Does a car speedometer measure speed, vettshh-c c2*.ux. hd4w69fpk y ntmen-pw2+y0locity, or both?

Can an object have a varying speed if its velocity is constant? If yvowdf(y, 4mg:enf0-o es, give examo ofwn,yegf4mv:d ( -0ples.

When an object moves with constant veloci4vy (+wkwpf. ri8v/rc ty, does its average velocity during any time interval differ from its instantaneous velocit wrf4.i+( /k8vrw vpcyy at any instant?

In drag racing, is it possible for the car with the greatest bxvmf -yuf 1fybz1owqd),( k*./rvy4 speed crossing the finvy4vfdroy/ bub).x(q ,m f*k z1- 1ywfish line to lose the race? Explain.

If one object has a greater spz/z)vs2eo -hzr6v.fc eed than a second object, does the first necessarily have a greater acceleration? Explai ovfv r)sz -26cez.z/hn, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90km/heylyjg2k3b-/ i7j 5f**jc( l9ozccs h with the acceleration of a bicycle that acceler*zjfb57e yglcjc/9ji k 2*(ho - cyl3sates from rest to 10km/h in the same time.

Can an object have a northward v j+6pn-ptaxz *elocity and a southward acceleration? Explain.

Can the velocity of an object be negative wc)n la5sse 02khen its acceleration is positive? What about ec5a ss2nk)l 0vice versa?

Give an example wherte7d::r4r wf ge both the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling withq7g, hxpc :d.+x hvxo: 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:xhh:xgcx ,+. pqv7do /h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing 9vvu3(4xv ilmx t2j,n in speed as its acceleration decreases? If so, give an xlun,xtvm jv9v(3 4i 2example. If not, explain.

A baseball player hits a foul ball stra,w kj3s)f; s3 blpp4r*bev1y zight up into the air. It leaves the bat with a 13z vk3swl,s*ppe;)byj 4 rfbspeed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is hapu b;cw nq a*kdhmll65p1-v9awie 8-z)pening to its acceleration due to gravity — doedw6)ic 9*nbqall8v hu -mez5ka w -1p;s it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a b ochur6,f2m :gj;deu-all vertically upward? How would-fu jum6;:cehg,2d ro you estimate the maximum speed you could give it?

You travel from point A to point B in a car mxtd -v3 k() f-u0hfsgqoving 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 f )dsu g(ffhvq-3-k0xtrom 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 to 4wv)wr fs cbki 2r6d)yw5 s;+xq)fu7 lit at equal intervals is dropped from the ceiling of the lecture hall. The string f+)ukdw5fv6fq by4 w2r7ix)crl w)s s;alls 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 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 acc1oj;nyh9 h9,eyt /twteleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish res; 9 j ehtyyt,/to91nhwting on a table?

An object that is thrown vertically upward will return tl8q ;f q m4nc67mrxyd(o its original position with the same speed as it had initially if air resistance is neglmm7c6nyq x8;4lq( fdrigible. 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 nonze3 -hn xn1 1e wij-fie)zmz(9mvro acceleration at the same time? Give e 3(-emviw)imz hn n1zx9j1f-examples.

Can an object have zero acceleration and nonzero velocity at th j/9*,jstfnp oyyh4c7 q,,iyit6b+ eye same time? Give examp/j *,fyneh yc6q,s9tip +i y7y jobt4,les.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etch5 aycf21ijb hv:q:k 3. [Hint: First try to duplicate the motion plotted by walkbhaq:3i5:2cvkh 1fj ying or moving your hand.]

