Does a car speedometer 68,3id:ydp:ai *qmmbkz a(exmeasure speed, velocity, or both?

Can an object have a varying speed if its velocity is constantzw3a;w nprequfe )i n3a,6) v0? If yes, give examples.zfu36ep,w 0rv3 nnaie)q)wa ;

When an object moves with constant velocity, does(yp2k 0)h itj jlup(d( its average velocity during any time interval differ from its instantane)(hkj tpyjp0i((2l du ous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing t)buljpj.(zq0e. j-sthe finilq-.(pujz ebst jj. 0)sh line to lose the race? Explain.

If one object has a glx)q4:emiicx*n sdc r8,za (- reater speed than a second object, does the first necessarily have a g(qedcs:-i * lxzc xrm4)ai n,8reater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that acc,oso)d;ka6eau,4xp8 js0 o h velerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in ep;sh0do6 x8)svaju 4o ,kao, the same time.

Can an object have a northward velocity and a southwardh(gnqr;on:6 a acceleration? Explain.

Can the velocity of an eer82s5jcep 1 object be negative when its acceleration is positive? What about vice v rec p8j2e5s1eersa?

Give an example where both the velocity and acceleration are negx hd6/fc kt- ;hv)bv3zative.

Two cars emerge side by side l*0,.zwgbxbe from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a0b*. zwl,b gex speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decrehmeqnj6q j. *5ases? If so, give an examplhemjj*n qq56.e. If not, explain.

A baseball player hits a foul ball straight up into t azk0jh6p)w t j+gz77qhe air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast wi)6jkwt7ghj07 + qzpa zll the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its accz) sd)t1y a kh )fh0d2tsn7zg2eleration due to gravity — does2s) z sthn 1dta)dfk z2h)0gy7 it increase, decrease, or stay the same?

How would you estimate the maximum he (jsc8esgc,/v ight you could throw a ball vertically upward? How would you estimate thcj,v (s/e8gcse maximum speed you could give it?

You travel from point A to point B in a carafpy mdic0x5) 6y3vd( zjw,3 g moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Ipj 36c, zxamf di3w)v5dg y0(ys your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstou)oyqb9q,:kug : vj .ration, a 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the cliyqu:,g bko q:ujv9 )o.nks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock f w0v ex3rbcsbk3 c302kalling from a cliff, an elevator moving from the second floor to the fifth flok3 cerkw320cv0 3bsb xor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its 7fesds(llm* z9 6ev,moriginal position with the same speed as l mszm7vs6e9l,(e*fdit had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero ve z k8,9bi4ux/ja 3e fortj-hb.locity and nonzero acceleration at the same time? Give-box atzr bi9fkjhe/3. 4j 8u, examples.

Can an object have zero accelerati(/wajo jcc-v6p./0 ud gta(dlon and nonzero velocity at the same time? Give example l/c gd(p06jwcad o(t/va-j .us.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a,7xr9d qc c9myd+n3 ud.9ykt-p etc. [Hint: First try to duplicate the motion plotted by walkind79m nc -+k9c9dtu.rxpd 3yyqg or moving your hand.]

Describe in words the mdh/ --krst4km-9vb- b7 u kj7znyt*a ootion of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to tabwvr)3+ 1 mdxravel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it taq -y mflu/p5d)x ejk/z;z yna9t-6z dc qv4:/mke to fly 15 km?    h

  If you are driving along a straight road and you look to th.5tw 0j:jpzvbg)cu 5 qe side for 2.0 s, ho.b5u0 p)qjtv cw:zj 5gw far do you travel during this inattentive period?    m

  Convert 35 mi/h to dy4;-0xy dhvs62th6,xv 9ehh6lemp w
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball movesd/a)tg sx;6p,j fuk 6n from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from schon4(72g t fs92 n6erkzqmu q)jhol steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours an4nz mh) e72g6qu( 2qs tjr9knfd 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 a lightning flas2 k(hr8ymg ; ko*neyd4h and the following thunder gives the distance to the flash in miles. Assumi2kyy4nek;*h dg8o( rmng 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 completbkv 9b3vw2()rue)7- b9 ndexj xs th8ge laps around a quarter-mile track in a total time of 12.5 min. Cal r-)g8 vne3v)7 jb9xbex9wht su(2 kdbculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, pimzjgjff62p9 7+ 0idmoving 116 m away in 14.0 s. It then turns abruptly and gallops d 7 f+6mpi 0pzj9fjg2ihalfway 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 otherg07hsjx8ngdx n+5tl 0mymf -*xbp22 i on parallel tracks. Each has a speed of 95 km/h with r0 h-g2ig5+mnl *pjmyfntd0b8x2xs x7espect to the ground. If they 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:ayn;v: 4bduox m:)llql.catewc5 0: 110 m behind a truck traveling How long will it take the car to reach the trd5maca y.v:: nc:q4lbl ut0;)x :oewluck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters 1;upvpvz;v)5n )5ds(zz4 zokom k n 8fa tailwind that boosts its speed to 990 km/h for the next 2(zzm;p4;fd uz)oo8 zk sv)nv v15nk p5800 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-trip9bb*habr- 6 awmp+n hj4j/8of in which the outgoing 250 km is covered at 95 km/h follo/6b8 onb4jbp9rh-*wjf h+aa mwed 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 the pins at the en)(ch73+q2fp 1 z/ ckakmeqckld 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 sound is 340 m/s. k 2kcfmq3+zk q 7cha/(1lcpe)    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. e:a2/gtz(blfb6 u9d7j d kvy:; w- 9orqyr(wlWhat is its average acceleration :: d b/-btw9wj6( l7kf(yzgdyuv2o9a eql r; rin $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What ioer d*8rlar4 o;du.u6s her acceleration oru*d u; 4eadr8lo.r6
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobitqpz)7oi s thb )o,:0rle is capable of an acceleration of about z)q,07tb :p)istoro h$1.6 m/s^2$ 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 brw7vghmt.o yhf7n- im/ oi 4+s)akes and comes ts +hti47f.vimn)g /ooy -w7mh o 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 racing car, which starts from reevb gaqx+z+jh. -1wd* st 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 fun vejw+ x+ dqgb.-h*1zaction of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 5y qd,er16i uf6.0 s. What was its acceleration? How faref1u,y6rd q5i did it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to restsr+ qat;7x7-ugx1: kf 0liwa/zn a3lu in a distance of 85 m. What was its accelerats/n +31ql a7:0-axxak7rguui ft;zwl ion, assumed constant?    $m/s^2$

