Does a car speedometer measure speed, veloco+g(9y:sby w6a:tcsz5akq i4 ity, or both?

Can an object have a varying spjh,kmf;q40 l j:a3( junxxf i7eed if its velocity is constant? If yes, give exampl374,q0xa(nj;uj j klm xhfi:f es.

When an object moves witex:7clwr e/,nh constant velocity, does its average velocity during any time: lx, /enrwce7 interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with33g.zo7:e7j y q1khjd ro6rin the greatest speed crossing the finish line to lose theord6er y7j31oh j3k.gqi 7:nz race? Explain.

If one object has a greater speed than rf5 n/j4ie0 /rrt2iedinv o;/a second object, does the first necessarily have a greater accele0iifnon r/rd;eevj /t/2i54 rration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90km 3yvn -fn0ftk2/h with the acceleration of a bicycle that accelerates from rest to 10km-ft0ynv kf3 2n/h in the same time.

Can an object have a northward vx mc,q 9nxgq8tj;(5,r xj0h0s n3 vwmbelocity and a southward acceleration? Explain.

Can the velocity of an o. 7dek3q(ztg7qxq( sr+u hw/vbject be negative when its acceleration is positive? What abovr7kqqg(e.wht u q7zs (xd3/+ut vice versa?

Give an example where both the velocity and acceleration ar n1ism (6b lw;u;2/umdyi3tu h2u-z hfe negative.

Two cars emerge side by side from a tunnel. Car A is traveling withti7i.w6ulfrpp*du2se ).o5 q y;g6g r a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your re ;t657e2 f*uiwp)r .. qrsuiyd6 gpoglasoning.

Can an object be increasing ,vuc t ans58y;in speed as its acceleration decreases? If so, give an example. If n5nvsy ;,uatc 8ot, explain.

A baseball player hits a foul ball straight up into;x,su m3 3cxvlv/ h/ph the air. It leaves the bat with a speed of 120km/h . In the absesmvx/u3hchlv /3,x;pnce of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, wha9h s*obq 8nxj q3u2 gzbh9(h2mt is happening to its acceleration due to gravity — does it inb 29xnh9h g(*z3u mshq8b2jo qcrease, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball verticf6x: l x+wmer/ally upward? Howxlx/r+6w :f em would you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant spw * axvvz6sp.n8)bym2 eed of Then you travel 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 no 6v 28vx wyp*zsnb.ma)t.

In a lecture demonstration, a 3.0-m-long vertical .l,k68 rqsosp:s0io sstring with ten bolts tied to it at equal intervs .6:qkpsss 0l8orio,als 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 clinks occur at equal intervals?

Which one of these motions is not at constant acz2irwwx 9nwo7;w v -1yceleration: a rock falling from a cliff, an elevator mov17 w9 z2ry- ;wxnwviowing from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original p+bkqqya +.b60cgyu v0osition with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction oppositq ycvk+0.6 au0y+qbgbe to the motion.]

Can an object have zero velocity and n:w2p ydg-h qevke8bb(7s(a 0sonzero acceleration at the same time? Give e 2(v(ghwqe-bsk: y08d ebps 7axamples.

Can an object have zero acceleration and nonzero velocity at the same time? lj2.51ysk cxd Give examplesx js12kl cy.5d.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [Hin1(nx.du zyyh9t: First tryyh91 d( uxz.ny to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object grapba7pb2s2 ac1phed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km+ln5wu)kyts e u(mp,7 in 3.25 h?    km/h

  A bird can fly 25 km/h How lomj.fg1()rwogw 4r/d q ng does it take to fly 15 km?    h

  If you are driving along a s ;;y-g6x:4qzszq eh wji9 ugz5traight road and you look to the side for 2.0 s, how far do you travel during th zjwq4xhze ;gu:5g y6i ;zqs9-is inattentive period?    m

