Does a car speedometer measure speed :ug48 q:w2p/v8mtji y 1xjk(zqcmg9t, velocity, or both?

Can an object have a varying speed if its velocity is constant? Ifndv83z 7sd 8 imah4se:g( to*d yes, give exa o dze4 s:a8*m (vdtig387nhdsmples.

When an object moves with constant velocity, does its average velocityz-zxwow dq) 2 *bwmveo ,g/)o. during any time interval differ from its instantaneous velocity at any in )oq- /oz dm*e 2,wx)zvgwwob.stant?

In drag racing, is it possible for+cetoa,c*7t (+yv0 ;5 mk(lovhotqbhd,z yv. the car with the greatest speed crossing the finish line to lose the ra ,.(zoo;t0+b lmv7dc+q y*ht (5 ,vve yokcahtce? Explain.

If one object has a gtl9yt:jm(rc c)rur 08reater speed than a second object, does the first necessarily have a greater acceleratit 89)l0:ry ujmct(c rron? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90k dp*n8q7xve/lsx. :pw(j ad4g m/h with the acceleration of a bicycle that accelerates from rest pgx(sn4/ l w*xe.ajd: dqv7 8pto 10km/h in the same time.

Can an object have a northward velocity and a southward accelerationj 5/:h e3yi*ek79zh w6v nzq 2bzn t8y4vwd4cc? Explain.

Can the velocity of an object be negative :g0bf j agdmndd-h:g,x :4/nswhen its acceleration is positive? What ab4:bd an -0 ndf sg::/mxhg,jdgout vice versa?

Give an example where both the velocity and accelera5w/ohk/o*7 hjz3ptf btion are negative.

Two cars emerge side by side from a tunn*tja- ianmy09el. Car A is traveling with a speed of 60km/h and has an acceley a9mj0* nati-ration 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 tunnel? Explain your reasoning.

Can an object be increasing in spe p: jp(adr7 jfpogb542ed as its acceleration decreases? If so, give ab5gpp247jdfo (p:jr a n example. If not, explain.

A baseball player hits a foul ball straight up m.hkcu3g h/q)gbs l*0shw r: tm3cx34 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 travex 33rhs 0)h cl/uqcbs4tkm.wg:g hm*3ling when the catcher catches it?

As a freely falling object speed3zhrl/n5a d k y69lfuw63r -pay5gf *js up, what is happening to its acceleration due to gravity — does it increase, decrease, or g3ak /6lawuf5d y9 z*pyn3rf6r-lj5h stay the same?

How would you estimate the maximum height you could throwoqifq* zx68 grm3j+2w a ball vertically upward? Hoqgjr8i+mx 62 f zw3qo*w would you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a t7 /u,9i s6gus;cdxcvconstant speed of Then you travel the same distance from point B to another point C, moving at a constant ss6 c;9xtu,/vi7 cu dgspeed 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 bolts tie qf wijk pj-ys10j4 )zc,c,)sx2noui6d 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 2y i jw1sjxsq)cz-pof),juink6c40, 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 motpu94fgtkt7j 3 mvt1p 7ions is not at constant acceleration: a rock falling from a cliff, an elevator mkvm3 gt4pt 197tufp j7oving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown verticah-h-m lq08tq p-rt q4glly upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreqq gh4t0-lh8-m rqp-t ciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and n6h xy(f829 qhdb h6hf uui1un4onzero acceleration at the same time? Give exampley df(hihnu 4u 86hx6qhb91f2us.

Can an object have zero 8ho s+y5l;mbr3pg 8zi acceleration and nonzero velocity at the same time? Give exa+is5 z 3b;8h gplorym8mples.

Describe in words the motion plotted in Fig. 2–qioo wb8c +5ofh(- i,d28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by wa(fid5c wo+oqib8,- h olking or moving your hand.]

Describe in words the motion of the object grvr 49lkq*lm fvzo9(o;yjh 4m8aphed in Fig. 2–29.

