Does a car speedometer measureptdf t5y/k4c+ speed, velocity, or both?

Can an object have a varying s5l(nj9 2,xh m btou8x5- q cl*kq1zxuupeed if its velocity is constant? If yes, give examples.,2mqluu1* l( t-bnh qcxjo9xk55zu8x

When an object moves with constant velocity, ) s;m*axjgj ; /c7xqs ) 4zwo.y2zjisrdoes its average velocity during any time interval differ from its instantaneous velocity at any instant?xs/gzr*)xcj) .yms4z7 ao; 2ij sq;wj

In drag racing, is it possible f 2y2/p9e r3gzkjow-s (h ehp*lor the car with the greatest speed crossing the finish line to lose th39s -welpz*2jh2 h(y/okprge e race? Explain.

If one object has a greater speed than ac d5zgxh;f*p, second object, does the first necessarily have a greateh p 5c*xf,dg;zr acceleration? Explain, using examples.

Compare the acceleration of a motorcycle wo:v*j5vh( my that accelerates from 80km/h to 90km/h with the acceleration of a bicycle th5vw ym jv:*o(hat accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleration? Explaiq97 0 9*a;qtxhbqghwspbn :5on.

Can the velocity of an object be negative when its acce yomwxs lw,/c-s9.e k6leration is positive? What about vice versake xwwm6y9l-, /. ssco?

Give an example where both the velocity and acceleration are negatikl1ank 6x8cg4ve.

Two cars emerge side by side from a tunnel. Car A is traveling0uz v8 wdgp5 sv c-z4it1v8n.w with a speed of 60km/h and has an acceleration of 40km/h/mw 0vv85g t-ipzdsz c1.uv8 wn4in . 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 the tunnel? Explain your reasoning.

Can an object be increasing in speed as its tmch.yp9 ;y w;acceleration decreases? If so, give an example; y;hct9mw. py. If not, explain.

A baseball player hits a f8 pe//rx 5 s,pbh,tzdlrf) o*bp +zey+oul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence e*tpfzb),xh yzd p8r +,l /bpor/+5se of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, ww:o5 wi 3kj-ujhat is happening to its acceleration due to gravity — does it increase, decrease, oju5owk w:-ji 3r stay the same?

How would you estimate the maximum height you couldok s/0pj;og7 r throw a ball vertically upward? How would you estimate the maximum speed you could gig; jros/07p kove it?

You travel from point A to point B in a car moving at a constant speed of T2met.u*-r h x3: *qul(koubr ehen you travel the same distance from point B to another* -rtb*k:eu(u r q2x.le3umho point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstratij3gf j fx7gb.0on, a 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. f3xj70g gfb.jWhy? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant accele8-nn3 dd: hdc:rju;hdration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops alon8;rjh ndn dh:cud :d3-g the way, a dish resting on a table?

An object that is thrown vertically upward will return to i*ta+lh(rggtd6(t*.tz4 *l+ytam)hdcmd3x g ts 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: Thd *4 d.lgya3g+()6 (tt*dxzhhct* lm +gmat rte acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceum og5t4n,z: d7isg3p leration at the same time? Give examgnt 4uiz g,d 3p7so5m:ples.

Can an object have zero acceleratio 9 tn5yhrfh6 ud09i.vmn and nonzero velocity at the same time? Give examplt5dymi0u r hv9.hf6n9es.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a0usr ,d8u5dvq, etc. [Hint: First try ,druvs q u850dto duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed ys j0 .ydlvx+ml6l0j/ in Fig. 2–29.

  What must be your ca-x8 obny/amep 87fpb 6yh7du3r’s average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take l,h36c1 ecghrto fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 g .jg41wz/fu0kyx- qq s, how far do you travel durink wqx.gf0j 4gq/-u1zy g this inattentive period?    m

  Convert 35 mi/h to a:,-vfrf/c3iz,pq r5h kd:/ l b9 azor
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves froty(i+w z/:jn - -ktd,phc jh-im $x_1$ = 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 forjs*fy9-6n dc 6ik5gwo 130 km. It then begins to rain and you slow to 65 km/h You arrive home jk*s56cyo6id 9wf n -gafter driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightning fhf1b b4ihlwe9 xk5w8*lash and the following thunl 5k4*wxbh wehi98 bf1der gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-milm:5 weh9ug 1pke track in a total time of 12.5 min. Cal:u91mh ew p5kgculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line jki3/g b+ug 6yi+ei.z, moving 116 m away in 14.0 s. It then turns abruptly and galy i gk./e6+3iu+izbj glops 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 hasj;i g*hq:1fsqx,j hh; a speed of 95 km/h with respect ,sh ;h*q:fgxqj; 1ijhto the ground. 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 travelinkzwp:tu) r t12g How long will it take the car:zkw)t2up 1t r to reach the truck?    s

