Does a car speedometer measure speed, velocil.v 84w;rqxv zty, or both?

Can an object have a varying speed if its velo9ixqk53jifya9)rq(up+ 4 qtfcity is constant? If yes, give exampl9xi3 4t9f (riqaqpkfqyj)+u5es.

When an object moves with constant velocit x. lc8thqm+q-y, does its average velocity during any time interval differ from itx qm.-tl8c +hqs instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing tdk rrj2)xy6e yj( 0/eear*7tjhe finish line to lose the race? Explajaxd67 jk0 erej/er)(tyy r*2 in.

If one object has a greater speed thae(c knig xm:72n a second object, does the first necessarily have a greater accelerat (2ic:nxgemk7ion? Explain, using examples.

Compare the acceleratiwsuvp6z- ;ly 7on of a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/upw-v;7 6zls yh in the same time.

Can an object have a northward velocity and a s dix+0 0 gluw5)oajxg(outhward acceleration? Explain.

Can the velocity of an object be negative when its accelehe) f0b9g4 ta.0 avagsration is positive? What abou4 gae90.hfst g)abav0 t vice versa?

Give an example where both the velocity and acceleration 4.i ;e1tqsm xahl+drnu5c d 0,ti (.pfare negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a,b:j 52a vnefk speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceeb5vjk n,2 :faleration 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 acceleration decreases? If so, gi6j vef0m,)ot7: mpn )opo9mlkk ,y;zxve an example. If m xny l)ko;o,0pmz,: j7pokt 6)e 9vfmnot, explain.

A baseball player hits a foul ball straight up into the air. d 8jy03 yefmdiez u5,.It leaves the bat with a speed. uydf0jeyzm d5,ie38 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-/l8 exgdj )qs.r0uge speeds up, what is happening to its acceleration due to gravity — does it increase jl d8erxse-g)./ ug0q, decrease, or stay the same?

How would you estimate the maximum height youj buxw4n(97s8zg v)rx could throw a ball vertically upward? How would you estimate th7w9 r 48gjsvxu )zbn(xe maximum speed you could give it?

You travel from point A to point B in a car moving apzyb my bk2y6.;62jxot 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 pyjoxz k2y;6by 2b 6.myour average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten boltshun/l/qu,eg ;h 6; 7,,rrhqplyw /qwr tied to it at equal intervals is dropped from the ceiling of the lecture hall. The strin7g;/w,lr /hr/ uwy h;r uh qnq,6pqel,g falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleratioky.vk8et1.uifk . p; en: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a tab;..pe.t kf ik 1vuyk8ele?

An object that is thrown vertically upward will return u1rnbxnb/:1 0vr; q82tihfm301jpd 8esved pto its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, bp0 vb0/81xmr dh1fp8n ;eu2sndq ve1i:j3rt 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 the same tieof./ e4f7 jorme? Give examples. ffeoor/ e4j7.

Can an object have zero acceleration and nonzero velo zu8.f ,xrs6oftld8)a3 k6oxscity at the same time? Give ex .)6f o zoktss8fal,x uxd63r8amples.

Describe in words the motion plotted h+1xje(kk6 nrka8e/l +zwd y0in Fig. 2–28 in terms of v, a, etc. [Hint: First try to dupli dl/y+awjrx(en k68e zh1k0+kcate the motion plotted by walking or moving your hand.]

Describe in words the motio+q2ej -zngy0r1mm9 tr n of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.25l ykzusic4be-wu * mnm.x:43 , h?    km/h

  A bird can fly 25 km/h Hownwhouh v.e3,5 long does it take to fly 15 km?    h

  If you are driving alo7qyp +obw(ylkj js: ()ng a straight road and you look to the side for 2.0 s, how far do you travel during this inattentive period? 7ly: oy)s jkqpb(( +wj   m

  Convert 35 mi/h to hvcpn/xz2w9 h5,e(s.- pg h9 jdnxe3w
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves ot)*4mzw6kmuq nmj )oiak- -0from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for+wiqz 83jins7 130 km. It then begins to rain and you slwi3jqs+i zn 78ow 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 flash and /y,(iw(e.n xy2 nvkw0 j-qusi 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 speed of sound in m/s fr2we/ ni-.ywvx(iu,kjy s qn0 (om this rule.    m/s

  A person jogs eight complete laps 9 ze1b;b-u4qpdd)p iftv7 jk;around a quarter-mile track in a total time of 12.5 q)kz7dpb4 ;ef -uid9 p1t;jvbmin. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from itsf;w(ardlxld7x cb+ cm/)-xrc;8 +eth trainer in a straight line, moving 116 m away in 14.0 s. It then turndr l(c;dm;8 /te+lc w)rxxhb+f-xa7 c s 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 approach each other on parallel tracks. +ifw7+6ddgti *-v,d 4zlwxd w hwrz5n.0ah-m Each has a speed of 95 km/h with respect to the ground. If they are in*ddh,ntwzw0-f5+w7 dawmdi -h rxzi 4vlg.+6itially 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 vg.z/hoa/ d k tez71gia;:v-b m behind a truck traveling How long will it take the ce-h/7a a:zg bd z;vo1gkiv. /tar to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and thev5rn p3doti 5x.(q sk*n encounters a tailwind that boosts its speed to 990 km/h for the n3s(pxtd*ri vkn. q55oext 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete round-trip in wsw u dlll9zl0w;k9m6( hich the outgol0d muz(k9 w6wll sl9;ing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with c5a,iru b28or oonstant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of5o2ri8uo,ab r sound is 340 m/s.    m/s

