Does a car speedometer nol/ l85jfsshxi.er - ok:1 p5measure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give exapc+ 3y.-g p)c+3fv5lbg d od r+kzewh5me) b.+pg3+5wd c3 yovcg 5l+zp -rkhfdples.

When an object moves with constant velocity, does its averag :-wz+ ga*fkv0dptmn:e velocity during any time inte ::da+*0vfzmk w-pn tgrval differ from its instantaneous velocity at any instant?

In drag racing, is it pout5 1qmldg; 2bvqrv7 6ssible for the car with the greatest speed crossing the finish line to lose the race? Explail2v m65v;7tqgb u qr1dn.

If one object has a greater tug-0 c 0+3 3i:xcxe nikxt*ojw,+zbkspeed than a second object, does the first necessarily hn t-g*cie3:cx+ko, xbjwku0t30z+i xave a greater acceleration? Explain, using examples.

Compare the acceleration of a motorc7i6.;x hyt zdeycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in x;zehd . 7y6tithe same time.

Can an object have a northward velocity and a southward acceleration? Exbk 5d v ;g 2*hh,ll*bc.ocrb;zplain.

Can the velocity of an obj8/a0s682nvm f c ewdosect be negative when its acceleration is positive? What about v68s/o0wa 2svnefmcd 8 ice versa?

Give an example where botvwrerekbfme+xh ,0* ;c,ou -/h the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A ; )dzkkr .e,* iepj7tiis traveling with a speed of 60km/h and has an acceleration of 40km/h/min . C;tr*zpee)kji7 dk .i ,ar 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 speed as its accele+g8 2d *ysjwszration decreases? If so, give an examplw gsz 8sdy2j+*e. If not, explain.

A baseball player hits a foul ball straight up into the aizm9*htrcs )d1wgre8) 5 ud:r ayu6 si6r. It leaves the bat wic gu6 9i8r m hz)rd: swea6tudy1sr*)5th a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, whay/hl,mysv -4+f,i1nr bz(dxa t is happening to its acceleration due to gravity — does it increase, decrease, or st l-y/+ih sv,mz4b,nra(1xyf day the same?

How would you estimate the maximum height you could throw a ballf.+qd ge /hg;l*okn +w vertically upward? How would you estimate the maxin+glg+.;*fk/we d oqh mum speed you could give it?

You travel from point A +r2yu.xv;e7hd4 cr8ndos uut . tik;3to point B in a car moving at a constant speed of Then you ttt ;+re o8kh.27 dnvuu4x.scru3y;i dravel the 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 wii/ux6h m+otf-g8xv znq90+l7lky* w 2o ahme)th ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, a+w2 +6o- elq *ioy)hh/x 07 zg9v8axmtuknlfmnd the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant zjsvf-5y*4ff2xnp -ralf z*h+s-qb 4acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifts5fl-p hn*-z4zrxqya bjs f4*2+fv- fh floor making stops along the way, a dish resting on a table?

An object that is thrown verthp.y)u 2mia3x3t nvn/ically upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The accelm 3 pi)n vhytn/a32u.xeration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity aau aw55c/a )aq091n . frwa rm:xep6jgnd nonzero acceleration at the same time? Give exa.9 1pfw5u)6r qrm/ 50axnw agaaea:cjmples.

Can an object have zero acceleration and nonzero veloci*y1ynlsy dmnpe1h*db:5 9;j xty at the same time? Give p1y9 s *d:jln1 nxb*;d5yyhmeexamples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc.. otmfq 5-r/za [Hint: First try to duplicate the motion plotted by walking or movi am5frqot./ z-ng your hand.]

Describe in words the motion of the object gry *:e9ydkk+a0(/ lkhgs ow4idw) 0-t txtvu 7raphed in Fig. 2–29.

