Does a car speedometer measure3z*hj+d+4 o1 oud ekcb speed, velocity, or both?

Can an object have a varying speed if its velocity is constant-fuay 3z 1)kqu,0+ vot5 sd9nk/djgfn? If yes, give examples)s1+fq59,vuy-3kuo d0 akjnn fd /tzg .

When an object moves with constant velocity, does its avew4 (dkkc8jwix+vd6.)nrx sg9 tgak ; 7bsf6,srage velocity during any time interval differ from its instantaneous velocity at rf ,6a+j 4 6sxdtsbi)8 dxgkv9 n. k(;7kwgwscany instant?

In drag racing, is it possible for the car with the greatestmcl8rg1 0p.wbx on kt);8na: w speed crossing the finish line to lose the ra):gpa tbwm nol 880nr c1w;.xkce? Explain.

If one object has a greate wz5 vnky114uor speed than a second object, does the first necessarily have a greater acceleration? Explain, using exampw1kuv 1 yz54onles.

Compare the acceleration of a motorcycle that accelerates from 80km/h t1 9n7y,r(wzbh gd9d7(s oynbe o 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h 9s( d,(hbd yyb n17zr9ge7nowin the same time.

Can an object have as*:ije p5jz174o hpwo northward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is posi4r3 t2,dra3cwi ,ojm ztive? What about vice ca3 2rrit 3zdj,4ow, mversa?

Give an example where both the velocity and aci/3rxxck) fiad4 t c-.celeration are negative.

Two cars emerge side by s6w(g l92n) wa hhcw*uyide from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of t hc(w)*9wlna6w2gu y hhe tunnel? Explain your reasoning.

Can an object be increasing inha9qq+3f-g* ppg*mkpl,iipj e8u q, : speed as its acceleration decreases? If so, give an example. If not+:qkap q,*9 gijp3iph e8,fmu*gqp-l, explain.

A baseball player hits a o 0 jtz2t:d+pufoul ball straight up into the air. It leaves the bat with ao2zpt :t u+0jd speed 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 happening to its acceleration du34 s o(lru wuul)qpw+5e to gravity — do)4q3+(luopwlu u w5sr es it increase, decrease, or stay the same?

How would you estimat+ixt /iqgtbu((,1ikf *v k /fze the maximum height you could throw a ball vertically upward? How would you estimate the maximum speed v u fk/i, /fiq(g(zx1btki*+tyou could give it?

You travel from point A to point B in a car moving at a constant speed of .kq3rps9 e:g/ yyn8el 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 y s y8gkql9enr/:ep3. for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied171v1k j:p5pfn jmlnt 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 or decrease near the end of the fall? How co p fpmnj:lv1nj1k157 tuld the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock faqol3/ -jtu/y knl+ xm-msv 6j6lling from a cliff, an elevator moving from the second y /j-x ukmn6jtlms6ol3+ /qv-floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown verticalla* /9joo02aupc 3 jqohpcq8(pj sr88b y upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will jspp8c p oura02(cq*jaoqo9h88 b3/j 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 nonzeu7 )lav-:cl/gge mp 6bro acceleration at the same time? Give el/bea7l gg:c)um-v6pxamples.

Can an object have zero acceleration and nonzero velocity at the samkf /mkd2ha tt;mrey f1/4o0f3j,)fc u e time? Give f3f41k e/ hk/ad,m20)u ;c rmyftfojtexamples.

Describe in words the motion plott99rzl(a ucjb)c3 kkxy4r-5m )truq*5ap mty 8ed in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking yq9-)kktjmtc5u a zr3 ay)x*l8up9m r 5(rc4bor moving your hand.]

Describe in words the motion of the o.h (z p0kzd6 /fgoso*gbject graphed in Fig. 2–29.