  Convert 35 mi/h to br0 .boct )9ql
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moveso tj0kp(0n. rn 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 school steadily at 95 km/h for 1x2k z r78ohy:z fo9c;f30 km. It then begins to rxf2:7zh y 98o;k froczain 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 a lighty d0r7i1xzvh-ning flash and the following thunder gives 1xr-y hzidv 07the distance to the flash in miles. Assuming 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 complete laps around a quarter-mile track idcg2xs b)v dsgpyy4)u1 *3n qo ce(2:nn a total time of 12.5 min. Calculabn2p:3vqse )4 og*cy2nx ds1uy) gd(cte
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a str5beh9ffkq t*s; 2.nnpvm ( fvd:yln-,aight line, moving 116 m away in 14.0 sepf 9 :n,n bdf;.myf h*vqlt vsk52n-(. It then turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Eachi g5s8j-xn;fy,-e gua dm)n6n has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km ad-es6axg85iyj;g ,)nn u-mfnpart, 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 aj6d/2cqovd10t t: v h-2o mory truck traveling How long will it take the car to rec /dy2qr o:6h 02 tvdv-1jmootach the truck?    s

  An airplane travels 3100 km at a speed of 790 kmksd u 19namt,y ,pg11(b goxwv w1t03 p:wq.ce/h , and then encounters a tailwind that boosts its speed to 990 km/h for the n3ac:p q t,bs0mg w.dnxewt vo1yg(k1 911,pwuext 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 averagr0:f impd;7dqt0r *bacjo: /f e speed 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-hour lunch break, and the return 250 km is cov 7*mc;r a:/tb00dpj fod:frqiered at 55 km/h.    km/h

  A bowling ball traveling with consn) 7hwah8y:d jxq32lutant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball :qd3hy )8nulhx27aw j 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.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is vc)nq6dzq0n //qua c2 its average accelecn a6 q qq0cv/zn2)u/dration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accelerati8e cvq6t er.ed7x0 rv.on x er0ecr68ve dvt 7.q.
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particuquw,pw5) v *n,lc02xrq.muud lar automobile is capable of an acceleration of about wr,p*qqm 5dw),l2u vuc. xnu0 $1.6 m/s^2$ 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.bd em l/vj:+e4t o ,4x728u v8kxwavpb0 s. If it then brakes ao8val /tekv4pm 8bx:2dbx w+jve47 , und 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, wh1 3j pt dzyuk8bf*v8r*ich starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (abjup13yzd*kv*88 rt f) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What9hu1aw3mav +p was its acceleration? How far did it travel in this time? Assume coa m vwuhap19+3nstant acceleration.    $m/s^2$    m

  A car slows down from 23 xa ./h1 dkdfuhi,ka* k*tkzf325gc.dm/s to rest in a distance of 85 m. What was its acceleration, assumed constantf.zd3k tugkakh/ cikdf *a2d*,1 5.hx?    $m/s^2$

  A light plane must reach a speed of 33 m/s fosobc5+ud3w 3/r bq*nt r takeoff. How long a runway is needed if the (const35b+ob r/3wcqsun t*d ant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of th,ydb a9f*y ,r6jf/58vckyatwm;r ; j ze 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 t c8/ dm6;yr;,wv ,yykff* j5tjabarz9his 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 k 8qzp/ wyi6-bof 12.0 m/s to rest in 6.00 s. How far didk pwi/byq-8z6 it travel in that time?    m

  In coming to a stop, a car leaves sk /,cm(hhwidq 5id marks 92 m long on the highway. Assuming 5hi,w(qmc h /da deceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the mf mzhf1-ygexe( 2) 4xcar compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the )ygm-e4 1f2mhxfz ex( 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 folft/ 5sq3 v8s( wmjk 46/pyllnr a car with an initial speed of 95 km/h and human reaction time of 1(/6 ls 5t/ vpy4qmjl8nws3 kfl.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the sr6 f5-j , gc e lf/gab)10u;f,rwk kkqmxes+p2topping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the hig 5gu3aeblu6, 2m0 hvruyo3du ,zj62dvhway. The car’s driver looks for an opportuni0ad2d 6 yjuuv6o,3uulmb3 gvr, 5z h2ety 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 thx()b(ds-ag.rypg 7 lro/sa( han 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The run-a(rr/gd(soal7(p bx.hg )y sner 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 justjqbx 1 kjl:)f. as the traffic light turns yel : fjkbjql1.x)low. 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 8f,9e5j bx qrir/3dxhof a cliff. It hits the ground below after 3.25 s. How high is the clifq8rie/jh x 9bdr,x35 ff?    m

