Does a car speedometer measure speehsqjhc m*.c h96sj-e4 d, velocity, or both?

Can an object have a varying speed if its velocity is co5 - mdg0(mywdjnstant? If yes, give examplejmdy( mwg5d-0 s.

When an object moves with con/nm;e2s3k v8w ):l h nqcx0x;y5gfshcstant velocity, does its average velocity during any time interval differ from sxn/ 5cs)k;c :ngwl vehm38f;qx02h yits instantaneous velocity at any instant?

In drag racing, is it possiblmg0gb dz1g3 0ge for the car with the greatest speed crossing the finish line to lose the racbgz0g31 g mdg0e? Explain.

If one object has a greater speed than a g4(zq0mu8 4 xbfpxu. asecond object, does the first necessarily have a greater acceleration zubu4 qgam x.0x8p(4f? Explain, using examples.

Compare the acceleration of a motorcycle that acceleratedbfd(;4 yjz7gs from 80km/h to 90km/h with the acceleration of a bicycle that acceler; byj7gdz4d( fates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward accelerato l7iv 4w7+j20nnv vxv)4i wrnion? Explain.

Can the velocity of an object be negative xuomg f3;()bwwhen its acceleration is positive? What about vigob)wf;mxu3( ce versa?

Give an example where both the velocityr 9ixq:0wob1umc.d1n and acceleration are negative.

Two cars emerge side by side from a tunnel. Cara9 nq y1sqekmc j/+:8e3t 7fie A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed q t+km/s3:18jf9ceni7 eqaeyof 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleratiob9h ;i,mgy o.mn decreases? If so, give an e9.hibo ymm,; gxample. If not, explain.

A baseball player hits a foul ball straight up inttnln ,b*l;dx4 o the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catchl; ,tbd*nnl x4es it?

As a freely falling object speeds up, what is happening to its accelerh:6; r1pmwjz nrif53 bj4hl :2rv 3x aaa3dta-ation due to gravity — does it increase, decrease, or 62z34rf: bh3rn j1xw t: jap-ldha ;ri5a3ma vstay the same?

How would you estimate the maxim*dapkfh p k,-dr:q8byv7 -5f zum height you could throw a ball vertically upward? How would you estimate the rfq-d78:k*hv ayb , fzkpp5d-maximum speed you could give it?

You travel from point A to point B in a car 0 j2zwehj -g4 ;3nbmhjmoving 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;mgw 3j h-hn4ejj0zb2 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 vertip*u k 47 gql7dvs7ie9xcal string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class9ig 4qs7u7lxp *kve7d 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 pkwqrt2d(c .mr cd/z5o e( f*3not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish rmc(5c(d.z*3ept2wd fo r/q rkesting on a table?

An object that is thrown vertically upward nt+ m,a ujir//uie;y 5will 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 to air resistance is always in a direction opposite to rmju5ay/,+;ti /neuithe motion.]

Can an object have zero vel6lm;2 ;gwg5 mvl/v0cqtr my- kocity and nonzero acceleration at the same time? Give examvrg ;v5km /ywm6 ;ltgcqlm20-ples.

Can an object have zero acceleration and nonzero velocity at the same ti kdk-artc8 o4j.:fom 6me? Give emk8 6 a4t: koocj.-drfxamples.

Describe in words the motion plotted in Fig. 2–28 in terms o14; b s )b zt5zhogwhxpf)h6r0f v, a, etc. [Hint: First try to duplicate the motion plotted by walking or m)0pswhbtzb orx4 hh6z5f g)1;oving your hand.]