  What must be your car’s average smefw 0)4ak qa2peed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long d1zmi (ufe *bvm59nft/oes it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side f i6da 7bmb5/dror 2.0 s, how far do you travel during this inattentive i 7barb/d6m5 dperiod?    m

  Convert 35 mi/h to h :7o6 tbop9fg
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fv)wfqa pjul++l q1o-+ rom $x_1$ = 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 k0je n8x7cy:uph+nk5srjj k.e aq--d7 m/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 38p7j7k d0u5-n yc+ erhxkj s-a:nejq. hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between fe5z 635sm7unkqm p c1a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate theuekzm spfm516n7 5q3c speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total tim;fkqga(bc m6iha *g 3n1*jdjgk h; hjn d+2;,re of 12.5 min. Calcudd1krjn;c j*;62 ; ahf+m(giaj3g bh h*ng qk,late
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight lineejy- ;cq:aqg-w:1 tuh2f8y./fdl sco, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfwaytgj;wycsc-fql1 yo:2de/f-: qauh .8 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. 0 ne-* -ikqb x3ylt1mpEach has a speed of 95 km/h with respect to the ground. If t13 -nq bkx-tl ipym0e*hey are 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 behind a truck traveling How long will-cr- h u1w5e i*(q ic)d wxjdyh./se8t it take the car to reach t.h sixc8dcjtd(5ew) - ur h*- w1/qeyihe truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and s/d tk.rcf785 fndh:rthen encounters a tailwind that boosts its speed to 990 ksn5dc.trd:7 hr k/f8f m/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-t(wlkgtd*7tuaepw36 4 rip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and th4agd w7 tk* wl(ept63ue return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pinfeqik3- rh7b/ s 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 of the ball? The speed of souh er-bf/i 7kq3nd is 340 m/s.    m/s

  A sports car accelerates from res50m5t q+*ef 1h)vawxkxqc0w gt to 95 km/h in 6.2 s. What is its average acceleration it)mcww5 aq e*hk1xf5 +vgx0q0n $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What a7e-.c+ovf r(c+xap em+;tkyis her accelerationc et(pe fa my.;-7vrc+xo +a+k
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is c6szstkg-2/,o4dfn hv apable of an acceleration of aboutfs ,zkngs- o/26dvht4 $1.6 m/s^2$ 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 m in 5.0 s. If it then dvs1 ;2 dd )/qvs+bhi;c dm+ngbrakes an+dd+2s ;1hcvdq dnivs)/ ; mbgd comes to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a raciru qt0/ +/2f5haxg uk a:nyt*oi*w hn1ng car, which starts from rest at t = 0 and moves in a straight line, is given as a function of time in the folloa orkgw2*tf5unh/0 th in1xyq/+*u a:wing 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/ n0dkbmhh *+,)xni9b ts to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assu0xk,b)n hdn b 9+itmh*me constant acceleration.    $m/s^2$    m

  A car slows down fro3 -*(jqnaigv jm 23 m/s to rest in a distance of 85 m. What was its accelerationgji(j*3-nvq a, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoffuv3v hv p. lpnh6f55 a72lp6eu6a jx7j. How long a runway is needed if the (constant) fev 62ph 5pp3lx7n jv7v6a .5hj6 luuaacceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially topfolt(lx5mv 2et4 ys5 l,q) :lr speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it tol:,tqx f2tl5l v)4sylrm( e5 ake her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed ol vi* i00ih6ktf 12.0 m/s to rest in 6.00 s. How far did it travvh6k i*il0 ti0el in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the )fwmp(f;bky 9 highway. Assuming a dece)9(w ;mffkpbyleration 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 en7y4k; .chvuiu d of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express thevi ku ;uh47cy. 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 forfj9 s mw t-5r5vxw04ip4 do1er a car with an initial speed of 95 km/h and human reaction time 44 5w0exmo5drrs1t p-fvi9jwof 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 umiij9 7b u08xthe 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 car’s drive5hgsb6f,v5bx /:t1xhgd j vhj* cri) .r looks for anhgvb6c*fvtj,1sb ji5 d 5gx h:h).r/x 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. Aff ,;:a5 v 2cvtevfb)ms) 5xpocwj(-vrter exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate atmc:s5vrtp -x, )b voa;vwefv2c) f5(j 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car e;mntmw 8l hyh z be0//wy2*plq.;*orat 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow li;*/e.h;q*lwme2olyb zw 0yp8 m h tr/nght 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. 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 c:*mere 6 bxy4oyfs(r0* hzc)top of a cliff. It hits the ground below after 3.25 s. How 4e(0orecfbz *:) ymchrx*y s 6high is the cliff?    m