  An airplane travels 3100 km at a spee4f3 fn doh ;* - pwnm+m*2od(bnou2t9t my-ggyd of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h f+numofo(hnyd4w f2bmp t2-;m9*n oty*gdg-3or 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 avb(2 k4aqdm s,/psw k1jerage velocity of a complete round-trip in which the outgoing 250 km is coveremsqs kjkd(w2bp4a,/ 1 d 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 th r 8x)f-d9hup7jibfv3 e 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 sfp i-bx)973v df8hujrpeed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its averag3:mv 4wp:aa .fo-n fhwe acceleration :f3 w pf4whv.naa:o- min $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceleratb0w 8al2atg6*eyw z8p ion6e0l t wzg*8a2paw 8yb
(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 w4818 pqvsi w(bwa2nbg3-9ug etx/xe acceleration of abouw 14-w 8eb3e s9 g/ anuvqxpg2iwb8t(xt $1.6 m/s^2$ 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 travelswqd9f+ 9533yqdjd zo xu,ei-t 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accelzfx 3,-d w+j 3d95q9ti dueoyqeration 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 rxdkr 8 jeci 8 *,rkqzr0(t3p*car, which starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following ,ki0rx q(kd*t ezj c*prr388rTable. 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 25 m/s in 6.0 s. What was its acfu6ut7e -xk /u;rv: amwz-4caceleration? How far did it travel in this time?aft zmecuvxw7 ru/u- ;k-46 :a Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 8 b8fzf*lfr8z5 5 m. What was its acceleration, assu5r*ffzz88 bl fmed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runf;; 5q,5w5eatvmn xbsway is needed if the (constant) accel 5xm5t5qawbn ;,e;s vferation is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essenmwq-ex4n )j;sfk)w) g p7ugc.tially top speed (of about 11.5 m/s) in the first 15.0 m of the race. W7-q. )nkjxwu f4)p ) sem;gcgwhat is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How fardnnu.4f6uid v 1b7z xo4a rx09 dion4fx9axd 1 d.ur0u76zb4vnid it travel in that time?    m

  In coming to a stop, a car le -hvrqzyr35*d aves skid marks 92 m long on the highway. Assuming a deceleration of5rqr hz- y3*dv $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car compresses *xrpkdm t6d-, and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the colli k,dd6*mpr tx-si on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car wil4 z 50orc 6uz0ccd. 6hjsi+s5sfts.fth an initial speed of 95 km/h and humafj4 + uccs.oi 6c65zfl5z0sthrs0.ds n reaction time of 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 distank /(x l ksa5:6qmw g3j8qp,wlsb ;qyb0ce 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. zmn,)gxpvth 0tl43 r-:0bfmc The car’s driver looks for an oppo0 t-gpr): 4fc vmh 0zmn,tbx3lrtunity 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 runvorh l xb:j.ij 8/7qb8 in less than 30.0 min. After exactly 27.0 min,7 /jhvlxjor:. 8qbib 8 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 inti)4w3e ib5pst* h:sj gersection 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 stb:i3g i5pj 4h es)t*swop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below aff e:fv/d71t-5srf(,q a)4ut uexwojo -guw e;ter 3.25 s. How high is the cl4 o:t ,7vju/ dfes)trux-;u1-wfoqewf a eg5(iff?    m

  If a car rolls gentl3nx-r- iglpnod0r pu0f ,wtkk9 41-tob tv).ly ($v_0\,=\,0$) 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 strahi2qj)(mftp+n je a:3kf k0ics j2c61r5q 2gwight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it verticac2l 0jiv acobrf:pz ).j 3nc6v+k .m)zlly upward. With what speed did he throw it, and what hez0 ) .z+vf3cp njci:2maj rk.b 6lv)ocight did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw g:xzg(5z jl pl0 :3nj; thcte)vraphs of (a) its speed and (b) the : jzzl)l jct h:pgnx;035v(te 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 ou, wupalm lkxn. ak8l:+316 jazjjc;hu.5y6 vf 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 equals pkxh,zc1l8: y uj5ma;+auv wj6. lkju3. n6lathe helicopter’s.] t =__ s

For an object falling freely from rest, showm /e/bvkad-n7j (uhd; jf/m 1p that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–11mbej/fd j dhm; (u vn/-7pak/8 and 2–21.

If air resistance is neglected, shx(zdv 5ajc:q9 ow (algebraically) that a ball thrown vertically upward w(q za9cdv5 j:xith a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a sp;p3if 0 c8s2inknt si0eed 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 earo6 )*la6 (ndo3sri tjch photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two applels 6a*(3 njt6i rd)oro 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 2.2 m jbu+m6x( g-i btall (Fig. 2–32). From what height above the top of the window did the stone fal+m6gjbxbi-u ( l?    m

  A rock is dropped from a seavltdksh.1 2cre 8 hu8j.gls 7) cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound ihlks2 c.v t7eg1) u8sr.ldhj8 s 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You point ,.)gnfcg+dtw 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+cfd .gwgt,n) it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a si))whr.21 wlmupnj b1peed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2–3 l1jh.1)wum)irn bp2w 4).
(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 passw4svv8so.jv y7qm t; hcv04(3qg1l bh upward by a window 28 m above the street with a vertical speed of 13 m/s (vvvqy 8stsq1cvm3h l.4;7w4o bgj0h If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a)e,l7myhi/, p h vwd/:p At what time was its velocity greatest? (b) During what periods, if any, was the velocitpwlp d7 m ,y/:i,eh/vhy 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 4b6a4l awy 4/v,tkuas lvhe55plotted in Fig. 2–28. What is its instantaneouklu6vaaywl4 t/4eb545s a,hv s 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 shown in9, o+x9tntrb q the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the+xto9nqb9 ,r t 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 acceler l a ltto+lb1+h:dqutjin2/) *ation of the car in the previous Problem (Fig. 2–35) when it is in olabhi*ltdl):u1t n 2++ /tjq
(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:z0ih oat 1nljj2ii86 the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t gpxq2 xz95ox71vdscr, raph for the object whose displacement as a function of time is given by v7s x ,xc rz19oxdqp52Fig. 2–28.

