Does a car speedometer ncay,v ucr 6;o;w6b 9+.ty v8q)iblyomeasure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yek59c x2c 6:.kwchs1*my puokvs, give exampl.1 vxk*u6khcw p:5kc smo c29yes.

When an object moves with constant velocity, does its average velocity duringege dt11mueja8k -pc/2 yr)to),3jml any time interval differ from itme-3eto1) y me puj gka1 ,tj)/d82lrcs instantaneous velocity at any instant?

In drag racing, is it possible for the carm)hz5h1mrl *); al drx with the greatest speed crossing the finish line a;r md)1lz*)h5r mhxl to lose the race? Explain.

If one object has a greater speed than a second object, does the first necqnlhxwt4vv ni/kj*p4 ,kmzbmy)3+ 1;essarily hx*j+ kvvw 44 kh 1,mytinbqn)pl/z3 m;ave a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80k2v:nz6rq6 yt z,ops p4m/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10vs:r ozp264ny,p q 6ztkm/h in the same time.

Can an object have a northward 7**ery 0s nsnki/u:flvelocity and a southward acceleration? Explain.

Can the velocity of an object be negatik(k , vconxk.uu1 b)p6ve when its acceleration is positive? What a p uvocbn,k)1x 6k.uk(bout vice versa?

Give an example where both the velocity and acceleration ap(v) (wml quj:re negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed id di:2 3n us(ppq7oq2of 60km/h and has an acceleration of 40km/h/min . Car B has a sp2oud 2ps3 dn7:pqi (iqeed 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 decreases? If so, giv5*hk +gwki90llow km oav-(a-e an exaoho k+5v0mw*w-iag - l(kak 9lmple. If not, explain.

A baseball player hits a foul ball sti 69v xmqshlw(69p od8 4,nacbraight up into the air. It leaves the bat with a speed of8nsd9(, hw4 bqlmp9x6oi vca 6 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, what is happening to its accelera2 vpc4k +jyxlg+ /:rtqtion due to gravir cy/:+4jlvkqx2 pgt+ty — does it increase, decrease, or stay the same?

How would you estimate the maximum height you ckns5me/*;s nk hk:tm +lbsb4sjdf)5k8y)v4dould throw a ball vertically upward? How would you estimate the maximum sped 4hk mmsnj5dyss k;/l5*sk)t +:ekbbf4v) n8ed you could give it?

You travel from point A to point B in a car moving at a constant speed oejj mu460 zfaew23la8, *kmcv f Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your averagcee6mj0 mju4 wl3kz*a ,f a8v2e 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 b9srh)kd er7c,olts 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 s 7kcerrd, )h9plate. 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 acceleration: a rock falling frcyzo4u- -5gmpom a cliff, an elevator moving from the second floor to the f gc5ozy -ump-4ifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upw/; yo 6+ -cvj6xcgocrm.cas/bard 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 acceleration due to ab; cc6scvmgoo.y6ra/-x+ /jc ir resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at c n*ia9qgn1 x++if)/avuu 1ygthe same time? Give exyvi9)q g1 uf+naxu*i + agn/c1amples.

Can an object have zero acceleration and nonzero velocityiy7zi4ffys ho 6ao 1j-:0+bnn at the same time? Give exampless -1yn 46zhfba+iyiofn7 :oj0.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc.n aukhl p267p) 7a32xpmvkkb, [Hint: First try to duplicate the motion pa7v72,6p 2 xabpnk kuphklm3)lotted by walking or moving your hand.]

Describe in words the motion of the oc5x csuc 05)cgbject graphed in Fig. 2–29.

  What must be your car’s average speed in1t 5wg p(9xcn0+hgj wn order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 6en6/myek 2pm km?    h

  If you are driving along a straight road and you look to the sidjz1id( +ef/8xu6k kv ;sxm q*ke for 2.0 s, how far do yokk dzq1v8(/ +mf ;6kujsxx*ieu travel during this inattentive period?    m

  Convert 35 mi/h to z6mu yk4j97 vq
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from l//r: tz8ao+gzv ,nqg $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for 130 km. Itnpt3* em nfu)pu4z3 3v then begins to rain and you slow to 6t3v3fuunn3 ep4)*z mp5 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-b(;giodpory5n* pi(*cwc5 7hthumb, every five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no p* i y r5(pc;*og(woih75dbnctime at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps x.-fyg4d.zi g6k+ t;gwp c.g9 uq ale*around a quarter-mile track in a total time of 1tl9e . g ufckz py+qi46-gwgxa.*; d.g2.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m away in 1uc 5tonq;e0 3c4.0 s. It then t;qu0c cne35 oturns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach eacq 9c61 t nt4hs(bgmn9eh other on parallel tracks. Each has a speed of 95 km/h with respect to the grou91gn4m9 h tb qet6(nscnd. 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 110 m behind a truc1 ;. cm(4znnwfm:k 8ocgr 6mklk traveling How long will it take the car c :lm.8n 1f m;ck4znmko6(rwgto reach the truck?    s