  A light plane must reach a spfo -g:xsjvz,k .:t v,ueed of 33 m/s for takeoff. How long a runway is needed if the (cxfv g :v-t,.kz:sjou, onstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essr+psb6v lyl8 ;entially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this s6yv lb+l8p;r 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 in 6.00 m)t hr62 on;uti ci,8)qo0mzes. How far did it t rqh6ce n;m)8 i 2)0zomt,ioutravel in that time?    m

  In coming to a stop, a car leaves skid marks 9xps: m38sb+j3a7 lc ot2 m long on the highway. Assuming a deceleratio oxsjs blp7tc:a+338m n of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strike) m.sd r3jlvee ,2x.vhs a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What wxjrse. ,.v)devmh3 2las the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 km/h and yy r1wg r-.u/khuman reaction ti/u1y. rwyg r-kme 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 forcj3lwkjb i7vrc p7+w *:53lo v 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 truup9i vi.0pp) vck going 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing viip9p.up0v) 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 l0jvhadb/b :(run in less than 30.0 min. After exactly 27.0 min, there /(:dlbj a0 hvbare still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection ja;7mrg qz us,v y9 :7g)oqkz8must 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 t) qzgm8z, yrvkaq:;usg 7m7 o9ry 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 tiagv*r wx+gm*v:ytzed 34+jp nm i a*0w- /(lzop of a cliff. It hits the ground below after 3.25 s. How high is tw*x +:p zaivraij( nz3mw0 +y4 *l-dv*megg/ the cliff?    m

  If a car rolls gentl+ w*uo0 -nq/7gp l3ri 4mgap svu2pff-y ($v_0\,=\,0$) 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 (0o)ny eh(gtqwith a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward. With gjwuf vh l*(960z6ed swhat speed did he throw it, and what( lhfgw v6s6* zj0ud9e height did it reach?    m/s (Round to the nearest integer)    m

An object starts from res5r e av-,b6ieat 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 from t aeev5iarb6,- = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 k*f;qv.x;j mh m/s. At a height of 125 m above the Earth, a package is dm.x qh*;k jfv;ropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance traveled ;o29.4bl9s1z pee i8wab o zwl9qm z,eduring each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown blz2 1zm.9sez4e,p 9q bl9wwioo; a8eby Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, shoy qgghcd3) rj :2yxtv*2i4:ibw (algebraically) that a ball thrown vertically upward with a :*4 2i: 3gcyxv dit2byr hjqg)speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed of 18.0 m/44ga.3 2ppoo, ;g/pq bxeafvus
(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 (or numbehl2cy5 *1uu 6wfl6yalht85k hr of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones akhhtf uhl6l6 251cwy 85uy*lat the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to trave/ku5,p7h(q 9bs8)fylljca x(u iysx5l past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fax5/ (iaxfljhs,qs pl)b9y 5yk78 cu(ull?    m

  A rock is dropped from a sea cliff, and the sound of it striking the oce-* tkf owbmde81yc5s fpvyfv q 727g14an is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? 7 f1yf-yvcso v251mk tdp8be* wqg74 fH =    m

  Suppose you adjust your garden hk vmd.0+krski6.0 opy ose 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 2.0 s. What is the water speed as it leavesy ps+0 ki0 .d6vo.rkmk the nozzle?    m/s

  A stone is thrown vertically upward eu+ *q,pt e1p hget)c q2rk/cd3kb6k(with a speed of 12.0 m/s from the edge of a cliff 70.0 m 2ud,b63 h*/ep1k +ceqtk )(tkecg rpq 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 window 28 m above the street wheoymt2rr yvd;;; :n:m1vx- qith a vertical speed of 13 m/s If the ball was thrown fo mqht:v 1 e2m v;y;-r:rn;xdyrom 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 ti; d *t33s7ql7 wpovc71 xz4hbjo9f kiwme. (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 constant? (d) When was the magnitude of the accelerationwbok7 tx*qhd3;i3j z7p sv7w9f4col 1 greatest?

