Does a car speedometer meadyge 8u3mem3g w p:,5qsure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? 5wb7j8u: mfghm;m dz3 If yes, give examplesmu35d:fmm;7g zwj b8h .

When an object moves with constant velocity, does its average velocitywdop +bc8 :q5 t41luqy during any time interval differ from its instantaneous velt41l:pwq58bu +dy o cqocity at any instant?

In drag racing, is it possible for thepqr, y65bfdy 1 car with the greatest speed crossing the finish line to lose the race? Expldyrby5qf p61 ,ain.

If one object has a greater speed than a second object, does the first nel3f bx e,t s85kvch*, a8ac rpik9vcdw13a3d7cessarily have a greater acceleration? Explai,8v9xah w,k1ka5fcp38 s*ib a r3td7 ed cclv3n, using examples.

Compare the acceleration ofs-t*x dte a.k. a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that acceleratesesatd*k -.tx. from rest to 10km/h in the same time.

Can an object have a northward velocity and a southw5f, hax7ie1+ deqqv)sard acceleration? Explain.

Can the velocity of an object be negative when its acceleration guo78zq ;d nl6is positive? Wha;zdo l6 7un8gqt about vice versa?

Give an example where both the r(; opz ci3b:rvelocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a spep +ckx d)pb18y6y kz ,uc+hs6med of 60km/h and has an acceleration of 40km/h/min . Car B has a ykp xksc m ydc,h1+ 6b6+u)zp8speed 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 increasr44b3f twf;ip s+/iv ning in speed as its acceleration decreases? If so, give an example. If nv4t4ibfws3;rp/ in +f ot, explain.

A baseball player hits a foul ball straight n,y(dvdp8um;yz+( sw up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when thes(d+8yy;mz,(n uvwd p catcher catches it?

As a freely falling object speev97u cbyq5 uwr(o,dk 0ds up, what is happening to its acceleration due to gravity — does it increase, decrease, or stayr5uyo ,ucd v(b w70q9k the same?

How would you estimate t6c7puz-xerm06 du +p77qc zk jhe maximum height you could throw a ball vertically upward? How would you estimq67um pzz6d puj x7-7k0+c create the maximum speed you could give it?

You travel from point A to point B in a car moving at anb* 7(zwndmf 8 s7zgw. constant speed of Then7b*w w7gmd.n sn8f (zz 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 not.

In a lecture demonstration)lv(a+0l.h/j v*ftfuq1v iz j , a 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that+/0vauhitvjfql ( *z.flv ) 1j the clinks occur at equal intervals?

Which one of these motions is not c.zp-vb1f5hp3 mwq5 9bam.k yl:* bmh at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to thhz 9lby.cva1b f qkm . m55p:phw*-mb3e fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward 1n5fr,:expgh f,e pt,*7lezd will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreci7,ng5xl frt1 fzp*:hee pd,e,able, 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 velocity and nonzero accelerb9qpuziy i br 8 )3mlza(0::vsation at the same time? Give exapl):(ius8 rzmiba93q0z vyb : mples.

Can an object have zero acceleration and nonzero velocity at the same tim : cvf9enrb*h+e? Give exampcr:e+9vnh f*bles.

Describe in words the motion etb,-dzdd7/ lplotted in Fig. 2–28 in terms of v, a, etc. [Hint: First t7 dt,b le-d/zdry to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in4 n 8felc *arr 9oz9i5la:9tfu Fig. 2–29.

  What must be your car’s average speed in or7- ebpo.r0mw 5-,k8f-vxda ph;rnsiqder to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/t f96 ppg8wz.jh How long does it take to fly 15 km?    h

  If you are driving along a straight road and you look tojwx p gj,+m i6:tz42hx the side for 2.0 s, how far do you trav:+iw4 x2zpjt ,hgm x6jel during this inattentive period?    m

  Convert 35 mi/h to t f*tcoo z+a7**e 8/jg/dhuv+y(bxt v
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fro2:z gz9q*w2 td.j6k7zwc kjjr8ra aq(m $x_1$ = 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 sswo2tgo 7h ; pap8mq;3chool steadily at 95 km/h for 130 km. It then begins to m 38ps2g twoo7pa;hq; rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five sec4c73 vd c) tov9)z5iuvv9ran wonds 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 v7 t)wi93)ncr 5vda vcuovz 94in m/s from this rule.    m/s

  A person jogs eight complete laps aroun7 r:+avkrpw:i7 +nx31j bvqrrd a quarter-mile track in a total time of 12.5 mi ri7xbp1rwkvr3rn : +jvq+:7a n. 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 i*s06bkbiu2+gefk* /fpy emr :n 14.0 s. It tef6bre u y 0+bs *2p/fkmi*g:khen 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(h(pe 38plh(dzn 8ka(vjghx7 b)q 7ps each other on parallel tracks. Each has a speed of 95 km/h with respect tbq3x(dp(7 g hkj((l7pvazhhpen ) 8s8o the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 k 32fmm, 3m.vabctm d8im/h is 110 m behind a truck traveling How long will it take the car to reach fmtmvam ,8dm 23.3bcithe truck?    s