  What must be your car’s averagw3*icc)ib 624 nwuc rfe speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h Hofkpa2 std dddy4/u86+w long does it take to fly 15 km?    h

  If you are driving along a straight road and you l ovpgol41+v g i148uw3rsp3rl ook to the side for 2.0 s, how p wu3v+o 8g1r1llgvrp3ios4 4 far do you travel during this inattentive period?    m

  Convert 35 mi/h to v0;zjq g wb,4y
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves nqtqn3i, 7w*q .dt6jlhsk:o9 q v.0 bmh:ch)z from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for 130 s+w2zq+s7-v(m8x vnn ln 7 e y6nh)rrskm. It then begins to rain and you slow to 65 km/h Yw s+8n)-qnr sn r 7hesl2m6z+vx nv7y(ou 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 lightn,0-)gdsne nccq7hp7y*kf dayz jw71: ing flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially-07 epy s7cddz)jayg7,*f nqn:kh1cw 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 total time of.xi +vvk5r e /ta6po3ys)jh b1 1) 15ha ksvtyvpi3 jebxr.6/+o2.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer l yr t9jz-*-dwin a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. yl 9tr*dwz-- jCalculate
(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 eacheuz,lmwq7za8 ) dh4v)jw:i r;54zxtp other on parallel tracks. Each has a speed of 95 km/h with respect to the grouz vhudelt,xw)4a)i 48pmr5:z7 q j;zwnd. If they 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 traveling Ho1sezt u.96bc lw long will it take the car to reach the trecb 9s. tluz16uck?    s

  An airplane travels 3100 km at a speed :j (dxhqt q3xb98g+hxof 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the n xjd(8 qhbtq+:3xxh g9ext 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 fvjq +p :3x3d pwmjh8:y.wi4eand average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch brew4h i 8 :+ev:xfq jwppd3j3.myak, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant 7 c jw*i9me5grspeed 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 or7cw m5e *gi9jf sound is 340 m/s.    m/s

  A sports car accelerates from :etzv ck2- w(arest to 95 km/h in 6.2 s. What is its average acceleratio (-wvzeca:2k tn in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accelerationza; 3q3 9 dsvo+4f;v9dqiczwrq+ tua- +q;+;odaf qd34crs9u-3 azzwqvt 9vi
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is ca 0hu-i8znmxjaaz)8jh 9s3 y5 ipable of an acceleration of about -iu)x3z8a a hji58n9syjhzm0$1.6 m/s^2$ 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 in u,t39+ bb ldr7+qcc2l m9zwat then brakes and comes to a stop in 4.0 ntr b+9qlccl9d,+ 7wabzu3m 2s, 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 stardu .rc2.qtf 03uq xo*bts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate o 3*c0b. 2qfqutrxd.u (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6. ; b2chwon+f90wfrcw: 0 s. What was its acceleration? How far did it travel r2:hn+;0 w 9f wocbwcfin this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 mdbko/w5aj9 ;j/s to rest in a distance of 85 m. What was its acceleratjkj5bd /ao;w9 ion, assumed constant?    $m/s^2$

  A light plane must reach a 0d 1gmb1gbd.fspeed of 33 m/s for takeoff. How long a runway is needed if the (d.bmb01 g1d gfconstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter sg-6bk (rrwg//lwve.bb bs(2 can burst out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is thvl2sbr w (bebbkw-grs. 6//(ge 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 6mkfm+ket. c .of 12.0 m/s to rest in 6.00 s. How far did it tra mmk.6+ etfck.vel in that time?    m