  If a car rolls gently (l/k w:h17 xeoit*) c.iwjjsj,$v_0\,=\,0$) 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 wgu1alot7t0( 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 verticg54:uia+a wdl ally upward. With what s4ad: + wl5gaiupeed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw graphe x2r37x*e ilds of (a) its speed and (b) the distance it has 7 reelx *3ix2dfallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending verticallg 3ot 8 gjdzpl(n,x4oc ib::i*y with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial spe:, ix*(oo lpggz 8njt34 d:icbed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance trck :utvtn 9-9maveled during each successive second increases in the ratio of successive odd integer9tnm9-vu:t k cs (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraicaipl9 n.snfv +f t ,)rq:7lqyy.lly) that a ball thrown vertically upward with a speed tys:ry)n. 7v9p lfl qn.i+q,f$v_0$ 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 il*nqrb2q ofrslh :np 5*8.k89zo /gcu/ qta7of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in Fig. 2–18 (or )0r7b-y 4vm1 7 pf dloa4xpenb;wjn1enumber of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple poslex7o0a -b1 nbp)4f1pnv7 ;4jwd erm yitions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a wind*(qkwa (apcc*mj(6xfi) rbb:ow 2.2 m tall (Fig. 2–32). From what height above the top of the window drb k(f(j*)ma c*p (aicbx 6wq:id the stone fall?    m

  A rock is dropped from a sea cliff, and f cpx ;6 v8-2afbpgfo9the sound of it striking the ocean is heard 3.2 s later. If the speed of s6;-pvgafcx 9o 82ffpbound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your gy+imdf7cdne8gee 24 6arden 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 fgem2 n 6+47 deiefdcy8or another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed x16 87z e5r1hb bl9w1anxkiqxof 12.0 m/s from the edge of a clif719b8rb i x1knw561e lahzx xqf 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 window 28 5r13bg0a;q)i*ue /m uqjdgptm above the street with a vertical speed of 13 m/s If the ball was thpibg;u)1er */ma5 dg0 qj3utq rown 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) Aood3yia ,:2uvf li9d+tde 6 w:t 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 u3 doea dod v :,ilwt69if:2+ythe acceleration greatest?

  The position of a rabbit al 0l(fj4-m-lzib t(j slong a straight tunnel as a function of time is plotted ii(0blz-4lj-j ltmf( sn Fig. 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can a.: mdw.cgq.jzuz6 uz(vei4/a ccelerate approximately as shown in the velocity–time graph ug4zdj muv.w z.:a e/(6.cqizof 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 previousihy 40 lm9hdqj63/a3c d 8wbig Problem (Fig. 2–35) when it isdlg384q cm /iywbj3ha0 h9i6d in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object srbk3 89u / ep /7*apbmc1jwtotraveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for thbg-no1 4wm yg)e object whose displacement as a function of time is given bwy o 4)n1gm-gby Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an obje 7-0;lsrmjgak ct along the x axis. Consider the time interval from A to B. (a) Is the object moving in the posim;al7j sg0k- rtive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the 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 firefightbwef(yz;ul5 )g4 aw u2er’s safety net. The survivor stretches theg; wuyuwbe5 () 24fzla 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 onenupd5 fx mze4;a8m1k.-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initia 1x;kdufa 5n8zpmem 4.l velocity?

