Does a car speedometer9j;(hqk q u(mm:w :olj*b+brqr dg,6p measure speed, velocity, or both?

Can an object have a varying speed if its velocity is j98k/ cgi as44cgomy,constant? If yes, give examp,4ycoi/ g4m gcjs 89kales.

When an object movesb:-kqdan2m7zxp 0g :h with constant velocity, does its average velocity during any timhzq x:-gbkd n:m702ape interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest , 2p, 7hmf1uhkq9+il *d*ajd/x r3phdwm oas ,speed crossing the finish line to lose the race? Ex* o,xp,aarjqid *lh3fm7kh,m/9p d2w sdu+ 1 hplain.

If one object has a greater speed than a second object, does the ( wp-wcf l*;krfirst necessarily have a gre* (cw;wp rk-lfater acceleration? Explain, using examples.

Compare the acceleration of a motorc r e4mkibn y76r-(a*ypycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that ack-ir4mr*ab y7n (p6yecelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward accz g; p9z*lk)aw/4bzv x4 ,eltzeleration? Explain.

Can the velocity of an objm2)cw pmxa *(cect be negative when its acceleration is positive? What about vice ve *m)(2mwa cpcxrsa?

Give an example where both the veloc8q1f l( rbj 3yt;3nvxbity and acceleration are negative.

Two cars emerge side by side fr ys;:s;ru; m lq(toh rde/wj9-om 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 drej m9ossr;;u:w-y tq/h(l;of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing i6,6 l,:w.*7qoz* noirtmwep9oh(uk 5hz uchwn speed as its acceleration decreases? If so, give an example. If not, uhhw, o6ep9:.tzq ,*k (wwz n5orl o* 6i7cmuhexplain.

A baseball player hits a foul ball straight up into the air. It leaves the.tb u1m9iej -n bat with at9u- nm1b.j ie 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, whatxcog/kxnam6, d*)( bg is happening to its acceleration due to gravity — doead)gk / nombg(* ,6xcxs it increase, decrease, or stay the same?

How would you estimate the n q/)pvjg5m/* f-cmtk imjb6 (maximum height you could throw a ball vertically upward? How would you estimate the maximum speed youkjmm -6)5bg/p tjqf mic(v */n could give it?

You travel from poinglwve 0 j( hmoi -oqr9/6hr 5cbd88c6vt A to point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not8/ d56hmvir9q8g(0e wbh6vro-jcolc.

In a lecture demonstration, a 3.0-m-long vertical string*nky.w0 jy mhg .c4x.v 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 boyk. h4 c0gvj..xmwy*nlt 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 mow9fev9huv/-/ + ybecg 8. uyfbtions is not at constant acceleration: a rock falling from a cliff,v/e8f9+9 ub.vy/ c ygb -efuwh an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown verticall4rpfse cps .(v.g b+irerc3 37y 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 this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction oppositeiprcg.e crr(fvp ssb .47+33e to the motion.]

Can an object have zero velocitwl5 3 le*ujxu)y and nonzero acceleration at the same time? Give examp)xj5 w*l u3elules.

Can an object have zero accelfdo5o5vl - na-j *ux5km bh06ieration and nonzero velocity at the same time? Give exa ld *i umf-55oonj6 5xa0vhb-kmples.

Describe in words the motion plotted insz)r2d 5 8cfbr:dh4l j Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by s lchfrd4:j8dzr) b52walking or moving your hand.]

Describe in words the m)(g x*hfw/phk/ln6o rotion of the object graphed in Fig. 2–29.

  What must be your car’s average speesmhc7tk 3t 8v2k3*egkd in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 u h/i al/x vl9qpj)mn-h3l u1; u39wjwkm?    h

  If you are driving along a straight road g.b;b3; lw3 1euj;axe0o gmt5b zx b4zand you look to the side for 2.0 s, how f wz4xl; 1bjx;u.b3z; o3g5bm0gb etea ar do you travel during this inattentive period?    m

  Convert 35 mi/h to +9 hk oo.siu-s
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fromqb ai /y d/))jfu/zso, $x_1$ = 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 s.mc ii75bulf) mi25lateadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and5l.bm)ii aimf5 clu2 7 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 fla1sbr.s2 ,,bdaosk cf y 5t3+xssh and the 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 sd31bys+,a2 sbsk5 ro.fx t,scpeed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total tixk tat2u*tp)c1,j 333ex iup c/qu7k jme of 12.5 min. Calcul xtpp7xt qj32,eu3ajkikccu1t/ 3u *)ate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m away-o*er05fkr915o lmu:toeb hi x)iq:c in 14.0 s.*e0 r:iem q19kioc b5l ):rhutx5 -foo It then turns abruptly and gallops 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 approa9heb+y/mfjr9,q d /s xtyp6 n0ch each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2,+ypbetxs /qndy6 9h0j 9/fr m–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling ey(5lh;kolfd 2zpy1/ How long will it take the car to ld1;/5(kfpe lhoy2z y reach the truck?    s

