Does a car speedometer i0 mp*b.x wl/ymeasure speed, velocity, or both?

Can an object have a varying spe e )lq:b3.jdmred if its velocity is constant? If yes, give example)e .lqjmb:3r ds.

When an object moves with consrwqvjr;6 ,o8b tant velocity, does its average velocity during any time interval differ from its instantjv8w q r;orb6,aneous velocity at any instant?

In drag racing, is it possible for t3;)yzqxgb o.n+;xic :qwyob 4he car with the greatest speed crossing the finish line to lose tgy:o;4)3xyc. q o bzxqb;+wi nhe race? Explain.

If one object has a greater speed than a secondr+ uiapt(r1dtv u, 34j object, does the first necessarily have a greater acceleration? Explain, using exr p,druatjt+v3 1( u4iamples.

Compare the acceleration of z6cso19m.1(k fhiqf dc4y,s p a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10k69qyf,.smsh oz4 f(1idp k1c cm/h in the same time.

Can an object have a northward velocity and a southward 1753uzfs6 uhor2p uttacceleration? Explain.

Can the velocity of an objeckwc-p ygk1nr2 qmr)0-t be negative when its acceleration is positive? What about vice versg1-pwc-qr )0 nmkr y2ka?

Give an example where both the velocity and ap q yi.i*rkmo(:a7;dmcceleration are negative.

Two cars emerge side by side from a tunnel. Ca9f g(aajzpnh ;q4(c7g4d +z tl7;t nyjr A is traveling with 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 reaj7t cpyg7zt; j;n(qh(g9d zl a44a+ nfsoning.

Can an object be increasing in speed as its acceleracem z(-s+jb/g tion decreases? If so, give an example. gs +jcme/b-(zIf not, explain.

A baseball player hits a foul ball straight up e;q7s a0unb y.into the air. It leaves the bat with a speed of 120km/h . In the absqu0ay.sen b7; ence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object d amd7q i/qfk-.7,jkaspeeds up, what is happening to its acceleration due to gravity — does it increase, decrease, or stay the sa7f-d7km/d qqk a.jai,me?

How would you estimate the maximum height you could throw a ball verticallyqneg/ y ,3qv8 /i4ppgw auy:1swt6msb,86mps upward? How would you , w 36q:v8pa6uyinqs/t,1 m/p ssy4e g8bwmgpestimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant speed ofb*gh -62,txs .wlol1vuvzu v u+zl 40k Then you travel the same l+xs*vtz -u4l hu 2uv0,zwgb.1k6l ovdistance 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 with ten uz4xcl3l 2gf, bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the boltszxc432 ,lufgl be tied so that the clinks occur at equal intervals?

Which one of these motions is not atblpfnahyb., 4cnye c02n )-ch0 cd59b constant acceleration: a rock falling from a cliff, an elevator moving from the second floor thy02e5lcab fdcy9) b4.c,-nn0h c pnbo the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically ot)ent: .)xisxr km*: upward will return to its original position with the same speed as it had initially if air resistance * tkt)o:mr:.)x sexniis negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero vd0arph ;* /sppelocity and nonzero acceleration at the same time? Give examda p;/*s r0pphples.

Can an object have zero acceleration and nonzero velocity at the saae5 u,a0ska4pme time? Giveea4s5a0 pak,u examples.

Describe in words the motion plotted inglgmk,j; ih 2 8ysm)l/ Fig. 2–28 in terms of v, a, etc. [Hint: Fyg;k8l,j )/m 2imgls hirst try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of thcku,t 3yb( 1bwb 8by.ae object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.251i dqgf1,fxy:x mqn5ued .1e 4 h?    km/h

  A bird can fly 25 km/hcc 9;s+- jn 2gpizp8if How long does it take to fly 15 km?    h

  If you are driving along a straight road and you look to the sin5u xqcdtawls(9a5/-de for 2.0 s, how fad -n 5xq wt(/5scala9ur do you travel during this inattentive period?    m

