Does a car speedometer measure speed, velocity, ogq 5ka :jre* l3y-+r)yufh( xdr both?

Can an object have a varying speed if its velocity is cons*9u, apbvc +wj-jxpz- tant? If yes, give examples*jz-v,bu ppj+ cawx-9 .

When an object moves with constant velocity, does wt jjyt.p2 m,/its average velocity during anyjpj yw,.t m2t/ time interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for theyia;x6t/ee4-1o ) fd rwzcqz 6 car with the greatest speed crossing the finish line t6e qw)fziye;rca 4/xd1 z-o6 to lose the race? Explain.

If one object has a greater speed than a second object, uw-.yuj5t:r-t /lr98 t gix5tinx w 7vdoes the first necessarily have a greater acceleration? Exw5n7-r9u/8gt r5: iv it-twujx.y lxtplain, using examples.

Compare the acceleration of a motorcycle that accelerat3hcse ) ggd-5ges from 80km/h to 90km/h with the 3g- egh )gdcs5acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a uma2f: n)yws:,slhu- northward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its accelerf rh5/f)r /fr6 fgj.wlation is positive? Wharf l.frr gjf/5) h/f6wt about vice versa?

Give an example where both the velocity and o avl,qk3) *i8j-himx acceleration are negative.

Two cars emerge side by side from a tunnel. Carx8bja1+7io +xatih9t 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 passi x+bjttoa+8xih9a 1i7 ng the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, gi;fd)z xbm9/1quy sg( zve an exampq ;zfd muxzb (g/1)sy9le. If not, explain.

A baseball player hit:ef7qtwc7s 060l7+jyagoyyds 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 traveling when the catcher catches sc y+7y7g060wjqatl:7 yfedo it?

As a freely falling ovan8ge4 morx i2x4 ;t4ker/i:bject speeds up, what is happening to its acceleration due to gravity — does it increase, decrease m44ig;irv:82rx n/e ot4k xae, or stay the same?

How would you estimate the maximum height you could throw a ball vertically (ws.fy:beeyc-4y aj6upward? How w :a cb(4-jyeyyfws6e.ould you estimate the maximum speed you could give it?

You travel from point A to point B in a car movinrew c4, kvh.v8dbp,:sd,t g7eg at a constant speed of Then you travel thvp.r 7dec8vg,, k:hwd,b4 ts ee same 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, a 3.0-m-long vertical string with ten b1+xd v; ho ovjq0/8tjiolts 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 nea;1+o0xjtiq doh j/8vvr the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motionsa)/bi/kw h eut 29: mdmeby85i is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor i iutekb)8m/y5bmd/a92: w eh making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its origweg.bw9 efg,oi*:6ho inal 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 wwee,fg. 9h6boi*g o :the motion.]

Can an object have zero velocity anxlgzrq y:)24nd nonzero acceleration at the same time? Give examples.qrxy l2 nz:g4)

Can an object have zero acceleration and nonzero velocity at the sa;q,2k qyv8 gudme time? Give 8 kq;2g,dqy vuexamples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. qt5p* az kd4g-[Hint: First try to duplicate the motion plotted by walking or moving your hand.]-4p tzaqk5d*g

Describe in words the motion of the object graphed in Fig. 2n5;k 1n2ceud k gt2h;c–29.

  What must be your car’s average speed n u9, b)rzizn,in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does pnwqn8,qk , 8e 34mde wq.vmkw g64mh3it take to fly 15 km?    h

  If you are driving along a straight road and you look ttsv p1gl jj:48dx4(gf/axsc -o the side for 2.0 s, how f8c sgadvtjxjs/- :4 x4(g pf1lar do you travel during this inattentive period?    m