Describe in words the motion of t6ugv3 skd6 ihf7qk 2*bhe object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 kpm *vtz )i1w )g *buv1yrj .t5xwpr-:jm in 3.25 h?    km/h

  A bird can fly 25 km/h6tf,p+ quo ls-ty0rm) How long does it take to fly 15 km?    h

  If you are driving along a straight road and you loo;nms dk*e.fot9(h( g wk to the side for 2.0 s, how far do you travel durinohfm9 kn ;*t (d(g.wesg this inattentive period?    m

  Convert 35 mi/h to 1c6sf42pg+ 8x/humf2 cy k iz; lth0wj
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from d9ryp 8nxey26 $x_1$ = 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 m 5,zeaji52w *6xabhlbegins to rain and you sloeb ia h, 6aw*2xml5z5jw 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 five seconds between a lightning flash and ueg( k( pv5rs0the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this (vu (e 5r0kpsgrule.    m/s

  A person jogs eight complete laps around pi,iyib0h4 e jq.v 9i:a quarter-mile track in a total time ofiv 9j4eby0pi ,.iqi:h 12.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from ewh.mk 5ifaks25 xpve 4emwgg(5z)89 its trainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway ek xw wfkg)25i5sz mv. 89gm5aeeh p4(back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Eacht.245fsa vjo n has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will jnf .s atv4o25it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will itk i5dcq8x+n/ a take the car to reachq+8nk xc/5adi the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , andza q7 :z1gko 2w2e2eie then encounters a tailwind that boosts its speed to 990 km/h for the ge:zek2q7a 2i2wzo 1enext 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 g/ n69u;h m3dvspj a8wwxby,* velocity of a complete round-trip in which the ohmgpvu 98a ,yn;6/x wdj3w *bsutgoing 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 hg sgmy4(5wcxk5 fb(.j its the pins at the end of a bowling lane 16.5 m long. The bw4 5b 5j(kgc x(ysfgm.owler 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 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its averafe3ck7lvg y i3tj. pgb) 88wx*ge acce8yxbcw.tvgp g f3e8j*kl )3i7leration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 8ng 6 ,k/rx 0i5hurvbde)mn-ts. What is her acceleration 8/ drh0t u 6)5kmx,nirgnbe-v
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acceleration of abouru2h2m4go1b m g+lfk 12uhqw7 t hmh24rg k217wlb1o+2fquu m g$1.6 m/s^2$ 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 brake g s2r b-bld9ae d8rfcgn,b2g- ey.i;*s and comes to a stop in 4.0 s, what is itsbaeb-ldeny2 2b*g-;gs.,frc gi89 dr 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, whicd 30s/j llr*ntetu+y4gd4 +p nh starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display eanls0 jt4* /l4edn++ tdpr3gyu ch in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleration? Hofz7 a,hw37ywrw far did it travel fr,7 yh7aw3wz 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 itsexfmz7 lv(6*qp4s 1 kn acceleration, assumed l4k *17 fpz(veq6mn sxconstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for t i7nq/yg rka8v4k 1-/*fhsdatakeoff. How long a runway is needed if the (constant) accelerk/y1g k74s/-at * q ihafnd8vration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentu g19g: 4 uvpmk5mr7zxially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration ofm7pz:5x v g urgu9mk14 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 frog8c3 -zuft9p ake k-e(m a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in that time? (pc9ft- ag3z-8uekke    m

  In coming to a stop, a car leaves skid marks +tt*6st su)tj55xv e e92 m long on the highway. Assuming a)utx e*stt5t+5v6se j deceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 kmd b, j1gzq(jr,xqbtn;ua e+5( /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 drivernadz x bqj(uqteg5,;b,+j r1( during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car +k9doww 1q,d2:yv9n6ip n: jrynjp1q with an initial speed of 95 km/h and human reaction time of ji2prw1n69j:okp9dyy :nqw,nq1 d v+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 f rw/f7l,g m8 wf)j-rgvor the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s one*jyzrx/k r(f 1ex6 o- the highway. The car’s driver looks for an opportunit/(xey16-ro zxf j ekr*y to 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 copnz l)zc.4.+h9 2prv2 mkxs 0mf0akyi mplete the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m 0pc ifmzal .ny +0vs.z xr9422 m)kphkto 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 tr)8mw go kiu bk0t90(qnaffic 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 intersg( kouwm 9bt i80q0k)nection (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. It hits the ground below afte/a/tlv.cankj/ 06- y6xfmj apr 3.25 s. How high is //6.pyk nxmcjl t 6aa-jfa/0v the cliff?    m