Describe in words the motion of the o -3zr 1vatdtf)bject graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 kmf88qdrmwt6bb8j*5. okv(x k f in 3.25 h?    km/h

  A bird can fly 25 km/h How long rm 0vpn83hz (kdoes it take to fly 15 km?    h

  If you are driving b8yd-q pp(g66qnfy m) along a straight road and you look to the side for 2.0 s, how far do you travel during this inattentive peripqb -myf66 8gp (qdn)yod?    m

  Convert 35 mi/h to 10 mexmk(m ei-
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from .s*mz:x,1 vszedwz k,$x_1$ = 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 ste c 9/. npchl4zn-shpy;adily 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 20 mnn -pc s .4/9hhyzlpc;inutes.
(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 lightn,ob9u g cz88 ujqz d4r64uz3kying flash and the following thunder gives the4j9rbzuzud 4 ,og zcyuq36 k88 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 lam* 7 lpcqt2y9,g6 kwdu 8vue/ups around a quarter-mile track in a total time of 12.5 min. Calculat8queu6v*mcg uw ,/9l2y t7kpde
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 115qi3ri)se9cbeghkoz5 2.u ,n 6 m away in 14.0 s. It then turns abruptly and gallops half,guq2e)bise35 ckz95on. ih r way 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 otherz (a)l) jvbvk( 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? (S)l jvk(b ()azvee Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long 5 b,ayt7*befefuzm,f+ 3k yz 8will it take the car to reach the truck? fe8fkyt*fe z+u 5by 3,ma7 ,bz   s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters r7yhq14:qfim *xi5-yex na,xa tailwind thar : 5yimfnixqe,ax1 q4-7*x hyt 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 a complete round-trip in whdrfh +.imrlf4 /hv7*pich the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km isfim r7.h d+l fr/pv*4h covered at 55 km/h.    km/h

  A bowling ball traveling with consgykgq9uf2fubk2m 80cj - 0rl7tant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 34c y08k0 lf rmkggu79jfbq-u220 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is ij)(tei(/,rp:nbe wo+6 zpa q ets average accelera :,toe/e r)ja n6(e+(wi bpzqption in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is h0x lp q 8g34d2j9f4(zjxvaebner acceleration 9 apn g4x8(de jq4bflz0j2x v3
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a p zjyin 96-jtbqwoy7 5rf4+8iz articular automobile is capable of an acceleration of abouy9ty 5noi 4frjz7-6jb +z8 wiqt $1.6 m/s^2$ 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 the/rn wn r(sf5w(n brakes and comes to a stop in 4.0 s, what is it sw wr(/5rnfn(s acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, +r+e xkw;cewt 0aqmh /o.(7b gwhich 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 o+o(xh baqct;0gew / .+7mrkw ef time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6* n++*0ypzeit2mx aseu6 u .rv.0 s. What was its acceleration? How far did it travel in this time? Assume constant acce.6pas*+ +r02xm nz*uyeuetvileration.    $m/s^2$    m

  A car slows down from 23 m/s lfmoruv+ q9+ 9f: psd/to rest in a distance of 85 m. What was its acceleration, assumed consfmfl +u+dq 9/9 :prvostant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for tak ;kj3np(3k wckeoff. How long a runway is nee;3pkw kk (ncj3ded if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst j0r+ s6 g9vmnlout 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 to reach thatnl9 rs60vg+jm speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How farh bzs3 0y6jayi8a-gkbqjt1; + did b zj+0gyh -iyqsa8 ja3k16t b;it travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assuming f7)g gwzep3f9a deceleration oegzff3)79 pgw f $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The fron7tq( ,bofz)d9h txaw9t end of the car compresses and the driver comes t)ho, wa9b9dq7x( tfz 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 tghlr r 90af3q)ox6o )o(eo2h a car with an initial speed of 95 km/h and human reactiongfrl0 9eo(r6hx)2oo3 qa )hot 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 is j hw-yyu64j).;u0v t mkm0pwt$d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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 car’s driver looks vuux5)*dx 7lje cdnt:i6k6 j-for an opportunity to pass, guessing that his car can accelerate at 1d juxc:n7 d5lj6 vtu)6x ki*-e.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 10,000b bt,utmc*:l* z 9p9mu-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then acceleract9,bbp*9m t uzlu:* mte 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 jus*o 5aafhjv 2oq2q6 l3jt 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. Her ja ql*qaf3o5jo6v 2h2 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 clifk:0jz l3i ns avua/b.-f. It hits the ground below after 3.25 s. . k/zisa0lu: -j avb3nHow high is the cliff?    m