  What must be your car’s average speed in order to travel ip da1x80 ecx4235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does i; 1ph js4iseikpc+3e28zggkr wc(3 5et take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s, huj1d2:t t9dn 5xudsl)ow far do you travel durtn9 jd x1lusdd2:ut) 5ing this inattentive period?    m

  Convert 35 mi/h to 1k k7ip qdhmiq;:o:s2
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fh,si qn 4,2o*3of ov ;ezjv30zp(ydgfrom $x_1$ = 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 schoof,cubx *cqp*.b+6za el steadily at 95 km/h for 130 km. It then begins b+* *fcbpx azce,. u6qto rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between as02n zz+il+fw:hyiu ;lt) 0fm lightning flash and the following thunder gives the distance to the flash in miles. Assuming that tnu);+limz :f fw ihyt0l+s2z0he flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total time o 71hws5dpiaup8i 9dx 8f 12.5 mi pad78u51dpwhs8 9ix in. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its t8xe*k*0 jqnf3:nmnonrainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops hal:3onmnn* x8qkj *f en0fway 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. Eag01v -t e b3,eho0b)aoi9q-v r tinw.jy-t7 khch has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, yhie 0v)0jqg,tvt-a.3eb-9ikn r-ow7 o thb1 how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 1t:sm94+x4 epzk v4 qok10 m behind a truck traveling How long will it take the car to reach the truc kp4m9qv4zs te+:4 xokk?    s

  An airplane travels 3100 km at a speexhd3x:+8.6m toqc7tq o5qhrw d of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 2800qh8 wx7q3t6 o:hot cmx5rq +.d 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-trip in whu 7cmn-lhj)4hich the o 74jl)cm-hunhutgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end of ai qnda:t6zz -owu7sqss,ytb1 we1nn5n)9)v9 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 ofbt:n5 szea9i)wy o6d7sq sw vqnzu-nt9)n1,1 sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is itsm;391c36 ;xmv no c s,wnah6kf lap-wm average acce x s6 alcvo3ca w;w9nn,;km-fmh 16mp3leration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates fr2tc3glbd+h 8 77hgus oom rest to 10.0 m/s in 1.35 s. What is her acceleration h+2ghgd co3lb u 778st
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile3uc a y vhjw;8b-,u1 es*w.cwx is capable of an acceleration of abou-su, xww vac.38cw*j1ehbuy; 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 travels 1;flj v.5 immv)zkot r 01j09o(niem,a 10 m in 5.0 s. If it then brakes a0)rv19kz ne(0ti,jlm m o.m 5f;aovijnd 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 racing car, which starts from rest at t =xn) el po.g;6r3 kqw8u 0 and moves in a straight kwug8. q;p3en x6rl)oline, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 myb wd+stxhn0nm :7z1v7 0om6 w/s to 25 m/s in 6.0 s. What was its acceleration? How:omwnn6v0bs0 xyzdm + 17th7w far did it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s t9k wys:bf:j/bvyegt9 - :zq0do rest in a distance of 85 m. What was its acceleration, assumed constant?-q:9dv tby wkey:f/bz j9:gs0    $m/s^2$

  A light plane must reach a speed of 3h. ;-e8pe ycvs3 m/s for takeoff. How long a runway is needed if the (constancp;y-h.es8 ve t) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially gyi/q)+s+hkz gh8 :fy top 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 howhq) hz:fi+8yggy +/ ks 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 o54nl y09q)s *wwdlapq f 12.0 m/s to rest in 6.00 s. How far dl*p q5)0ny 4 9wsdawlqid it travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assumtq0,l4 *hsyz7oby gos) 1q+vehj17 m jing 1 47mjoqt)eylz1o+gybj 7 0q*,svhhsa 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 tre0qi j5: 0jx p ,lp5buza)q-exde. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was tzja 05q:x0p qe pdj,)i-5uxb lhe 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 ofha8di2c y,9by4xz: qf 95 km/h and human reaction time of 1.0 s, for an acceleration :q9d ,yaif24 yc8hzxb
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance o.bnu le0y0,zy3rpc2 lf 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 highwayd(nte+8cpejaao)c, -. The car’s driver looks for an opportunityad+ont ce(8)cpja-e , 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 ao30a uc-mz;w. After exactly 27.0 min, there are still 1100 m toau ;0cwomz-a3 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 just as t) 8lxzo6f6gayli e z9+he traffic light zz6 +ax8i)f y6el9 oglturns 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. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the groundv3tssdn (f/3u below after 3.25 s. How high n fuvds/ts33(is the cliff?    m

