Does a car speedometer measure speed, velocity, or both+/wfk zg,d+- hx/lg2e czc)mn?

Can an object have a varying speed if its velocity is constant? If yes, give e 1wxv -2qnojdwyh:d*j;5ol(bxampb-j (ojw xd51qo2 lnv y;d*wh:les.

When an object moves with constant velocity, does its average veloci y,,djb 0tj.b;x nzqfd6.l5ofty during any time interval differ from its instantaneous t jjf;o6 lb,z.b5,qxdd0. yfnvelocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing tm mhcjn97,n g;he f9m;gnm7 c ,njhinish line to lose the race? Explain.

If one object has a greater spq3sw kmk2 f.n(eed than a second object, does the first necessarily have.w32kmf(n qsk a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km*:jcecw+ll8zl/qo*4b rn u . i/h to 90km/h with the acceleratz icn8e:wul *blq.c/lo4*+r jion of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocit1ewkqp85r op* qh+6lzgqe u74y and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positive? Wuncmz*:k n;xn 0n-awqfs kw 0p 30xq9)hat about vice versa? ;n qf0:-*u)nw9c3az0kq x0x pnm wnks

Give an example where both:b o2+f lj/wzk9w5tbw the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a sqx :lpe0k/ uiu/ 8-xiuah )-tepeed 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 608ulp h iu )kux-0at q//xi:e-ekm/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decre ksoaak116ahar13 2llases? If so, give an example. If noka3a1 o hkals1 al2r16t, explain.

A baseball player hits a foul ball straight up into the air. It levlzwur-z,m/g tb7s8, aves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the bar-zw7u s,/mb8,gz vlt ll be traveling when the catcher catches it?

As a freely falling j12r22wlw bklow/ho:kh 6:ixrji7n5 object speeds up, what is happening to its acceleration due to gravity — does it increasei12ko7w: 2n2j5 rohr 6xh:lwl j/ibkw, decrease, or stay the same?

How would you estimate the maximum height you7pyyvzv/ itp hzns 7m; ::vk5- could throw a ball vertically upward? How wou v vhv ny7/y;zs:pp7 -km:5tizld you estimate the maximum speed you could give it?

You travel from point )vwsnq31w :2j4u 1y s bajrs4d5fekr. A to point B in a car moving at a constant speed 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 not.kv)bfn1324 4 ysw.u q5wrjjsd1esa:r

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied toyk0*:p -)( djcos6ntksw )swo 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 notdy 0:t(os 6cw k)osws-pn)k*j occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock fall r-7tigvrae 2/lp:h*o ing from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dishlv/2tpeo-g 7ra* irh: resting on a table?

An object that is thrown phsbfkn/ r54+vertically upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due torhb+f/54pnk s air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and notvrc wr)67zi91riwn2 nzero acceleration at the same time? Give examples.)cnr9v76r2i rwwz1 ti

Can an object have z o9:sern 6.pairgl2p z x36g:rero acceleration and nonzero velocity at the same time? Give examples.ros6gelx .3:r gp9npaz:2ri6

Describe in words the motion plotted in Fig. 55 t)mkpkpvb54l .om bi:6cr c2–28 in terms of v, a, etc. [Hint: Fi5 6 5:)trk4p cpbmv.lci komb5rst try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graph6n,7h bv/ /x51iw,du etr0sktpiq3fled in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.25 h? tsv)syj/ux3 vrq /,/e    km/h

  A bird can fly 25 km/ nhgp- ecj/.o)h How long does it take to fly 15 km?    h

  If you are driving along a straight road and you looin9xygjghi2*2+agoli(.e8sg;b xb f. 9- qqck to the side for 2.0 s, how far do you-j 8gn+xl.(aq9gbb .o2 iq*2i cyxf ghs;ig9 e travel during this inattentive period?    m

  Convert 35 mi/h to 325ytk j9zvc,,8e agwr3emgutkt 9p 5
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fr*qe j*7-k +j ej2hy;gh9itiasom $x_1$ = 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 ford;+sds*(ego zfo4bu37 g e)om 130 km. It then begins to rain and you slow to 65 km/h You arrive home after d4*se mo dugfb(;s zg73o doe)+riving 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 seconnw djnc2wi 2(.ds between a lightning flash and the following nwi. d2wncj(2thunder 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 from this rule.    m/s

