Does a car speedometer measure spetqwn,m c d9v xs.ls7gx0p/jnnt,/-x6ed, velocity, or both?

Can an object have a varying speed if its velocity is ccdunb7voiq1c +.s 7 4gonstant? If yes, give exampi7ocu71v4qg.s db +n cles.

When an object moves with constant velocity, does rd7 a50/7mgwzskx -2w o py5-cunbe-g its average velocity during any/bwa o5- z-x7725 gum0nkpgycr-sd we time interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car wijxgliq./afu-;f 8/dj th the greatest speed crossing the finish line to 8xl;djaijq/ff- g. /ulose the race? Explain.

If one object has a greater spee5+vag- gtz usv y54i-kd than a second object, does the first necessarily have a greater acceler +4s5vutavygk- -5gz iation? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90by3i1zn.f (k fdqb m8o0d (mu/km/h with the auo1(q/8fdn. bbm0 i kdf3z(ymcceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and 4.fig azpbers2w18 e2a southward acceleration? Explain.

Can the velocity of an object be negative ifxfu: jk1j(edp5/g . when its acceleration is positive? What f1dg(j e:5.x pikf/ juabout vice versa?

Give an example where botc08ckm1ik1rl 2t0g fn h the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Ca)o* p xq;hf8rhr A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your refohx 8;*) pqhrasoning.

Can an object be increasing gdyr 5e1hye g 9mk-9v)g6q i*ztz:o2 hin speed as its acceleration decreases? If so, give an example. If not, explde *zytim y 2ezg6h-)h95ovk :1g9rqgain.

A baseball player hits a foul ball:fu3y7fbgpf) fun:0v e +.vj m straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistanuvjffy u3+70::vf mp .egfb)nce, how fast will the ball be traveling when the catcher catches it?

As a freely falling object s-sepa8) +ngeypeeds up, what is happening to its acceleration due to gravity — does it incp+)g 8e enysa-rease, decrease, or stay the same?

How would you estimate the maximum height y1 vkp; plzkk0:ou could throw a ball vertically upward? How would you estimatep0v;zpk :1kkl the maximum speed you could give it?

You travel from point A to pok-fxk2*8agjqq 4iw3e a180fcf1kp 1ts h;doiint B in a car moving at a constant speed of Then you travaae4qo k3f2 hk x1k1ifqpsjgd0c*w ;8-18 tifel 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, a 3.0-m-long vertical string with ten bolts tied :uphnr y/zrfqt5d(d: :n4ucya( y62eto 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 d:ct(42 f6uyndq p:ay( rdeun z:r5y/hecrease 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 accqw-l7q89t; ulsl1p-pc o,nmyeleration: a rock falling from a cliff, an elevator moving from the second floor tp7q luo,l1w 9t-8p; n-lsyq mco 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 pos43n 5)kgk isz e/lztej)dn,7xition with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistadizsj /tn)egl53)xne k4k z,7nce is always in a direction opposite to the motion.]

Can an object have zerny:4v/1cy- uu lkgjjj9 +r m4 qh;y,zao velocity and nonzero acceleration at the same time? Give examp9-;yznk,gq1hvm u uy44yj/r: j j+lc ales.

Can an object have zero acceleration and nonzero velo*rpdv *1v 8bcscity at the same time? Give r1vpcs*8 d*bv examples.

Describe in words the motion plotted in Fig. 2–axnu+y3z6+ebr i4q l 128 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or z qa1iy 3x+nul6be4 r+moving your hand.]

Describe in words the motion of the object/o5cq5m kv vk5k v6eotvpp)n /76go 6t graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 230 mdh8l 4mfg5 h)l .gk-xz+pqjc*gpwlp59e k.5 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long (n , yddhp2jg06qu nbwi:l0o;does it take to fly 15 km?    h

  If you are driving along a straight road and you loin6o6r-rjw +)f5 rg cuok to the side for 2.0 s, how f-r6uiocr) f6rjw+ng 5ar do you travel during this inattentive period?    m

  Convert 35 mi/h to n+3vho0:8j cbgog*qm
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball movesx,5 ktnzb 8*yn from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for 130 km. It then b7 + jur5tws;cregins to rain and you slow to 65 km/h You arrive home aftr7t;w jsu5+rcer 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 seugp1 pfr4/6-fyj;mw yconds between a lightning flash and the following thunder gives the distance to the m1-f6p4p gujy y/rw;fflash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in ;67u1q uy7*n ykkdd pea total time of 12.5d1yu pq7 k7k n6ue;*dy min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a 02p8suvj nr ml7sog9)straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 sp70 o8mrlu vn2j9 )ssg. 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 speed ofi81 gpr0r5imi 95 km/h with respect to the ground. If they are initially 8.5 km ai 8mg50 1rripipart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m bm 2/hjsu d l+ad)03smvehind a truck traveling How long will it take the car to reach the tlv u m3s2)s0h /addm+jruck?    s

