Does a car speedometer measure speed, velocity, or botnkn/i;j wx/a4ud 6,o mh?

Can an object have a varying speed if it pkj0-fb,ddp;s velocity is constant? If yes, give exa0pdpj; f kb-d,mples.

When an object movesy .9gggz9 z 8i f4p*h3eu5thkb with constant velocity, does its average velocity during any time interval differ from its instantaneous 9 i89tghk4z y.bguz h3fp5ge*velocity at any instant?

In drag racing, is it possible fo /d jd1):fg ,h7a5eqtjo1z jerr the car with the greatest speed crossing the finish line to lose the race? Expl7je ) dhfz/ ojq,g1:1 e5radjtain.

If one object has a greater speed thaoi tb4ee(1;n7 iuaiv,yoz.g+ n a second object, does the first necessarily have a greater acceleration? Explain, using exampli n (. ,1got+o;u4be7yvezi iaes.

Compare the acceleration of a motorcycle that accgs azdj4y .+jzl)r0/sdbr 2,s elerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the samszrb0+2szdjr4a g/lsjy ,.d )e time.

Can an object have a northward ;3hf+ m)r mjipvelocity and a southward acceleration? Explain.

Can the velocity of an object be negative t ge-j57w l+ brr9yss1when its acceleration is positive? What about vice vetws l+ y51 7g9r-rsbejrsa?

Give an example where both the velocity and acceleration are neury h0or*0: jo7 zcwn+gative.

Two cars emerge side by side fbt84bwtf+b 6ixfsj0a n41xm 2yo k2xi)o9t u1 rom a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B f92o+4bx)syout b1w1 j bt8xxi6m4ikf02an t has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration d20 efuh2af14qfjw; k recreases? If so, give an exra hf4kj ;221qew fu0fample. If not, explain.

A baseball player hits a foul ball straight up into the air. It leaves the bat w t u87lt5s ;.e)rsj8wtnlc+ygith .t s gls u58c; lytrj8tw)+7ena speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what. fs3hsy)z lu8 is happening to its acceleration due to guy .fls s)z3h8ravity — does it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball vertically u:kom8cd.mumekasg1kb oxb 6po .i(j k63x* . -pward? How would you estimate thegekkxxmkojb .-: .mpom3k s8o ic6.a(d61bu* maximum speed you could give it?

You travel from point A to point B in a car moving at a constant spee,r4/f+xu0 f xihmm o4vd of Then you travel the s +fi,4 /vu rh0om4xfxmame distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, ars 6jr1+wuy 8b 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tie6uysrwrj8 b1+d so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock falliek1k. ru( y-r-ed/spp ng from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a tkk d(yr-.e1r p es-/upable?

An object that is thregd8xbi mmj j8n2e0;6own vertically upward will return to its original position with the same sn8x 8emb02ejgmj6di; peed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero5 7rja 9tryq:6 q7bz3-fiznb jd-. juf acceleration at the same time? Give e bzijan73u:frj-jbqr qy9d6-.z 5f7 txamples.

Can an object have zero accele: w+ vnaimf;:0hzfq g3ration and nonzero velocity at the same time? Givezvm i3haffn :g:0q+; w examples.

Describe in words the motion plotted in Fig. 2–28 in ter)n-wgq x/ tlx*ms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moving your hand.]nlxg *q-x t/)w

Describe in words the motion os-1.u/j4siytyc;im nhw f)c6 f the object graphed in Fig. 2–29.

  What must be your car’s averagpo+p(jwg0n -.m y q(mle speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 th: 9me,ud fpflgm1,4km?    h

  If you are driving along a straight road and you ls1gjiipt a;hqff m4/vo2x:23ook to the side for 2.0 s, how fa;oath1xig fpfj2i 2q4 vm s:3/r do you travel during this inattentive period?    m

  Convert 35 mi/h to i;t5w m - nf ak+lqmeb3 igk6l./b1)oy
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from 5yfz ) /;cdhz+gf 8vtb$x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily at 95 km/h for 130 km. Itr6t-mzosi+o 0 then begins to rain and you slow to 65 km/h You arrit +srm60 -oizove home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between rzd1 bn v nnxf28x )n6etj1j3,a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in esse)j6 b e dtjvr3f1,x1nn8z2xnn ntially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quar 2cmrs:s,a46x*uw3 / f5dbd c lrfgci-ter-mile track in a total time of 12.5ss*:/i 5r f6u-c4bl 3drg,w ccdam2xf min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer ia -0dasd5( moxn a straight line, moving 116 m away in 14.0 s. It then turns (so5ad-dx0am abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has oyl ) w3;x-t6g(zhujo5mvz2s a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? gj 6l-ov mu;xzyzt 2s3 5o()hw(See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truc c6woepx 1vx91k traveling How long will it take the caew6 xp 1cv9x1or to reach the truck?    s