  In coming to a stop, a car leaves skid n ymc7)q1+ e e*ev:rlzmarks 92 m long on the highway. Assuming a deceler nqv)7*: r1zyee+elcmation of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. Tsi qn8wpyy7cy) ).06cl,zi ozhe front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the an i7 pyo,cyz8 wl0i.ns6 )qc)zyswer 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 initial speed of 95 km/h i-,p :btqbt -:tbm4te and human reaction time b 4,tbm::ttq e-pt-biof 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 distancoqc*d . iyy 0ghi-1t/mrf n(4fe 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 truck3 d9jbd5p-fx hsvlz8h 2)*ck8aqp3 nf going 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can acpp) fhz q -jd5sd9x8k 8v3n2l*hf3a cbcelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. After exactlu 5,gp 6ob5tify 27.0 min, there are still 1100 mfop 5ug b65it, to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as t 4/f jxi4zwp.eayhn9y b-4lt 9he 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 widlp 4/by9enz4i 9fxy .4h a-jwte. 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 topk(jdo0 lt7j .u rmhxsnev77 1- of a cliff. It hits the ground below after 3.25 s. How high is.h 7u j7 jk-tlrev10(dx nsm7o the cliff?    m

  If a car rolls gently3te)a yad 4;+d q4z:awdld0d i ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

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

  A baseball is hit nearly straight up into the air with a speed of vrq/km:0zq20kfkt8) , ytv jl22 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 a/(/ b,3jl4xx mh6z5sr; ksnmbvvj.ma fter throwing it vertically upward. With what speed did he throw it, and what height did 6/4smjbax. hv /r5x;v3ms ,j( zblnmkit reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw graph-5vxxwe2u* hp02(p 95mb ox xrj*l uqus 2 h5(9ul epxmxvo bw2 j0-xxr* q*p5uuof (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a heigq1, tn7*adacs. c5iqeer q9-wht of 125 m above the Earth, a qdce. w qn i71crq5* ta-a9,espackage is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, sh6ncdbdbj-/o x68n4t sow that the distance traveled during each successive second increases isdn -dnjt6/ 4obb6xc8n 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 (algebr+ rkvfg*t* zew:4-yxk aically) that a ball thrown vertical tyxkg*z:+-*v ewrfk 4ly 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 upward with a5 j ofbldn03x8 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 appl pli1-7uusga ,k x5dyj367rdue in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Useulp6a1-j x uku3g5di 7,d7rsy two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travew. pmbi; 5wwa,l past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fapbw5i,m.ww;a ll?    m

  A rock is dropped frr/lif fp o9: ja*gm+ 15ehvlg;om a sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the pf*5 lr9/v1jioe +gm; flga :hcliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard strap2 )xz i0qsz-eam of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle 2)p zq-xa0zisaway 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 upward with a speed of 12.0 m/s from tl m g g.sc*f8z1k.f98a:fzxh92yh1. pchq i kmhe edge of a cliff 70.0 m high (Fig. 2–34)i s1a*k.m8: 9kz98 ..l zgfhh 1cg pqycfx2fhm.
(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 b:.fkpoqwq2 3 0 vynht)y a window 28 m above the street with a vertitn v)k2qy0.qp w3ho:f cal 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 oslj/ g6; rlh1u 7d0j qyk1)0b,4jza pkyur*kof time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) 1d*0;jjuopa17bzl rusljkkkyh4/ r6)0yqg, During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along 7jiaflur*7. j,ny0ed(pe )pl a straight tunnel as a function of time is plotted in Fig. 2–28. What is itsda 0 p.jelpe i7(lj, fur7)n*y 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 cat gezv 65l:e oz8nc19tn accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.) t8ve nc zlzo95g16te:
(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 0r/ut g2qkk rii-2-y6ot9jaa car in the previous Problem (Fig. 2–35) when it is in2 ar j2ka9tiu og0q6/rtk-i-y
(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 travguc/j/n2b/i d8 / yaqdeled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function o2u(nas8 b fmf2f time is given by Fa22n fmbf8u(sig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an ony;vhhj)9tq-a3 -32rdq roa d h7d1orbject 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 slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time inrr-atj d3h;a dqv13o )2ho-qry7h9n dterval from C to D.

  A person jumps from a fourth-story window 97fx9 ovdp 100ljrbznytt55,agc( w n15.0 m above a firefighter’s safety net. The survivorbj9tp rlx90a5t nv z,1dyg7(0 cw5fno stretches the 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 t:z6p7zlwg hm9;w 147j stsxteo gravity on the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocityt 9lp61wsxg4;:w7 s7ztjhemz ?