  A sports car accelerates from rest (6,5grbkfh0p7 qq rib 4hm8ng to 95 km/h in 6.2 s. What is its average accele 4pqh7khq (gr85nbr0g if,bm6 ration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is hs sv8o5 dq73c;jx u7cher acceleration 857sqc ;jhv3c7xd o us
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular4n*u3z92 e 2q pttxjpu automobile is capable of an acceleration of about jq92zx4neutt32p* pu$1.6 m/s^2$ 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 con871gw s3 r-jcx( jt6cvcvl6 aastant speed travels 110 m in 5.0 s. If it then brakes and comes36av s 6cctx (cgrv-aj81w7j l to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car n*km2kk8eg(h , which starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimathm eg8 kk2k*(ne (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 1kfuo99( d5k y6xjx egin 6.0 s. What was its acceleration? How far did it travel in this time?1 5u9x jgoyk f96ekd(x Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distavrxdrt.8s bl(utzwof6i0 (9 +w -.h yance of 85 m. What was its acceleration, assumed constan -0+ht. vsdrxo i w ab(u.t6(ryw8flz9t?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How lom;95- 1dxmzjbbo ktr2 scj/gv;ob7 k*ng a runway is needed ifvobzbmojk*g;/kc2 5 xbdtms; -1j9r7 the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to *k n6nvb m.grs4 3b+dhessentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average accel3*v rkdhn4b6smn + .bgeration 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 fas7 xy t-+2ev1diztgw* r did it travel igtyiz s*v7twde-+2 x1n that time?    m

  In coming to a stop, a car leaves skid maoti sc /tsox8okv g87:1yihi:3s)p p( rks 92 m long on the highway. Assuming a d:i(o8/ :)s ioph pxg8t k1ist37 svcyoeceleration 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 end of the car compresses ra/9o51lvs9dqrr4x( i51 nt)) nf.rwhlvu x tand the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” wh45) vi5olusarr( ./x1n9nrrvt1w9q )xlf hdtere 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an in bp:;3lt.j s tqul)0bnitial speed of 95 km/h and human reaction time pstl:3 b;0qtj.)ubnlof 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 j:pzww8p 1sa0 stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The cavv;g 7;9td(, uscc6k y*c:uliyav n3pr’s driver looks for an opportunity to pass, guessicl ;63pvv,i(gu* 9c 7ytcan :;ksvdyung 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 com1-m3*4 sd +ubzneneehplete the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runn-bh *3u+s1 4nd emenzeer 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 approachessg5s 8tu2bgu(kmdjjn 9 v0) 9s 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 sgd m0()tg5 jsu2su9nvj9skb8 ide of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from thex) ,3to: avv, j+riunp top of a cliff. It hits the ground below after 3.25 s. H pxtir) oauv+3,n:,jv ow high is the cliff?    m

  If a car rolls gentla ( j2woo1 fy9aopc)2iy ($v_0\,=\,0$) 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 thd)x+ p32uumd re 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 afteib*jop* uma+5 +z5wq9pjw;n fr throwing it vertically upward. With what speed did he throw it, and what height did it reach? p+ w;jnu i9qo pw jf*m*z5a+b5   m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence n.3u4bt4i u;4it bkliof gravity. Draw graphs of (a) its speed a 4 4kintl3;i4tu bbui.nd (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 heig x85 .u+:ejosyzo4ry eht of 125 m above the Earth, a package is dropped from a win. 8 :4z5 +yxureesjyoodow. 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, show that the distance travez5h+q6l 6 tefbled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Gali 6fqh e+l6zb5tleo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraicall3 -. nb7 vq;dwyp*jts+p1hf opy) that a ball thrown vertically upward with a s p7pqyd* v.+on-1 3;jbsthpfwpeed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed rqtgl(fkm 3o 84)-qo nqgq( a(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 apple in Fig. 2–18 (o 7kvb*rzdt xrpgu3 +67r number of photoflashes per second). Assume thet u 7pk7*d+z x3rr6bgv apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–3jasck1z.g kr9c8 v 70 +p:lfnr2). From what height above the top of the window did the stonf skc.r:+0 vrl 89 1njpk7zcgae fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean ac ywq)-m3e 71)rumcais heard 3.2 s later. If the speed of sound is 340 m/s , how high is the1aymq)uacc 7 )3 -wrme cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream ofkd/u4r c w sig(35-yyp 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 no/rp-3usg yw d5cik( 4yzzle 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/s from :4ce+ wkhntl/ the edge of a clin/c+ etwkh4l: ff 70.0 m high (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 abov7x,n(3hei lth i:ts5 ne the street with a vertical speed of 13 m/s If the ball was thr,ein:s h3x5t hl(n7it own 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) At what//q tvg4cxc p4 time was its vep/c4qcgtvx4 /locity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straiqse/lh,g2 xv*ght tunnel as a function of time is plotted in Fig. 2–28. g2xq/s* lv,he What is its 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 accelerate approximaknlo2djf fl u; 6,s5d;tely as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve rff2d kos5n;d,6;l ljuepresent 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 Pri8k mvena5*n:5o 3p s5q;dhh uoblem (Fig. 2–35) ;io s aqm h5h8:*dpk53n nvue5when it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object traveled during, tpo5q; 5iicig,/zk m
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function o.a3rn bq/t+u3 xy;x deozo, 2of time is giv;2xtn yubozqdra, o/. ox 33e+en by Fig. 2–28.

