Does a car speedometer measures;,4kmf1 +g e5fy lmff speed, velocity, or both?

Can an object have a varying speed if its velocity is consteph2b5v o2h :tant? If yes, give example 2ptv2b eoh:5hs.

When an object moves with constcnv,hiu1idt ro;:yzrvc .3k mo1 *h; 3ant velocity, does its average velocity during any time interval differ from its instantaneous velocit3c vkomod;zn13 h; tu*v1h.: r,iriycy at any instant?

In drag racing, is it possible for the car with the greatestng q*;m u z:y6pvvl3,; 1yaydh speed crossing the finish line to lose ug;,phv3y1n vq6 la;y*zd:my the race? Explain.

If one object has a greater speed than a second object, does the first nec 6hp3reb,amzy 1(yf,fessarily have a greater acceleration? Expb,y1r,z mp ahf(36fy elain, using examples.

Compare the accelera-/l)oowymv1wi c f9,gtion of a motorcycle that accelerates from 80km/h to 90km/h with the acceleratio1fiml, c 9/owwv)gyo-n of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward3t2rplid-gbo fn462c ,pod ) h acceleration? Explain.

Can the velocity of aow *tjyogyur7mh2/k/ u *zwmkw5+x 5,n object be negative when its acceleration is positive? What about vi5rku+khm/ m*o/,*7gww u2wxyytjz5oce versa?

Give an example where both the velocity and acceleration are negyl5 59damcroo :4:wr mative.

Two cars emerge side by side from a tunnel. Car A r,zs.4lt l d(iis traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h.l,4dlzsr (ti 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 inc4uef:,qsy3qk b2)h qa reasing in speed as its acceleration decreases? If so, give an example. If not, ebqaky,hu2 q :q) fse34xplain.

A baseball player hits a foul ball straight up into the air. It leava t1js;.beyrbvjg-k ;3, l9y6obqd xcw4e 2w +es the bat with a speed of 120km/h . In the absence of air resistance, howv;4+ c,sg eoj ; r9a -3x6jlew1 bbkybw2qdyt. fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its accelera664tcca/,6vgh cyx9 j1lbyis tion due to gravity — does ivayilc4c91/6jt6 ygh ,bxc6st increase, decrease, or stay the same?

How would you estimate the maximum height you could t *9. gf(8yxkqe07iqymsga o k7j* /qjvhrow a ball vertically upward? How would you ejy gqm7. xs*ykv j(kgq/a8 0*iefoq7 9stimate the maximum speed you could give it?

You travel from poinopp 8a+o*xhn4t A to point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.*aon hppx 8+4o

In a lecture demonstration, a 3)id9+5qn+ m +dmrry cp.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase q+5 d)r+cp+indm9ymror decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rockq3hhk;t fx-5 ft 3kle8 falling from a cliff, an elevator moving from the second floor to the fifth xkh8ke fth 3-t5fl3q; floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will returnefpxxqf e*i0e xav;s8*2:k i7 to its original position with the same speed as it had initiafi xe*e vfike0sx2a7xp ;8*:qlly 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 the motion.]

Can an object have zero velocity and nonzero acceleration at the same time? Gis+*ct3 lt 9cs)zt)hvs 2t: hxtve examplhs 2tx s zts)vhtc3)l *9+:tctes.

Can an object have zero acc0*vf b9 i+bfbceleration and nonzero velocity at the same time? Give v0f 9b ibbf*c+examples.

Describe in words the motion plotted in Fig. 2–28 in terr./bn2yatabm* u6a a-ms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moamya6 .-bba*/nu 2r atving your hand.]