  An airplane travels 3100 km 3tlty9g.0 6 fwmwn+t9cva * baat a speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for thngwfm*w. l t+9 yvatt60ca 9b3e 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 mhfso ,0*xdp *9 +zu+az (bafqspeed and average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0- (fz+sp* qofhba0z ,x9 um+a*dhour 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*++ rtyh4n 8veip ycy. at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting vtecyh++ ni p4r8.y*ythe 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.    m/s

  A sports car accelermt mcf:6mfj:bw-r/ 2x ates from rest to 95 km/h in 6.2 s. What is its average acceleration f2-:wmfm:tb /jm6cx r in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.3dm9*sh-a3q g xo sfz40 m/s in 1.35 s. What is her acceleration omfh- s9qs a*x4 3dz3g
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an accelerq-q1jt/+tnmyj r z2o*ation of abouty+ 1q j-t*nqj2om/rz 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 constantl x+hjtp8*bxep-nh /; speed travels 110 m in 5.0 s. If it then brakes and comes to a stop h8+-npx*;lj /bphte xin 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 = 0 and moves in a smx3u5fms m))c db/*e ctraight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Dmc)5m/f )sm xde3ucb*isplay each in a Table and on a graph.

  A car accelerates from 13 m/s /x).mr ao c g))etrut;to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assr ot/ge)a)t ;ucr.)xm ume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a1:fa6nf lnhnp6kuk ihn5 jt337 p*cm4 distance of 85 m. What was its accelern4h hjmknf :u1 3nflt5c k6npa7*i63 pation, assumed constant?    $m/s^2$

  A light plane must reach a speedt wsua8xj7) bd-d+; dm of 33 m/s for takeoff. How long a runway is needed if the (constant+daw8 ) -bdu;sdx jt7m) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter ccv fg(zjm )- ezk73z(xan burst out of the blocks to essentially 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 how long does it take her to reach that f)3j( e7-gzk z(z mcvxspeed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down unifo : pjl4(yt9 4bbsltl(crmly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in thatlb:4 c pl(tjb( 9y4lst time?    m

  In coming to a stop, a clo :cs4pco7 ;war leaves skid marks 92 m long on the highway. Assuming a decel 7pw ;4osccl:oeration 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 rw ) jw+cun1webxr9v,z (l; :pyur58ktree. The front end 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 colliswwlwb:8r)ej nv5ukrx u r,yz;(p +19ci 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 withpsnewsa1.k ,, 2h1pym an initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleratiyan2hp,s1ke1 ,pw m .son
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping dis d38*tpfy gv,etance 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 gwy bru/ij*uax,xn155 oing 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can acceleratw/in5by5xur u,*1 xaj e 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 33a; .)yywrsw4cz3hw f0.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner msa y.c4rw;3fwy hw3z)ust 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 jr3u gep pb) khggbz,,p9eu*3 -ust 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 trg u,bpg ,pp9h ebkg*33z)ru-e y 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 hiti607;ig qq xl;cyh4tp.kao h9s the ground below after 3.25 s. How high is tihl aq7y9;h0go 4 qctxpi 6;k.he cliff?    m

  If a car rolls gentl t2 nnx*4u7azgy ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up into the air with a speed of 6bt ,xa+y5vim 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a vcpcn7j* s;8a fx7ue +ball 3.0 s after throwing it vertically upward. With what speed did he throw it, and what height*8v u7j;sfn a pexc7c+ did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influencfwj8 ,;d/ gtiee of gravity. Draw graphs of (a) its speed and (b) thedjw g 8ti,f/e; distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speedbk , 1z6u3ao4 hjlp ivd1 e7ezm3y4jqb-o7 ij6 of 5.20 m/s. At a height of 125 m above the Ear7 6q-63 mpb413jo dova1e zkjjiu 7bly,4z heith, a package 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 0ay8b n jffmul0 3wubv-o-:8 hl-w634xqgo gffrom rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first showuoh -a8 : nbgjmfgwv-b0 3wfxl38640 qf oluy-n by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball t zj ni,ulgmrf(x(j76e3i,s x)hrown vertically upward6jel( ,j x ,(mz)isru7finxg3 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 verticak,cprhnz j,8hs7 jb)3lly 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 gz-f:m6q f dn9each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apm-f: dn9gz qf6ple 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 0.28ywfzl)(oa/10l 8q(s wlkdw:2 - zon fz s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did tha( owdz 28lozlkfyf)( z0w/q nw-sl: 1e stone fall?    m

  A rock is dropped from a sea cliff, and4r oo6hntl0 n ro8:ln9 the sound of it striking the ocean is heard 3.2 s later. If the speed of so9:nho rnon0t 6rlo8l 4und is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your gardemlzy3gp to .3b9rx(-:wb. jbfn 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 2.0 s. : 3tfzxb9g..l3 m(jw -obr pybWhat is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a z.*4c d5loctn speed of 12.0 m/s from the edge of a cli.l*c4zn 5 otdcff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a w -l;iog/a*jklvok 3vx19q) q findow 28 m above the street with a verti1kq 3* ;o9vlila vgkoq fx/)j-cal speed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a) Atn5rbiif*) f 9 8ngfg;k 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 a;8k*n5)iff9rig ng bfcceleration greatest?