  Convert 35 mi/h to zvrr /xx;:kr 2b dhj7:
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from 1c;jj)n* pp, v qrf.2-ev4 gulyzr mh9$x_1$ = 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 kbk/aaiqs b lpxqma448 6b;-i1m/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after dr l8ma6aikp41-;/sq b4qbai xbiving 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, everyaw26 erk,yxdf6 ed3 m8 five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of ligw8 x yeed66,a3rkf md2ht 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 quarterbgdq 5/ k3m qzd8ftg21-mile track in a total time of 12.5 mik3 b z2gdg5qqm 8/d1ftn. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its ( +;wr mmfpytz2hw*6mtrainer in a straight line, moving 116 m away in 14.0 s. It then;h 6wm+pmwmy t(2*rzf turns 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 approachw xi6./vw h6 mcj,4 mpuyexo)4 each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they arw4uihc6po 4mvyj., we 6m)/x xe initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m bes9id,u0t s8vgx;g *a ehind a truck traveling How long will it take the car to reach the trucge8t 9uds,x ;gsav0*ik?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters s-*a) xy p,tcwq :8j5w+m0 cvpp5qscba tailwind that boosts its speed to 990 km/h for the nex5+,yx cms5bv*wp :qq 8pwacst-cpj) 0t 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 anjv*ge; 4dvm i9okl /,gd average velocity of a complete round-trip in whio,kd9/v ;iev*lg mgj 4ch the outgoing 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 wi2z:26mq aaybt 1z*,hdaowp6zth 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 bao ymz wbpa2:q6,26*ztza 1ad hll 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((cqjjq0lfeu vd qe5 rp:td*42c x25n 7f:sza its average acceleration ip t7qej snf224duqxf(adqc5l0z r* 5 :j:cv(en $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceleratiowy h wxrf30.n/wl13av n a1 .vh30ylrx3w/ nwwf
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acceleration of abou l2eyy)b/m numoku/:nj,l+u 6 u /ymlle)um, :j+onu/ykb26n t $1.6 m/s^2$ 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 tr1-tet: ;;pa0ekczx pe 76dp xjavels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its zep0;6pj1 kpct x7 xadet-;:e 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 94*ukzz dswvx9q g/z9car, which starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time9wq/ x zd94vskzgu*9z. 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 acq67 dlaemyfd (l0pt/m+ l)d6mceleration? How far did it travel in this time? Assume constant accell dlm /676a)ftmm+q (ypledd0eration.    $m/s^2$    m

  A car slows down from 23 m/s to rci *-oksin17ltd l9 u:est in a distance of 85 m. What was its acceleration, assumed cons1ind:i -oltc7s*9ul k tant?    $m/s^2$

  A light plane must reach a speed ofza s2c9 lqvh7- 33 m/s for takeoff. How long a runway is needed if the (constant) acceleration is7h -9c qlas2vz $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentidt; bqrq *hpb*0t kvxkmi*sj t8;q241 ally top speed (of about 11.5 m/s) in the first 15.08db xht1 t 0qptr;*bivsqj;*qkk 4m*2 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 12.0 m/s to rest)1 r10lcw pf)dg1ntkt in 6.00 s. How far did it travel d g)fr0)c11ptlt k nw1in that time?    m

  In coming to a stop, a car leaves skid m91wsgk/ out. j4flo -uarks 92 m long on the highway. Assuming ao jt1/f w9u4lg u.-kos deceleration 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 the car oyj) mr ;go,v:compresses and the driver comes ;, )oym:rgjovto 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 fwahan dyn(q7: j) yp,k 0w13gs z9:xitor a car with an initial speed of 95 km/h and human reaction time ohaqd ) j1xpzi07nwyg3s:,a9nktw :( yf 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)yy76l;n7vbsc rfh +kr/ 8ju f for the stopping 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 cai6im7z im/a ll36:xe-cp eqr 0r’s driver looks for an opportunity to pass, guessing that his car can acceleratecq z3 6/leimxli 6-e 07apmr:i 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*bvz rz3o )t.rby iijem40 6x, run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner mus xmbozibe0 v3. y,*jt4z r)6irt 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 intersecti(76hv 0akizqu 7zs aqo *t3:thon 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 should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Hes7ahva k3*zq0t 67:i zouhtq( r 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 +3;st x/dzeo 1)tn7baa i9cshtop of a cliff. It hits the ground below after 3.25 s. How 1cs/s3 dbi9 txa)aeo 7zth;n+high is the cliff?    m

