Does a car speedometer measure speed, velocity, o g9ma* mv7lfk)r both?

Can an object have a varying speed if its velocity is con,,s gr;u6d-8q31i uzgo aaj4v:vlra dstant? If yes, give exampler3dagu a8v4r:d ,is uo;v6,q g1a j-zls.

When an object moves with constant (k304lb rtvogvelocity, does its average velocity during any time interval differ from its i ok3(lgb0v tr4nstantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing the +kw,thc2 v4 vxu;ci. dficw 2.ck,xv+ uv4t ;hidnish line to lose the race? Explain.

If one object has a greater speed than a second object, does the firs4nqi:fd32w *8 hafkwf t necessarily have a greater acceleration? Effin4w8qkha * 3d2:fwxplain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h t)uy-uoq 5t6jzo 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same time.t)z5uo j6u- qy

Can an object have a northward velocity and a southward acceleration? Expl0)flrgyj rh1t1q :j -vain.

Can the velocity of an object be negative when its acceleration ix p* eq:gv6;riy14yczs positive? What about vip 4v 1yxr6 *eg;zqyci:ce versa?

Give an example where both the velocity and acceleration are negative.ivh.xixh-8rlu ) - .oa

Two cars emerge side by side from a tu mdckvxb2qr d ;-u.s02nnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B 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 oqud.rd2cxbm;0 sv-k 2f the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, give 5ap3;:;05 n,nopa qtcc xiri nb7pk2w an example. If no oan3n:rw20; ic;,nciqktpp5 p ba75 xt, explain.

A baseball player hits a foul ball straight up into the air. It leaves the batz;c q0md02a f.k(byifgke f-; with a speed of 120km/h . In tk;( yfge;k0- f.cbf0 dqa2mzihe absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling obje: c:cfkol,48uf/1h4 ny q;(uwcfjry rct speeds up, what is happening to its acceleration due to gravity — does it increayl ffh:8(rju 4cncf : urc;q /w4oy1,kse, decrease, or stay the same?

How would you estimate the maximum height)pitz 40y y/+xpo,lkn you could throw a ball vertically upward? How would you estimate the maximum speedtop l4y,0ip xy/)kn+z you could give it?

You travel from point A to point B in a car moving e tj:teyb8a( )at a constant speed of Then you travel the same distance from point B to another point C, moving at a atjb:yte 8 e)(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, a 3.0-m-lhqo .humv+ ,dxtus -o5r:lg (t9+vvr1 ong vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The vuu,h5l(s h + trrt.og1o9d:qm+vx -vstring 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 tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration:nukqzx;b snt a9m( jex* c0v+ ;;7lwxt .)v+yc a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making x(t+xc+tkewv;zmsvn.)un;9 ;c *q 0 b7 ajxly stops along the way, a dish resting on a table?

An object that is thrown verticabkczgp52 j6 5clly upward will return to its original position with the same speed 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 motioncj 62pz cb5k5g.]

Can an object have zero velocity and nonzero ac(k4a cjrz b4s p39q6bcceleration at the same time? Give example9cpb4(s4kz cb6 qa 3jrs.

Can an object have zero acceleniuw /njy( 80+4anpktration and nonzero velocity at the same time? Give tu nn8(nj 04pya kw+/iexamples.

Describe in words the motion plotte8 rz6ff, -lv1dz,eld :ut; fqmd in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moving your hadr e,,vlfulztf :6df8; -zmq1nd.]

Describe in words the motion of the o lt7ob+hn(mw(c nrw*;3 /dceir g69mcbject graphed in Fig. 2–29.

