Does a car speedometer measure speed, velocitye4q nl+;w, 3ee(kij+cq si2 bf, or both?

Can an object have a varying speed if its velocity is constant? Ifsg2h7vcf/ph jg7 7,vy yes, give examplespvgh vc g7hf2js77/y,.

When an object moves with c4sy 86qkrec-sonstant velocity, does its average velocity during any time interval differ from its instantaneous velocity at a yc-ek6s4rs8 qny instant?

In drag racing, is it possible for the car with the 59 wm,axxmgk 69ju q: i1*9 hls4zuvdxgreatest speed crossing the finish line to lod9 x4isug16mqwa ,m9kjhz x9v*:u5x lse the race? Explain.

If one object has a greater speed than a second object, 8 n,s.j d+fbh5g4,t2 jqrjenmvr2 ox4does the first necessarily have a greater acceleration? Explain, using examplm2fjsdv4 r gbher nt,q. 2oj5,4+njx8es.

Compare the acceleration of a moto(kk)+r xcfk ;e0nwmv/rcycle that accelerates from 80km/h to 90km/h with the acceleration of a biw cf/n ek(0;rkx)+ kvmcycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velociv8upr -n vmk8m cz:+j)ty and a southward acceleration? Explain.

Can the velocity of an object be negative when its7sv1prw w+c2hh1z5y n acceleration is positive? What about vics hhncvw12+zy 75rwp1e versa?

Give an example where both the velocitye.zcc 2*yc lx7 and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is trav d15z0oam.+dzv5 jdx:lo q-wr eling with a speed of 60km/h and has an acceleral:vjmzaq zd5od ox5w.+ d01r -tion of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be incu, j/cs z,r90p aikf1qreasing in speed as its acceleration decreases? If so, give an example. If not, explairp a,cf,9i/ j01uskqz n.

A baseball player hits a fo r :0ga 29lmtfo j5rb*2vlz epx6e.r7sul ball straight up into the air. It leaves the bat with a sp bzsmx 2lvo0 rl 62rr5e.j7taeg pf9:*eed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acceleration kt8 gso6zz,( 25bi*irdji+d u due to gravity — does it increase, dbdd2(856*gii r,t+jikz zou s ecrease, or stay the same?

How would you estimate the maximum height you could throw a bj m,t- i:p0;h efgy7ay-gurz)all vertically upward? How woueg 7a, y:try;-)juz-m 0gfh ipld you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constan3*me7bxhxe f+cf hi5yd6 2d0q t 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 q 32 ie6hbf+xd5emyf 7d*c 0xhto C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten b5nzb mi4v 5y,golts 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 cginbz54v ym5,ould the bolts be tied so that the clinks occur at equal intervals?

Which one of these mo nsfc / bqd0cel-50.yxtions is not at constant acceleration: a rock falling from a le /nc 0 q-.5byfdcsx0cliff, 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 vertzs 8 h;vguln99ically upward will return to its original position with the same speed as it had; nhzlsu9v8g9 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 opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at th*sw( r me.u;mke same time? Give examp( mr.uekmw;s* les.

Can an object have zero acceleration and nonzero velocity at the same timedfer ,n:d2cmhqls8 p8 )bd.* v gck)1ovd)s2t ? Give exampleltrds*q.1 d)v)m8ohd:pf2 cbvne,c)g 28s k ds.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [Hi *yfgtgc14eo /nt: First try to duplicate the motion plotted by walking or moving you*41 tey focg/gr hand.]

Describe in words the motion of the object graphesb t;,e1 tq/l(s0efhd t2vo2aq 1faw+ d in Fig. 2–29.

  What must be your car’s average speed in order 0bm;1 hsib ad.t 5,u8kiftj1o 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 km? czkevv5:-( 0a: ewox -wdv e6llu )l3l   h

  If you are driving along a straight road and you look to the side for 2rm7pv qcskdkq9s 5- *a*5cl h1.0 s, how farh-1p55r*ckavqcd7ssm9 * lkq do you travel during this inattentive period?    m

  Convert 35 mi/h to .92krn4fqog w q8/psr
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from ur9lhcn i xy-. i*gqpx5-; ;yp.,zpi f$x_1$ = 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 fro ug5e0 j3hlq0 1qwtz.fm school steadily at 95 km/h for 130 km. It then begins to hqje 30z q.tul 15wfg0rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightning 4;8-u -piuwk 94eulaf ber) iaflash and the following thunder gives the distance to the flash in miles. Assuming that the fpfi) ee4 i9b84aku lu -w;uar-lash 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 quauhm.gdair.utjmj l/ 1 aid62 3 dl).t.rter-mile track in a total time of 12.5 min.m d.) h..dliu2 i.61 ljd/r uamatg3jt Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away f kf-0kdq8j qa (+wib1brom its trainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfw(-q f8kjdbb wkq0 i1a+ay 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 othdvdq, rwe1 2j,er on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If2 rq, ejd,d1wv 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 traveling7qd: kunv9ff0 How long will it take the car to reach the truc0 uq9:knf7dfvk?    s

