Does a car speedometer measuk nfq(2dpooi.fh l 1ep8bf,(( re speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give 2 z ; aaf)4oilbl-r,lkexamplel2 af zlr;, ia4-klb)os.

When an object moves with constant velomr z: d0 cfa;wp-nu,8 hb8gp6gu95jju city, does its average velocity during any time interval differ from its instantaneous velocity at n 5w;zagcd p-,hb8uupjgr0j:f8m96 u any instant?

In drag racing, is it possible for the car with the greatest speed cros29hnvza b7mfl 8b5y:vsing the finish line to lose theb8fmb5ya :vhzv7 92nl race? Explain.

If one object has a greater speed than a second object, doesn2 oro*st 1y*d4f 47 lsn5dfwp the first necessarily have a greater acceleration? Explain,*41 t472nr5odswsp d nlf*oyf using examples.

Compare the accelerat f*su e2 wg*4anl 5srp.pkaa)*ion of a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of e4 rg .pnss2ka)wf5apa *u*l* a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward veloe gfrg:z;0:ea city and a southward acceleration? Explain.

Can the velocity of an object be negat.v3cnid9o;jg)ultt 1ive when its acceleration is positive? Whatd ;o.l9)n ciut3v1t gj about vice versa?

Give an example where both the velocity and acceleration are negative.s/tcu)ir1rl-j( a+e :mnwps2

Two cars emerge side by side from a tunnel. Car A is traveling wit cf2vw3szxn :ju -c2(d riviv;1-b(eqh 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 of the -1jv3s ice(qzni;fc22xd: -vv(br w u tunnel? Explain your reasoning.

Can an object be increasing in speed as its a0+uo dcr v35o*v3i .wswp++/sq o uwzmcceleration decreases? If so, give an example. If not, explai ws.o3*u svv0izr+p3/dwu+mo +qowc5n.

A baseball player hi smopmk0h-/h16*x u dzts a foul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be travelingm6kuh hx-m1d/o zps *0 when the catcher catches it?

As a freely falling object speeds up, what is happenib mo:ev2w-s9tng to its acceleration due to gravity — does ito:s2 mbvw e-t9 increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball vertically u)2c0gqg*+re *xaelhm 0oiowwh i, *o8pward? How would you estimate the maxim*w h *gec08ge2+ rohoao0x,qiwm*) ilum speed you could give it?

You travel from point A to point B in a car moving at t pheov-)6 fw.a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/w)op 6hevf- t.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-long vertical string m4eo5b,pve wwip6 9 /xwith 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? Wve65imp poxwe9 ,/4b 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 acceleratir-ded0 / gw/-uh-bb:vi)p9dz a,lh yk58 oxneon: a rock falling from a cliff, an elevator moving from the second floor to the fifth flooeplhd/dawbhe/0u)bk5o9zr x :-v i8-d, -yngr making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its orig/l2kibs +c 7pmho(eu 9 e+hhb-inal position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciobem kuh-c(79she2 h+/l+ibpable, 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 zero7b wl +tk btggo)2s+ka3 zm-q3 velocity and nonzero acceleration at the same time? Give examplls m3 w +ok2tbbq+)k zt73ag-ges.

Can an object have zero acceleration and nonzero velocity at the same at i qa 16,)pve:kshp2pd ag**time? Give examplesa*hakt16pqav i2p*edsg : ,p) .

Describe in words the motion ploc;wf 5jd r+f8atd9ff)ll +*bitted in Fig. 2–28 in terms of v, a, etc. [Hint: First t+i5 awj;dc fftf8+fl )bd*lr9 ry to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed bcwq5)1ynx;m in Fig. 2–29.

  What must be your car’ ugn xqs2/rhyb3bk/);s average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it takea y d4n+k8b)r uj8t4lg to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.+uuk: 7 cqj5r0 fdmxvc5.mvu40 s, how far do you travel during thisuq cm: 0kr5u5vdum+xvj 4 .c7f inattentive period?    m