  Convert 35 mi/h to x:*lcgga17 cmb: x- nw
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from7zx/r qsi,-as) m- bgu $x_1$ = 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 130e0m-.u tyk/ xj km. It then begins to rain and you slow to 65 km/h You arrive home after drix/0-yet.k mjuving 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, evexc8izdslfp+ 5 5:rqctmbz 867ry 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 time at all, estimate the speed of sound in m/s f p8 drcmlzs z 5q:xf8t6ic5b7+rom this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a y6gb63m0)6 qihyfsz/h vzy v (lrt71 jtotal time of 12.5 mi j6 y61z vg7lfiy 3bth)(6zsvhm/yqr 0n. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straim82;y pre)ct/y(h ho of3h pg:ght line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s.(p:yt/h38 o;2e)p y hmfcgorh 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. Eac;j,-;n jdv,4y 5 se.ajbhpke b2ghgm 3h has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2e5nb2j d pk3g,v -sh.;yhmgj a,e4jb ;–30).    min

  A car traveling 88 km/h is 110 mnac q0c1b2uym7l mf .2 behind a truck traveling How long will it take the car to reau fqln2mm27bc1c .0yach the truck?    s

  An airplane travels 310(2wkl0t hh. rswih d0gu crju(12,h0 f0 km at a speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/ t(hrh 2l0(wd sw1c,02ihjuf0urk h g.h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and av8 ;awap4x oqpn:- hi/,iobx 6rerage velocity of a complete round-trip in which the outgoing 250 km is covered at 9a- o4aip,q rxobnh ;:i/6xw8p5 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 travelingbuz,2abp b 1m/ with constant speed hits the pins at the end of a bowling lane 16.5 m long/bupabz mb,12 . The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. Wh (o9cnbypv6p hiv)z*mr1v; jz; *ev 0wat is its average acceleration imyr h n)v* po 6 9j;vew1b(0;vpi*zczvn $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.z+w+/e2ibb- 4*-gtms k grjku35 s. What is her accelerationz/s-k+mw4ibt r* bjgkeg+ 2- u
(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 accgb0i+ 5qrp8om eleration of abouq5 o g0+brmi8pt $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110 m in 5.0 s. If it th r0gu7oexf4fm5yj74u9:h f( z.(iy + maxvfjhen brakes and comes to a stop in 4.0 s, what f :ajgf4794erh vj.mxfi7f(yyuzhxo 5+m0(uis 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, whick gqh phjh 7m*0d09yt*h starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its accelerg *dk 7qj hhm9y0t*h0pation as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/yo1a;avcp): ;wj)sbbs in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant acya;sb :)1;wojbp )avcceleration.    $m/s^2$    m

  A car slows down from 23 m/s to resteuwkbwg2;43 zh+ snt / in a distance of 85 m. What was its acceleration, assumed constsh2uwb kz ;+ e3/tgn4want?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a rul(* bwrc bx;,e 3/* mf:mavurwnway is needed if thvw;wr l/xb,*3 fcb e *m(maru:e (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially tofg60tb 5oucgza.8r5 q p 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 t6g0aqgt8u5.b c or5zfhat speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/sd614k5glqud) 5pcbqq v4v c 8p to rest in 6.00 s. How far dicb8dl v) dqp 5 vk45cqqg1p6u4d it travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assuwv d/zeymxk/xq8lll7 ,k0 6i yej03t;ming a decex7z,0kyydk3e/ 0 j iq /;lml8evtlx 6wleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h ( en)a3+wwy:m,wc px/.pcrnr strikes a tree. 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 d ap(n.cmpcw,n r3+:/)xre wywriver 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 distas 3q7bhnh9 ax0nces for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an accb0q 73x9ahs nheleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car i,8mf hbp.qv6rx 9 8 kinprku5*s $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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 on48 . 8b96ijekh2sc sw1ttja2 yjez mg7 the highway. The car’s driver looks for an opportunity to pass, guesbwe2 968 .2azskhty4j7it1jjm sge8 csing 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 mij azw4gws*(1 gn. After exactly 27.0 min, there are still 1100 m to go. The runnezw g*1(s jga4wr 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 the traff gm8;gm(ct,:h4w* ,b4fjdpdk hlpn e/ic 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 try to stop, or should she speed up to cross the intersection before the(:g 8ph, tjd ;, /w4kcn* eh4fmlgpmdb 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 groe,n-h iv;zql; und below after 3.25 s. q-, v;nl; ehziHow high is the cliff?    m

