Does a car speedometer measure sped+.n 7n7xg-re wdno3cc i/iq6ed, velocity, or both?

Can an object have a varying speed if its velocity is constant? Ijqfke g6fcnc t4gl8:0shvwa 1v6q* 7 )f yes, give exampl0w4jv 6 q1t g:neafghkcs)7 f8*ql6c ves.

When an object moves with constant velot70pc,0smh txvud 5trqwm +,,p9z- ducity, does its average velocity during any time interval differ from its instantaneousu-xczr,tt5, 0mmv 7p 9+uw s d0tqpdh, velocity at any instant?

In drag racing, is it possible for t + *ajagg fkjcz9plgm0so fu :w(8;q3;he car with the greatest speed crossing the finish line to lose the ragcwo;kg: pl0a9f+zm ;j*3ua8j (fsqg ce? Explain.

If one object has a greater speed than a second object, does the first:hy tg9f;srhdh 1 ve97 necessarily hav; v:r7hhsh9gd9 ef ty1e a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 8 y4h .7;yby xn,nfqoc20km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the sayoyx 7.n4nq cb; 2f,yhme time.

Can an object have a northwd q,o 6n1cz v:or/ma:ward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its accel+ :pgazs0e6 zferation is positive? What abogz fas+6e:0pz ut vice versa?

Give an example where both the velocity and acceleration are nn ru4qdrj 5ti/axw9 08egative.

Two cars emerge side by side from a tunnel. Car A is traveling with a spee2rk++0tko2q2ye4bh2mv uyl u d of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which ca4lry22e q hk2 y2vmokt0uub++r is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in ship7 )ug24i/1cd)pc bxykz8 z peed as its acceleration decreases? If so, give an eu1bc p7 x)p2gi) kdiycz8/z4hxample. If not, explain.

A baseball player hits a foul9;u3e*iy2 ybo4ik: ) nf hk0mdyolf/g ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence *;n o:iuyfk y0fkdb3 /2)y9elo4imghof air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what3fb8lp tmt(2feb zk)* is happening to its acceleration due to gravity — does it increase, decreatfz mkb ef 2p8*b3lt)(se, or stay the same?

How would you estimate the maximum height you could throw a ball verticallyn5y1m,ho884 box (bpldsx bw)ko1d 5i upward? How would youd51ywsp x o1(kbmbldo 8x4 58,h bn)oi estimate the maximum speed you could give it?

You travel from point A to point B in a cd* jh tqm+8 42hyekw)aar moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average s)qamew2 8jyk +t*hdh4peed 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 l6t.jrua ls-j.o5v:y string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts jtl. v6so5aul-.jy r:be tied so that the clinks occur at equal intervals?

Which one of these motionsf-fcb 4zj 7ay7 is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor tz47a 7fyc- fbjo the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vry, gzz17 d:m7ob(2yg g.sogsertically upward will return to its original position with the same speed as it had initially if air resistan:.7g(ys oodg 71z2bzymsgrg , ce 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 velocityzco 2,xuial-1 and nonzero acceleration at the same time? Give1l ,c2 -zoiaxu examples.

Can an object have zpn : cewnx 6j0.o 1 3f(v,:6dwmomkbkoero acceleration and nonzero velocity at the same time? Give,om.n3:0 po(e 1w vkfo:6 jdn6kcxbmw examples.

Describe in words the motion plotted in Fig. 2–2jsx-q 67jvdhm:+1 l(vb 1b.qrgwo8r o8 in terms of v, a, etc. [Hint: First try to dupd1qmvbxbwro:g j s7 6lqh18v+or.- j(licate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in Fig. 2uu4(zj k;- b gxxq1ql.–29.

  What must be your car’s average speed in order to travel 235 km c e)yeu-) v,.rqdy+ qhin 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take ns- ddb(ymd.9to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s 972sk8gzyt3 uj;c1wyryzf o3f1 ix) y, how far do you travel during this inattentive px;y133yfu7wz f gy2)ciykr1j ts8o z9eriod?    m

  Convert 35 mi/h to 5tp/w0 xr7ft7l(d-bdn: kjy t
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fre;p:0. gqr -/m uaoyxtom $x_1$ = 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 13 u1p r6 psv/8m-x-m5kqcukf3 n0 km. It then begins to rain and you slow 3ckp 6muqf-umv/k sx851n -rp 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 secondswud ol;np7;o, between a lightning flash and the following thunder gives the distance to the flash in miles. Assu o; uo;wnlp,d7ming 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-mile tefi:h/ o49y4h3fezz zrack in a total time of 12.5 min. ze3ihf4 o/ ezfz4y: 9hCalculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, mx (kvpnrvpvytd d6vg(:4t f4)r3e2;roving 116 m away in 14.0 s. It then turns abruptly ayfxtdptd rv : vk)(24vrg re(pn3v6 4;nd 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. Each has a sp7z)zoc (0r yu9a qq2vheed of 95 km/h with respect to the ground. If they0uh(7 q9q2aozv)zcr y 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 traveling How long will it t .o4rq(xeo; hds-ts6 eake the car to r- e;orsseth q(d6x .o4each the truck?    s