  Convert 35 mi/h to o-npf i. la:m6
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frov ,93kqjtz2z,z i5 cnkm $x_1$ = 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 13i(5.kc79zw*g woyp fo0 km. It then begins to rain and you sloww .k(owp *gfzc5yo 7i9 to 65 km/h You arrive 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 betwe*i3 5yr mlnxjt0+wm4j en a lightning flash and the fj ix* 4tw0 nyj3lr5m+mollowing thunder gives the 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-mile track in azk zxn t71cnya0oi;(9 h.i* bs total time of 12.5 mix;ct9nn* oh aziy .k1b(z7 0isn. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 mo1wo gk9 4ss;w away in 14.0 s. It then turns sgwwo4 oks9 1;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 a speed osbj: )t3f.fsdd*b :tlf 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long wil t):s b jsf:.dd*3ftbll it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will it ta0 +z ,ww h7-wr/bqewvgzhd/ m5ke the car t/qd,e +vzbmwww7 0g/r hh5 -wzo reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and 1:uhb5 cgv sd3then encounters a tailwind that bohv: sgc53 1bduosts 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 vel vzgw327q.3m8r op5pu / na bme6yeck1ocity of a complete round-trip in which the outgoing 250 km is covered at 95 1z6po p7wgrnke/ 3.3 b mmu8va yqec25km/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 speed hits hyo59m;4 gbtgv vc3p 2the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pinso v ;2y vcp4gmbtg359h 2.50 s after the ball is released from his hands. 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 in 6.2 s. What is its average acc kxvp(s)gt:smp.a 8p9.a1rp o1rgr5 welep :ptg) .rar.g8ms kv r(s9ap5wop1x 1ration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accelerationv,2k +vv*anz.0 psjb pbkp+0 a vnjz ,sv2.pv*
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a pax5) 7 4qevl lg;qbosq6rticular automobile is capable of an acceleration of aboutqe4 6ovq7 sg;)l5l xbq $1.6 m/s^2$ 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 110 6l4-wj hb0 zrxm in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what ibjwzl - 6h40xrs 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 fromrw0qz nm9 v)p2 rest at t = 0 and moves in a straight line, qvm)09 wr n2pzis given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration 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 acceleration?qe)sjq n;j:u2dz3fv) How far did it tv uj2fd zq:);3)jnq esravel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was s / +-elaj9(xbuup m+,kl2h +cuols*rits acceleration, assumeuh/+2ak-9 +upxl*, r+m (es uoljlbsc d constant?    $m/s^2$

  A light plane must reach a speo3f8yq/d uhd.r/ qi1 eed of 33 m/s for takeoff. How long a runway is needed if the (constant) acfoei/dq3 d1.8uryq h/celeration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentialil uxxod /y.8-lks;-d tgzit+/ v6q(g ly top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average accelerati6oi lv.+udggtx/k qly/x-8;d- ztsi(on 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 1*n n::cu dq,xu2.0 m/s to rest in 6.00 s. How far did it travel in that time? cu *dnux,n:q:   m

  In coming to a stop, a car leaves skid marks 92 m long o4*xxzni 3aw d5hx+8yi /voi e6n the highway. Assuming a deceleration /6ix nixh *doai8z354wvey +xof $7.00 m/s^2$ 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 compresjt ne.y0 x(.clv(5t c0: uukwgses 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 answer in te.0w unk xgctue .lvy t0:cj(5(rms 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 s qr,i+i o)4,cocls4e apeed of 95 km/h and human reaction tii4, l)oo,iqrc 4as +ceme 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 betwk .il4 f1*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/s on the highway. The car’s driver83v4q;tbbc u w looks for anbu 4wq8;tcv3 b opportunity to pass, guessing that his 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 than 30.0 min. After exact if0)g f6uci bcbv/mr*v9 ;p;xly 27.0 min, there are still 1100 m to go. The runner must then accev6 0m/pxbi9gu;); c frvb*icflerate 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 just2:mmo 6i:50fo ef xmky as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 mf5:y:m2o0foe 6kmm xi 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 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 t b56a9pt1)u fem( rrlhits the ground below after 3.25 s. How high is the cliff (5mfeutrral 1b9)p6t ?    m

  If a car rolls gentlyyoa 870 bgq/gu ($v_0\,=\,0$) 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 s+ka13qiab idubv:jb 8xy4up1; ,wn8 o*tml3v traight 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 s4t psn7k2vqzuh *x;o:x; cjf s3+ire9 after throwing it vertically upward. With whatecrsno h;x493p +tj sq2vz fuxik*;:7 speed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from res*uem q p27b-gi7zas0wt and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has faup7 q7z 2e mb0g*s-iawllen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height o:f+k.;cxe k ou 8(yzwnf 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? [Hin; o8x ycn+ezw(kku :.ft: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely wpj:owqwn5ok sgs1 5u-:k.+l from rest, show that the distance traveled during each successive second sj- n:5wo:+k1l .qpu wwso5kg increases 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 ball thrown verticb8 (jcm/fd63ccu 9havagpkw 6pod/6:ally upward with a spee9c6amw8 jp3voafd(uc: c6d/pb 6 g/hkd $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a5uk yd-xb,+mo 2nf (vt 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 photoflabq qu2j+28v4d xkol f*sh of 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 thq+l4djb *ku2ovfxq28 e unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to toxw1 * m7 ,-f9(: zehtfeo-ur )jnoujaravel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the windo( m,oxawo * 7uof)frhjnue-1j ze-t9:w did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it sm9q3blh-mc 8b dm3 l5qtriking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the climlq9- mhm8d 53 3clbbqff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You poingwe d tbc*-jm-)gjz:)t 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 the vertical, you hear the water st-ge:dg) mj cj*t)zb-wriking 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 spef* 8qp ehttvpc;f2) v+n-6sbded of 12.0 m/s from the edge of a cliff s 2f)v6ev*pn8 ttdfb;h+-cpq 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 bjj.kai,g s/6w.8 wgi 9daql,yy a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from t,86g jy.awi l/qdk,sia 9.j wghe 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 o )b g/s*g3f)t(bqc)7jsolf vvf a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, ivscf)( g tl)q3j7/vbfo)s*bgf any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunf yd; fudv l5wu.1tg+6nel as a function of time is plotted in Fig. 2–28. What i 6f1l .;tvuwyddgu5f+s 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 can accelerate approximately as shown in c;ne8+w aziz1t9 wo /k6sol(ythe velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the ga/ 1k ( zsl;o9ei68o+zwcw yntears.)
(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 th+ cdd esbe)hj77.f/hze previous Problem (Fig. 2–35) when h+dh b7ec z .7d)f/sjeit 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 /*x eh juldy5*traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function of pkm; tc /nud(.time is given by Fig.d;ctm.(uk n /p 2–28.