  An airplane travels 3100 km4 wiw0mpv9 ekbvh6b2 / at a speed of 790 km/h , and then encounters a tailwind thpe04b6hm 2w bv9wvi/k at boosts its speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average )2 mrj2 /m5gxl7:smnrlgd 8qh velocity of a complete round-trip in which the outgoing 250 km is covered at x5l8jgml/22 rngmd )r s7hm:q 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling t92)o;wl mk kxu z(df mn4xru3x u3/m)with constant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hwz xf9xko/tummn d 3)(k2x3rm ); lu4uands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h i4r61ilz uc4(g4az0:vf/ jvk rk 8wp jyn 6.2 s. What is its average accelpiga cw1u 4z jyfv jzl8r6kk(4:v4 /0reration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s6de;ivlwn9dz6k3)v g in 1.35 s. What is her acceleration de9idvz6wklg)63; vn
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a papejbvsg9m;n :3vu7bk7.4b nw 8hovy,rticular automobile is capable of an acceleration of abouuypjb7k 7 vvme43.wv sbgnn9 ;oh,:8bt $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving atal5rej5caq :1b-;xlt constant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop ic5-5a :eatx1 lqb;rjln 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t = 0 and moves in a 4+y s5dtzuv b3pk :q +ngun:h9straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its accelgs 39 45+dkuhzp b:ntqyvun:+eration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to cpe6w+kf25, 4 e3p qf 3hbd89cwa cmrc25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Ar ewp5 a+ccc3ce wf dm8p9q hbk342,6fssume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distan ipy*1p ;gnpg8h6oit0ce of 85 m. What was its acceleration, assumed constanti*1 6gyghnp0 ;8ioppt?    $m/s^2$

  A light plane must reach a speed of 33 m/s ;zkt/6hvb ,y ufor takeoff. How long a runway is needed if the (constant) acceleration ib h6t;ku,vz/y s $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essential7t.8t8vjr p w6svcvy /b hj2/a8h4qmlly top speed (of about 11.5 m/s) in the firstmjy2r.a6j 8th8lpvh q7vb/ /8t4 vscw 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 1a1: vu6cvmn; w2.0 m/s to rest in 6.00 s. How far did it tcw;a6un mvv:1 ravel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on thz5.qhiaf.erur k0 *u4 e highway. Assuming a de54.ku*z raehf.qu0 ir celeration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the3 p;w d+yv)lr:ya l6n;oe4ybe car compresses and b4a3evrylw;np6y+d:yo);elthe driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95jm(f z2:lp e/mbyf5e5 km/h and human reaction time of 1.0 s, for an accelerejmp25(zey / :5mbl ffation
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stoppiqkw i)a4xdk1 a3)6fcxng distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m ao1 bai3e*.vdwhjba3 sh:6 cx+4ah4 l/s on the highway. The car’s driver looks for an opportunity to pass, guessing that hi:3 ls436a.j ehach*vab4x +1b i awodhs car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less til4lf:b9y3x 7 ,)b .tnwa1d3ryl rs hbhan 30.0 min. After exactly 27.0 min, there are still 1100 lbr. hy rbf)3wl4stn37x,:9y1bid alm to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as the jm-l9s6mr rk+ traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns6m krr+j9 -lms red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. Itiw/l0 ncv 45.a a/u6p+wb kuue hits the ground below after 3.25 s. How high is tuw/n5l. au/ +u6ie04vwabkpche cliff?    m

  If a car rolls gentl(oss5zp q(1aoy ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly stxx*:i6 tfgbs *3yune.raight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after ts)- 0v;jg)jr i, fr.wim0 bzkqhrowing it vertically upward. With what speed did he jriqw );i,vjb0 .f krm-z)gs 0throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gm -dw-mnt16 jcravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a fud6m-cjn mt1- wnction of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of ,b+ewz f3ml*1+dv b au5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopau+dm*,b1+vb3e flwz ter’s.] t =__ s

For an object falling freely from rest, show that the distance )ilu9heh i(.ptraveled during each successive second increases l.hiei(hp)9 u in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a bauo4mv) 6sij+f ll thrown vertically upward witho +6m4isj )vuf a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upwardbg l pz0ppi)ftq9y9/u)5 dux / with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash ofjg65cx6hm v8b gi ,qk8 the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at ix6b8,cj 5q68mv hkggthe top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past ld,ni2ql-g rgf) 7fv4a window 2.2 m tall (Fig. 2–32). From what height above the top of the windd 7glgvi-2r 4 nflf,q)ow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean ib r1-3 o)n.a2ygst.+shn elx11crz)zbzy5ms s heard 3.2 s later. If the speed of sound is 340 m/s , how ezayongnz +zxlt.crb11r)351shy-).2msb shigh is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of wattc4dbyb j5f 35er. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). W3jy 4db ct5b5fhen you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of acdk;y rp etr:zp8n:h;1y us9( (hp sdr; kryez:u p91c:yn;t8cliff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by add9+e* ivt56u fqq)b g window 28 m above the street with a vertical speed of 13 m/s If the bal)qvu gtb9iqf * +ded65l was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velociz if ph-agq e+e gi-)j+a2 0d0g*)qzimty of a train as a function of time. (a) At what time was its vzi )-)0 f2a0h izq+jgeg +aegp-dq m*ielocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight ty rmc 5q-2 (nudvbbdp m6.tc7d+4l.k wunnel as a function of time is plottedu4.c6ybd nc 5kb -2l.tqddp +7r(m wvm in Fig. 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile 4b h;o5efyk c,can accelerate approximately as shown in the velocity–time graph of Fig. ,yhk4 cfb5e;o2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Pro/zenucxi dx g3wzjb1 492)gl(blem (Fig. 2–35) when it is iecxxld13z24wb (i9/ )j g zgunn
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the objecth wn7se7v3b( u traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose disp nq7s(vs fnlexm)t9*5 lacement as a function of tim (mns ln5s*) fvte7qx9e is given by Fig. 2–28.