  A person who is properly constrained by an over-the-shoulder seat b.qn+ -.rylohzzxm 1y 3fsg90nelt has a good chance of surviving a car collision .mnxzq.lhgrn-90y 1zo3fsy + if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the rosbn* xx(7(hr0eu al6j3nnp9g 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 is3(p snb9nhex a*lnj0g7(u r6 x 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested y;pb y4ag( *vdwd qk+3qoq 171yiscz) its cars for front-end collisions by hauling them up on a crane and dropping them from a i ; dgd)3pq4(sa*b cwzy1q+ yvq 1k7yocertain 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 tr8aueet)esp l )/4lnl5avels 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 t42f*h bc;sh7a fj3+oxjlvn otq w;00the 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 tojxlc;hfj0t2;b s 0a+vq o *fn43w h7be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving 2g zam8;e cxgd4ow2apgu j,li(z/.w2board 4.0 m above the water’s surface into a deep pool2uz( 2 o2jw4emigp8 a;/aw g c.gl,zdx. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transiu)z mm4k w+3phh ,d+brt system, 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 to +hw4 + ubh)z,dmpmk3rmake 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 di:o m f6khmw0fmdintgh:72 d/+dqj l:1ving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to j0+ i::6fh: m/m1kdd2wog tlnhd7 fmqescape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikey ;y+uj+kn c8+cfd;jxd 4t.lcs a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, a 4;y+ k+f 8ydc lt;x.cjdn+jucssume 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 tl +9mjbget tx071*iq znx:e 4araveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive sma4: 07g n bit1tj+ x*9zeqexltarts 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 buil jmmhh l+dw8aeh0 2.0jding. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a speed of +wemhja2lh00 mhj 8d. 12.0 m/s ?    m

  A race car driver must average 200. i7nqyb;bif+eqp6 ,5za;aw b*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 npbywq;ba ba 5i7*q,z6fi+e;last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 ja +m:j 9(b.bdl:iwt qkm/h . At the bottom, 4.0 km farther, hisidml.wb+b tjjaq:9 (: speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. Thz*4dgk2e zo 6uy /dzk2e first child can bounce up one-and-a-half times higher than the gzdey/z2k4z oud 6*2ksecond 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 et0 b-b)e xwb mp6: )scild2igx1p*ndp0o4+ntrain traveling in the same direction oolcg s+6*edbiwt xmnpe0d-px)i:b4 b 01n2)pn 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 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 basebal6tihan) j4r+ * tsj0rdl 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). Estimate the average acceleration of the bai r)hd0n6*a rttj4+jsll during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with anhs cqv;,sy+ n2j(:orx 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. Each intersection has a traffic,pa ahn1)bjw.vtj e 20 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 eachptb02a ehwja) 1 v.nj,.
(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 trax09f+3.c (f 29ubqmrg*lqucmvvcz;h veling 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 accelerat (h2*cqc9 9z3l.r0fbu x mmu+cgq; fvvion.
(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; 2fo:k;a 6j,pg o -gwg7g.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and g,7fg- 6gp:ag;wjook the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The fsr4l pud-s7f +g6z;u mirst stone is thrown with an initial velocity of 11.0 m/s lp7f g4 m-+;rduus z6sfrom 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-5ebtwh l8 e5dh79 oz,cg2e0ynfalling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would he ec dh nhz7t,5y8b2o9gl 5eew0r speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt tofz(a(d8f(6 xi hxdr1dhlba6,d 5tu u( send the burgers through a grilling machine. 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 s,dt izxab((xh( d86u f1au(fr 6ddh l5paced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertje ( c:r)erknzip75s -ically at a speed 1.5 times faster than Joe can. How many k7zi( npr5s )-erje:ctimes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cli,k0w15*e*qn l f byuzrff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your h *ynfqbwe1*rz0l5,kuand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using a baro2 4hzjxj; hog3n)vfnwb3p+u8meter. Instead of using the barometer as an altitude-measuring device, they take pj;h3o)bhn+8 jfngv 4 uw 2x3zit 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 vq1az8 q4 gboo*sqp5 n2s. 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) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocq a1 o5oz2q q4*pnsgb8ity? (e) Which bicycle has the higher average velocity?