Does a car speedometer measure speed, velocity djc((our xsu.5ndk :), or both?

Can an object have a varying speed if its velocity is constant? If yes, give exawfhu3s6t v p+w0)9xcy2 o+wjzmpzxft9wh++ c6)so 2 w0yw vpu3jles.

When an object moves with constant velocity, does its average velociq3s6kjti 2u 5 ;c:gl(ayl. shosyd/:rty during any time interval differ from its in s/cgrl(3dt:5y.qo2ky;usah 6:sj ilstantaneous velocity at any instant?

In drag racing, is it possi8w) elhm znd39ble for the car with the greatest speed crossing the finish lined m)el9 h3wn8z to lose the race? Explain.

If one object has a greater speed than a second object, does the fora md;c4p9l3 irst necessarily have a greater acceleration? Expo9c 3;4 pldmralain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h toy(1rs) 0zcsi :pz-wz;/bz pgm 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same time.zp-z 0) s zpz(r1w :igbymsc/;

Can an object have a northward velocity and a southward acceleration s,jojms0h- 1(o*z7 wryk (ylin+ voe*? Explain.

Can the velocity of an object be negative whin(e adm 8ogvqo:v3*(en its acceleration is positive? What about vice versa?g omdo8 3q:na(v iv(e*

Give an example where bothzvfb ,ot5sa. 4 the velocity and acceleration are negative.

Two cars emerge side by sn ;qdlv*xd97 aide 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 ; dvx 7aq9*ldn60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration desw9a 92-94fbcy),rqubig d ge( 7eba wcreases? If so, give an eiab 9w cu9f-seg adeq(wg4,b 7r9y2 b)xample. If not, explain.

A baseball player hits a foul ball straight up into the air. It lcv1f5xu9fonmm4v k j1i 7:3kxeaves the bat with a speed of 120km/h . In the absence of air resistance, how fav:mvx7fkmo n3 11 k5cuxif49 jst will the ball be traveling when the catcher catches it?

As a freely falling objec vtzv00mh. 7zbcb1xu)t speeds up, what is happening to its acceleration due to gravity — does it increase, d70hv)zm bu c.tz1bvx0ecrease, or stay the same?

How would you estimate the ma a;n)t apu)ghxs1x 2s zmsg3*,ximum height you could throw a ball vertically upward? asus,z s1*x)xt2 3n)mg;gah pHow would you estimate the maximum speed you could give it?

You travel from point A to poin4ci1v cb6m 3piy70l nwt 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 sp6 nbcp4 yi0l vwcim173eed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-ip0,sxwyat,zj56x y3 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 or decrease near the end of the fall? How could the bolts be ti6ywy,p5sa0xt j xi 3z,ed so that the clinks occur at equal intervals?

Which one of these motions is not at constant accelera3y2 cdsu(i; nief22t ztion: a rock falling from a cliff, an elevator moving from the second floor to the fifth f;2fzsi t(nd 2u c3ey2iloor making stops along the way, a dish resting on a table?

An object that is thrown vertically uptj3lpm)+ed k 0ward will return to its original position with the same speed as it had initially if3ld+m0 ) jektp 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 acceleratpuje(;k. 7j ogion at the same time? Give examplesj;e .(kg7jpou.

Can an object have zero acceleration and nonzero vel awle o18 l3:hx/w osjs97usvpj*7) csocity at the same time? Give examwxs7e7su sl:p)jv*3c woh9a oj/sl 81ples.

Describe in words the motion plotted in Fig. 2–28 in teru :i r:w17tsvwms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking oru7srvwi::t1 w moving your hand.]