Figure 2–36 is a position versus time grapx3,s uwa;kn) c(n;.m4gqb h ukh for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing d43cgxs wmk)nqb(;, ;.huk au nown? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m a i4zxgbe,)nd(bove a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, 4ngx,)(ebzdi Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-six;ab8s*bg8 n xvth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go tha*bx;n bsav88 gn it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an ove2vt 4 (e ixmmo:k1qde*r-the-shoulder seat belt has a good chance of surviving a car collisio vq(d* :im2eot 4kme1xn if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the roapxrt hxmn-mo-0mv1 :1d below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the tepomxhr10m- xvt1m:n -lephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by hauliwasrg tv :add) 0vhof)(1im--ng them up on a crane and dropping them from :f(iag mtwh1r)d -0 d-vao )vsa certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels about igb ib5)3h zh1$10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of thgw pzj:t1,z9qj44 zc ae train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front o c4jz9jg1:zz p wt4q,af the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a deep p *5 wfweq+ ol07sh3g(uv a4pcvf xs*s6ool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration o wqghs c6*45l wvs70*vasux3ff op+(ef the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit 2. ecgb bk5tt/system, it is necessary to balance the average speed of a train against the distance between stops. The more stoptb25kgc/e .tb s there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight down when .ru hr.0c4.lnii,a gx diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to penu.hlix,rg. ac4r0i.rform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ballu2;iy,d-(bxh 1qpkk wn5fh4o is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a pa( dhou;f, i4 -2bh1knkxyq5p wrticular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freivy n-ewz(*mx 8ob; lh-ght train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and acceleratle-wxzy vn* mo-8h;(bes at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second st9vupi8c e e +lofahe5u)9uz8 2ia4+w c nzht21one is dropped 1.50 s later. How far apart aro8haeuhpt)l8c4 +u 9e+2v za1eiuc5 zi2fnw9e the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the c bn5:wa fxep7)ourse of a time trial lasting ten laps. If the first nine laps were done at 198.b: pxa7 5newf)0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a momg3bq6,xusg:y w:a; oad1ef2untain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/hmd, w;xsqggfyu:oea:23 b a61 . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing oyi z85tbspw4o a//tdi4* zr8wn two trampolines. The first child can bounce up one-and-a-half times higher than the second child. The initial speed uswi8 4t4zy tp dwb5o8ai/*zr /p of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train travelitt7 uh cyk(try/78:q5.qk ubang in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. Wh:ya cbh5 trktku(yu7t/.8qq7at are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws1bp ;(tfoi-r1l qeh*h a baseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the thrhbtrpl(1 qo;1e*ih f -owing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an acc;kbg ex)qltrf4s3amkk2 o8gg 3 / y*.ueleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2c3a l(q 6vrss139fk od–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose ao f( 3vqls9k6dcs 1r3you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km/h tak77l/hbw 1 k7+xuqvsx9 zvtgwy0grw *;es off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant accel; l77x 1 z ghs0wuww/xqgvv+b9tyk r*7eration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped fromnmjt/h bg8, 2f the roof of a building; 2.00 s after that, a second stone is thrown straight down with an ihfbmnjg / ,28tnitial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The first stone i 0lx06 hk ;jfye+9uaejrsh j:6s thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second s ljjr sye00f; +ea h6jhx9k6u:tone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resist3o(.ycyw1,m n(xpde (hxbw( pance, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m1e x,((od3ppyxh c ymwbwn. ((? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt 1t c9 ;ktwyic0to send the burgers through a grilling machine. If the grilling machine is 1.1 m k 0tcw cit;y19long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball ver)ksc el7 ciy31tically at a speed 1.5 times faster than Joe can. How many times higher will Bill’s bal)7ek1 ylisc3cl go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the grif8zq ikk t/zh.h-5py/wv0 j3ound below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is /h. q-zi3/08ivkf wkjhtzy 5pthe speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using ajmp8*7bl e7(gj i rj3d barometer. Instead of us7j8i 37rdbj*jm gle(ping the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycl;z+6q7k kmriv b 7 fjl2:4cnqyes, A and B. (a) Is there any instant at which the two bicj4qk qm2i+77l6 ;nyvzcfbkr :ycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?