  An airplane travels 3100 km at a speed of 790 km/h , and 2* hf zlo8, b8h jncd721gymoythen encounters a tailwind that boos ybn2fmj hdo h7l8c1*2 8yz,gots its speed 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 complemhzp/ )sz8.6xdze - qste round-trip in which the outgoing 250 km is covered at 95 km/h fox)s.qzhd/8- p mz s6ezllowed 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 sp jzs. *b+5kvapeed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 .zvka*+ s5 bpjs 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 acceleratestcmi ) w g)usf-6-w70ghv dmr8 from rest to 95 km/h in 6.2 s. What is its average acceles- )f hm wcr-)dgwtim8uv0g76ration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceleratio, 8ie nrhzpe.1n z,n8 peh.i1re
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particulzw5gpaw+8-uek t 0f 2mar automobile is capable of an acceleration of aboutawugzpe t5f8 2+- mw0k $1.6 m/s^2$ 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 v1 wq9 t-y8 rpj;geeceth3 --hconstant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, wt ;t 8h9-cjpyrv-w3 egh-ee1q hat 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 8lkk3+gpu -uucow ( k.at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its vekcu8 o(u-uk l+pwkg.3 locity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates frmhkg43 9a8ha rom 13 m/s to 25 m/s in 6.0 s. What was its acceleration? How far didg 8r4a3 mhak9h it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its accedi8/r+oz 6bx3m3h nd eleration, assumed con deh/6nmr83io zd+x3bstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s mr (2ew0dh7(s8tl8rnkrb3s x for takeoff. How long a runway is neederms2w0( r8k7h8tdxlr 3s(neb d if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks v9)+sx j1tbjczzw;.9q ukw ; sto essentially top speed (of about 11.5 m/s) in the fir9 ;.ku9)xswv z1b;tc q wzsj+jst 15.0 m of the race. What 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 2dw2:ilqhd+ guky-f4.00 s. How far did it t2-d: i4lg hyd+qukf2wravel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m /96lr )ne, qsjf 3ay 6yw/1j0nsrnu- za,s vfllong on the highway. Assuming a decees 9,f zf-sa3j)yj1wva/0 qrn/nu,ll 6y6nsr leration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front en0:989 mfq-tehkxrj l2t 9y nczd 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? Express2y qh0k99t-l:jtcfn9xrz 8em 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 distancesu-6ckr- cnuk; for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an ac6--ur ucnckk ;celeration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the9nat rkq/8 94tem)kzv 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 gos6y me4k+ cm/jc ea+v;ing 25 m/s on the highway. The car’s driver looks for an opportunity to pask+e/mys cc4+v ;e6jmas, 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 mi7gvk n kk78:knn. After exactly 27.0 min, there are still 1100 m to go. The runner mkk:n g77n v8kkust 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 ) eeukua sip 4/y ldqx6- ;ibcbr3++1ian 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 intersection before the light turns red? The intersectiona 4i sydbr;6bi -ql3/k+ )c1xeipuu e+ 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 zhlzky z,3/k- a cliff. It hits the ground below after 3.25 s. How z/kk,h-l3yzz high is the cliff?    m

  If a car rolls gently (tm6gir 9,m pf0$v_0\,=\,0$) 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 vk;(: krids0b straight 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 catchesa1c(k scj1 90x g5desj a ball 3.0 s after throwing it vertically upward. With what speed did he throw ig5ec90jjssk1dxa 1 c( t, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under teh4tx:2c*blthe influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 tte4hbx :c2*tlo t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a sm d1n c7l.rhb0peed 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 pac17c0.nlrbdh mkage’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show thatbwk l)pu)p -y6(r2k*qxbb 1 ux the distance traveled during each successive second in)upb1x lbywqxb) kr2p 6-k*u(creases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, siujg i5 /7.3 doyih,zbhow (algebraically) that a ball thrown vertically upward with a speed hb 7o3i.jig dui y/5,z$v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed85 0suhcey c /0;jjkoz 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 phot(a ) wy5w((u;v*rpd d*govcehoflash 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 ew 5 pcyu horw(g ;v(*)da*dv(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 2.2 m tall (Fig. cq ooxs6l 9ob+5.q l0f2–32). Fro. lx+o0 fqo65 b9qlcosm what height above the top of the window did the stone fall?    m