  An airplane travels 3100 km at a speed of 790x+gd:1pu(th( 1 ue:/ yrc(.uh jicvvt km/h , and then encounters a tailwind that boosts its speed tov/th(( 1.:ui( p ctu1dehv+yrcu:jxg 990 km/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 average velocity of a complete v:1k: 4jjmy lr78rpfcround-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and k:jl8mjpf:v7 4rcy r1 the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with const 1 r1ukd)k0 /smf2obilant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is /2bkfliod u m1r )1sk0the 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 its avermx1lkyttlcyk 7p 5-l1+ pr/uh:-iw* nage accelerationki-pr yk* ul7m5 ny 1p/1 -+tltlc:hwx in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accele19c o*sngwxdgue) f ;4ivgn3.ration de1i3f4uwggxn.s*)co9v ng;
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particulau0 tqw6mgm(/ f ;rihtg,mt/o7 r automobile is capable of an acceleration of abou;og w mi/ttu/0mgt7 6qhr m(,ft $1.6 m/s^2$ 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. I)xzgn zq,(f:q9e* cosf it then brakes acs)9f*qon xz,eg(z: qnd comes to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest a )c+fxisb30ag t t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Disbc +as30fi)gxplay each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleration? Heoo )1c /4k3qf2du))mbwirddow far did it travel ind r21mdui)3q/b eokfow)dc )4 this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a5amt0t/ua p7v 30e.lhb d2kni distance of 85 m. What was its acceleration, assumed c7nktvd0 e5a23 pl.ibh0um a /tonstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How lokoann+(g/ +2 p* tzzxmng a runway is needed if the (constant) accelera zkxp(/*n z2amontg++tion is $3.0 m/s^2$ ?    m

  A world-class sprinter can burstbq6 g: 8q..kubw 377h r9i tinbszi)ni 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 taker3 n:s6hikbt7 .q7ib)9 i ubwg.in8qz her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.008kr5zszb-:27i vuz8kn;n aju s. How far did it travel in that k5 anuju8s7irkn8:z-zv;2bz time?    m

  In coming to a stop, a car leaves skid marks 92 m long 54t8nwtk )j fdon the highway. Assuming a deceleration j4twd kt85)fn 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 tree7hpfhbu*7ee3 vz)7 y q. 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 collisi on? Express the answer in terms of “g’s,” where f *heb e77upqz3hv7y)1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 93 shb ms:vjy n(b)p;i;5 km/h and human rs3mpisb b );n;vy(h j:eaction time of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distan+gpj.zi -:0dbdbi7 vv9s 0cfy()b) /tbgfjc ace 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 uar)cqt :mv:;j s5d.don the highway. The car’s driver looks for an opportunity to pass, guessing that his car :j .sac:mt)dvq;rd u5can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. After e+jrc3muafeh)y.b 5:exactly 27.0 min, there are still 1100 m to go. The runner must then acceybrha5fjc e:.+u)3 emlerate 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 justzbrimwh 4 zkc94*/,bu as the traffic light turns yellow. She knows* zbkrc94wbui h, 4/mz that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the u p d;c lea(/ dxri4z( kg8.mv)lgxu-:ground below after 3.25 s. How high is the cliff? :puz.(xrcaedggid); /k8x m-4lulv(    m

  If a car rolls gentlkygni41 b7+gjz 2 3pbly ($v_0\,=\,0$) 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 ag(v n0be3 :jc,.foit gir with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after thro:qifaxc we bk )hs9;:5wing it vertically upward. With what speed did :h5 w :ic x;b9)qfaskehe throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and f y4m ;b9fnxh/ialls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a functiox;nh9miyb /f4n of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speedx)/okt+7; s.d xsk rko 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 par/tsxko ;.xsko+ 7dk)ckage 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 dists: zovd 6ja,9ks34ggkance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, 9ksa: g6,gs dkvo 3zj4etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown yl)a ccu4la.:qxfbrf 0f8n/ 0vertically upward with a speed 4.nb lr/f 0 yf0 f:)axqu8clca$v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertica d 3u;4)sm9ujpc;o wlt7nz+ tvlly upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apic02jsfe 3n vhs4 v(a0ple 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 tj(vnv23s fci040ehas he top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–32). Fro6khs( b*zq 35iv0hta iz-0jaqm what height above the top of tj*k0ziz 3h 6qshtb-( aqa 5v0ihe window did the stone fall?    m

  A rock is dropped from :cbc,b g (h5dvho, id6:3wamka sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the clifo :c(:cgd,3bdkmb hwa i, 6vh5f? H =    m