Figure 2–36 is a position versus time g8u.*u xt vtgsug(v7v9ey4q)k dw06 tcraph for the motion 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 or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions fe*q 9vwg u8).xg7s4ukt06tuyc(vdt vor the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s vrewjzsawl*ycq0:,,r y*q 7 ce2 ,c9hsafety net. The survivor stretches thez qreh:*s*v , cwrj2q a09ec,yylcw ,7 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 t9 usg5kuid.4 dhe Moon is about one-sixth what it is on Earth. If an object is thrown vertically upwugi4 .9u5 ddksard on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constraino-)jb-3 cede qed by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 30 “g’s” coebe3) q-d -j$(1.0 g\,=\,9.8\,m/s^2)$. 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 aeo,(2ljfs or8 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 knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the t j,l(of8sre2oruck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by hg 1747rk2pl dcvigf o(auling them up on a crane and dropping them from f od l17igcgvpr4k2(7a 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 travels a3rr y(-tz 78 xf:ifhfjbout $10^9\,km$ 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 a;kyn: ymc90 xzcceleration 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 front of the train started. What will be the speed of the last car ayyx:k9 ;nzcm0 s it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving b6dwdy1 wt:1kml vj n9lqw,mwelcj6 83794ym moard 4.0 m above the water’s surface into a deep pool. The person’s downwa3:vjdnel ym 9m, d6w7tc j9w llkqym1w14w8 m6rd 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 trans i y6jsn-/ww+*ewq+hp7fzlg8it system, 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 av wil 7sq/ z6wegp-w*+nyf8 hj+erage 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 andgjx d20kihbot*32 s o1 free fall 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 heightdght so 3o2j2x0bi*k 1 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 ball is planned so q+f 1b/u/j.wlqr s( hothat 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 difficufwqo/1b./lj hrqus ( +lt 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 t90v)pgh hd13lzl4u ktrain traveling at a constant speed of 6.0 m/s Just as an )kgdlphz 149 ht u03lvempty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is dropped 1u(n5tv)c ol7 j.50 s laterj 7tv(uo)cnl5. How far apart 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/hh) y8:awm woa( over the 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 maintainoa8yamw( ):hwed for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he movn7u m7w 7wzt0yu d,q+ees at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . Ww,d7 mz0qwyu7u+7nethat was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two tra6 3leh5len,lds 6ws+:j0kqh p mpolines. The first child can bounce up one-an 5ksw+de s0,qh6jp6:le3nlh l d-a-half times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-lmsa6ch( m g/*long train traveling in the same direction on a tracm6ga*hc ms(l/ k parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are 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 bas(.ccjnmw,hz 5 eball with a speed of 44 m/s In throwing the basebc 5mjwz.h(nc ,all, 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.    $m/s^2$

  A rocket rises vertically, from rest, with an acceleration k :pt*j8/8ja2l xi.4 idhkmnjof $3.2 m/s^2$ 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 6:awzznt1p d52scs6oovg s cm((0ms+ in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s 1n:o+azs(g cdwcm osmss2z 5p( 60v 6t. 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 traveldpuem136on :yl(k w b*2wocq,ing at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a cons pk13mwuq2l *b,wc (odoy6e :ntant 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 ro96gbryt/*kjlr y2 70 x.qqfb xof of a building; 2.00 s after that, a second stone is thrown straight down with an initial fr9bq0ytj .qx */kbl 6r2xy7 gspeed 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 vertically74e(r3l+wukpzl2m l 7y b 7hiw up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone beebw pzl7 urh4 372yl klw+(mi7 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-fa9lu qv /r)bxt q2vk2d1v q8m2tlling parachutisttvqr2bq21 xvl km)2v/u8d qt 9 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 conveyp8 n5pc t5w4mgor belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel?n4m58c tp wg5p 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 vert/jzwlb7* 8ml4qcygs +ically at a speed 1.5 times faster than Joe can. How many times higher will Bi y s b8qlcjzmw*47g+l/ll’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the toplwuq)n: ipf4 ; of a 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 if;wq:u4n li) pn your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked t3o5s 8 wkbc;60gujvpto find the height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its 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 forc3 bsjv8k6u g50pt o;w the estimates of the building’s height?    m

Figure 2–43 shows the position -48g z pfr-nahcbn:y1vs. time graph 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) Whihn-apn zry1b8:4 -gf cch bicycle has the higher average velocity?