  If a car rolls gently (fgvs6 4c)p2d/ d (xysy$v_0\,=\,0$) 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 wit tvf9 +* 5q/ k.pdni *ow*zbovqom0zs.h a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catchesm /gdjpyz87 l8p(rwyx hqt1v8a 2n 7a, a ball 3.0 s after throwing it vertically upward. With what speed did he throw it, and what height did it/zy8jhm g,r ppaw2x(7la yt 8qvd 817n reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under th d2ozstk bz)l:zve*ffr. esl3*j o-*0e influence of gravity. Draw graphs of (a) its speed and (b) the distance it has eel tf) ok:r*. jzz0-slv fd*z2os3b* fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height ozeb4s 3t 2m667yryhh bf 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: 6 z7mhyr bby243tse h6The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the o shsvr;t8r, -distance traveled during each successive second increases in the ratio of suc r- ;orshtvs,8cessive 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 verticalo*vmman a;r1xm 2o/6ja2nj1m *vm;orxm/oa 6 ly upward 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 qd; tjl.a/)vn1hz qi8upward 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 photoflash of the apple in Fig. 2–18 (or cp ,+gh9hy wt+number of photoflashes per se+ tpg+h,9h cywcond). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.*(oe a ;9ajzy*l*ylb09 qq usy3(dtde2 m tall (Fig. 2–32). From what height above the top of the window did the stone a l (qz3tdlea9y;j sbq*y*ye*uo(9d 0 fall?    m

  A rock is dropped from a sea cliff, and the sound of it strikinub:vq1k7nn y;7b s sd-g the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how v bsn:nsy;qb 1d-7u7k high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You poinzha l )1cvx9a3 qa61xct 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, youxla1 zv9 ha3xc)a6 qc1 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 upw+yxh4 bg z 1pvbunvxjg- +h;9 .z-pmx4ard with a speed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2–34). pgzh9 - xp4xxv-bhmb+vg+ ;yj z n.41u
(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 with a v ypklw2i- 67y7:li4; llj ffojertical speed of 13 m/s If the ball was thrown from the stry-4 6l;7l 7lf :jijkyl2owf pieet,
(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 veloc+i, zim4 dx5lem+ pmv9ity of a train as a function of time. (a) At what time was its velocity greate zv l5emi9mp i,x+4d+mst? (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 tun0e bo;i1l1ggkq w96vs1t h zz/nel as a function of time is plotted in Fig. 2–28. What iv1 9t6/e1g;hsq oz b zil1g0kws 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 s/n g9fspcg5.psjo4i(-zmo9 accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short fgf45s( 9miz9onc.j/so s-p gp lat spots in the 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 the car in the pl4:iypcpfa w/ a w)sax)v3.,jbzzk7 5revious Problem (Fig. 2–35) when it is i7wbkp3 i)w c,a.pv l:z4fx)y5js a az/n
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object travelnk ci ysb2w;:9bxrs 3m *c2qwerv.d))ed during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t grap rh/3rl dn3+oi 1cvrd2h for the object whose displacement as a function of time is given by Fig.dc lnd rv23orr1 /+3ih 2–28.