  What must be your car’s a0 fthwsb.m 8y9verage speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How +gs.g+c -4vuf5jtvxglong does it take to fly 15 km?    h

  If you are driving along a straight roadvxc5 p aso yw(68o8(eye *oyj /5sd :jd5qd,ic and you look to the side for 2.0 s, how far do you trave6:(e p5x8s,y5 wod*8odcco e syyjaivq/5jd(l during this inattentive period?    m

  Convert 35 mi/h to z6riyngpm)9 uadt*1+
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball movesr-: bfubxt91 boq n7m 26ogxuu,zko** from $x_1$ = 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 pj z.p5;bdev6for 130 km. It then begins to rain and you slow to 65 km/h You arrive hom;p6d jzbpe.5v e 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 ber* x:a4h)bz0 6 wt;ocaef,e t5mwko 1dtween a lightning flash and the following thunder gives thezdw4;1 5 thfoawk) txeba:,cm60ero * distance to the flash in miles. Assuming that the flash of light arrives in essentially 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 quarter-milgv;m spuo642ok-sjbj vcb/lxj 262 h.e track in a total time of 12.5 min. Calculate p.lo/x o-b2scmu; v vghbj2j46k j6s2
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line,7tg -cl vp6c.u moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calculateu6 t-lvc gc7p.
(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 appr hgo4njyu* cxuqy 6-76oach each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initialluq7u*-6c y4nhxjy6o g y 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/84 jb4:pol7wurdv1m bh 5nqo4h is 110 m behind a truck traveling How long will it take745njh:pr qm4 uoolw1b84vbd the car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encopal )1k p-th*ounters a tailwind that boosts ita-p) kt1l* hops 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 velocity of a complete round-tri/ay-h ik z0uvl*(1o gyel v-7bp in which the oule-og a*vkz7 1/-uyy(lhiv0b tgoing 250 km is covered at 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 with constant sdj(5. qp t8 w(7ejzpugpeed 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 hands. What is the speed odwq j(j7pue.z( g5t8pf the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to qxvk; u(b)t 6wu l0*ry95 km/h in 6.2 s. What is its average accelerati*lw06)byuv kurx q;( ton in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest towln.mfgy7; z evv )n) w9nml)u25 sux) 10.0 m/s in 1.35 s. What is her acceleration y v2wlum)fl gnnwm9) u;xzv)sn)75.e
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular auton ofulo2+iscw (vfsh.s 9 5:.hmobile is capable of an acceleration of abouts.2wf+ivnu ls:9oh o s( fc.5h $1.6 m/s^2$ 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 at constant speed travels 11d9 w2ecw 2hyi 6v24xou0 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleration in2v492ehdwc 6uxy wo2 i $m/s^2$ ? 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 an ( ku (e(dhf.+ybunoig6ti;v:d moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its accele.i f : d(t6uhun+i by(kvo;g(eration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its.jw xg7q mxefl3xf6;1 acceleration? How far did it travel in this time? Assumeegq;.x 16xjw fx3fm 7l constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its accz-t; 1i 3btq5 z*r d4o(d*5idvlyxfazeleration, assumed constant1av t(z q if5zdb*xi;43 r-dl5o*zyd t?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takjxrk ,2o .;xo50rgskveoff. How long a runway is needed if the (kx o.,rk jogvx2r;0s5constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the b8, jxnv .s/sx+gvr6yelocks to essentially top speed (of about 11.5 m/s) /js+ex8gsvnr ,y6 . vxin the first 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 spe;uiwd)wtg uss: l3-e5ed of 12.0 m/s to rest in 6.00 s. How far d ls-wgiu wde us;:3)t5id it travel in that time?    m

  In coming to a stop, a car leaves skid .f6us,dxd u7xmarks 92 m long on the highway. Assuming a deceleration udd,ux7x.f6sof $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car compresses yvi oo r qjj+4vne8.+,and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the anyr48ve.v qjj on i,+o+swer 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 9dizctjmqexz6w9cx 1 : 3 v(+ cbmi+7r+v zu*dof 95 km/h and human e(bz 7 +uiqr* c mi9xjwzm cv+193:6cv+dt xdzreaction time of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car iwl p,vrsn)r);resqaw7o cy e/ 658kh *s $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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/s on the .,kz6y gt;bsxhighway. The car’s driver looks for an opportunity to pass, guessing that his car can accelez yk,gtsx.; b6rate 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+ s b9u+zth m.au3i/oa less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then acce uo/h+itmzb +.a9as3u lerate 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 appr as:8/6rv h*(sghy 6n iw-vihioaches an intersection just as the 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 shou /hyw : 8h6vsihsr6-ig*vni (ald she speed up to cross the intersection before the light turns 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. It hits he/e4g4eg0 8 u x*rhbvthe ground below after 3.25 s. How high is the0vhuerge/44* 8 h gbxe cliff?    m