  The position of a rabbit along a straight tunnel as a funct7tis c.22w sh uoes*w*/lcr 5 o6xst,zion of time is plotted in Fig. 2–28. What issho 225s ezo7u*sl6, ts./cwwi c*rtx 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 automoz*;,u3 v t25arpkj,6zpqof jybile can accelerate approximately as shown in the velocity–time gr zqpfu,k ,zjjo2a35 v6rt*; pyaph of 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 pc r*ns.4jclp+revious Problem (Fig. 2–35) when it is r*+pnj4scl. c 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 rx 9 lq2m4idvul 0mt64the 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 fu8mighe5n pq5bk w-*p6nction of time is given by Fi5q-6*5n p wbge 8pmhikg. 2–28.

Figure 2–36 is a positio f:,vq)q0vp2j5.ba pob bt/ fdn versus time graph 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 u) pv2jdb:t/aff q.vq 0bo,p5bp or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safe5( phu.6rcdc lty net. The survivor stretches the n5.du6( pc rlchet 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the -csh i,ufx(u.) xe5vm 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 ti x.xvcsuh-,f (5e)umhan it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulde/ui ,wt8neh)vr seat belt has a good chance of surv ntve/ ,ihw8u)iving 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 me b3e amq35qok91 n m.wf/hj8x 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 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 em bo3 59kf qw1aeqhm38nx./jhe jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested itssm 4p o1 hz:1rg )8vemfhk,wh1r xu/y9 cars for front-end collisions by hauling them upo kr1)u 8yrhm es,:vh9w /hp1m4g1zfx on a crane 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 ta nrdmc3jkv3e86d *x05rjq)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 uniform acceleration from rest. The front of tm(;g;zk(z1krm ,pm guhe 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 wilm u1gzmpm (;r;zg(,kkl be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surfacdz/zq o: w.(zj )a3bqje into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate tb)qzazz /jdqw3(o .j: he 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.m+v qnw5 oy:mr f3zz+, it 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 idea of this problem, calculate the time it takes a train tv:+ .wf5+m3 oqmznzyro 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. j-8 lzjsbx17jk7 .b,bsxc0 zpSuppose 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 heigj.8xs1 bszb7bckxj 7,z-pj0 lht must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with wz 6wkge01bh k4hich a golfer 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 li0e61 hkkbwzg4e (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 freight trbu 4qo*u9bxba7ge 3 5gain traveling at a constant speed of 6.0 m/s Just as an empty box car passes hi ao g94eb ugu7*5bx3qbm, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a t95 mc*e35okzbm: fmz. 4smjx,arn+ ehigh building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reaxjn5z moc, 3s 94:abmm.me+kt frez5 *ched a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course o:mxe;ljp ng 4:t+ koq,f a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap:x+:mojn, ;ptl q g4ke?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves f(gw+ua/kx c* at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average accelefc+w/xkua(g * ration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. Theok/kc,oy-.y (rjuwh yc) i/l3 first child can bounce up one-and-a-half times higher tha(h)c/ljryow .yci 3ko /ky, u-n the second 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 a 1.10-km-long train travebb vt* lb t54lxt--h3 cdxwc/-ling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are travelib-hwb bl3*tv4 lxc-tc 5/xdt -ng 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 with4f1w5 y4aakv ox(l ah( a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is rev5aohax4k(w4(fy a1lleased (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an an 2*lhtthy4fdwt -/b2cceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42.(c)tzr:,fw2 evbu sb0 Each intersection has a traffic fw ectubrvb(2zs,:0)signal, and the speed 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 constaa7p oz7yg9uo8i q6cs 2nt 120 km/h takes off in hot pursuit. The police offio 7z9p2ci7syg8 ou6aqcer 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 k2l t;m(in xt9building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones in x(t9m;lk2 tland 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. Theo ci)-l,ga5jj 9ur 4jp first stone is thrown with an initial veu)-p954rjga o jj,liclocity 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-fall3t*8(wt ,ajvif;2o36 bnqcxwg q3 smwing parachutist to fall from a plane at 3200 m to an altitude of 350 m, whoqw,3 *i6wsf3t x8cj3 tb2av gw;q(mnere 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 cof x0 5r6*duv f1mams:anveyor belt to send the burgers through a grilling machine. If tauv d:60a5f r1x*mmsfhe grilling 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 at a speedmy zw)vj1t/ 1x 1.5 times faster than Joe can. How many times highe m1wxjz1yv t)/r will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top ozlh0:/ ;b kdd4d0ajzrf 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 belokrz0hdl 4 0b :zdd;j/aw. 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 particula8v t w/i fy0r .,r- 4orpvvibwq,me+,or building using a barometer. Instead of using the barometer as an a,w, /r mq .t4y+vf o0r8 pb-ivvwiroe,ltitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) I 8 /+qgsw4esrvs 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) Which bic+esr4v/ qs8gw ycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?