Does a car speedometer measure speed, vea6;ka5g e 2 vlajm+qx4m 1rp4hlocity, or both?

Can an object have a varying speed if its velocity is constant? Ifaj5smy x uhols /;6-r1 yes, give exaox; r5m1/hla-6 us syjmples.

When an object moves with constant velocixkvh rkv13i; f.sci1 yvf ;3u7ty, does its average velocity during any time interval differ from its inst skkc ;i;f3i7v3fxv1h.vr u1y antaneous velocity at any instant?

In drag racing, is it possible forzlpz g6 )8vn:p the car with the greatest speed crossing the finish line lzz: v)p8png6 to lose the race? Explain.

If one object has a greater speed than a second object, does the first necessaqnmidj gbpyizh2* gyv;914cr3t.8p5 rily have a greater accele *2.qghb81z;3d4r ynvgc 9tppjmi 5 iyration? Explain, using examples.

Compare the accelerationsvi7rilfon6l * i :nh5 2fxh;8 of a motorcycle that accelerates from 80km/h to 90km/h with tvofl8x 5:nl*i27 ifs6hnh; ir he acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northwq 20fp+;gp *a n (g0urg+viddnard velocity and a southward acceleration? Explain.

Can the velocity of an objec(t; 8j z2u-jb lkjfqm4t be negative when its acceleration is positive? What aboutt(j8jjb 4 - lu;mk2fzq vice versa?

Give an example where sn.nw p 3.o)7jazlg9:msg3is 1lh; csboth the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Ca ukb87 og0ml1kmt:ecia /6ds ,r 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 tun kk,a8: t670/ glmuib mdosec1nel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreas l-uq 9mudfb 7/(54ut4k4ytduxl ynt* es? If so, give an example. If not, expla5/tk(du 9x u4nl4t bu dfqmtuyly4 -*7in.

A baseball player hits a foul ball stra f1 ka6u*q. rh0zjmof2ight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will thu *z06krf2h.j1faqm oe ball be traveling when the catcher catches it?

As a freely falling object speeds up, what t*r*+r nql:zl7lfj-qis happening to its acceleration due to gravity — does it ilf-+qzlj 7rn r*lq*t:ncrease, decrease, or stay the same?

How would you estimate3ly7p a npldt*q8e:.n the maximum height you could throw a ball vertically upward? How would youn d8e:3n.pqy l7p*t al estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constau9uyv7ylw 0 c2n dgk7-nt speed of Then you travel the same distance from point B to another point C, movi-2un7 vl7 c9wdygku0y ng 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 bolts 6p4n a zj7jo+ytied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tizo6+4pynja j7n plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant ecp dc 0gdb qt.:r7o;qi+/v6b acceleration: a rock falling from a cliff, an elevator moving from the sed.p: 6 o t0qg7+vqb;dbc/ rciecond floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original posiz.hnbk i roi s(,9evv 6785yvin.8codtion with the same speed as it had initially if air resistance is negligible. If air resi vin(ve87 y.ski5d .orb hiv9 n6zco,8stance 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 velocity and nonzero accelenoe( ar)gekp3 5z,( ddration at the same time? Give exad n5d(3 (gk)ee ra,zopmples.

Can an object have zero acceleration and nonzzqkjf:66+3z9m -hf7 bql famjero velocity at the same time? Give exampleszzl+qf qmha6fb39- k7f j jm6:.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc.bh3 b yuma5n e,du(,6k [Hint: First try to duplicme(a buy b,d6 ,u35nhkate the motion plotted by walking or moving your hand.]

Describe in words the mot)h1. btlb ;1ynoih-lbion of the object graphed in Fig. 2–29.