  If a car rolls gentlh*bmuv ;:h(dv, lr jj7y ($v_0\,=\,0$) 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 speey:+a7j ,uh;v1t i (/i lixoamwd of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upwardbmfhc : v s;znq-60r+x zgnr1q:6qmz*. With what speed did he throw it, and what height did itf+ bh*:;mrcq rx : 1vsq66g0nqzz mnz- reach?    m/s (Round to the nearest integer)    m

An object starts fro i704plx6nkn/ c52hun +m jhlwm rest and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from72 5jwi0u xln+4p6hkhn/ lmnc t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascenc ;qe0z,)tgm q d1fhpjf:cz2 4ding 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 the ground? [Hint: The package’s ie ):1jz 4tc,0ffqzq dpg2 c;hmnitial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance trave uc2ch0:tt*s-afq a-uled during each successquh ac:-0-s* 2acttuf ive second 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 fopf5j(,px7x h swg7( ty,jv: ball thrown vertically upward with agsp7f(:xh7w,v5,pot y( jxf j 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 spx fikd1*y/rr6(f1nm deed 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 Fi1 7i ldle+1yngg. 2–18 (or number of photoflashes per second). Assume the+7l l1ig1enyd 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 0w ;z-xmkv18ug .28 s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fall?gkv-w; zx1mu8    m

  A rock is dropped from a sea cbkez t7z 0(s0wliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how0z0b7wes (k zt high is the cliff? H =    m

  Suppose you adjust your garden+6umj7qg: vxz hose nozzle for a hard stream of water. You point 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 striking the ground next to you for another m+uvqx 67:zjg2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speey, 2:dip ef:cld of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. :y:pf dc2li ,e2–34).
(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 window 28 m above thpzbdq h9 ;gltv1z4y)t0z 91uce street with a vertical speed of 13 m/s If the ball was t)1 u4zp tbqlvczyh ;t9g09dz1 hrown 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. zt.cp, t0qnvrikaq2*,nc ntbc6v5 .. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration cocv.qn,tv0cp crz at6n,*kq .n25 .bt instant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function o) * -br;jfj7ka6rnf +mnpkt2hed4b8jf time is plotted 6 b t28d * j4fpemk7+rr) h;an-nbkfjjin Fig. 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile ckal)vd +j:zd r,q rq);an accelerate approximately as shown in the velocity–time graph of:d,+ ar dq jkz)rqv;)l Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previohaw4mfnx 9 -bx 7.k9tcus Problem (Fig. 2–35) when it is in am 9 9k4 .nftx7wb-chx
(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 thesjfm2l ,9h/t glk9 vl1 distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a fun yh8 4dfnft6r j6mf(fok z)5c4ction of time is given) j fh5f4m6d64 cffzorky(tn 8 by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motzgrhh-tni ,mr:5q68 eion 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 t-r,zm6 85th ig:qrhn ehe 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 or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story windogr 0o ;qqazik9:e,e x8w 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.9,or i8ek: 0qaz; gxeq0 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 wh t gi0k705qv r.vx2rahat it is on Eart0g7haxv0.k trriv 2q5 h. 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 initial velocity?