  If a car rolls gently xdpb8.f,c m60pjtq8 c($v_0\,=\,0$) 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 inl1mmbv5wmhg3 q82x,dp7fj; i to 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 it verw6 -g x8jzb*cgtically upward. With what speed did he throw-6* cx j8gwzbg it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the in. e9wei6( yx s:myu 7/wzg+nrufluence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallenxwi uwr. 6ne /z: y9gus+(m7ey, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vpweb cgb6s4 ( f-*jaq0ertically 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 re*wb4j(pef6 a cbq-gs 0ach 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 travele flo ;:wiw 9us5okk72lgg, zlc*se1 j4d during each successive second increases in the ratio os54 lguk :ijwelz;ck29 wo*o7glf1s, f successive 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 vers8*9ieo ozc3e vo9iz c4*bhp4tically upwiohe* ecso39i8v*bpc4 zz 94oard 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 ve5wft,i4y /dmar7n1zg v ,wl5xrtically upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflashgt : 37q, tiwhd-,pkdr of the apple in Fig. 2–18 (or number of photoflashes per t:w-,r tk ,dghd73 piqsecond). 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 wik 3:wm8zfp)g75 en jdyndow 2.2 m tall (Fig. 2–32). From what height above the top oe)mn7yg5zf8 pw:3k jdf the window did the stone fall?    m

  A rock is dropped from a sea cliff, acrkguqwmw/ n ( qq: 41j4r5ik8nd the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s /ur kw:1qr i48nmcjk5q qwg4( , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of wat7fm5/c i.exhser. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). Wh h.x7f/mi5ecs en 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 nozzle?    m/s

  A stone is thrown vertically upk*.yvy b (jz(:lmzg d;ward with a speed of 12.0 m/s from the edge of a cliff 7(dz*j(z vy m:;kl b.yg0.0 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 b )rnxh8/hq / bz.il,qupward by a window 28 m above the street with a vertical speed of 13 m/s If thebhb 8.,ixrl/qh )/nzq 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 functionkc kyeb jtcw0:-e 2mvo: w0kz mgr-++: 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 constant? (d) When wa+rc:+k2o: vk bw-y:tc -kwm mze 0gje0s the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of tix6lp+ qf2n:nu( qr:wtrvhn29me is plotted in Fig.vqq2(n:u +p: w2f r6txrnnh9 l 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accelerate approximately 0 dt)kw gv)seij;x*,g:dnab4 , gats3as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in thxt*g t4,) abg3kdg , esjnw;0d:avsi)e curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of tzkwpvv07raf70 .g811 uagmdb he car in the previous Problem (Fig. 2–35) when azg dkv.ga u0 1rpbv7701mf8w 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 distanc1pau2fw51 bh0o*x ryd e the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph fo3.jmh +i, dvogr the object whose displacement as a function of tid,3 hig+vjm .ome is given by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motic) 89kno d2tpgg*w (6xxuh/q f+ sfqo6on 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 the6cq6k* fpt+w x fdo(u)xon/gh s q8g92 object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safety nfyu;,jx fmloocnb e -.yp154, et. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–3ly 4-m y.1up,nb,joc fo xe5;f7.
(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-1w,)s fz+w dwzu(w/cveagz c59mh0-qsixth what it is on Earth. If an objec1cwzvaf h gc05z9 w(uw,s)qwz/-d+emt is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is propeo )u+uv8jet 1gfks a- 1e7jm7jrly constrained by an over-the-shoulder seat belt has a good chanc e j8u maju1o1j)+ks7f etg7v-e 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 d;f sheg4 :;vcupcm9 w3 tlet4uavnod185i6( a 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 ca6uw; sh:9 v43 v8tdu fca4g(m 15citnl;eepdolculates 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 sz5lsb;q *p ;rv0jvs, its cars for front-end collisions by hauling them up on a c;b qrs js*v0 z;v,pl5srane and 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 traio6k;kv h 1f 4+lvh pyys+-zdd(n vj//vels 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. T,1 dqfdqd w qk+ipv(ys70(xm2he front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (Sep0w(dx 7(f, d2kdym1i +qqvqs e Fig. 2–38.)    m/s