  A rock is dropped from aaixy70gn:9 n: zrko0v sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sog:yikrn0 a 0nz 7x:o9vund is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hosekirrga+i; iw 6.v:,h+wxvtef j*; g1i nozzle 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 tkg a:r6x.j1* ieri f+hg ,wvivw;i+;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/sl8l ,fli c0ikx 0)rzl4 from the edge of a cliff 70.0 m high (Fig. 2–34).f,l 8 ri0l4l)xzcli k0
(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 fk9y,kz;f v xhv/gmsm1 kt;t,h(-z-f, t7ayythe street with a vertical speed of 13 m/s If the ball was thrownthf;ag- /, k; -ktmm1yy h9tf(,yvzf zv ks7,x 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 func+ b- hbdf4xu+0 ltbj99n9hz antion of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, id9b4+na zj9+9nbb0hhl-fu xtf 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 func9 h:g+xty)0qki7 cczrtion of time is plotted in Fig. 2–28. What is i+qrz0) 9:7t cygihxckts instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can acceleralws-pa 5,dz6.rggn jcl, :t( ote approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve rep: gdsl,lng(a-p ,wzrt oj 6.c5resent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Prulj ekh8*qt/ 5to6. * tdmg.nwnm8ca)oblem (Fig. 2–35) when it is in m*o8m h aj t)u8 c/el.ntnkgqd 5.t*6w
(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 traveb oybp+b2azd(-y; g:xzt;y- n led during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose d*w+ax; 4udtz jisplacement as a function of time is given bj ;x4z+*tuwday Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of( /kh) l91k+vkhwtp il an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in pihlv+(1kk k w th/l)9the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a ;x4l)6cvmpkl3kbw kg, 8sjv ; firefighter’s safety net. The sgmbvj8pls 4kw; v3; cl6 kk,x)urvivor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is aboutkwum0.xt eaep)2uuq .i) och 2rp+:8w one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same ineu +:pae)u c.w 28w)kto 2hmi0rpqx.u itial velocity?

  A person who is properly constrained by an over-the-shoulder sez3lg, k of ;+dnesqj6 *9, u1zyncyq9lat belt has a good chance of surviving a car collision if the deceleration does not exceed agno ln1ye yl* qd k9z6,+3u9qczf ;,jsbout 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 kgj/mqi ct 1*.yrr6e: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 measures by knowm/6 * r:qc1eiykr tj.ging 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 cn;m*ri n3gk r1d8p0hrars for front-end collisions by hauling them up o;rd*ig mkn380 prn 1rhn 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 eqmcfwg* qx m4g8p. *1travels 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*ng. lw9ll 6na uniform acceleration 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 from where the w*n6nl.g9la lfront 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 surface1j2y 9wy48pvulo yp:1vghq y( into a deep pool. The person’s downward motion stop9 h yyvvlyq1w28ugj:yp 4o1p(s 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 lnmk u.ie5t 2z)*0qvxsk,x53t2(3 md avtt vlis necessary to balance the average speed of a train agauv* 2t vve(kn 2llxa0 s3kmt5t.ztdmx5i,)q3 inst 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 down when dn:bwb 6tm8ohacj, . .c rg;/zriving for fish. Suppose a pelican starts its dive from/ nr8c;:.rma., o6h tg bbzjcw a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikfge:) :gq8 kx4xg4ewbes 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 8:ge:kx)b e xqf4w4gg 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 ho qwnt bu5n*)k,p on a freight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and 5 nukt, w)q*nbaccelerates 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+ +x .* aox i hardyhn2.ilk)e25(5xazqzzju+ roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a lx52 y x+oh(* a25r.kx+n)hz+d qizajziaue. speed of 12.0 m/s ?    m

  A race car driver must average 200 qc o0t9/qtym2hnm6u; .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 . wtm09ot6cqmu y /2n;hq hat average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as hxg4- y :a1rdate moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 k :41aaytd-xrg m/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playinw9 3u e dmcfgt* 6)f3pdsy:wq3g on two trampolines. The first child can bounce up one-and-a-half times higher than the secwe)3f q3fm9 y3 tcsgu6 ddw*:pond 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 overta cvo7/e svvm ,:kyh5u,5 e( pyghw1;aikes 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 havepomk ys ec1/( hw7ue;vvi ,g5:,va y5h traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/s In throwing z7. ar2 audoh98qyg2kthe 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 motion qz y7ga82.d29kah our.    $m/s^2$

  A rocket rises vertically, from rest, 1jjfe-lbr 9d .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.ss ho.l-eed( j 7wc8(y 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 you are 10 m from the first intersection, all the lights turn green. The l.y od8-(ls(e swe7jc hights 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 s )njcjfjg 3)ov/l1x ;lpeeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintai xf/jjc v13 nll)oj;)gning 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 46zogw3:09 iuv- y8z qwmtjzobuilding; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stonesq0gz w4zz u9 -ym3wji vot:86o 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 gf5:j8 fri+0i2c8bk0 lgr zjlurq;h2v z1 )knwith an initial velocity of 11.0 m/s from a 12th-floor balcony of a build : ;brgk zv5lgi828hij2 f )fcr10q+0zurlknjing 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 wbv8sk;.88h y wgylasn vi 3h:;i f,g4pould it take a free-falling parachutist .8vs4w:hgbp ya8vk, i3gisnh ;;fly8 to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a g,uy*2tvq1t i rrilling machine. If the grilling machine is 1.1 m long and tu 2tvqyt, *r1ihe burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a ) ;jxp bzis06tg.zpq8speed 1.5 times faster than Joe can. How many times higher will Bill’zz0 6xs)t 8 jp.;qpbgis ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground3;a -)zrzw. yvgi))vyi w5rxy below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Youryw;wz ygyx)zv r5.i- i r)v3)a friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to fingt7od1*fnv/c n3 q/ vsd 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 fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s hein1// dqvv7ston*3 fc gght?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) I- osu ypn;,2r*6yfynms 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 otheo; nyyu6 rfs2pmny ,-*r? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?