  An airplane travels 3100 km at a speed o 3f64hczyay1 bf 790 km/h , and then encounters a tailwind that boosts its speedchf1 yb3az46y 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 completg0(yn qd o,.bme round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the o0n y gm,b(.dqreturn 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with const.(pxq) iwrh7t ant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sounp 7wq)t.i( xhrd 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 of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is it)pd0w-.v nx zjs average accelerativ)0znd.w - jxpon in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is h n8 .u;vx.mqqcer acceleration8vx.q;m n.uq c
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acceleration of rdx5 p. r;p.w-hzcri.abou. ;rw .rzh -ixcr5dp.pt $1.6 m/s^2$ 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 urr-/f6t 8av ctravels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accelera-/urvcra ft 68tion 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 stay i 9i7ulia(;prts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table.i9a ;7(u ilpyi 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. Wtv*g7wp8ioa;*rd4r0 oj6aa q hat was its acceleration? How far did it travel in this time? Assume constato* 0i *r7gvqwo6a 48pdr ;aajnt acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its /8+kad4c7ns q zg*e9cqx-as yacceleration, a+qkndex *sas48qa y7g cc- z/9ssumed constant?    $m/s^2$

  A light plane must reach a speed o 7;mxjx yb)ga(f 33 m/s for takeoff. How long a runway is needed if the y;xb( xg)m 7aj(constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of rp9u k ly+hwp9z7v9(pthe blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprin+99zlv ku p9 h7(wprpyter, 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 f)e dm7 ,c( s7io;ofbh iwoh+est(d9,har did it travel in that timd()t77osc , soh fde+ (hbeoiim9 h;,we?    m

  In coming to a stop, a c-:w myo ne4zq1ar leaves skid marks 92 m long on the highway. Assuming a deceleration of yqw:-nzm eo1 4$7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tr-8:tyha tj0ht ee. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g =t:-t 8yh0jtah 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances fomp-ta(vw:gt+;44 w+bsx oz ryr a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an ac w4-wbtx+ r:oa;z4tms(gypv+celeration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stoppin(x0 *ok+. lot )m(qyof1+bok5 jttthrg 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 goin2jk9 +tnc al,)* tqu6yua 8ilpg 25 m/s on the highway. The car’s driver looks for an opportunity to pass, gu+68,iyl *u9ttunljpqka 2)caessing 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 runw6 a. 2x)) g;o4x*zmhi fgbgch in less than 30.0 min. After exactly 27.0 min, there are still hxg4mxb2.o * gc )fhia;6)gwz1100 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 knu a t3pd+2+;mwvr-yxo-x2q om/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed uq vd++n2mu-3xar pxt;2 oyow- p 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 frzbn 1b:nq*iq/e,0 klo f,fg 6pom the top of a cliff. It hits the ground below after 3.25 s. How high is thezp/q*ibb:f,,01qngo kfn e6 l cliff?    m

  If a car rolls gently ( mc z4.tdz 48hkphkdbn -5q8g;$v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up into the air with a speeu2 fhti+ns(g* d 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 v7dqt-h,n leg 3/gkwx, ertically upward. With what speed did he k, l qwxen/h7g3 tg-,dthrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falub(rj/mbe cdp4vvwye /lq(7 /1.5: m dzkj3u mls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignor duv:wplvq/b(d.7yjz13 k4e (/ r/ eubmj mm5ce air resistance.

A helicopter is ascending verfc ijud1c0r 15ioy2*gtically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped fiigj25 oc0 yd1f1 *ucrrom a window. 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;kt9q)nuw;b llr5l11vptr / e 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. 2–18 an;q)1t9r l /k wrv5upb1le;l tnd 2–21.

If air resistance is neglected, show (asj2 e: acsl.+mlgebraically) that a ball thrown vertically upward wis.je:2cla s+ mth a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertica/)k)jmgs-n3q/ns0y s stp +ehlly upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in F mhp 32 . ;qf-hq9xfdikaxej8)ig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positih)x iaq9dk ;fpm.-fj3 he8 2qxons, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to trg0c5qr;v lb9.) ennu savel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the 5r0se u;b gq).vc9lnn window did the stone fall?    m