  An airplane travels 3100 km at sf+y a b8l4fkxh c/ n.am0fo/.a speed of 790 km/h , and then encounters a tailwind that boosts its speecf+// .yf.bx8lna 4 hkfomsa 0d 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 rol8 yfc2 du,,bll0:q pzund-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunc :plzfq, culy dl,280bh break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed h0dgey.z: w / l+me;jvn;x;ifqits 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 aftexzl w efiv;je 0g.;;yd+q n/m:r 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, q0t,bjk/qje 7 apii+ s. What is its average acceleraia0,/7 kie btq+ ,pjjqtion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0v0r- xzj6;xtz o*pse0 m/s in 1.35 s. What is her acceleration zo*sxt z00-j6ex r ;pv
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capabl+gezkqn mdjr3mnui6c .) 6e30e of an acceleration of about eed i306zj6m)3.nm rugnk qc+$1.6 m/s^2$ 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 constaym 9:2fqpwme- nt speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is it2p weym-:9m fqs 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 frpnjw;j v y18i)om 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. Displayjvy;ipn1)jw 8 each 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 accelerationt7titcgwbgv ( (u)m4v4da, 6k? How far did it travel in this time? Assum4ivk) 6v((b ag tgdc7tt,w 4ume constant acceleration.    $m/s^2$    m

  A car slows down from 7-,q4es pldf hlx2u*s23 m/s to rest in a distance of 85 m. What was its acceleration, -74qeuh*lx s2pls,df assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a7.g.hgv.hd 2bqjqb hq-q /t8t up+cp. runway is needed if the (constqqhtdb .t+ h hb..-qu q2gvc7pg8p/.jant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can buonqeb(r t,0 xuw.3:dafx/2.k5 qarye rst 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 the average acceleration of this sprinter, and how long does it take her to reach that spe03 ot.e,5/que xa x:kqr 2(b.nfra wyded? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in d*x(54cy pjol6.00 s. How far did it travel in that time? *4 5y(xcpdolj   m

  In coming to a stop, a car (mwp3g(sc mt *leaves skid marks 92 m long on the highway. Assuming a decelep sm(cmwg(*t3ration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a7nw2 oe3xk;d 1 ,aljoo 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 d3x1 woo eo;72j,adknluring 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 stoppingkqe g (03pe+if )sg6sc distances for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an accelf+0c)sqg gke (36sipeeration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation5ye 3z3 lkb6tzi9 *afsh,vuu9 for 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 2c-u s6j h-got+5 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate at 1.0 ts6c-huo +gj-$m/s^2$ 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 10,0h8z r;r9c ;oxb00-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must c8hz;;9brxro then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving herp7 4g dq/g.ew23fxlni car at 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and 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 intersectig7 xw2i dn.l4/gef3pqon 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 clifvh1 nyz84sjl -ae;hn )f. It hits the ground below after 3.25 s. Howh;nl)8y n zsvh4-aje1 high is the cliff?    m

  If a car rolls gentlm 5ux*rl pq/rbfo(2ep:, k g0xy ($v_0\,=\,0$) 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 22rikv /x hbke9ux(0 g:9 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it ve89devmld 1g:h,o xh 8ertically upward. With what spee81xe,d 8govh em:dl9 hd did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falns w c6e:s(h1o4o7t1lsd gl.uls under the influence of gravity. Draw graphs twog 6(lu1 7hc.:n1oselds4sof (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 height of 12ay 8rxn4 am/0x5 m above the Earth, a package is dropped from a windoa4a0 yrmn8x /xw. 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, lddfarrn(9 vkd1 5o cdk1.g-/show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This 5a-rk d1ndg o.lr(9 kvcf1dd/was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algeb kr:h,,+/ngl k-ytlkeraically) that a ball thrown vertically upward,,+kkgl: -n/ hty lkre 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 wb.;yv 0okts 5nnb y/9jith 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 apx.. qq e,fsw7yple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is abos.7 fw.qxq,y eut 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 2.2c6 n;(hw73 bylzmn 06u vec1ir m tall (Fig. 2–32). From what height above the top of the window did the stone 0u( n6l vczynh i; e13b6m7wrcfall?    m

  A rock is dropped from a sea cliff, and the sound of it striking t:t:qtuxb9 .+d h )c(f14vvh.trlx c tahe ocean is heard 3.2 s later. If the speed of sound is 340 m/s , howh)qv : x.t t1cbldf4tucx.v(ha:+9 tr high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard streapn(d txer*/ 8mm of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fid/8xmrnp* (etg. 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 the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/sz9ki .2)rt.z5 ,eodtxuzyehtp)+ lj ; from the edge of a cliff 70.0 m h9z5d2p). tozzi elry)ju+.x ;kte ,thigh (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above tygrp:+:gom5; k7 4drs6ysm c*vk2u cu he street with a vertical speed of 13 m/s If the ball was thrown from tuumkc sor26 gg5src4 v+*7km: d;:pyyhe 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 t:lx svcc;uoh fd0 8p*mc/uk-z+(7xh l rain as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if a-o hu:kxl0csx/;mz+d 7 ccl8 v(h *pfuny, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time is plo1r ns8mx9l g;f5h(fvptted in Fig. 2–28. What is its im ;pv 1l5s 9h8rfgnfx(nstantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can accelerate approximately as sfy,ay6ka569o sz *u5/dd huyshown in the velocity–time grapy9dsyska,* ua5665y z od fu/hh of Fig. 2–35. (The short flat 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 averageovrcd,.d+cs- -9oqutqnc *j ; acceleration of the car in the previous Problem (Fig. 2–35) when it is in crtdo9c oduscq,+;-- *n qjv.
(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 traveled during o p1- vkx4wtz2hwi 1,o
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t ggk3o 999ji m j2shnar w:ayxbr22o8zjd16ca, raph for the object whose displacement as a function of time is given by Fig. 2–28. 2h zda12 ns9jxa2co , w:96j okjr8riab3gy9m