  If a car rolls gently (6w zqb.i,4t vt$v_0\,=\,0$) 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 straight up into the air with a speed of 22 m/s yl;;8, aaw7szxj n3uo
(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 throwing it vertically upward. Wl*i; :urshnx8ith what speed did he throw it, and wshrix :; *n8luhat height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of u8yhfa2yr1+ z-; bwkz,x7 o-.tpcud ygravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 t7zy xpz+2-bt y yucrh;oa d-.1,wkf8 uo t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.2mde8l8 lne4zlfua6bi 6+fwt9r 84 (gh0 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 id4ame 6 (+ fz8lei4hwgturf 8lb86ln9nitial speed equals the helicopter’s.] t =__ s

For an object falling freely alh t/b;.,vitfrom rest, show that the distance traveled during each successive second increases in theih vl;a/tt ,b. 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 a2 rg cldk0a ;ef6c+iv- ball thrown vertically upw-di 6lg + vae0k;2crcfard with 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 upward with a speed ob+3 rezyvpzsv0xa9.2 * majj,f 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.ty9x.tnwsl2b4k o56m/a(ezv g ur8v 8/w ysv of the apple in Fig. 2–18 (or number of photoflashes per ses n/ 59.tze82ya/m6.(vv svgkxtb 84 lwwrouycond). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fi owm0i3 ob.k9fg. 2–32). From what height above the top of the window did of0o.9mb i w3kthe stone fall?    m

  A rock is dropped froma a, e1jlcw/w4 a sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is jwl4ae, /wa c1the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You p7p n5oko ,a5jroint the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from toojn5k p,75r ahe 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 :p n1(wg.w::8;pbsj pahr cd;j gtfp 1m/s from the edge of a cliff 70.0 m high (Fig. .:;ppp::wdhtbc(rjpjan g 1 wf18s g;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 u+jr* y yk/t 2a;jwrp9htzn 7nw14x 5mbpward by a window 28 m above the street with a vertical speed of 13 m/s If the b45y+t1tjypjx7b;*9 knm/w2wzr rah n all 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 velocity of a train as a function of time./nc 7ww:e/ k*urqd m)k (a) At what time was its ve/w r)menqd/: wck7u*klocity 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 tunnel as a function o5czn8m* x/m kwf time is plotted in Fig. 2–28. What is its instantaneous veloc mnm8zk/5*cw xity
(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 automobilep xg::3 mp* tfs,-bt 6:vytdtz1wr :np can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve r :3tnzgm dfpx t:vp1p,t: * wty-bs6: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 ac gq()55i,asu)arm hpz 7bb3 hzceleration of the car in the previous Problem (Fig. 2–35) whe bszgprm q)ibh)(zh 5 ,a753aun it is in
(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 object traveled4-q7 an9 ouizx during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the obj8kftvsb(ys)2 xz,,6 v yy;lfsect whose displacement as a function of time is given by Fig. 2–2kyv v)6;,zy yss2f(tf,b8 x sl8.