  A rock is dropped from a sea cliff, andjhy1l8n sdji(q) mj7( the sound of it striking the ocean is heard 3.2 s later. If the7qs8jh ((nld1 )ijjym speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden ho8g0j n.8t oznqse 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 waq8t.n njgo8z0 ter 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 ujtrl( l9,v 3wxpward with a speed of 12.0 m/s from the edge of a cliff 70.0 m high 9wv (lljt3xr ,(Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the streynv0jeh c m ktq-87 i2h6/+lboet with a vertical speed of 13 2v mqklen t-/jboy607 8c hi+hm/s 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. yenl-dho( ) u)(a) At what time was its velocitdo e)n-h)yul( y 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 strexkl;6 383bu*agc ubf zr.ku)aight tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneous velocity z6rc )a3e8ulf;b kxub3k*.g u
(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 in the vel+gxpej ,g8 j (fag0q2rocity–time fpe,gax2+ (qggrj08 j graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average q8,q wh f-ydg;acceleration of the car in the previous Problem (Fig. 2–35) when it isyf;8wqg d,qh- 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 thbz9:pu+p8 m d.vd aqojgp d 1n37s.bl*e object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function ofrsza /18l ao67nu r4rt time /nl8zr u as7r1otra46is given by Fig. 2–28.

Figure 2–36 is a position ve i4l/ ngrot/3lrsus time graph 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 dr/lo 34 gntli/irection? (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-storu-c8b2 h71t5 l-4do mi lyjemdy window 15.0 m above a firefighter’s safety net. The survivor stretchest4m 1-5dy 7jibel2omh8c- dlu 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 about one-sixth what q 4 l6vyeq)qly;mi8zw8; b-ql it is on Earth yvliye4q-lz q l)qw 86bm;q8;. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shbg (rv)2i2;l :xrauoy u.a8xkoulder seat belt has a good chance of survivrab y gxv : i()2akrl28ou;x.uing a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his auw+2hwve4y x3( 9pbpibx+h7 pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by bx3+x ipw4u9bph +h7(ew 2vy aknowing 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 tq5fhk04y - ntiested its cars for front-end collisions by hauling th n q4h5ytik-f0em up on 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 travel(4sgxx x)cr, 8bzz:u++wb hd+r pc,dfs about $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The fronw. bdzkoq 4.y*t 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 staz.o* .4k dyqwbrted. 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 /gdr t3e4aeo8the water’s surface into a deep poor43d/8 at eoegl. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid-(jcq9 sk*y gaw4b1wafat6u 2q1 sjp6 transit 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 average speed. To get an idea of this problem, calculate the timea s19ukbtfa6qs4pyq6w g-c(j*2wja1 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 diving for fis l1nho 9ky.c*)pczi.b ;xui0ah. 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 k.. nh*uoy czil)iab xc;1p90 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 sopw c4g1-es8 *zm- hstag5(vi c 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, pus(sv5pg*za -m-tgeiwc 4 hc1 8tting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train travubi;mm6/u)2fu r)kj zeling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitivuu 6bm)2u mkjf)r z/;ie 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 secoky9- mme 1fu9du )opw(nd stone is dropped 1.50 s later. How far apart are the stones when the second kup)fe1uwmd9y9m -( oone has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the c,f)wym4; qfxpourse of a time trial lasting ten l4 f, xqw;mp)fyaps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de F kxzw6k58t* pal )exc+rance crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his spee6*zxlxt cwk5+aep) k 8d 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 trk41jzct-5td ghbr4 b- ampolines. The first child can bounce up one-and-a-half times higher than the second childb-4t t 5dhk1jcg4 rb-z. 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 travelin4w vlsv;k jc ;mja6c41g 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, amv46ac l 4;vcj 1sjw;knd 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 tn l)yn/( g)heshrows a baseball 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 behin) /ys)g(nhl ned 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, fmib +qs7ny/l.:q n0slyu ( mehxe8y;5rom rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a tr/do 6yhj (waw.affic signal, and the spe(wwoja. h/y6 ded limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a ,(z 5 pm+grbex(ziu.jconstant 120 km/h takes off in hot pursuit. The ( zxujbgr.z( ei5p+m ,police officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s afrq 2w7ni 47oo9er3tw sdwu8- fter that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two sw-8rq32ft e rusi no 9wd7wo74tones 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 slfgs13.lw3 s*4i1w vp n( hm2j czwb.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 second1ngcwss3l ( m ijbh 2p*w.4sf vz3lw1. 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 mv8-q*uj4 zjfnv(2kznxg: 5 zit take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What wouvq8 2ju -f5nz:*kz mvng(z4 jxld 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 grit9a(b c bos7dljb7;;a,mcn 2l lling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart,7l ,jb;onb9al cdsb a;c7(t2 m 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 timefxhl szz;9bg79m kq6/ n y.n)ks faster than Joe can. How many times higher will Billqbx;/7h6zskn .ny g k9)mfz9l’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands ond qp 2g a3x1k7szw7 ld4oqj76/+p35suiahq cl 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 i2p3kiqo43 l j56wspd 7 +zdscg7/1 axqlh7au qt 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 find the hei3u n:hby hdy98ght of a particular building using a barometer. Instead of using the barometer as an y98h 3ybdun: haltitude-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 height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and Bfc8naw0pp5+5 seb zy4g3 px*j. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which i5waz jb8c s54n 03 *gfxe+pyppnstant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?