay :6 xlx-sjx*)6oo7:y,id fn j8kjface (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 stati)0 e.b cy 8;dlj(jfjsgc 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 the cab o;jflbc( ys8j 0edg j).f 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 worrg1a 2u rsh-c4iy about parking your car in your driveway, which has an incline of u1ric ha-4s g212$^{\circ}$ . 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 4i:hp32eva mfn3 dg6va 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 a plane tilted at an angle z81xnj0+pd:n2je ggg $\theta=22.0^{\circ}$ 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 speed of 3g,u0w*rh.2 o pehqc1 v.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 hillj * tobh odm44nxp5(cc1s1 e2g 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 place against abm (.4fiioqwh)p -ovt0)* wgo rough wall by someone pushing on it with a force directed upward at 280 h)wv4g mwi fqoopbt-i.o*()$^{\circ}$ 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 pnni9zqmk+u2 .rojectiles as they melt. Couq9+kizn .m2n nsider a chunk 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 minimum stopping distance for an automobile traveling at spee c*+nsud-86a x3bhcbcabn2v;n 5 dy5az,gx6 od v isxzcd3x*2; a 5 58ay6saobbbu6gn c,vcnh+-n d 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 forx-eb if*wpi/(ward on the dash when the drive w/*e-i(xbip fr 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 wut a 9t-/ikjs.(;olkan 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 from wh 5wi35q 5vbt8wcfog t7ere 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 gt8qwbw i5753c5tfv oaccelerates 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 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 coefficient of kinetic friction m5(oc) u(ul u* /ch vks(9prf7w-fkrzbetween $m_{1}$ 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 (includinc n 6y txnon:a7j13c4p3yvbo c-v9g1p g the bicycle) 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 each pulse4o;mmfcdlu0ru8/ 6 df 9jm *u71ae mkf approximately 20 g dm*8e 4mr967ao /fmdu f1klj;u0ucfm 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 survivinf(e)h+cop/,6xmkbt( * svfwk g an automobile crash if the deceleration is no more than 30 " g(ksmebp , kvf( x/)ctho *f+w6 '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 produced by an earthqa8)2hosr+(1eu9rh(i c pdz eduake is a , and if an object is ge2isr +h8 u h(oderpza)1 c(9doing to "hold its place" on the ground, 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 sot. qoyx/w;b 9cene of an accident involving two cars, measure 72-m-long skid marks of one of the cars, which nearly bo;y.t/q 9oxw came to a stop before colliding. The coefficient of kinetic 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 a 1-inwl w/k+u99 ww-j )wl mis r:e2y1rf4ak-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 bottom after traralw2 /ur1 9w)f kl+wyw4imew9-j:sk veling 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 fx mao.,zpbq89 alls 55 m before reaching the ground with a speed of What was the average force of air resistanc.p9aq,zob x8 me?   

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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 muddy stv.b r1p0 hj9 w.bvpbd)retch where the ef0p.9 d pvhvb.b)rj wb1fective 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 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 oc4;99zl zq g*pl0/cdgixc5;j ea s( bwn the redesign 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 w5/ zdbxegi s99a l*;gwlp4z;ccj0c ( qithout slowing down. A particular 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 p/b 4t3 o8jevqw) gi1g m9henl(hysics experiments, dangles her watch from a thin piece of string while the jetliner she is in t ) /3jhqnmvelg1bet (89wgo4 iakes 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 ar 4ys ei7h.pc; +kdesr0e to be several ramps connecting different parts of the sps +eci4d. ekrh;sy07tore.
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 lift the piano (mass M ) usikeg(7u63:b/k:nab uuxh 7tujng the pulley apparatuu37:bgjk: tu/ kh7uux6(nabes 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 accele0wj5 iywmm13v1xape.)no, ka rating at 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 childzx0ed j7r 0ek1z rgo q(f9.1v+aa oal*-restraint chair, an engineer considers the followvlrzxek*aadfaz oq1 70eg .(0r o1 j9+ing set of 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 660 metric tons (66,s* c k;(mxxgt0,000 $\mathrm{~kg}$) . 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, Bill and Karen, use safety ropes of similar length. Ky0fbnup7 x/uq+ un p*6aren's rope is more elastic, called a dynamic rope by climbers. Bill has a static r* /u pxnqby f7un6u+0pope, 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 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 boat is using a ek2j36acucf3x og4 4 b" 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 bui3b-cx o-3 od.admk ,bilding is allowed to reach 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 p2;4xdfx0x .kri)o vpinclined at 21.)xv. po; fpir kx2xd040$^{\circ}$ 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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