  Suppose you adjust your garden hose nozzle for a ;5nvzb1a7r tthard 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 strikin;5vbta1rtzn 7 g the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the efy 3w9lw (ya*hdge of a cliff 70.w9yflawy*( h30 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 wi7 iuj wt,6.nr2 nu 43nxbqfii+th a vertical .i fwn+inr2b7njtiu,43x6u q 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.ak:0qom61x*u vmj p9 gu0 ro3p (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocit :p3ojmmu9qxv0p 1 g6a k*0uory constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of 9fn w og(isw+ sv8t0s-time is plotted in Fig9sww+( -s8nvs oti 0gf. 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 accelerate approximately as shown in th2u ozxoqq:le 49z*;r ue velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.) z l*;q9z:4euquoro2x
(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 (Fipk29 oujn)5l 8is fjuz+jz /r*g. 2–35) when it is ikzj+8 nr 5/pji9ju )fls*z2oun
(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 traveleok5m7s a *le.ud during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement ao0;ky9 fvs 8hvs a function of time fv9hykov;80 s is given by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object m,vvu5b (km .ealong 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),.5 vk(bu vmem 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 firefighter’kdz4ocv yli1n. a25n 1s safety net. The survivor stretches the net 1.0 m before cominld 2 aic1nvn.4y1 ok5zg 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 0 jop0*zvlt.* ye;x,lgu8 w wbone-sixth what it is on Earth. If an objecep,0gu 8 vwwbtzo*j* 0l.ylx;t 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-the-shoulder seat prlm4 spx -8hs1pyyc 5wda s84h,c:7 nbelt has a good chance of surviving a car c, ss:17yy85a cw-p 8hsp4dprxlc h4mnollision 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, and his pursuersp.v iwq.n2,o f are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getawaw2 .o.q p,vnify. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by haulinqtx;hb9 mo61 p/+vql lg them up on a crane and dropping them from a certain height. xvlq q/1pl+6tom bh ;9
(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 wr99/ wgfh:wl travels about $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of t3grvsbgy + rpxikh(5:)o l:d+he train has a speed of 25 m/s when it passes a railway worker w(x d+l:ks)5b+p:vhorg ry i3g ho is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’8kd exo: )s8dg/8u witz7iu1ks surface into a deep pool. The person’s k/s7d k8guwzi8 i:xo e1dut)8downward 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 transit system, it is necessary to balvh iep1sqfuc0 f; x7 5(r6xd(gance the average speed of a train against the di rgu x1cf5 hxe6q0s((vpdif;7 stance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two 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 fnyjkn6 4rox :9all 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 i njnyo4: 6xr9kt spot 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 ball is planned so that uy 1a4tf8a 8avkr*c u.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 (trk1.c* ua ta88ufv4yahat 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 travel 1sv) xwky. l9l3(ozzging at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive staklwyz 3s ()o9lg.xv1zrts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is dropped u2 p9uht;8 l49w3jyjju7jri r1.50 s later. How far apart are the stones when u9j;ihy j4jr7 juu3 829prtlw the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time t/cag vvrf48 oh*uwcrc:2 pj-1rial lasting ten laps. If the first nine laps were done a:v oa4rp-vr u* /c gj8c1fh2cwt 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain foxd*3u h8*pg0m 6iry ;f;uhv pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 p8*of;umxy ur dv3h;hfi6 g0 *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 bounce up wocbt-yhb is-w40d xj4s0 km-.07dbjone-and-a-half times higher than the second child. The h kjj 0bxobwyc -.ds-b0 m7iw44sdt0- 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 overthl2d 1)m (0u hhwnrw-kk82sxa akes a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are travelik0da2nh82lrkms1 w- )hh w( xung 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 m/s In ,jq6- gnc+d8 m7d(sluu+ ev nithrowing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to thdiqnl+s( 6guv dc-e,8m+nj7 ue point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically,vejb6f(t 695c4 r62hkyzyr gc from 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. Each intersection has)2ergp(w bq:(5 zty. 8fzh7 jeuu8 aac a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are gree :et2hb( 8z w8acgy.zu uqraj(f)7 p5en 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 kery,r+ugq zjt7 xu6li*g64d7 jj23 ea constant 120 km/h takes off in hot pursuit. The poligq7 6j u*je +dgk,3yixr4er6ujl27t zce 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 building; 2.00 s after that, a sec,ob7.b y1r/nftrfkv7ond stone is thrown straight down with an initial speed of 25.0 m/s and the two st/ tf krrfb yb1n7o.7v,ones 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 seil1/gxxzy+a- 3l v*l v s0db,tone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a buiiy lab*zse 10x/,v3l gv-lx+ dlding 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 wovtvb,nl6) *8jmu x or0uld it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350j0 )tmrl *xvbuvn86,o 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 bel+ey +5xz0mzm3arr ols:rl p*:t to 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 mp0x+z:r3 * :+ eayzrslr om5lare 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. ko )(vmgcp ouc//o+x2How many ox k) uo//ogp2+(cvmctimes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend s qj *.*h7 e:5totunejptands 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 picph jqe .t*o*t:7ejnu 5ks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular buildingj59gn,k w .oas 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 tgoj9.5s, wank he estimates of the building’s height?    m

Figure 2–43 shows the position vs. time gra )bt7jg,keozn1 7hy/aph 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 jto/1e kabzn,g7h y7 )the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?