Describe in words theps9s,ikw-6 xtz wv1w99q -w hf motion of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 kqp(hc d+/ubg z4*k0i 8 gqxdi,m in 3.25 h?    km/h

  A bird can fly 25 km/h How long do;29b9gym .fp mf/xc qres it take to fly 15 km?    h

  If you are driving along a straight road and yo9v7tmy .pr5g4 ka7sup u look to the side for 2.0 s, how far do you travel during this inattentivep7t7gs9 4pr.a vmuk5 y period?    m

  Convert 35 mi/h to )oe(o4 ik/gz fefq :p q0 s3p(fru8yb.
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from :r8f/s-ltwa qi g0 m f7q-cb4r$x_1$ = 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 hr0i p08 wc4x,)zqwwp km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and prw0, chiw xz80)pw4q 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 secov9h*veivf t4g u+r, y-5 jxjr u3;yww1nds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash xe3uw4w1rv; v9 rfj+t*hu5, v-giy jyof 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 complp:mr oy/m 3sj.ete laps around a quarter-mile track in a total time of 12.5 min. Calcula:/3 jpomm r.syte
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its tra,2so 4df33r ll. ieyjnd,i +wtiner in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gsl elf3o3ny jrdt 4i,2.d +,wiallops halfway 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. Each has a speed of z0/h 6mz(0z m,zr rbbb95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach 0m br6r, zzmbzz(h /b0each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 1; fhb**kqh 7ls10 m behind a truck traveling How long will it take thhlk7f*bs;* qhe car to reach the truck?    s

  An airplane travels 3b2s) gx xfug,o)3c,ux100 km at a speed of 790 km/h , and then encounters a tailwind that boosts its spee2o,cxbg, )x)g ux s3ufd to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete round-tri;524ey4z o rb 9jbmt,thgva3fp in which the outgoing ;5j2h 4o 3mb fztgbr y4evat,9250 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 jd*bpk4 6u hicgi4j)/k8)xgcthe pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of th*)44cjkucg6i i/j hp xd)k8 gbe 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 *mj2-xppk j.ffrom rest to 95 km/h in 6.2 s. What is its average acceleration p-pj2fxm*.jk in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in nfq o:klqw;.+ 1.35 s. What is her acceleration . +k:flwoq ;qn
(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 abofz n e:de6 gi0h-kg ,hs6pzs+7m+9gd rut g06e9r6sf pndh kshiz mgd+ e,z:- g+7$1.6 m/s^2$ 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 11 tkg(+ .e+ knocykh30z0 m in 5.0 s. If it then brakes and comeyckzkhe(o.g + 3+t 0kns to 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 and movyf75+3 3 sfvupqo8gydes in a straight line, is given as a function oo gupf53vyq87yf+ ds 3f 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 a graph.

  A car accelerates from 13 m/s to 253 :wjo.np9ckc:;j o bj m/s in 6.0 s. What was its acceleration? How far didjn 3w:cc;ojob: k9jp . it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from vvhf0hy 4e 25qdsf1:p fd5;oq23 m/s to rest in a distance of 85 m. What was its acceleration, assumed constan s:qovdv54 hhff;dy15 qp fe20t?    $m/s^2$

  A light plane must reach a speed of 33v p3ijf( 4fdnge3q 37u m/s for takeoff. How long a runway is needed if the (constant) acceleration isde7q g3f3npj f(iv3u4 $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blockswpjo d 256*rwd to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the averad jdw*o2 p65rwge 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 spedau hf. e-qe(m teq)3/ed of 12.0 m/s to rest in 6.00 s. How far did ta )he- qu(qed/m f.3eit travel in that time?    m

  In coming to a stop, a car lea ;if)e)pm9 ya(8w ssois,je u,ves skid marks 92 m long on the highway. Assuming a de;) 8e y,u,s9mf pesa)j(owiisceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 k l5mrd b:ne4(km/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 on? Express the answer in terms of “g’s,” wherr5 :4(kmled nbe 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 b; s-tcwq5:tnou:ypp ( )yov9initial speed of 95 km/h and human reaction time ofo q bpywyt5 nc(v; pus:):t9-o 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 th v /xyewo7bua. qgw9;ynoa :(ld(n0s7e stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The cae ;*:(sjk7pyr z;k xurtlm+8er’s driver looks for an opportunitesrpxre:8t( yu7;mj l*kk z+;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 complete the 10,000-m run in less than 30.0 min. After exactly5o. 4bcxw mth; bt/9:lry *,p c,iubrw 27.0 minr9 ./4rcblt* tbi:, ww;ybcmh5up x o,, there are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as thpg2eh)xh( 0sn e traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before tur(g sphx )eh2n0ning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her 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 gifr 032s b.-iq hltai2ic 5 ;prghj3q2round below after 3.25 s. How high is the cliff?;ri-i2 tj.i0b3h hrg5l3q 2spcqif a2    m