  If a car rolls gently (,2 yu(mwitv8e *k:lcu$v_0\,=\,0$) 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 straa phbzji :q8m au4 wdrq:9c5fod)6(9q ight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwiuod vj7u m5qdq79b-+cu 3fywu30 e5otng it vertically upward. With what speed did he throw it, and what height did it 7fb0muq 9- uoqw3do7je+ y tv5udc35ureach?    m/s (Round to the nearest integer)    m

An object starts from r.k1 zyapqzxp4) ;a mn5est and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the distancy ;5mq1nz)kaa4.pxpze it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertic2 w;g4e0gcf9 jq,pwult(m f mfkw6 2)hally with a speed of 5.20 m/s. At a height of 125 m above the Earth, a packj( h 6fmuewc 4lq f 9;fkgp2mg)w0w,t2age is dropped 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, show6z-7 rpamc ed0 that the distance traveled during each successive second increases in the ratio of successive odd integers crpzmd6e7- 0a(1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown v)0ov1rlg2 amb ertically upwa)2alm b1vor 0grd with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticallqdf8r n 1p(mpgfzkf,k- k,.+zcq (1mly 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 3bktq3 op;7pxthe apple in Fig. 2–18 (or number of photoflashes per second). A7o3 xkbpq t3;pssume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–32). F6 zchnthiqw 23xmvna d17o+;:rom what height above the tw cqxnh idv3nt 1hz;:a6om7+2op of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean is hgvi89p zoyh+ b/eb(k*eard 3.2 s later. If the speed of sound is 340 m/s , how high is the clif ob* kv8i /gbe(9+pyzhf? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You po4- + mqkamvl;/+a juzuint the nozzle vertically/- 4azluvkq+u+ ma;mj 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 vertically upward with oxi1:4c m4 lcbt j/+eqdl1(ona speed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2–34). 4lmxq 14:b 1/o(i lntd +cjeoc
(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 abo6ji6v2fl e9luve the street with a vertical speed of 13 m/s If the ball was thrown from the sti 6lf62l9je uvreet,
(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 oe bhhd.b50b gg.1ir b7f time. (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 5 hb.b0rehg 71dibg.b acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time is p8kz*s 0a in0gxlotted in Fig. 2–28. What is its inznx 0g80s *kaistantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can b:gny5 scn)3v )ixi -faccelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots:nvn5)i yb s3fgx-)ic 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 previous Problem (Fig.dett -5)xo1bgeib22v dut -k/ 2–35) -g tbkvbeue2-2)ddx /ti1o5twhen 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 obje s qcd;*k, wtc0fo6t(tct traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function of tokfgx8d7rsh;6;npq /d0y c -fime is given by Fs;hx ogfr/c;n7d0 8- 6fkpy qdig. 2–28.