  If a car rolls gently vbkd-hb eua6 09m6d z ug+04hq($v_0\,=\,0$) 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 speew;baf1 f7mtto1g zp9fl 9 5vp4qaai9(d 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 aftimwwwnlf/(* 16va4 s cer throwing it vertically upward. With what speed did he throw it, and what hmwwl( /v* iaw4c6s n1feight did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gx1m-9rsq i ,jt2rl-p y6d c4dgravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistancdgr -yjr 2 xi9,6p-lcdt1q4m se.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height of /eqr byc9 o1m:125 m above the Earth, a package is dropped from a window. How much time does it take for tbrm1 /q :ec9oyhe package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance travelezh5h ihgyi,:sl0y u8- d during each successive second increases in the ratio of successive odd integers (1, 3,z 8h:-i 5yglusiy,0hh 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected2b im z2w+ru urdb)27f, show (algebraically) that a ball thrown vertically upward with a sw+2)zri7rm 2bfdbu 2u peed $v_0$ 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 o mzos0sf97 (w98as 0kf*rv iwrf 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 be j.jnr72itkf pq*-wx. tween each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at k*jtqwrn7f x.- 2pji. the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–32vevo97b vjw)wb 3.fus g ehou)qs 6(2)). From what height above the top of the window did tvbubo.u )wj2 9he36v v7()swqo )sgfehe stone fall?    m

  A rock is dropped from a sea cliff, and the sos/qtedrxm8jg+q-j5 * und of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the clifme+8 *qdgq txr js/j-5f? H =    m

  Suppose you adjust yokzzbz)1 (x9dt 7sk.-wzh(fb y ur garden 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. What idshx) ztfz.zbb(-k1zy w9(k 7s the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s frv:rmg5z- f1mx om the edge of a czr:gxm-mv 1f5 liff 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 m above the street with a vefdaww0 4p0 ,)p6xecprrtical speed of 13 m/sp0 6 xfd)p0r,4wwecpa 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) At what:by480; cqdl zght 7c,nac;uc 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 ,ylcq adc8;g7t: nh 0 ccu;b4zthe magnitude of the acceleration greatest?

  The position of a rabbij6 0o;pye:mdm t along a straight tunnel as a function of time is plotted in Fig. 2–28. What is m6p:j ym0;eod 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 ac0:pmb)1)e 1lzoklzcr celerate approximately as shown in the velocity–time graplo) c)kmr1zpb:lz01eh 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 Problem (Fig. 2–35iema 60n1nh4ii 8 yedapl/*v5) whena81yliip mv4 h5i0eeand*/n6 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 object trav nw- repgfbjoz63og2,81 4xufa1e fw)eled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for thumnh 0qd.+eb-e object whose displacement as a function of time is given by Fig. 2–28.d- em. uhnq0+b