  A person who is properly constrained by an over-the-shoulder seat belt has a gomnujru1 44pb3oea f, 5od chance of surviving a car collision if the deceleration does nor43b euo,napf 5 4ju1mt 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, and his puy o *k bbtx9z/rd rh/,fo;ef6.a2 )wzorsuers 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 sh / tb.z9fo6/x w;odozf,e2ryk*rba) hould be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars cuiez-zf 3ux5f6)3gx for front-end collisions by hauling them up on a crane and dropping them from a -36iuzx ef)fgxzc35 ucertain 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 Earthpy (urpkn6 p3*+whz 2g3 qkwo; :jwi8z travels 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 begc,tu9/xvf1go:m 1q x uins uniform acceleration from rest. The front of the train has a speed of 25 m/s when it passgq/u:mo9x tc1 xuvf,1es a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above* dqcfh jpl1,,xw72fcs1j;ioom; lz+ the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the avera ; cpqc 1f1+w2jsxzfl ilj;7oodm,h* ,ge 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 b2.ygb i0iw9ku alance the average k0w.iub i 29gyspeed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, 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 strr;g7a-* uzesnt w*k*vaight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change itskzr7s;**g-*envwt au 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 golm w7q/+egin y:42z degfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putti e+mig/nq4d z2e7:ygw ng 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 o(q 6zrxsw a9b4ys-8j train traveling at a constant speed of 6.0 m/s Just as an a(r zsy9j8o q-b6sxw4 empty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is droppeyuvz8g/u zs0,d 1.50 s later. How far apart are the stones when the seconz/gusz8y0v ,ud one has 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 aeru-esi20o3 3;z7*foine wstrial lasting ten laps. Iaz -wein fu7eo;*os is0 er323f the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tours;odqz4( qz2e de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his a;dz 2oqqse 4z(verage acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounce(l/:7pq qr5r gya-iwr up one-and-a-half times higher than the second child. The inlgr 7i(wyp/q 5rraq-: itial 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 ew zxjfrtl,; ,:xo ofia50r6zilz5b z1j35v6 95 km/h overtakes a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are tra;f jzzlj5606ife1oixwxrba:t53l zzv,,5or veling 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 sp1strj ddw9,2 5aio rw)eed of 44 m/s In throwing the baseball, the pitcher t9sdiw rwor 1a )d,25jaccelerates 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, ffzadlh(4 p u .bxb:w9:rom rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a traffk b 5/nslk93sh3k ohd.ic signal, and the speed limit is 50 km/s . Suppose you are drivih9.shklkb/ok3 3n d5sng from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km/h t0ywogs9lbzda6/gw 16 wve3 7r akes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acce17dawzo yg sgw3v6ewr6/0l9 b leration.
(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 after that, a secon6v/dj5s e 8dmyd stone is thrown straight down with an initial speed of 25.0 m/s and the two stoneseyd5 j/d8 sv6m 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 u/ekagl q/xo ; .cv;wb1p at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of. ckxva l;bq /w1g/eo; 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, howd m5u:zc0k p7x long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed td z 05cmp:kx7uo perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor beltfn 9knh. j+a( uvka:l2 to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)? 9ah ljun:an2+.( kfv k
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speedes0 )g8kant n;n +mo9m 1.5 times faster than Joe can. How many times higher will Bill’s bongk 8)s9mt;n 0n eam+all go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands g/mvne7 + wiwa*meu -9on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball tog iawe+ew9-n/v7mm u* 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 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 qg8n vlnqg-0it p )2j/*o/l xmparticular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of gpgnl/0m8-/ xltqqv2* on ij) 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 graph for tww*xp.*w12+ j (mdtkfznv,vg+ sgm 9muo bicycles, A and B. (a) Is there any instant (+kgv1w.nm*9m2tj dm *g,vfu spx w+z 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?