Figure 2–36 is a position versus time graph for the motion of anhm d5 *-mz v-ahx2:nmt 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 fromnhh5 tz2md* m--:vxma D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourt:v4;n.ac yi)w); ilrge-awr xh-story window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. g cxen;4;l . iaiw)v:-)raywr2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it8hk h pand*0 b8unkjb g8;qil6w) w/;r 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 6hb88 r8*b) anjld0pi/wkkqgunw ;; hvelocity?

  A person who is properly constrained by an over-the-shouldero /g4j,) yymsv seat belt has a good chance of surviving aom s,yvy/ j)4g car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing 0fsv8qu tb 9 ,wfbnvkav8+c wy )/z,.qon a bridge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he meas0wasv, 8ytz,qu vvck/.) +9f nfw8 bqbures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer u o;:c,jp/vo 3zp7tr wtested its cars for front-end collisions by hauling them up on a crane and drzwpjct, o3/;v:u7poropping 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 ti(zwa cy 8j((q/t ;fcfravels 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 anjop2py 4lqc372 wih; cceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m ;3 4ohj 2npl2yqw7cpi 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 oh0rayu/p7i . board 4.0 m above the water’s surface into a deep pool. The perso y a.poi07h/urn’s downward motion stops 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 ba nhgjv5y6d*cew. x 625ndnobmwkm/2 fuf,r5 7lance the average speed 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 /.cnbd 6 ogjdfxn55,kf 5nyh2*2m 7m6urvwewtrain to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight down whe 4n8*p 4vj0;0aftf xqyy5chbf n 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 miny;n0fq4f48ja*cbxpyv5f0 ht imum 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 v sw 2vbh+z-w(hk 8op2a3 qy-qball 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+ws-3 q zo-qkhbav(yhwv22 p8. 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 constant speed.pgg 2ymie-p7o qg1/o of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest .oqoe/p 7gmi2 y-1pggand 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 pzm :,tn/*5wgqfbn3 cstone is dropped 1.50 s later. How far apart are the stones when the second o tqmc, g/ zfnb3:n*wp5ne has reached a speed of 12.0 m/s ?    m

  A race car driver must azuv9zry1og2 stom 0 :3verage 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h gu3m2ztr9y1 vooz:0s . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France kg(e* :al xmzf*ez1h3crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his (zhg3*m:l 1e* feazxkspeed 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 trampolines. The first child can bounf0( 4(nvk;0yqa )ahy bges ;aice up one-and-a-half)snaif4 ;agv(k a(;y q0 eyb0h 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 onle6 x (jr+jadsh7n ; m4p0qd3vertakes 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. 2–43m (0 dnnplj rxqs adje+h764;0. 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 wn/3 6*w0a sccxuyfcn-ith a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a nxy0 /u6s-f3wanc*c c 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, fromazpt3 i,(i kfari)b;y b8 n;b9 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 interrc va s r n/ug,t5z/k)-yv;d8)qw l;xvsection has a traffic signal, and the sp/- ql5sw r;czvvd /)gu,n y kx)a8;rvteed 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 constant 120 km/h t h -wr9pacob2 up39;a6kd;s+sn/z8g mp 0nsyiakes off in hot pursuit. The police officer c a un;9zoss ;/+ 9nmskhpbi8rg 30-wc ppy26adatches 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 roofe:n(m:2 yalxm of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25eamm:x (l: 2yn.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The first stone is thrl+tri)n.x2 : igg ofn.own 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 the second sto.n+2itxor i.gl) ngf:ne 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 loniqa hgu1u p8;;g would it take a free-falling parachutist to fall from a plip;gua ;q hu81ane 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 to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgoe1s k(l nj26sw9bth :ers 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 productijw1e2kb9s 6ol ths :n(on (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 timeat3 fq7vj 7-hcs faster than Joe can. How many times higher will Bill’s ball g-qj 3ft77hvaco than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while 9gv7xd5.qy iq* pa -ooyour 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 throws it up to you, such that it just comes to rest in your hand. What is the spei y d -po.qoa*qx9gv57ed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a : u-b,;x hx4zy)rxfq iparticular 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 r u)y,hqxfzi;4-:bxx estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, vuva.kgkqbm8819s ( yA 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 whicak qvb k1.9 s(vmugy88h 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?