Figure 2–36 is a position versus time graph for the motion of an vw6:s gj))a5 g9(tlofp edqd 7object along the x axis. Consider thd gea:9w5 js7o(v6 )fgptl)dqe time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding 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-storyu ms dkr:.wgo07po1n 3 window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before 0o7 k.1dums3o rnpgw: 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-sii+lrx 6v1 ahndhspzt/+or2 wdk9-4, kw87j gm xth what it is on Earth. I4dnmz-dk,9t2 kwhj6sv7h p/wo 1ix+agrlr+ 8f an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-thebj4 a/g(big .z-shoulder seat belt has a good chance of surviving a carg4.bja/b zi(g collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below)k). r-tyu/ aqaxroh+ , and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 2t+.ao)y- qkurrx/ h )a5 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 bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for frjzy zxk22gv3 pd4h t:q8h +k0wont-end collisions by hauling them up on a crane an0qdt4 xh 38pw:zz2 vk2hkygj+d 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 travelptym1ioy:j*st 5 / z) y e7cxig+q9hs:s 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. wl9 wft.:jz6 ak ,a0+dyn*7wz 4btoekThe front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of 6w.kj tk+*4 b7fn :9ad0a,ztlwzwyeo the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a divin :hxd yl9f7m q7xh.+yng board 4.0 m above the water’s surface into a deep pool. The person’s downward motion stopsx:n7.myfl9 x hyh7dq+ 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is nec +s(5/mdtsarl/ztm9 iessary 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. T tild 9amt+/m(s/r sz5o 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 winx.wldtd6 9 a 7ow(m+ ,t/ zz7qr7vucqogs and free fall straight down when diving 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 mw7q.t6l7 z ( uo wdz9+od rxq,/vat7cspot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a b3pjfo.g 6fe b8koel e;pu dm8s*,4d p0all 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 (tgu pl.p*,od3 f6s 4 8f;80pjbme oekdehat 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 constant speed of 2+a2uijgl 1 ej6.0 m/s Just as an empty box car passes him, the fugitive starts from rest alg2e +12 iaujjnd 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 buildi) kfv;t*up,;hivfdn 2 ng. A second stone is dropped 1.50 s later. How far apart are the stones when the sehinf;f2t , kvdpv*)u;cond one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the coursgoli8 wn1j1kc1sg ;w( e of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be main1ogw i1;wj(kg l 1csn8tained for the last lap?    km/h

  A bicyclist in the T gmau gc y2d(7*p--qdcour de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, h-a(ygg- cd pumq*d27c is 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. The first child can bounceu*e ljmov47;v up one-and-a-half times higher than the second child. The initial speedev jo7v*4u ml; 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- //bm jxplb1 r6irue st0ps06 nj6:,nnlong train traveling in the same direction /r 0b s/nrx1 etl 6bi6upmsn6p,jjn0:on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 t1hck/5 g b1qdm/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 acceleratiob15 h/1 kqdtcgn of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, 9 ,-iv0ut97slpoo+e hmeb(ue 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 Fid.( mts652f mcd:uqk.z rk 7lcg. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from u q:6k k.m.dmd7cs5l (rzt f2cthe west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a conyzdo1;bwc9 * v :ogxku n4w6v*icvs68 stant 120 km/h takes off in hot pursuit. The police officer catcv vg6wswkdv** :c io4u o16;y9bzc8xnhes 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 building;n1 /hj(xx2m5f42m(gmk n s e 89wnceqr 2.00 s after that, a second stonem2n2h(g8xm 4mkne1xe w( qsrcn9j5f / is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the sa oge7 r2ymfq+8me time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be theq my7fgo 28r+rown 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 wow-qvtwc /xy23h s7) qojzgp) s7 0a/lzuld it take a free-falling parachutist to fall from a pla3wj z-y)s702gh/oqz7pcsx )a / vl qwtne at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers t ih-zjz llyb( r*cm05*hrough 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 aj-m *ycb5 llzh(rz0* ire 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 Joe can. How mdgy p k3 dgzg.-m7( ut-x3oh6oji5v6eany times higher willg6.x 3 y76t3(5pv oj-hm d-dieuokgzg Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top 6mm(q9puyi,f of a cliff while your friend stands on the ground below you. mq 9u6(yifp, mYou drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to fi(i 4o(ecuqpv* 40 s-nceuyfd3nd the height of a particular building 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 the other, 2.3 s. How much difference does the 0.3 s make for the estimateuniyeduc vo(3404 pc -ef* q(ss of the building’s height?    m

Figure 2–43 shows thetje.g(*emi 1cxl5 uk3 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) At which instant(s) are the.xm5j*tu31 l c gkei(e 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?