  If a car rolls gently /zlkx9 .wxox( ($v_0\,=\,0$) 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 f)t v2qzzv(c-cx/ a b422 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 throwing it verti 2qy(8h9ymeu tj8 35alqz:ma rcally upward. With what speed did he throw it,5qu8lymm2:(t8z a qey a9j3rh 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 gravity. Draw grua0 licgh8 +d8aphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t8a+du hl 0gci8 = 5.00 s . Ignore air resistance.

A helicopter is ascendine hgs:n(9 ip-qg vertically with a speed of 5.20 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 th- :s eg9n(piqhe ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distancu ,tmr.l9 59gc3a6phl+wk+q x 5wmlode traveled during each successive second increases in the ratio of successiumcr wdmql9 k xo5l63pwl,h.+g59+ ta ve 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 (axkdvt )rtb e1).b2 vd,lgebraically) that a ball thrown vertically upward wirx,k ev).)d dv2b bt1tth a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticallora(zdm- i28zly34 r9gp ox mj af:f84y upward 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 of the apple in Fig. 2–18 (ozq2tw.+rmyu548cni)j s dy v3r number of photoflashes per second). Assume the apple is about 10 ys4nur5y vidc jw3+).m28q zt 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 zsf/vh7e .s r(0l(t ompast a window 2.2 m tall (Fig. 2–32). From what height above the topre 0o v.tm/s(s(f l7hz of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sxth6 4vn *zfo1 u/3kqbound of it striking the ocean is heardtun 3xbzof6qv/ h4*k1 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle fol -;p3ie gc. vr i/1y;w9ndysdr a hard stream of water. You point the nozzle vern/dwy 3.g 1 ds;-;ier vipc9lytically 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 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 verticallxui006whpge bvx7 5 ym5a+am) y upward with a speed of 12.0 m/s from the edge of a cliff6m5b 7+yam5x0vpi xwau)h eg0 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 a windo vgq* 1htinvvh;0dh-kq -gcz++ )3uz*1i rxlfw 28 m above the street with a vertical speed of 13 m)v1z-0 ih3utrglx1+q-* kz ch+fnidgh* v;v q/s If the ball 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 .e(yvo4 ow6l2,qy8j nbv9 ticvelocity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what period jolny8vvq9eb(4,2 6wo.c yits, 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 tun-ix3 rhy b6maoe (i.b:nel as a function of time is plotted in Fig. 2–28. What is its instantaneous bxam (y: 6i- ibor.3hevelocity
(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 ac-ed4t 32uvn bpproximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)ubv 234ec dn-t
(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 acceler*2 frt* kn(pykrvh xaud8m /,-ation of the car in the previous Problem (Fig. 2–35) whe/rx-*mkvaud ykth, *2 (rnfp 8n 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 traveled adoxt pptr3:ac+c3 u 8f+ix- uc-r/4aduring
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the obmnq (.knjyzof1dl+ h:-ksv. )ject whose displacement as a function of time is given bym.f dkh( ko)l j1v.n:s yz-qn+ Fig. 2–28.

Figure 2–36 is a position versus time grap/ts3 r.lwhqof0bc28 n(:tgmn5s: c d zh 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 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 at::c 2hswcl gtb5qm.n3/ 0 zsnr(d8focceleration 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 wink 20+gk9mp nafdow 15.0 m above a firefighter’s safety net. The survivor stretches the ne0k+p29fg kmna t 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 o 04cah-8xceq an the Moon 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 on Earth, assuming the same initi-caq 08aecxh 4al velocity?