Figure 2–36 is a position versus time graph for the mor rwistmi7 2i x-q-fq*rv dpmr3t*0)+ tion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up -iq7r-r3+f t) v0q*mw irximtrp *2sd or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s saf; k0* h x;tnbe7 te:2qy.nhzbdety net. The survivor stretches the net 1.0 m before coming to t e;te7*bz nkny.xb2q ;hh0d:rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on E :(d0*rxskku.iczrx 65d8vl6 rn)nf m arth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Eaclx zs:n *xddk5(ur.fni r)vm668kr0rth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulds y3j p12omd/eer seat belt has a good chance of surviving a car collision if the deceleration does not exceed a1j dopm/2 y3esbout 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 roa) ahheqe o (p;+v6 ,rt9dl w5ljddg.v+d below, and his pursuers are getting too close for comfort. He spots a flatbed truck a w .l)dha5edrlgp t;j ,+vhe oq(69v+dpproaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer te6*fj p-.kqbn vf ixf11sted its cars for front-end collisions by hauling them up on a cr fxp1f6bjf qn k1*.i-vane 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 trav-nkjcun2c3f *j k2 -hlels 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 reozhp;y/,-t- 2a ,lsablm(wz bst. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the frontst (w,pb oyz;alm-l2-/,za hb of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a deep ae6j;cmqdp )) pool. The person’s downward motiedja6 qm); pc)on 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 syst)sf xy;r t5gwj/ek7 3cem, it is necessary to balance 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 train to make a 9.0-km trip in two situatifrx)t 5 /egyk 3wscj;7ons:
(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 falo.)w)d90ey n 0s- x jikq,pbnwl straight down 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 esc,)ww.nyd9 0ei0 npoqk bx)j- sape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer stri55kv0e 7haahsg-1mvr kes 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, 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 const h15 avhse-rm5a vkg70antly 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 const u/o(2773yzi*vw0afpvj)buv n x/dn y ant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest anov( 0ayzj/7i/ 73*wv yx vupunfdb)n2d 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 37x v vw8v7+gl)wswap888glk ;qvpaxstone is dropped 1.50 s later. How far apwvg88s;l+ kwvpvl)7aaxwg3 878q vp x art are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over g:/g0 inrhh:mthe course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for th0m:hgn:g/ ihr e last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18e m7n+nwpay5qgu2bu;g/u 2 , j km/h . At the bottom, 4.0 km farther, hiugqu2m n ue a;/ybgnpj,+752ws speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child caiigut1 dg7z,1n bounce up one-and-a-half times higher than the s,i d1gi tu17zgecond child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train travelkmg9co9z g7lvz d/*o9)c/d ni ing 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 t zkdogdml9ni/zg *cc 79v9/) ohe 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 bat-e;xoduf+ haik1) -eseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing-;+ u1d ifkh)- xteoae motion.    $m/s^2$

  A rocket rises vertically, from rest, with an acceleration o goiog0i0;bfnm n6m5)9 yrv,hf $3.2 m/s^2$ 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 p e y;fm/ d2ycky+k*u0pattern shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When;kdyum2 /*e+0 ky cyfp 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 tuzj1dyb8 + ap+raveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant accelerati8j+ +d1 ayzbpuon.
(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 ua u6 ,0rc*35xta7a)o)boo( f ahn qrxa building; 2.00 s after that, a second stone is thrown straight down with an initial spe3 x6ur)x 0aq(hroan* a o,uoc7a t)5fbed 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 up at the same time. The first stone is thrown m ( se/r26pktqwith an initiaq6s t/(ek2rpml velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-falq3sydh9 yy9mq kqe2avf v69 3;ling 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 r ;qy93dk6a2f9ve9q 3smvy q hyeality, 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 burg6uszizhv-j: w p:xj 38f cq1;fers 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 convz:8; pi :zvj1f 3whj 6-fsuxqceyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe cuo8f;r w r)9pdan. How many times higher will Bill’s ball go thdwf9;ou8)r p ran Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of c -u8mepa y1)ia cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is t amp1)u8-cye ihe speed with which your friend threw the ball?    m/s

  Two students are asked to find the heighdtz53w v1echrn6q9tv7t.r3s ;jsva )t of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s.h5a.ssr qv9ve 7d3z)6 nt tjcr;3t1w v 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, ix/os.xu dqv5;4 dks for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicud;sqv/ 4o5x , xisk.dycle has the higher average velocity?