Figure 2–36 is a position versus time graph for th,e isih-pz+93vibm ) pe motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slob -hsp ,zip9 3+ei)imvwing 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-storwt8n-5n* vy u3 )enhshy window 15.0 m above a firefighter’s safety net. The survivor stretches the5) *8tvwen n uys-n3hh net 1.0 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 qpf .y z:5qc6mgravity on the Moon is about one-sixth what it is on Earth. If an cyzpf.qqm 56: object 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 properly constrained by an over-the-/u 07n/+ ,tthqnezoo4ha/ylx9w2eu xshoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 30 “g’s” ,tuy 7/h+ha 0xotenz x w2eqo/4/lun9 $(1.0 g\,=\,9.8\,m/s^2)$. 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 bridc l 3k5u9h pt5nbe,1uvge, 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 in159hnuek 3lp b5, tcvu 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 manufajz h.jmnn89bu/b q t t+)9wwm9cturer tested its cars for front-end collisions by hauling them up on +./ mq 9j 8nnbwhtzb9wu m9tj)a crane 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 t, 2k6q0obgp cx/mdpr7 ravels about $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of the train(hxq/ ozytdw xp4qxx1)81oh + has a speed of 25 m/s when it passes a railway worker who is stany4xo1h/otxz)qx dx81(pwq + hding 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 suroad 8rqsem+4,face into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the averageoa qs+, rm48de 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, i* l/w 9aapmgzaqb 9*-ft is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slowaq wgm-a9 /p*9f labz*er 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 free7u.g qtk 2n(oq6 kr/at fall straight down when diving for fish. Suppose a pelican starr2q(7gk / 6kqot.nt auts 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 which a golfer strikes a ball is planned so tc3m i* aj(o(*lashx /phat the ball will stop within some small distance of the cup, say, 1.0 m long or shp( x*(olh jia*cam s/3ort, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a c nld.bh8lv-9 0g.cwyi onstant speed of 6.0 m/s Just asbhdl.lc .i- 0ywg9v8n 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 hig.scqx0 r-;c:ygsc +qoh building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one hasgrq.os0s;cq: +x-yc c reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial lasti* 1g2dq xebug3y/ri-ev or: (dng ten laps. If the first nine laps were done at 198.0 km/h . what average speed mus1drgvdri * y:ue qoe( 2g3x-/bt be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests ao*d .nne -p3;xyujt0 z mountain pass as he moves at 18 km/h . At d;.- *n0xej putyz3onthe bottom, 4.0 km farther, his speed is 75 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 trampob -bfj -n-r.acds )/vrlines. The first child can bounce up one-and-a-half-a-) s.rj/b d-rcfnvb times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train traveling in xdfr 8s i1i,8nthe same direction on a track parallel to the road. If the train’s speed is 75 km/h . h1nr,i f 8dxi8sow 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 with a speed of 44 m/s In throwing thhdtc ygs43 h fbgp,7byf52 4e,e baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during pyh ecbhf7dyg,bt 3 24sf5,4gthe throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with vg.xtt3rhd v8,co0 )q 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. Each in +cx ry/77xbcttersection has a traffic txcx+cr b/77 ysignal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green 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 constantm e/ib*x u f+03e6lq5 oporus+ 120 km/h takes off oo*q r35p+b u s+e06f/imlexuin hot pursuit. The police officer catches 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 buaip our,o 1m0t0* 1y tm+eqhdp;pp3, silding; 2.00 s after that, a second stone is thrown straight down with ap,0ep0 hydrs3oat* p+ 1iqt ;mpu,mo1n initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically upx4r*p 5lwwwf9pbn/ j:(3-uz0 uvrx pn at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initxr r/ z5nwpw-w n*l:40xjfu 3bp v(p9uial 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 tt 2okax7 vdnta1(wh90ake a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will rent1v(o2 t 0h xka9d7wastrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a grilln +fmlcok)4 ugx4m* pyw8;pa2ing machine. If the grilling af 8uc4g kmwl+yp;)2mpxon* 4machine 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 verticao/ozm1 5 b1pb *e/xz5gxkw)r fdj.o7nlly at a speed 1.5 times faster than Joe can. How many times/x1gp)o dzoo1b/kzw5*xnm 7r jeb5.f higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while .um,:y-x,q b 1qotbrc your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and tb,uy,.m 1rb:ocxqt -q hrows 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 heigh zv pl7rk,97-cni*gtgt 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, 2.3 s. How much difference does the 0.3 s make for the estimates of the buil-i vzg*r7 n,lg9kt7pcding’s height?    m

Figure 2–43 shows the position vs. t.24d i jqyazyf+3c+pgime 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 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 aveg. qca23+fyjz4id+yp rage velocity?