  A person jumps off a divins/ 8jlc.2mrgvg t gi-1g board 4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0tcjgs28 -ilgv gr1m/. 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 balance the averma4kohf m708kp z 4st,age speed of a train against the distance between stops. The more stops there are, the slower the train’s average s mt0zof8kh,4s7mka4 ppeed. 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 straight down when divh3m2t 97y wjfq 9wzm3hing for fish. Suppose a pelican starts its dive from afmy7jm9tw 23h3z q9 hw 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 which a golfer strike+rl a)de0wa/ vn.kx i3s 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 particular green the ball decelerates constantlde. 0nkar/w iv+a3 xl)y 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 freighp:pui 5 t/ xpr(ig),hhci1ae+ t train traveling at a constant speed of 6.0 m/s Just as an empty bihxie/tru pag +51phi(c, p): ox 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 s2 vcvem t1inx3ttw 2uh- *8h+roof of a high building. A second stone is dropped 1.50 s later. How far apart are the-s3 8wnh+ itch 1um*vx2 v2tet stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average ndr-e1ag,5jw200.0 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 la5ewg 1n,d-a jrp?    km/h

  A bicyclist in the Tour de France crests a mountaas(,w a )tzkk/in pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h .,( /tsk)w kaaz What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampol j2e4 ppc6)lquines. The first child can bounce up one-and-a-half times higher than the second child. The initiqu2jl)p 6c 4peal speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-kmqes 7 20gz2uua-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 zqs0 eug7 2au2far 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 m/s In thbw h:ggim7py/vj.c kfo4cf96+qp)q * rowing 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 dfv*iqyf6 . + 9w)ojg:k7cpgc 4h qpmb/uring the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an acceleratioyp2 diq3 8a;ak xc8,1vxxy9bh n of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intemiq r .ktpjtr,62fi myi.14t6 rsection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. ,rtqi6 6. rifm1ytmi.2t 4k jpWhen 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 120 km/h t7rw8m3r;n r hkakes off in hot pursuit. The police officer catcr8 whknr m;r37hes up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s w kb2;v9ild arcysod*k76-f0after that, a second stone is thrown straight down with an initial speedod2r av0;wklf76i-y* bsd k c9 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 ver+w4m*c3 hcfq qtically up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor b*cfcq hwm34+q alcony 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 takjzo z 5m qwurogw2zu 0 3b:qk2;zd4d8f;3k0the a free-falling parachutist to fall from a plane at 3200 kubd0;mzz2wg0hq f 8zu;53dwj2 q z3k ot4: orm to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restauran( 4bhqqfe012c up mqnm8n380dnoa b s0t uses a conveyor belt to send the burgers through a grilling machine. If the grillingd2 148b 0nahpncb q38nqf0u0om mq(es machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers 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 )8 7cg7i xer3rfmqx97zfpj 7w b/i;sccan. How max js78 )3qi m7x;wr9 rg fzcbeicpf77/ny times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands onihqf4:q1gygf24 p8zf 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 you, such that it just comes to rest in yozhfg2 :q44f1g8qf piy ur 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 b.5pltsav itk0lz5z ;6iysd2w .br:x ;uilding using a barometer. Instead of using the barometer as an altitude-measuring 2wkd5 b0.6r: ts;tyzszvxi;lil .pa 5 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 height?    m

Figure 2–43 shows the position vs. time g nphf dq:kod.r8+,od8raph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are ther+dopn: d8d qk.8,fo h 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?