Figure 2–36 is a position versus time graph for the motion of an object along tncc5e* (6 hyifxf h q)86xn)x;qy:rzthe 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 down? (c) Is the acceleration of the obj:xnf; 6fih c c*8(y qtx)he y6)rzqn5xect 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 above a f.d8 8ioz vjj(girefighter’s safety net. The survivor jdjgi(8 ov8 .zstretches the net 1.0 m before coming to rest, 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-sixth what it ism9ol/v9h eg+y on Earth. If an object is thrown vertically upward on the Moon, how many times hi om /+hlvy9ge9gher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly con,n q .5fg (ee*i0tkkublal-+u x0b8gmstrained by an over-the-shoulder seat belt has a good chance of surviving a car ceqm5utxg ubi ,*e(-08bk g0 n+fl .alkollision 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 road below, and h(oh4yvsid 7i7 is pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone 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 vh4yo(s i7d7itruck 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 haulldkcja if .2yp 6bm;vsl- 63y*egt4 5eing them up on a crane and dropping te2lji.53 bs4 dpy-;f*lt yma 6ge6v kchem from a 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 travelshc+veq d/z:l8q:c e9oah zs 28 about $10^9\,km$ 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 acce;;o.a urjgc (qdj8 +vjleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker?.j;g+ ;o8vjjd(q cura (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 me1a+ djh)zo)trc 2b (v above the water’s surface into a deep pool. The person’s downward motion s e+)dzo2rah j)c1t b(vtops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it i mtuq-o2m qxu;w/pk0.p64hs z s necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea 2h.mz u6stkx4po qqwu/m-p0; 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 dize8t6/nanm (own when 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 perform evasive action, at what minimum height must it spot the pelicann8te6zmnai(/ to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer s+6iorzt xkc( 5- taz4 8vzegw1trikes a ball 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 particular green the ball decel+kxo-vzz aw 54t6r 8z ei1(gtcerates 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 freight train traveli(x2jqni 7dxwytibv* 68 kg(, vng at a constant speed of 6.0 m/s Just as an empty box car passes himx2wyvgvxb7 tkii(,(qd6 8*nj, the fugitive starts from rest and accelerates 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 fro,hvcg.ql*p 2nm the roof of a high building. A second stone is dropped 1.50 2gp, q*n.vl chs later. How far apart are 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 course of a time trial lastin 4*z xfhk7d7(xkfvh 1gg ten laps. If the first nine laps were done at 198.0 km/h .zf h1( xhk477kfxvg*d what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour b:xljc2qzh1 4 de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his averagh4 lq:xz2jbc 1e acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. 2 r0 jyep xl+efe 4*ec(n6o:2dyf:uvgThe first child can bounce up one-and-a-half times higher than the second child. The initial speed up o*0u ::f(2de cveg4e62jx fyye+ropnl f 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 95fgd 9 a2-of9iz km/h overtakes a 1.10-km-long train traveling 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. What are the results if the car and train are traveling izgao9if9 f-2dn 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 throws a baseball with a speed of 44 m/s In throwing the baz pm2*8vlf7go seball, the pitcher accelerates the bafv 7o8 mp*2lzgll 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 throwing motion.    $m/s^2$

  A rocket rises vertically, from rest,yf7 ub.ecp3 51 ,cp7 haeeork8 with an acceleration 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 /30i o5)gox:lqiyw k iuy l9(xshown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from /3 q(i0 y9 :loxi5ylk)iwx uogthe 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 +; wx85s nyqcwtakes off in hot pursuit. The police officer8sqww;c n5+xy catches up to the speeder in 750 m, maintaining a constant acceleration.
(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 from the roof of a buil49980f)n6 gsng uenpx d2rt*. uidzjbding; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.t9redbd)ngzgn x*ni0j4 f2u 6s8up 9.0 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 as*r8f u y9qfr+t the same time. The first stone is thrown with an initial *yfq+ frsru89 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 stone 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 resistance, how long would it take a freuhf-y ; 5a ,jldnog9/de-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripc dgh j/59-yl,dnf aou;ord? What would her speed be at 350 m? (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 to send the burgers throughp+60r jjo yih5kus)ak0*6 af p a grilling machine. If the grilling ma6ar 50kikpp* s6+oj j)yfua0h chine is 1.1 m long 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 vertically at a speed 1.5 times faster to3tp.) 3 u) n3h s luzg2zs.vpqgi*ap*han Joe can. How many times higher will Billsv*pzl)3pu* ) au23ggs.t3 h.qzi po n’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while v 1 (*xb b)fdol 2fb0;nlv1t7d+uexdt your friend stands on the ground 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 j(; *e dvl1+ttonxd 2)0dlbf bb1xfuv7 ust comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the heig1 jbs-(;ygzc2 r(g jikht of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it 1s-2rgy jjkb c(zgi(; 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 bicycles, A and B. syib -w+*f09qo vz;va9d) boo(a) Is there any instant at which the two bicycles have the same velocitzov b o0 bs-)+dfiwya;*9q 9ovy? (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?