  A person jogs eight complete laps around a quarter-mieglvmz6 6 x7s1j +x39ku .zostle track in a total time of 12.5 min. Calculatg9+1k. zl7x m u36sjzxevt6soe
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its t x (aoi 8i97nbq-4dtl d64xbfe *afk+nwt;p0z rainer in a straight line, moving 116 m away in 14.0 s. It t;t*-e x70bn dokziq p9anfxi l4da486(fwbt+ hen 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. Each has a s3lsrd6:kf: rje;r0wfhm wi 6/peed of 95 km/h witfir 6/w:k;6rl f :0drhm3wsjeh respect to 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 km/h is 110 m behind a truck traveling How long will it k7ua7i(f sd t:zvbyql ;,zb+ 1;xbc1dtake the car toz yf:(q71 bz7b1icds;b+lukd;,x va t reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h w v30 sba,nb3b, and then encounters a tailwind that boosts its speevb3b,3sa b nw0d to 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 lz3 :d )77)ipbvr:roj.npurz 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 l7:zi)r : p3.n o)rjvlzpb u7rdunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant lx yzxpo;m(2jjv *v/mn7f ur :5n-h8espeed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of ;hnfv2:n-jvx( *xmozy/ mu75 je 8plrthe 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 toxg0i2e. eaq()*i wnbr 95 km/h in 6.2 s. What is its average acceleratioxn*0 (2 q)eb.wag reiin in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s.pmmw8m l ,90nt What is her acceleration mp m0lw8,n mt9
(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 accjr u i5.yqa-g-i ;e * eeiq.)1ioxe ;1bln;vaueleration of about uuxn*;;1ab-qg;.ai).yioe eile-1 ri v5 ejq$1.6 m/s^2$ 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 then braz7qmk46+nx.b(cxx7 nx d s-bikes and comes to a stop in 4.0 s, what is its accemxsbck+(.7x-6 qb7nxidz x n4leration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t = 0 and moves inrhy 1rhyf3,e1 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 tifhy3 r1 e1rhy,me. Display 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?tu5 h: (ixb+t1kd d9bo How far did:d btdikh9ux b1( +to5 it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m.(+qhbugh.:2i erx y(b What was its acceleration, assum:eiru .(2 hh(bg+yxbqed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runu 8ua /6krvz-1e0oek p/yw2u hway is needed if the6 /1wk/k ua20u -vhep e8uroyz (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the bwi-gq/ry.7 fq locks to essentially top speed (of about 11.5 m/s) in tg7qrif/w - .yqhe first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed ) :8wqhj8hq6z1vdrx yof 12.0 m/s to rest in 6.00 s. How far did it travel in that thwd )yr8xqhq6 z:1v j8ime?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highw) e0 vrsni +ohr3,: r7c b:ysxq(cs*away. Assuming a decel oqaxw(*yh ,:cir:e+nss ) r0v3c7rb seration 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 car compresses au.p agu9 4xxw519jgpf nd the driver comeuxj f99u 1w.pagg4 px5s 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 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car withwb- kc3e yat1/ an initial speed of 95 km/h and human reackyba1 - wte3c/tion 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 distance of a car f8uhl* zgg: u- q-rgha,mh2q,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 mrt 87 qn c(g: 7f3lcnw c+h4ro(xmx8fm/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerat r(l+4cc hrf3 t8qn fow7m7c8xxng(m: e at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. 3 5asbohn5g. qcm0qc 0u b:u8mAfter exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at 0.2 hnuq:mm30g bs0.5a 5obc 8quc0 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at q .lwsfs1ci6o7lic:5 +c7 nfp45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2q: s p.clis6cl7fcow fn5i7+1 –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 ground bhjv- :-w/ .zigtbb.wb elow after 3.25 s. How high is .b-hg/bt jz bv:w wi-.the cliff?    m

  If a car rolls gentl ezqqk4 /1it pdikq 9.;ypzkt:* 00xlly ($v_0\,=\,0$) 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 strai(a r.- n7xetlught up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing- -,cu,- /iv(flb) efahceqoz it vertically upward. With what speed did he t (v/fi,q,eo-l huc-- zfe b)achrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the infl ;w nvtk)ez7n.uence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = ;e) tvkz7n. wn0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascen2 dg.cxi 6lurqfwk5gn5 + 7:mgding vertically 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 reachgnk:ic qlu25 xw5+d gg.m76rf 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 travelrspsn15 ; fn5aed during each successive second increases in the ratio of successive odd integers (1, 3, 1npf5s5sr ;na 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is nklp 7) h/n zr*ouf4c9reglected, show (algebraically) that a ball thrown vertically upward with a sz9rkn47 )cuh p*lr f/opeed $v_0$ 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 of 18.0 m/,klu 1+yv.ms hiwm,1b2n wu9ks
(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. 2bh1 86mb-luqk)gh: nu–18 (or number of photoflashes per secondb1uhmhq6 :u) gl8 -knb). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. bpdye3jv r/62v 20/8dqeohxq 2–32). From what height abop qhdedryvb/qx2ev j 2o/038 6ve the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, k+)t-,5cpq2vq xvxaz and the sound of it striking the ocean is heard 3-)zc q2,ptx5+vkaqx v.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard strb wc-rt48lrc(eam 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(clr r- 4ct8wb the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge ofd n*(i*9-; kwbm cca kl+(ac h9dyif,k a cl( m9iy( d*hka+la-kk,w db nc;cf*c9 iiff 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 tgsoqs)k 9 .;og9re) kghe street with a vertical speed of 13 m/. o9e)qr g k;g)ssg9oks 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 odfb f8bkx e29bk c9/ib5qxp/)f time. (a) At what time was its velocity greatest? (b) During what periods, if bbxde 8x q9 ibk)b2ffc/9/ k5pany, was the velocity 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 di qoh/vs73 p4of time is plotted inpdo /3i 7vsh4q 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 accelerate appr/qykx ta2dk4 zcit2.( oximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the g4(kx. 2tikt2 ayzcq d/ears.)
(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 acceleratim) 0wujpe0;d kon of the car in the previous Problem (Fig. 2–35) when it is0pmju)0 dkwe ; 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 thxos** o isykt2+)z ;ige object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function)tm u4:wb5fml of time is given by Fig. 2–284lf t:wmm5ub).