  What must be your car’s average speed in ordx:a(mr;p o8wr0p k6hu er to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How t3m h.zjdzhtw;5-dy1 long does it take to fly 15 km?    h

  If you are driving along a straight road ams(dpu(xh(kek 0 p5 aleh,/f/nd you look to the side for 2.0 s, how far do you trave( fp,dhm/salp5(e/u( hkkx0 el during this inattentive period?    m

  Convert 35 mi/h to vyjeo1l 2;zmvl 8i6s.
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball movesm*kbt, y cd-:h892txlo*qlmo from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school - nof3sf 2irkcz:04 ktmott57steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and 2ik-32rt0 nfto7ksm t 4 zfc5o:0 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lighubgid .u/vk 1 guk+i**tning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time gud*i k+u.v*g i/1kub at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a qa;v/7 cr;:;m4aqw-sdv m dv;rfp /cyuuarter-mile track in a total time of 12.5 7sc;d;d;: rm wu afc;4rvm yvq/ap/-v min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moviq1jr+sw :rs *pvyr4o6ng 116 m away in 14.0 s. It then turns abruptly and gall4s: +1rrp *qos6y rwjvops 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 appr2moj 5be8 s,6; zut7b yu)nln)apa)ff oach each other on parallel tracks. Each 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. aso um ,6ln7) abbnz 2up8f);tyj)f5e2–30).    min

  A car traveling 88 km/h is 110 h2*3 b1tz 1d iinnd3zym behind a truck traveling How long will it take the car to reach the y1 3n*1 3 znddhz2tiibtruck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and theny8v-qaysuo, . u-d+ym encounters a tailwind thaoa qs.+u-vd,yy u my-8t boosts its speed 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 and average velocity of x;plk4i, ieqd44g2 nzup dv87a*2 ixoa complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return *4,d8ip u ;x47l2vidak i 2qpgxze4n o250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hitxznph2ea oghi2 rkjuzs1 (p91, 22;wbs the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hittuk1 9ar(ihw22 z1j,z;go bns22e php xing 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. c- k8+b.adkkmWhat is its average acceleration ik k.mkc +-8badn $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her b8/caou; y ;sh6fyp,l acceleration ,uh; s 6c8yyabfpl ;o/
(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 acceleration of abovzs)sz wzeu)(no : /a5ut svuezw:so5z( z )) /na$1.6 m/s^2$ 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 ty px; d2/u3a*ov pyro1hen brakes and comes to a stop in 4.0 s, pvo;pyd 312u *o yxar/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 raci+ ug81e ,g)y 6usnvasvng car, which 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 acceleration as a function of time. Display age vngsus61u8y v) +,each in a Table and on a graph.

  A car accelerates from 13 m/s to 2v/fkg:q0,kc)2vvc jm yz:g)-1kwil i5 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant acceler k2lgk/)-yw,vq :ii c)gkj v0:c1vmzfation.    $m/s^2$    m

  A car slows down from 23*caxflv2jo-t 124srb m/s to rest in a distance of 85 m. What was its acceleration, assumebr x2j1c-l2t4*vasf od constant?    $m/s^2$

  A light plane must reac qjcb.dq e+u9 f(.6ifhh a speed of 33 m/s for takeoff. How long a runway is needed i eqhuc(9f.q.fji 6+ bdf the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can bspafin (84 .zrurst out of the blocks to essentially top speed (of about 11.5 m/s) i .(4pisn r8fzan the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a sp( lzcug0ivt- 7eed of 12.0 m/s to rest in 6.00 s. How far did it travel in -ulvzc07(it g that time?    m