Describe in words the motion ofly2 f2r)lcb1oh,qeeh +1v3r d the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in ,,+duvh .v2+ gx lvznrycx6t5q,7vzj l41faz 3.25 h?    km/h

  A bird can fly 25 km/h How loj10 kfx0ab 9ythqga (yp(+b;rng does it take to fly 15 km?    h

  If you are driving along icii bc epg5u-x0xeg8+5gj)d6.b 6fpa straight road and you look to the side for 2.0 s, how far do you travel durinpx6j 0gbec)bgid65uc gpe5+- f i8xi.g this inattentive period?    m

  Convert 35 mi/h to m wm ) qa9,*k*:le;sap+t odga
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves k4 cpdx;g/;tselc j9,6* wb vdlf 5/ exc,y7alfrom $x_1$ = 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 fof3i2z6sb y 1bjms g1e/ l8daf.r 130 km. It then begins to rain an by3zj2 .16elas/ sdff 18bmgid you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every fiv gz +1af(eb+rj7w+ztge*vt, be seconds between a lightning flash and the following thunder givgegb, eb+zw*zftt1v7 a(+r j+es the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total9 qjqk.8u1 d2wj+m60liq x i+yd3bdfl time of 12.5i q.xlq08lf23w+b6u k+y9i1dmj dqj d min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a stra5roep xiwp:9ppue8)n2o f)v0ight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Cafe )98wpxpinrop: 5uove)p 20lculate
(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 of 95 s*i2(ou3d 40 gs 1ub5kgwr sclkm/h with respect to the ground. If theyg2(15clu0bu d3*sg rw sik4os are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck travelzd5aqxlb: v4 ur3+l*xh+t g :;r :dmbqing How long will it take the car to reach t rbb m4+ g::ztlduv:q3qa +l5;*dxhx rhe truck?    s

  An airplane travels 3100 km at a sy*57-x dvowwph9tuv a; vl s/a :-2ngnpeed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for tw;n5-n: /9vdlt gwspvu xo*a7avy2h-he 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 h, qoayx7m b:06m.8kpbxl :nqwhi ay,nh :xmb8 pm0xb.7kl:6oqqch the outgoing 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 constant speed hits t l vz;w,k o5zlk.o+b(bhe pins at the end of a bowling lane 16.5 m long. The bowler hears the souno wb;bo(.v zk,5z+lk ld 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 rest w +v mh,a o:hfui3u57oto 95 km/h in 6.2 s. What is its average acceleratium 7u,3v+h:fw hoa oi5on in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rescs )c+so0 ij9wqn5, gvt to 10.0 m/s in 1.35 s. What is her acceleration vwj 9os q0cg)+cins,5
(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 accel8,uy66d5zure+ i /xpj2g s 9y fmyo5coeration of about 569g5yjy ox urs2 c f/uemp,6doiy +8z$1.6 m/s^2$ 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 speedom;.*ot) c gdv afv-n3 travels 110 m in 5.0 s. If it then brakes and comes .ovn-av g; d3c*ot)mfto a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t = 0 asu oo8u7 0vchbqkup:tf3( .p; nd 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 each in a Table and on qu 8uuft0ov:; p 7. bk3ch(posa graph.

  A car accelerates from 13 g x)g3shrmaj pmd1 ;k/ac0)g1m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in a )/rs;jdp gm0hc1 g3m)x1 gakthis 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 its a+7j2kehq b+e nw6ql, fccelerj2fehln +q6+ kbq,7ewation, assumed constant?    $m/s^2$