Figure 2–36 is a position versus time graph for the mj(w: vej6 ljf*otion 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 or6f:jw*jj(ve l 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-son+7 4w2 *jxh+ii) z1g o az,9yxtkgvgtory window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m befok4z+ia2*+ gvxg,7h og1znj9x)ywt iore 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 thvvn9sb9 (e/ei e 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 onvv(/e9 is9e bn Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat belt has a + ,g ucoiv,p axn5rtme*ds8xx2f:,5o good chance of surviving a car cont,o m x: 8cg,a +5di,sf5pxurx*o2evllision 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 b9m;j sqjf,lcxr m, 3n;ridge, 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 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 bridgerf,ml,j3 ; m9 nq;xscj onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for fryje -asv7h;i8 z24h brj) h*deont-end collisions by hauling them uye rvse* j7a-;4h j8bhi2) zdhp 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 trav 26ap2c, yyuhuels 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 fc6i2k5e gi*x eront of the train has a speed of 25 m/s when it passc *ie65xg kei2es a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a dejaxs9 mhlx1) 3a*:db kep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average decel m jxbaa31:)* dxh9skleration 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(pzrxi kw2 z: gtfp:5:m-zj*up wr +c; 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 to make a 9.0-km trip in two situpgrz irp:xz;:-jk+(z*5u2:fwwp mctations:
(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. Supev4xxgs jfb/4csn.z 0 r) 3o9zpose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. rx s)4vnj9gz.s3fzo4 cxe0b/ 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 strikeqyl9-i)1r rl 9o kizwq t)3o/hs 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 mi9/w)yiq- 3 zo1l9tkl io) rqhrssed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freigh.upsan8jz *i;t train traveling at a constant speed of 6.0 m/s Just as an empty box car papz*sj8 iun a;.sses him, 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 high building. A second stone is dcislzv arl+k684rbn +1p-m6v ropped 1.50 s later. How far apart are the stones when the second one has rep8+lz1kn smrbr+a4- v6v6i l cached a speed of 12.0 m/s ?    m

  A race car driver must ave lkx(,tw a 9vi2h 2g/v-nfrm:-t-ftjerage 200.0 km/h over the course of 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 va9hj,v(f n m /g- et22tliw--:ftxrklast lap?    km/h

  A bicyclist in the Tour de Fra y+p i4zmpj:0tnce crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What wapj4: t mpzi+0ys his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child 0pwl:) ( qol b(avq x-ew6koa/can bounce up one-and-a-half times higher thaxoaqpqbe/ w6 o)-w lk((av0l: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 traveliz0 1,trbu4.9bmvt3 veeb*hy n ng in the same direction on a track parallelb. t* b9mtrvve,03z41eybuh n to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling 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 baseb 3kqgxg8k*l6 mall with a speed of 44 m/s In throwing the baseball, the pitcher acceleratesqg g6xkm8 lk3* the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerat))(p bocn v1g wr- heiz7omy+/ion 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 showna.)nd /n6 jucd in Fig. 2–42. Each intersection has a traffic 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 intersectio)an /u6d .ncjdn, 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 m3 q ipgl7y4:straveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acc: g4iy3spmql7eleration.
(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; 2qxutwmz u 5*)a i0p5z/.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time. p5zz/i ax5m wu*tu0q)
(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. The first stone is thrownkey 2whk -glw :c34o;l with an initial velocity of 11.g4lwl3 hk;cw 2:o-eyk0 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 lo;r5bk48i wark ng would it take a free-falling 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 tki kbrr5;84a wo perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a gril nack)n6z3+we/r7ajnling m6a7 z)nkrc3 ewja +nn/achine. If the 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 speed 1.5 times faster than J yolqa2 x v4hb-:j;pgh7k6u)fvp t2v3oe can. How many times higher will Bill’s ball go than p2g4uty of72 l;hvb k:vj6 v3xp) h-qaJoe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the grou+x 4je2q qej4dnd below you. You drop a ball from rest and see that it takes 1.2q+4x4djje2e q 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 .fx c 5:t5arqhqw, .9 b j8smtaq(o3fvbuilding 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 student reports a fall time of 2.0 s, and.5,qmtb 8rj5w3f: q a q(vs. hfaxtoc9 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 the2wo: 5 z glfqbpalp5 +,+0qsn ,dqyh1xd,/ffb position vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c lxb5+qfodfs5qw zgb1+p,q/l,fhyn dp :0 ,2a) 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?