Figure 2–36 is a position versus time graphbhsyvcr d;k ;nv)) t1olp*1 a9or8-k yb)t,ke for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive 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 frpk,sk)1eblbda o9 )vrny ; ;81 c*th-ykv) rtoom C to D.

  A person jumps from a fourth-story window 15.0 m above at gws ns-.q27x8 i9gma firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, F7m8agn 2-9qsxt sw .igig. 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-sixthn;ug ,rwt7-mwx6 neu, what it is on Earth. If an object is thrown vertically upward mnx, uug-;rw t n,w67eon the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrainergod 3 7t6e ay6d.lo;kd by an over-the-shoulder seat belt has a good chance of surviving a car collis7o.g d636lotrd aye; kion 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; 8ju/ knaww4t-o x a9+ q1ehyaf,uu wge66u0l bridge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be whot wjhu+wa81x4 qw066uuae,fe y k -/g9lnau;en he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufactureez 2dnh w+8:nnr tested its cars for front-end collisions by hauling them up on a crane and dropping d :8e2nnhn+ zwthem 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 traves vfcb01 9df *g8,keqzls 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 the trpuc5s(b *v- ztain 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 pb 5 (-tucsvz*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 ab5tn3 bmihn)j( ove the water’s surface into a deep pool. The person’s downward motion stops 2.0 m beh ibn3tj)5 n(mlow 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 ij;cu: q wfy t6i3ecg;3s;y5dbalance the average speed of a train against the distance betwe yy;qe:ui;jg53w 3s t6ic ;dfcen 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 fall bpbi,qmj:8at,ucn1wq( l() w y ckty(31kx: mstraight 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 m yl 1)bmq b(, ,:c(wi:ayxmtp(jcnq ukw8tk13ust it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer stru0nd yu3v: 78mfvcpd 4ikes a ball is planned so that the balm yn3cu 7dv048upd:vfl 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, 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 xbe/0g+cqr 2bkf ,l8s on a freight train traveling at a constant speed of 6.0 m/s Just as an empty boxrlgbxsq8 , 2e+c/0bkf car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building)ad:: p7n3+fnvh z g+corn+ dm. A second stone is dropped 1.50 s later. How far apart are the stones when thnr3gv :dh+z7nfpd:+oncm ) +a e 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 ofw:f:vjpn. lays4 )hg , a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed my:a,pws)4gfl j h:v. nust be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 km a ))s.wutsb7u4 *odnm/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What wa)ub)d 74 uto n.m*assws his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The fif p0r jukf 9dnn74(j;arst child can bounce up one-and-a-half times higher than the second child. The initial speed up of the second chu ; 0pnjd4 k7jan(rf9fild 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-4p d.yd uijq7 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 .-ujd ipydq47 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 sp jslld0 ).vsr:85x;nmije0 v68uzkz a eed 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 ball during the dl8m. ;v0jkzsi5l6: 8 0veujnas )rxzthrowing motion.    $m/s^2$

  A rocket rises vertically, from djy w dfmx:+4nq:0 6z64sk grurest, 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 Fih4);lhjyx // mol3gb ig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green ;h /g hljli/m)b43oyxfor 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 t lz9q-. m0gsux-,vf+ kam4eeh2 t+x toraveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a cons+lu -m0e,qsk2+x4vzft gox -.h9am tetant 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 afte rtn 1chu1lu-z0t.) fc( * gplml9wf;tr that, a second stone is thrmzc . 0t wu(tpc9glutf;)l*11l-hrnf own 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 same time. Thsijr81b t jc- l3.i*31nfcahf e first stone is thrown with an initial velocity of 11.0ltfrn ab11-ci hfs 3*8c3ijj. m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-fallibz -twv3p; egc)bma4r1u9sg( ng parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resi t;3vw9gc psue1zbr)g- mb4(astance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a y+w9uxs+3n/8ybnj hd conveyor belt 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 fast3n8+uxh/nybj+ w d 9ys must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball verticp:kv77wu s m/rally at a speed 1.5 times faster than Joe can. How many times higher will Bill :rumk7/ s7pwv’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a a loe)v6/.f+1 ta)vpjjh wz :ncliff while your friend stands on the ground below you. You drop a ball from rest and see that it ) +l ejav1tph6wf) :jao v.z/ntakes 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 find the height of a particular builf a axi.x29iwf* /h)v lp;rlq6ding 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 estimates of the building’s he/6lir 2 qw;9vxi*paxh f.)laf ight?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and*s;n z/ d1vabj B. (a) Is there any instant at which the two bicycles havebjz as*n vd/;1 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 velocity? (e) Which bicycle has the higher average velocity?