  A light plane must reach a syhpw tc-; rf+ er(v,d1peed of 33 m/s for takeoff. How long a runway is needed if the (constant)hr-wdvec 1yft,p + ;(r acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of g:;hhx842i j .c lpstv ishkz84 gq)a+the blocks to essentially top speed (of abohpz 8icg ; g sk:.x )4+sil82t4vaqhjhut 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 that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How f ubwiq)tlw ,iyg0/i 6,ar did it trave/yi u,t) i0i 6blqwg,wl in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the hiqum /w0f22u jbghway. Assuming a mw2buq0u/ j2 fdeceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km3j ):9wb)od;g0g 6lcf rrhuey/h strikes a tree. 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 3:c9dgrgy6owl fb ;re))0h j u 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 an iniw/rb z6ps3af5tial speed of 95 km/h and human reaction time of 1.0 p a 3sr6f5wzb/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 stoppixnej25-* r;:, zo lmpjng6l stng 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. 4pz/ojx.7yqd The car’s driver looks for an opportunity to pass, guessing that p/y4q7.zoxj dhis 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 tc* szrbp/ up u0 zz/u1dbg2 w-f;2cni/he 10,000-m run in less than 30.0 min. After exactly 27.0 min, thed1nb g 2zzcp uu*0;c- /wz spbf2i/r/ure 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 7c1g-w ppnrjnv(ro+ 4t 7i9lq km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and s79q vir1c npl4 -no+7p(rtgjwhe is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. I357 zmnamwt4at hits the ground below after 3.25 s. How high is the cw 54m7na m3tzaliff?    m

  If a car rolls gentlxpd, l,l5zoy.y ($v_0\,=\,0$) 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 inmqp(jt (u8 cfq/q,);yzim7dc 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 vertie+l 5uzpp: ee.cally upward. With what speepul+ 5e epze.:d 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 83ruy c(izpe;+ nu pi oiqd,27j92gzmunder the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Igoq e2znp7mzguc9;+32y, j8iu ri id(pnore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height oo4l w4klx w4u (dv 1hrox7./ywf 125 m above the Earth, a package is dropped o7hykwvl44x uwr 1d.l o/4xw(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 distanct 6xkdrlrojbyt-- 2;0ry- s+v e traveled during each successive second ir0y vykd r-6-+ t j;b-2lrxotsncreases in the ratio of 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 balg(d a qez(:bo;l thrown vertically up qo(z:bed(;a gward 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 with a spo-iwvv ju0x 2 :z +yv17essd3ueed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash o8z; +kwcpex4- vz.k ip)adia-f the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the ).-+wx;ak z48 - zvciadkipe ptop.]
T =    s
   flashes per second

  A falling stone takes 0.2xnry ;; ea;z(di+ioper0kc.1 8 s to travel past a window 2.2 m tall (Fig. 2–32). From what height abovryxeo0 (i ;r1. apcznd;;k+i ee the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking p j*71hu p /:p)xf0.5sckly0xq xpdm gthe ocean is heard 3.2 s later. If thf kppxlgmxq5 0p7*uc 1:/d).x spj0y he speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of wate+0 1ll4 krcf)tox;q u cr(6cezr. 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 waterx(kro4fc1zcerql 6 0u+);c l t speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/equ zu6dwdcf/5b,rzl 7 .1k9 zs from the edge of a cliff 70.0 m high .w6er5d k1/b f 7,zu9qcu ldzz(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 wicxk p8kzk 2x..th a verticz 8kxxkk2. .cpal speed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of z)ej. (zw57iwo -lupctime. (a) At what time was its velocityipww uz5lj7 o.e) cz-( 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 of time is plox0b8o.l 3r6v o6 xeinutted in F6 0rox 6olne.3xu iv8big. 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 approximate7phh+aw1zpy , ly as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the ppzh+1 7a, hwycurve 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 accelerationx*j2f1. kwx mq of the car in the previous Problem (Fig. 2–35) when it is inw* xjqxk2 mf.1
(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 h.+tibv /+z q.d)cht 2xq0 spethe 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 function j7 ;(z:ng zdzlof time is givennl:z jg(z ;7dz by Fig. 2–28.

Figure 2–36 is a position versus time graph for thdz51u7*t8 h sex: t ddx9+ihvne motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the pos8sd nh7d1h x9*dtev:ix t+ zu5itive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safety ne080gnltc,u njt. The survivor stretches the net 1.0 m before con 0lcn0gju ,8tming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on Eaja.a 7 lr3of+lrth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velo7ja+ fr l3.oalcity?