  In coming to a stop, 1 pa0rka db p*5nyky+*-p fw2uyi ;ys/a car leaves skid marks 92 m long on the highway. Assuming a deceleru+y wyps* 2b0*aia5- fpkpy/yr; dk1nation of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 kmb+kfhxu;7vl*4sc tlu f 6 /ly0(u.tk x/h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. f;lb (u7tlx/v 6 k 0ytlc+u.h*uk4xfsWhat 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 with anb-hd;we +b)jm initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleb e)dmbh+ -j;wration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation fon eay).vxe3ke4xp,s-v+. ct8vm mt k17r u fj3r the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The c wxc7j; /nwwd(ar’s driver looks for an opportunity to pass, guessingwjw (c ;dxn7w/ 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,( w)cmtxj 6,b al5:idc000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The rut:c6( c bl5)d,i mjwaxnner 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 ju5tu/ hy*(um1ht3x2.m2jr 1qa cxdoylst as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. thq3xmaylou2/5 ( x12*mrcj.udhy1 tHer 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 below after ba;rkzw l/;p5/(ofwk 3.25 s. How h lr/pw5bo;z;/kfw ak(igh is the cliff?    m

  If a car rolls gently;jpfj3z 6+b3q 5bhw,t f8mlob ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

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

  A baseball is hit nearly straight up into the air with a speed of 22 m/s p1z0:7fyqgs:xzpt 7q:v eq3m
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically u)4:pll 7y8mic0c fg6 v fw3eurpward. With what speed did he throw it, and whatcc08lplvm):i6ruf7 3 ewy gf 4 height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influe n4or7s4 j:rqince of gravity. Draw graphs of (a) its speei4sr4qonr 7j :d and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. qn-)jm3;v +dgz ue g8tAt a height of 125 m above thu 8 ;j-+zmtde) 3ggqvne Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance travelaaqii -p(2f w s50hdmqakm1,rm2la8:ed during each successive second increases in the ratio of successive odd integers (1, 3,(a m8 ia r5p1:0f sd2mq-aqaklwhm2 i, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is ne s7 iuy4.qcxkehr; 5*uglected, show (algebraically) that a ball thrown vertically upwardyeq7ish*. c;u4rxk5u with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward w obz9k)-eb)b uith 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 photlrly)q- r2qw/oflash of the apple in Fig. 2–18 (or number of photoflashes per second).y w/-q 2rll)rq 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 winn3qkr 1p6bo5ndow 2.2 m tall (Fig. 2–32). Frorbnqp51n3o 6 km what height above the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean is h q*irrg2ffjvwa+w /,w1r h/o-eard 3.2 s later. If the speed of sound is 340 -aj/wfw2+ w/iqfo*grr r,hv1 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard streai*r4 ntnby/ 9im 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 is the water speed as it leaves the nozzli btiny4n/*r 9e?    m/s

  A stone is thrown vertically upward with a speey,(mdbmw -z:mcd j)1od of 12.0 m/s from the edge of a cliff 70.0 m hig,(d)o -y:mmwmz b 1jdch (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 wlv fmvnsf4q93,mg-vqt51 j 5a ith a vertical speed of 13 m/s If the ball was thrown f54gtfj qvqn9-5vmavfs ,l3 m1 rom 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 velob(il)jtc.l o;ov 1pb oqj7e( .city of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration consta.ib lol.7 o)qtcj;1j e b((opvnt? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbitkp(ktcw0z0 o7-. -dsjshuog 9 along a straight tunnel as a function of time is plotted in Fig. 2–28. What is its insksw-o- ( cgzod0ku70js9t. h ptantaneous 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 th9 ctscm2o 6e9/kibpb)m i/gd4 e velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shif9cce)pgo /m /i 9bkbmd64i2tsting 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 t94lgs;omz*pg z1 5;r hyxb;yqhe previous Problem (Fig. 2–35) whenq1 r*lzzyg ;9gb;5 po;y mxsh4 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 t t.xcy ift5sfh;; dhuuq:h-s/4,h(onsj8 /y lraveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whodn288wu t1 /s9qhq vxcse displacement as a function of time is given by Fig. 2–28n81wd28 tsx qh c9vuq/.

Figure 2–36 is a position versus time graph for the motion of an object fh.,mpsm 1g4onx/ qv3along 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 obmp1 4v.s,3 foh/qgmxnject 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 firefighz*fz..v n;k nc8 pwl5ol79io gter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–*z nlip.;85 9ol wkc7nzvfo.g37.
(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 gravr lbv qt2u0tdk(a)2q /ity on the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the sak rl(dtb2a2 )qqt vu/0me initial velocity?