  The position of a rabbit along a strai +md nv,mj(0lnght tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneousjn(m+m0l dn, v 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 z- e acnb,(m1vcan accelerate approximately as shown in the velocity–time -bn ( ,cez1mvagraph 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 previous Problemq,mjq(af 24uqp40 txw (Fig. 2–35) when j04u,m qqaf(txp w42q 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, estimatn o4ddw,0n)zj e the 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 2aartl1m2j- e a function of time is given by jr2la1tea- 2m Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an(eb ti3 kukosi0s56w8 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 objeoie uw k0368bs (kt5sict 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 window 15.0 m above a firefighter’s safet1-y*y3xh 2rdan (gog ty net -ny1d 3xgya*ghro2( t. The survivor stretches the net 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 Moon is about one-siyx/x wjjexc+n1u565m 4h k-:*glq1c zv mdkm4xth what it is on Earth. If an object is thrown vertiyxdxux5:+z 1jm-eg wcc56mvm1 jlhn/kq44 * kcally 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 *ze)ojzm* e92-vk x wqby an over-the-shoulder seat belt has a good chance of surviving a car collision if the decel*z xqjvm9* w )zk2-eoeeration 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 rogjv2d ln2*1cg3bz p t+ad 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 abp jzn1tg*c2dl2 3+b gvove the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions (qj0d:ea k-kq ts(,)gekgsz +by hauling them up on a crane and droppk:qk (0ks( +ez -dgje qsagt,)ing 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 trave(o2 ysd29td4jf jrbl+ls 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 frontj r uf:vapf8c))sx ).5mhrcu4 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 the speed of the last car as it passes the wj)r)mr x cu4as).5 uvh:fcp8f orker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface intzmz:37 pb wj6xo a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of thzxm36j7bw :p ze person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary 5o j4nnplzlnsk;59n u/p, 0ay to balance the average speed of a train against the distance between stops. The more stops there are, az opu/n9 45pj,lnnn 0ly;5ksthe 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 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 andyt/n0n)si aw2pc mkxo.nt8+( free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16cn)08imsx.ao+2n p yn/ (wtkt .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 qtwughdp hy ,l7.86) u j;o/lrwith which a golfer strikes a ball is planned so that the ball will stop within some small di,rpw)8yu ohl l6qt ug.;jh d7/stance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball 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 train traveling at a gm:z c(g:axmtw /;qx5 iy*:mlconstant speed of 6.0 m/sx 5gmx wlqc(mit::zgy*am;: / Just as an empty box car passes 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 ihx.mhith;umfd0wz m :a;s(+ *g+lys; dgb( )ps dropped 1.50 s later. How far apart are the stones whetpw(h d g)lsgmf+ahz;dmmx(b+: s 0; hi uy;.*n the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must avipl)cq 4v7gr )xz:r -vdoz-f /erage 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 maint rzq-di-p4 )/7ogvvxl):r zfcained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 km/kwafg2jjawlb1 vy m 7).l(2sle u5o 75h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was hiv57ys1 wf eg)j am(ul7 b5o2lkjla.w2s average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child canyw72c h* 7hima bounce up one-and-a-half times higher than the second child. The initial spehcia7 2*m7wyh ed 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 1.1sg0 lp 9 m 2t1ma9x/y1n:vbxui0-km-long train traveling in the same direction on a track parallel to the road. If the train’s spe92 tlbgmsy9 x:a1/n1iupx v0 med 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 5 d)grnqa wqvs7z07mu9* iu(ijbe ( e(with 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 released (Fig. 2–41). Esti*7ab9qd( sei7j(( rzwueu)g0 iqm5 nv mate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, frot t6fm:mn4b ijsh,:*aijd;4b m 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 shown in Fig. 2–42. Ea :.acbin w5b4rch intersection has a traffic signal, and the speed limit is 50 km/s . Suppose y .4ibancbw5r:ou 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 trave c3ykcs:gl6t2ling at a constant 120 km/h takes off in hot pursuit. The poli kycct 632gls:ce officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a 7c04nwa9cza )x wp;2jtujp08ez1d exbuilding; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and c xzp9jpe18aj)7 zc dne t20 04;uaxwwthe 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 same time. The first stone is thrown dopai4z +.z;w with an initial ve i;adz4p +.zwolocity 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 ,xf f i +aim4o1quog8:)rvti6take 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 ra q imofvt) r8f+1u 6x4ogi,i:eality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor6gy 2njn pk:7r belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and tjry:n62np 7kghe 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 thapx8ssc;/k9m.- cjplnn Joe can. How many times higher will Bill’s ball g k ;c.plx9jpsn-c 8sm/o than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stxj(2adeq 2ws 1gk;8gg ands 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, 2dq;g(8ekgxw1 aj2g ssuch 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 oz-ccrp-f8o5 f-fc/r 3scsf3a particular building using a barometer. fospc -f-fzr3c/ f3r -cc58osInstead 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 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 j8j jap7jd *u7b8l:.oc pv2jm 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) At which instant(s) are the bicycles passing each other? Which l7bjd jjju:pj .8po8*2c7mv abicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?