  A person who is properly constrained by an over-thh 9vy9w1; eqxme-shoulder seat belt has a good chance of surviving a car1eyh v99m xw;q 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 below, and h2hf7(tkz/0jwcq tx v4is 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 abov(0cxz2 tk4w tjvqfh/7e 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 itsz) wdfmro4) u6 cars for front-end collisions by hauling them up on a crane a)ofwu 6rdm4z )nd 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 Earthaq0bqp/a 2ej 4pk3;ze travels 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 uni*o- lj xkv ye09hi7iw1c.g2jvform acceleration 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 egw*-7vloiyx 0ihj 9.1vk2c j 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 b4tg4du z:w* s dh3m edu7us.,water’s surface into a deep pool. The person’s downward twd 4*d:7 4uzusdg,ebms h .u3motion stops 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, im-3mwi/ flkwu7 zb3ygkuw (v .w9q9w(t is 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 idek-wbg yiw7. 39f93uw/wul(wq( mkmzv a 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 wvnd; ie foiv 1)+ s.zpf;2db;xhen diving for fish. Suppose viffino d;ed+; sp2xvz;.1b )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 surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planned qzj aj ,231hgpso 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 difficult23qg p1hja,jz 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 freight trainu9p* i;qv 6tst2kqf(lr+ gn1o traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and a6k pln to1g;+rtuq9q fi2 v*(sccelerates 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 tq4mjanzln - cd .tqupw/sd/3 3h,j-4qhe roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the sec4zt q3cp-/3ns-w jh q duan/mdlq4j.,ond one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the cour)t10i q5h,r w1exk bgese of a time trial lasting ten laps. If 5h1tie, )gk0w1 qbexr the first 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 pass as he moves at 18 km/f 91 e++ ch gpnikj5bqqvo:k+,w9i gy,h . At the bottom, 4.0 km fartheynfep9h+kjwc iv gi1,:q b+ok9q,5 +gr, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on t4 c ooehb32rw/vi(f6t wo trampolines. The first child can bounce up one-and-a-half times higher than the second child. The initial speed up of fv w436c (hiro2e/otbthe second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a te.f1(xk8r:)h y 0p nun3-gy6godspy1.10-km-long train traveling in the same direction on a track parallel ty 1ng )36o-kf(0 ypgt 8hue xspd:n.ryo 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 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 themijut9rn ph( 5+hp/;t baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during thuhmj 5n+phpi t/rt 9;(e throwing motion.    $m/s^2$

  A rocket rises vertically, frx4 9 dch4w6xybom rest, 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 r - o(vwqwb5kj;w;g:mshown in Fig. 2–42. Each intersection has a traffic signal, and the srww5 j :mbo-k;qgw( v;peed 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, passed by a speeder traveling at a cons;(ro bpv ,nzuod;e8u7 tant 120 km/h takes off in hot pursuit. The police zu;rbo,8( nuoep;7dv 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 fr0nreg gosp7a )tv/y62 om the roof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/se g0r/sva)62gtyp on7 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 5g k+5ddp e5,ceto9 pbsame time. The first stone is thrown with5 p9et5k5,dg db +oepc an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second 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-fa;nro0h cwm-u/t+ /nee: spo e)lling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 kcn0) ee oumsp:w;/ o-t+/nh erm/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers throughceexyvh5p ld q 0*2(niz1l-,y a grilling machine. If the grilling machin2 -0pdlyz *q,i5(x1ecyevlnhe 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 fal 8 kroxlo)x p-z3pd,y;am:d0ster than Joe can. How many times higher will Bill’s ball gyorx 0):l-;px k8aodl3z p,mdo than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top oqi027u+k4ow *tfqa kl1z 4qg if a cliff while 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 just comes to rest in your hand. What is the speed t 4qiu iazgk 0w1l4+ kqfq*7o2with which your friend threw the ball?    m/s

  Two students are asked to find the height oq (f (4j+aeue :82vgnlo ds6xuf a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take ieosjeqxd: ( 6fv+l( ng4u u28at 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. (a) Is cp9ey.8(l ql6 p:wfhy 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? Which bicycle is passing the other? (d) Whiyl6 whlype(p q :9c8.fch bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?