  A person who is properly constrained by an over-the-sd1 w/ 0pb ,(fypnfj4hohoulder seat belt has a goo fy/,bfh0p41np(odw j d chance of surviving a car 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, 1**,bifhe2 hov7gh 0en 2 m above the road below, and his pursuers are get ,iebh 7*2gehn*fov0 hting 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 getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end col5 lyx4*1qw 9riaaq 9rllisions by hauling them up on a crane and dropping them from a certainq*xqaa wi r99514 ylrl 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 wi9mpod/sku+s4io9w q( :j5xf / xj -htravels 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 res(kz9s9vij7cyu(0 loz t. The front of the train has a speeol0 js kzyi(zu 7vc(99d of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a+o4. slgu lkrts )y- ((wv2giw deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while und4oir )l (l-swsgt g+k2.u(wyver the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance r grup )a 0,jg;n0x5fkthe average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this kuj;g fx5r0 p0)g ra,nproblem, 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 straight down;wuce/mwz d ,5 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 mus/d,mceuwz ;5wt 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 strikes a ba1dtjxg*.b qr4mrtoih. 3w5 g*ll 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. Acrg .*t4 tjmgqb*r1.i5xhwd 3o complishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight8 8dgk mjdmbp f68z6*v train traveling at a constant speed of 6.0 m/s Just as an empty box car pas f8d 86mj*zdkvmp bg86ses 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 hi*hs)xh gevefg; e0w -(gh building. A second stone is dropped 1;)hv fgh0ee-e* (gxsw.50 s later. How far apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must avera+*2ayof rweex e; a5m)ge 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last la)exewfr2m y;a oe5 *a+p?    km/h

  A bicyclist in the Tour de France crests a mounn/y9 i)lly-ig tain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration yy g9l- /lnii)(in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two ww n)2z (avw1dkdxeq:j1p/:mtrampolines. The first child can bounce up one-and-a-half time/ n11ex:a: qk()mzdjp vwwd2w s higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile travelbyr2e(2bs bd8 rp,mp 5*sl ls6ing 95 km/h overtakes 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 traveling in opp er62s sy2 srd,b (b*58lbmlpposite 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 throwing the , jp5:f fhtrhr ,/y9fn7:mlyl 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). Es:lf ,tr/,:7jnhhl m9 5fyrfyptimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an pyb;* c2h5 odahy7u )zacceleration 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 patterncr si*uf+f* gtl(jir dab:599 shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Sr 5f(*u r*b gl9t:jdi9 ci+asfuppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s 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 constant (ty:- jnb:.ogphoq 2eu q:)rd 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintainir-jp(ohtu)oen:q gd2 .qb:y:ng 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 amsz+23m *sfhe building; 2.00 s after that, a second stone is thrown straight down with an initial speed h3*+efm2sms z 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. Thelu(le*91iyz zii 75:z 9fypwg 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. Wiyzup*9i:l5 w 1egfz9izi7l(yth 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-falling parac s4oxv d 7nknn:)iv7d3max7-zhutist 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 atz ndx 4xaivndm3kvs:77)on7 - 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurantbcfm m3jx 26:l uses a 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 fast must the conveyorbxjc:mm2l f 63 belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe can. Hoc.+qgsj1p/ fb w many times higher will Billbqsp/1j+c .fg ’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of;pvu r9)uv0du a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to yr) vuu0vp 9du;ou, 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 built j3er h,yeil), z:0gkding using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop0keh3j, leg iz) ,ytr: it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) vo kem nuk9mykds q5-) qx+6kt9. /f3jIs there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the5 )qsv 6.mk3fqx9y m+odk nt/eukj-9k highest instantaneous velocity? (e) Which bicycle has the higher average velocity?