  A person who is properly constrained b/5xwzs v s;7qacj3j*sy an over-the-shoulder seat belt has a good chance of survias*sjxw3 v;qzc 5 j7/sving 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, 12 m above the road below, an9q3:wj e/c7cpe x:fnl d his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto thq nf/3wpcj:7x 9e: lece truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collim(,ljr/ fjqps 0 .:yozsions by hauling them up on a crane and dropping tfjo:j.,m qlpryz 0s( /hem 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 a bo-zxbcptg*2wwj -5q,f*lbv6rc-:h bout $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins ubn: 3x 8g6zxlxtg5y/gyp 6r:gniform acceleration from rest. The 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 lg3/8xy5g: t xnp6grx6:lgbzyast 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 pojd5f)+ 0ih illso)xn fn5vk11ol. The person’s downward motion stops 2.0 m below the surfaced1+)xki inf lh5vn0)j15lo sf 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 averar:;gxe zplg) ):h(xauge speed of a train against the distance between stops. Thh )glu a::;e(g)pzrx xe more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight down when diving for fishkwm ljahwr *p5 d:6vw6f1z:l,. Suppose a pelican starts its dive from a height of 16.0 m and cannot cha6zll , pfka6wmv5*:w1 j d:hwrnge 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 wxq1 +zbn m7xh1ith which 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 t 17+qbnxzxhm1 he putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at/ t *o.ox gxkm 67+ ktv1ix6hl0p3myno a constant speed of 6.0 m/s Just as an empty box cao. xin /yg 6l0t6pmo*7 3vkkm1xt+ohxr 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 second stovh9qr,. p0w omp bz.d7ne is dropped 1md.pvz r 09h,qop 7.wb.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 averjs 2v 79 zl5;dhacvkar)4z n :jiw0k -w7/igtjage 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were jch9aw4 zn -r07gvj)5:ai i7kt2v zj/ls dw;k done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he movd+jt2p-t9ax k es at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (inj+9 t dkp2-axt $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two t m ra/ik.izo n 4/zr-21q:8 (iwjaihawrampolines. The first child can bounce up one-and-a-half times higher than the second child. The inirz: -a8iakzaiqnh/ o .ijw4 ir/m2(1wtial 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.( ,gk 7kav:g hwkz zi)m5cx08p10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed i g mh0xkk58cwzg7 k)pav(i,: zs 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 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 witlq .fo+ 0 zl+t*8pvmirh a speed of 44 m/s In throwing the baseball, the pitcher.+ vo mi+*l 8qfz0tprl accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an acd5t14rn+efyl z)mc q1celeration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a tri-4yj8ru o:px6b +tcvaffic signal, and the speed limit is 50 km/s . Suppose you are driving from the wvu p6:iybr c8jo+x-4 test 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 o6ky b5e qeml(r (teb6iv6t 96by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintainin9tokbtlm (( 6 qi56yb6ee6verg 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 afteki.9 tx:fzfe) r that, a second stone is thrown straight down with an initial speed off)tiz:f k.xe 9 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 tin sq488zbha,cl/e ;jx me. The first stone is thrown with 8e 4 zlhbc8xjsnq;/a,an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-fall2g. z.z shc inw5g/bb.ing parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull bgs.ib5 2c/ zh .ng.zwher 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 bur+ 1mcce 7.vnleb)g2p fgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/m cc)gnvfml+ .b1ee27p in)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe ca9vbw9:9tc j5ptjd*.m0lcfukkx r u2 )n. How many times hi2ck bvt :rwmlupxf9udt99*0) 5jc .jkgher 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 on the ground below yos.u7rb(jur)fpuk +2 qu. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your frien+( .ruqk2pu7fb rsj) ud then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a parp q xay-nx:,7dticular 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, 2.3 s. How much difference does the 0.3 s mak,dyp q axn7x-:e for the estimates of the building’s height?    m

Figure 2–43 shows the position 1zhv; erbq( w1:9golnvs. time graph for two bicycles, A and B. (a) Is there any io1 b;h w(rl:v qg1ne9znstant 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 the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?