  A person who is properly constrained bko*v;rd eh.h) y an over-the-shoulder seat belt has a good chance of survi*.vr; hokh)d eving 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 britryobwa 04t, xn1p.2 odge, 12 m above the road 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.,n ro0yow tb pta214x 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 manufacturer tested its cars for front-end collisions by y )jslccd,2avcv1*t* c2i)r yl. fgz1hauling them up on a crane and dropping them from a certain height. 12ylac*t*z)c vc vid,2 1crg) jfls.y
(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 tr( gov8fzk ;*dyf iq.p8kbb6 m3avels 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 acceleration from rest. The fro r9mf q+;iz. y/z3txlvvkimg 1.kda4:nt of the train has a speed of 25 m/s when it passes a railwayd:tyl3kif9i v1+..rk zq ;mmv4x /gz a 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? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the wate ,6uk0x ;zlvtjr’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average;ljt,u k 60vzx 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 is necesvfn qxkzndr29;5my)ij1 7 5xqsary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average sx572;9xj f ydiknqzv )1qnm5rpeed. 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 diving for fish.;pvpw g7 k3imf *h2h8b 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 pelican to escape? Assume the fish is at the s pmh 2vf;p3k8hbwg*i 7urface of the water.    m

  In putting, the force with which a g3kd2wrdgx9 h/olfer strikes 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 dk 3d9xrd/wh2gecelerates 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 traveling at a constant speehds i*1 h 8s4bihd)mr-d of 6.0 m/s Just as an empty box car passes him, the fugitive starsh )d4dhsh8-*irb i 1mts 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 fro9;x.lwpb mqpm; d( t)nm the roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stones whpwlnq(b; . x)p;9mtm den the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/hi(8,itshu,yad8 y sc) over the course of a time trial lasting ten laps. If the f hid(cs yaiu8y t)s8,,irst nine laps were done 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 pgz- 01 x uhvc2o)7jfbzass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average accel2cvhb zz xf-j71gou0)eration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounceiyw5egbbnb8 9/ )g08gg(clmj up one-and-a-half times higher than the sej9)b 8bn g0/l c i5gygg8wm(ebcond child. The 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 95 km/h overtakes ams 3(ny +5 rtm2u3vsaw 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 travnumr33wta ys 2(v5 ms+eled in this time? See Fig. 2–40. 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 of 44 m/s In throwing tfc g esj gum;uz4xy6h.+0v-u3he baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, +yu;xhsg ezufm4 30.6 g-jvcufrom 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, wlrxsj4 4. oaf64x3wuzith 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 shown in-i4 1z: qkz6er 2mfk362ods vflhru6e Fig. 2–42. Each intersection has a traffic signal, and the speeo-6f k dre23u6 mr64hel vi 1zsfkzq2:d limit is 50 km/s . Suppose 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, pasr i7l+o4n* bsgdw*l t48j+xxb sed by a speeder traveling at a constant 120 km/h takes off in hot pursuitl*j874xlwb+gnxit*o b4 rsd+. The police officer 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 building; 2.00 s after that, a p,seloq6)q)vn q*;4 ubm k dr*second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones la*qsl) qo 4e d );nm*q,urv6pkbnd 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.kzxb: b3e-kb+2 +cok r The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits t2k3- zr:ko +xecbbk b+he 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 fre x;4s xdj59rs6gdhx*ne-falling parachutist to fall from a plane at 3200 m 4s9dxd6h5j *xsg xr; nto 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 perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a grilli2o5.td. a)jkj-iysy 6vsb0rt ng machine. If the gbk2. y d yjjs.a)-65ott 0irvsrilling machine 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 k4ldr5 t u5/ytat a speed 1.5 times faster than Joe can. How many times higher will Bill’s ball go th455ruy t/ldtkan Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top olj9.a6 b/ jpwvf a cliff while your friend stands on the ground below you. You drop a ball from /j6jpw9 vlab. 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 the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular buik-ndem,(cq9; g (zf *ilmp tx9lding using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One stfp9dc -gi(tlm*q9 n m k,z;e(xudent 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 coq.zqxy0y q c/v+*/igraph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has th.cz//+i*qy q 0cqvyxoe 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?