  If a car rolls gently : j6qlwxl8v:7x cjsh*ks :l-k($v_0\,=\,0$) 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 as2/tths2cs4 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 da z y2gxlbm1kv11i, ,ball 3.0 s after throwing it vertically upward. With what1x ,ld,iam vz2 g1y1kb speed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravk3ov8* s0ntg2r ;go7 jknjsz-ity. 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 . Ignore air res7nrk0-ogjs3kzgtsjn 28 *o; vistance.

A helicopter is asce5qzm*2r ab *( i8jfrqinding vertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed az(ir*qb 85qjmir2f* equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the disfe- 9 yrvs)pn:tance traveled during each successive second increases in the ratio offys9n:e) r-vp 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 bal7f4m( qyh elgpeh +o+1ao+p. rl thrown vertically upw+qog+h4pofeap.mr1+y e h(l7ard 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 witvru t46b6mip*d-w i j;h 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 photoflat7af0 6p6w ib1ycrr3q sh of the apple in Fig. 2–18 (or number of photoflashes per secondbwrtpf6i31 a7ry6qc0). 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 t+ea q73bxhq9q y9m pc f2pl9c3dq 0mn4ravel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the wilq3nf+ m4b 927acph 9ye qd9qqmc3 0xpndow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean iw*jx /o00 nrjok kqi61s heard 3.2 s later. If the speed of sound is 340 m/s , how h q/0n6woxik* r1k0jojigh is the cliff? H =    m

  Suppose you adjust your garden hose nozq:810 8n-g,nl()ot pyapwkzeaf9yx l zle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves th 0)xz:9py(fa , qangp 8lowt8n1-y kele nozzle?    m/s

  A stone is thrown verticafo2- +hx j*mahekk6 mzz54sx:lly upward with a speed of 12.0 m/s from the edge of a cliff 70.0 m hi a m f5 xkzh*xeo+h-jk42ms:z6gh (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 up l):opz6dini9 ward by a window 28 m above the street with a vertical speed of 13 m/s Ii6 nl9pz):odi f 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 trainvbww *a;f6 5i5ipr :bf as a function of time. (a) At what time was its velocity greatest? (*p6ii w5f:bafwrvb; 5 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 6bbnv3yc 6xg8+s6meoa straight tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneousg366c e+6vnmyb oxs8b 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 apm-nciu9- hzl3proximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent lcz- im-3nuh9shifting 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 i(z -il1eov( rkn the previous Problem (Fig. 2–35) when it ik( 1rl-(oeizv s in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate thev4pul jhdak3+6+cy o- distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacemen1+t r ;cq hh(bakn9a)*tdtx1 ht as a function of time is gh+rdt(t9 1)1kxtaha; hcbqn *iven by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an oyd. h(j9d bgm+bject 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 th d9jgm (y+.hbde 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 firefi;nx83ay8snt-kq+e* p xtclcf k55l+hghter’s safety net. The survivor stretches the net 1.0 x*8q5k 5 8f+c kex3ych slpat+tnl;n-m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixtuph-0 i w//vvoh 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 vevi- p/ohuw0 v/locity?