  An airplane travels 3100 km atdb,c7 48yhw+-if;mb qy:cvdbo qvv3 6 a speed of 790 km/h , and then encounters a tailwind that boosts i b:hv6yc m8qqw+ cfb; ovbi3-7vd,d4y ts 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 f mnpiv h2f+xz 8f//dpf.ea:(of a complete round-trip in which the out(.8fhi+f n fp2d/:ea/vzp mf xgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constazfl51cs/waw d1 4 7:tjemsyq: nt speed hits the pins at the end of a bowling lane 16.5 m long. The bowler heaqd4jw:7:y/ss 15a1wl mcf e ztrs the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from reszf7 pe-/)vfu xt to 95 km/h in 6.2 s. What is its average acceleration /) 7uzf ef-vpxin $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in uot mduh;;c4s: i1 l:j1.35 s. What is her acceleration td :u;c1 msj;:uo lhi4
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is cammv6)dm bs*)jpable of an acceleration of aboum)m)dmjs6vb *t $1.6 m/s^2$ 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 brag0 v 5limz o-d8 *p9mb,j55: t3nqnpryt bn7hukes and comes to a stop in 4.0 s, what is its accele 9l0uppj mt :-mrqogzibnn* 83tyh 5n, 7b5dv5ration 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 z5(6uj;y pjxt = 0 and moves in a straight line, is given as a function of time in the following Table. Estx (yz;6pjut j5imate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was iv2d7i4 qsd) .pcono -tts acceleration? How far d7-4p)dqdoc . so vt2niid 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. What was itw05,qyjrar lw5 wg2th.;5a.rq: v ayas acceleration,laarw2h5,rv:5gqaqyyw .;wa.tj 5 r0 assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How 41f57uzwaucr long a runway is needed if the (constant) acceleratz5 fruc7a4u1w ion is $3.0 m/s^2$ ?    m

  A world-class sprinter zwtkxv+9m1syl-147c tgk 5 hrpl:6 qwcan burst 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 take her tol5+ r :kyk91lxv61cqz-wtgmp thw4 s7 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 rurc3df l0lfb +nde::8,yi7dk est in 6.00 s. How far did it travel in that time? f l8b7 dni03dcu::lefyr+ kd,   m

  In coming to a stop, a car leavuiq3 oje*. 0wves skid marks 92 m long on the highway. Assuming a deceleratiojoe.v0*qi3 wun 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 treem:tm uf1k)el6r xk q7 yx4.)vs. 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 krs4v7e .))yx 1lx:fk6mm uqtthe 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 f :i hff6mqqhi;i1 4i.xor a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an accelerati 4 :qi1iih.ffih6q; mxon
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for thesq 7)nb7drfs9u kl.vp k7d-k5 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 cart1o8zh6d u .pj’s driver looks for an opportunity jt1h.d6o zpu 8to pass, guessing that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. Afteriw zpu0s2;qf ( exactly 27.0 quzwp (fi;2s0min, there are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as the traff; g zrb7- uj0m;msc7klt e8:eyc1hmv-ic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Shoulez-k hu ms;71g7veb0ctl:c-j8rym;m d 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 below aej (7* ovg0ihef/g tj1fter 3.25 s. How gh7eeg(* / o1 fjit0vjhigh is the cliff?    m

  If a car rolls gently*s7 m*6cjsca,, oapf d ($v_0\,=\,0$) 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 witf t15fs: yeo y 3,m3sm4gp4bxeh 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 throwj;69 xnfmm c6bw-v8dring it vertically upward. With what speedcjm d- v86; rxf6mnb9w did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw graphvqg 3:6rkyce4 s of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = c3 4e :r6gykqv5.00 s . Ignore air resistance.