Figure 2–36 is a position versus time graph for the motion pe0 a,zd *7eyeof 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 down? (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 oz,edp* ey7 ae0r 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 mhk9m *syte.s w3cq4f ,m y1ih8t+ay)above a firefighter’s safety net. The survivor stretches the net 1.0 m before comin yq +myf 38,1mw).t kchs4siyt9*amehg 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 c)q dn3qnwv*6 .)pdvd is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would)d c)v.vnw* dpndqq63 on Earth, assuming the same initial velocity?

  A person who is properly constrainuc k;.e jx.krcu 3nqk*j 8z/bpb,/ 0zeed by an over-the-shoulder seat belt has a good chance zzjuk;neu.b/kx, b q3ep8./k 0jrc*cof surviving a car collision 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 bel:ji h3wm z6+w9kf3is:cfp z2uow, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s ,z3j fmi c 23pwwu6zf9+ki:h: 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 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 manufac sf wlfaw*8.)f:ms/n qturer tested its cars for front-end collisions by hauling them up on a cran *:sf.8wanqf ml/fs) we and dropping them 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 h - on pf(ky3 1ds9h:/urv6:zb g*pifztravels 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 acceleratif9d6. nhg/oeion from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is 6/iogh de.n9f 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? (See Fig. 2–38.)    m/s

  A person jumps off a wm7kgi;g ,a)xeb:v *kdiving board 4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of ibgwv);xa*gekk 7:,m the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance thkryharcg3ra56 h-y2sz v+ ipl7 az*;(e 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 of this probly6i a-* kashp7;5gzhyv 3lacz+ rr(2rem, 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 diving for fish. Suzlvoe .kr(s 7* vn+f;tppose a pelican starts its dive from (kz;.rnlve t*7ov+f s 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 pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is plfg7ir+031 scwhcd( n ranned so that the ball will stop within some small distance of the cup, say, 1.0 m long or sd10cnrs7gw c+f3( ihrhort, 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 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 fre2oey /scaofl 0a8 (fc*ight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from ro 0y8seacf*oc( 2 fla/est 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 from the roof of a high building. A second stone 9nhqn z:4:8 emf/h gjtis dropped 1.50 s later4:qth:ne n/hm8f9 zgj . How far apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver musxhyiup (-62;cctle h8t average 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were do6ycxphi 2-;le(h u8t cne at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 km/h 9oww* 2yoqrt1o1qjw 7. At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average accelerat21wr jw9oo7 o 1qy*qwtion (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first(.g4fnr f)me3/8rnlr7-i sutta u,s b child can bounce up one-and-a-half times higher than the second child. Thburt7f-() 8.gus,m r4nnlet irs3f/a e initial speed up 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 o9j:spd5t mk0d* uw6mafz2 vu,s m2r 495 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.m95fo2va ,dksmdr: jp tu*0s42w6u m z What 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 throws a baseball with a speed o-um ,zmn skpw w4avw4m: ,h*6;yev9cmf 44 m/s In throwing the basebalcu4 emvm,p: wmzhva; *m-6wn4, w9s ykl, 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 throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, waht :o:rwugm+.m +no9ith 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 patte kb6cpt2r)2ov rn shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppvt22r6po kb c)ose you 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 traveb) pulzdi.acw f-(; )yling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintu; )()icwlbad z. pf-yaining 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 fr ogjn x0.)rf0m4lb + pjlg-.-gxogza;om the roof of a building; 2.00 s after that, a second stone is thrown straight down rggf oj)-0mx0gn 4xbol-zlp ag+ .j.;with an initial 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 savpef2o jj +r/e h)tq6-qnju;1me time. The first stone is 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. W u+v -jq1eqnhfr6tpjo /)2j ;eith 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 free-falling p.m6rrfyt w9- garachutist 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 m? (In reality, the air resistance will restrict her speed to perhag-rtwr.6 y 9fmps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers te 2s.r7omrd/ro/ +p bbhrough a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, h7do/ /bob.es +r2rrm pow 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 ver3nyn*frp t;e 24wfi8y tically at a speed 1.5 times faster than Joe can. How many t4nn* tr2y fpey38 w;ifimes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground belo7 g5l0zdnb 5(awhi (uaw you. You drop a ball from rest and see that ith(db5 ni0wl5 uz(aa7g 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 the speed with which your friend threw the ball?    m/s

  Two students are asked to find k6bsqt +nj6:1jdky,d -)aongthe height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the buydka- 16j no,:tb +sj) dkqg6nilding 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.j( xlrnb-) 3ni (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Whicx-rn3) nblj (ih bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?