  A person who is properly constrained by an over-t28 qs. i elg1pb7mo6,6oytspehe-shoulder seat belt has a good chance of surviving a car collision if the deceleration s8ep6o7p 6se gotlmi q,.by21does 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, and his pu eoxm1jtt7cfpq*85 d) rsuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowq*xt c1d7 po t5mfj8e)ing 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 the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-e7a2 9 el;skeulnd collisions by hauling them up onesek7 a2llu 9; 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 travel6 )nh8jzlqjy+pwn 8.bs 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 zbdajw/lgmpv,b2j 0imp)uwy4 + /92 bfront of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from whebm+pal v9p/ 2j,4/yjb m0d2i)buwwgz re 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 th7+ rbkv8m bfc8yn8u ku+logq7 i2s* r*e water’s surface into a deep pool. The person’s downward motion stopsmbg8kq +*vfir+y87u 2n*l7o rcbu8ks 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the av3jw kqj 781k72isjawferage speed of a train af8k27 3w sijk7wj j1qagainst 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 straight dnbv1oh(:5 1wi taip(5msso pm4,vq3bown when diving for fish. Suppose a pelican starts 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 ep:viqn tw m(s1h b155(sov 4bim3, oapscape? Assume the fish is at the surface of the water.    m

  In putting, the force wykxz /n+vxc/- ith 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 the putt is missed. Accomplishing this from an uphilny /xkvx-cz/+ l 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 oe 5xu7j qtz/6xn a freight train traveling at a constant speed of 6.0 m/s Just as an empty box ca 6 ezq75jutx/xr 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 high5y3w+tue7rlkce c 0n 8 building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached 8uwl 0c5re +3cek7yt na speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of ak g y*y1qe/wj cmy+36m time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the lastymw1jq m+e 6/*kgyyc3 lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 1s3v6/misuxx si r0m.g)7 yh. n8 km/h . At the bottom, 4.0 km farther, his speed imx n0 uvs.h3 )yisg.rsm/6i 7xs 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 trampolines. The first child can bounce ug(k/pg;c fbff ;o;f2ap one-and-a-ha f2o;; g a;cpffg/(fkblf 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-kmmu7idmjyn(0i ;f9j p)+:lf ;/ dts dkm-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 resultsjdps;im f k(mn)udtm:l+i jy /;0d97f 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 thev*5d n.i,vkhj baseball, the pitcher accelerates the ball throu.kn j*vihv ,5dgh 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,)y8 m5r,d8( l.n*/4jx ey oklvgovx qr 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 traffil 81agpe3-m 5yi 5jcvata:u0n c signal, and the speed limit is 50 km/s . Suppose you a3cuea0av5a1 5ymlit 8:ngjp- re 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 b7yird4 cb66j;hcbw ) ) lsm+hsy a speeder traveling at a constant 120 km/h takes off in hot dwic6 b6h 7blcs+y ;)jm4hsr) 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 building; 2.00 s after thagfhaivv+o4 :o76/u5 egv-q6yammp ;jt, a second stone is thrown straight dov-5j a;uv m oo:qi+6/fgg4 vmpey67hawn with an 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 ujfj/ ng:sg4e1zwy*0v ys:y q+p 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 initial velocity should gw0 yjysy/:gjsfn *4 :eqz+ v1the 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.ow c qj8)c2zl resistance, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitud.)wc qlcj 8oz2e of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restauranaaoy3x5eqa; 0t uses a conveyor belt 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 ay0 ao5qax; 3eis the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a s6tn./btajt4 :nu4rku peed 1.5 times faster than Joe can. How many times hit6a4jut u:./ n4 ktbnrgher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friettrz9 *ge,sg4nd 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 throws it up to you, such that it just cz,4ts te9gr*gomes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are askaxc3cd e. 3-;otfxi,i n0)ukhed to find the height 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 f3i,hu n ifd ex 0-t3ck)xc.ao;all. 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 two bicycles, A and B. (a) Isumsa,jr0w-mq 0jn6v 1c+qr5 o 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 instantan+5ja6c-nmr 0jo u 0,wrv1qmqseous velocity? (e) Which bicycle has the higher average velocity?