A helicopter is ascendie uo 3s1 j ky;m0pvwo61.3l,-rey cjxjng 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 reach the ground? [Hint: The package’s initial spym6 3 jjow1vue,;c3 -re01.p j klsoyxeed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that th8y, y- c5kkjgvmn9 90 9yfftm)oloj.se distance traveled during each successive second increases in the ratio of sucyo k.,y -mno ) kjstvf5y j90lg8c9mf9cessive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown vzecc)h l2szu)o: 9pl +k bae16ertically upward with a speea)) h sczluc p9bl:ke+12o6zed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticau7 3zjqs)s2su lly 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 betweenil*).g 7 zt,p vygxwjf*(; lzi each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the applefz)tj7(zli*;y. gv wxpl ,i g* 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 ,j3vje 4o(4qlwj pj;u2.2 m tall (Fig. 2–32). From what height above the; jl 3v4o4j eq(uj,wjp top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of i (wi 5j-ad ny,1/bfbwat striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , hod 1awb(,n5 wfjiayb- /w high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard vqfu; 8tpcz sxid)vq+ln:3)* stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another dfu:p t8cvx+v* )ls) ni3q;zq 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward witj*ux ax20+u knh a speed of 12.0 m/s from the edge of a cliaj ku+*n2 uxx0ff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the*(44 .3l1uhhl(aawk gmbgauu street with a vertical speed of 13 m/s If the ball was th4 gauu (hbawh(*u1g.lka34 mlrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a) At n 1k7ry/***fy l)gsyr w7frmowhat time was its velocit)yr* g*o17k / 7ywfy*lrfnsr my greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function ofyiq2 bnvd4m3r, (2nu-ten e+r time is plotted in Fig. 2–2-2ne (i2rv+nrmenq y d,34 ubt8. 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 automobilebg9z+8xbt xk nnoafn94 k8)3r can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represofxz 9abkgxn9) brk8+n3t4 n8 ent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in tj *j86hj3/,*v0l9nkx, x mrxmstc lmzhe previous Problem (Fig. 2–35) whmcxxmlnjkrsl0 /xtmh8,9,*6 jvz* j3en 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 eyg9nxx .+.p tci6y. rthe distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a functic ryt8cc:nd 10on of time is given by8 ctncd:c1r0 y Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion o w :iq7vag(sew984 txe:ctd .wf 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 fromg s7:tiew. c(xatw 9e8 qv:w4d 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-stor+p* e(ds:h dg5ro, h fyk3 whqr97o:gmy window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.qhdrhod+y:g73re:m 9,k *pwhg(sf5o 0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon xhu6 tum;yh39mjz i-8 is about one-sixth what it is on Earth. If an object is thrown verti hx;6 iz8hm-tyujmu9 3cally 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 belt has a9vqiuk+ o9).u ievte 8dn+d k. good chance of survivingku99e.+ 8dv)ui+ i.to qvdken 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, ztv1m linwy ht8g.,vf-hi 6 (,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 n-imhlhg v(1,8yv ztf ,6.wi tis 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 8:ddv8tgu w6 zfor front-end collisions by hauling them up on a crane and vt88dz d6wug:dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels about 4x3(o8avvis1udsah6e00 ywj m(cl -d $10^9\,km$ 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 fronnm 94b1eyy8hp t of the train has a speed of 25 m/s when it passes a railw byy4p m9en1h8ay 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 deep ryfdde j b(*f:rn4 )6g ol7kgz2h2qy 7pool. The yknej4(d2ry d7hzlgb)frqof2*g 7: 6person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balancr ;5kztg 5b4ygit2c4y e the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculatk gbygr z ;24yi5c4t5te 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 w0hmi7n,mhm,j ings and free fall straight down when diving for fish. Suppose a pelican staihmjm hn,m0 ,7rts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with who:is9ff2k(+u wof 9yfich a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a partif2ui w sfoko9yf f(9+:cular 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 traveliib *;er-hnf6xo p*2j(o 0fi1 *7u8cs sqwihi hng at a constant speed of 6.0 fn8i s602rsh*o; 1ob( i*qhixw chuj*e7 fip- m/s Just as an empty box 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. A s./b2fgx ;c gx/zhot u3c-ur.second stone is dropped 1.50 s later. How far apart are the stones when the secozxf . ;/ .bxotu/hsug3crg- 2cnd one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the c 7que3ttnvbi2 0d.bx0, to; fm8qm; vmourse of a time trial lasting ten laps. t; mnqt 2 ef8bb,qv x7mto m03dui;v.0If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de Fran2ckuewg4,pv0hdh 4a 5 ce crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75hduv4h,g4akpe05c2w 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 bocok )7xd489dxu):la:tls hvvwrml /2 unce up one-and-a-half times higher than the second child. The initial speed up of the s 9xtl lx/ l)r:od dh7kmv28vw: as)4ucecond child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.y3 6x97atm; gs5/2a)downtf +ondpvf10-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, anox3nfp v;6o) nsgy9t5tda+/a2mfd7wd how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 tu wrb799s 9loawr9c :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. r:bs9 wl79uwoct99 ar2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, fr,o7 ul*y 4:jkfi+vb1gw/ vtzxom 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. Eac( wvwpwk(m8 s;h 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 w mp(sw8v; w(k10 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 trave pz- .p- v3u,4bpoj4ird. cy0 hy3fjgiling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 7pz.j rg0-o h3ppdf434iyvuj.c i- ,by50 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 buildib44u ms)ey e6dk 2nc/rng; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stou4er/yb6) kne2scmd 4nes 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 t0kr l t)d)hns(jo-u 1cime. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits trdkcjh- nlt())so0 1 uhe 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 airzyq: mtrwez.cqs373kf:6 1wd resistance, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pul .fzcqs6wmwerkqy: 173:z3td l her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a grilli.j t 7jjfdrl1mrc8u776rntw 8*vei,kng machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min 8d7*kl.,rrcu 8 jtw7 7ef6 ti1jrvjmn to cook, how fast 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 vertically at)+i9f549w vbglsnrnozrw.i kbq. 8/l a speed 1.5 times faster than Joe can. How m5nvlozw 4skwirfb ni99b 8. . +)rl/gqany times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while yo6myx;i 9eicone::x 1t4b(g)xnj bt*vur 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. Youm )oy *j9vx1(xtinene4tbgi 6 xc ::b;r 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 he kjjn6 8 v 3ztvnmp(5epot-n3)ight of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.vjezovp5tkn)- 8njp 3 t3 nm6(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:r0j u3 upv7q) sedple8 n,v,j position vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the largeree s0r)jl3j8d, 7uun :,p vqvp 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?