Does a car speedometer measure speed, y9hzu n,)e ai8npmv1 (velocity, or both?

Can an object have a varying speed prb4meb+a a-8if its velocity is constant? If yes, give exa4 prbma8+-ab emples.

When an object moves with constant velocity, dovp4:6p v 9onzqcx8/g tes its average velocity during any time interval d8tqo4 v/ z 6pvxpn9gc:iffer from its instantaneous velocity at any instant?

In drag racing, is it possible for the 1et whsfd4nj 6q07(eycar with the greatest speed crossing the finish line to lose the racees7et f6w4j( h ydqn01? Explain.

If one object has a greater speed than adcg lb( t i*a7:ubtpmrgtt *vo) -43s; second object, does the first necessarily have a greater acceleration? Expla4g v m7-bpotbgtu(*a3;lit c:rd*s) tin, using examples.

Compare the acceleration of a motorcycle that 0mlx asm2z +pjk9w9 r8accelerates from 80km/h to 90km/h with the acceleratmwjr8l2p9 9+mxs0ak zion of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a so 4eyc;,nj nke jk9s0.yuthward acceleration? Explain.

Can the velocity of an object be negative when its acce9l .hwzgeix *-fu(j, pleration is positive? What aboutpefh9u ,.* lj (-wizxg vice versa?

Give an example where both the velocity and acceleration are negative bqm;bklm*w)ifb123g.

Two cars emerge side by side from a tunnel. Caujo k3fmx85 /pqsq*/l u-i* dmr A is traveling with a speed of 60km/h and has an acceleratiol* o8x3uqd j5/ip*mqsfk-u/mn 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 increasing in speed as its fon 8aavxrh8a17v 3m7 acceleration decreases? If so, give an exampleomx8fn a7r h1va7a3v 8. If not, explain.

A baseball player hits a b- au:wxz) s3cfoul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance,u x) bw-az3c:s how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acce,mf27 e4mcqs ;otlc.gleration due to g,c7ms;qc o mt2g4e.flravity — does it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball -f 2xmksdj 9q ky0/8lbvertically upward? Hoq90s82m/kk dfl-xy jbw would you estimate the maximum speed you could give it?

You travel from point A to point B in a car+)vjxn7cwdt qy (r6 j; .bv7ph moving at a constant speed of Then you travel the same distance from point B t +(pdv;jryh 7q.w6b vcx7n j)to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.e.qz( :,)iyemcp 1lolao4ec, 0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at eqe() 4czml,ea.lo,o: qc1i ey pual 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 accelera/5hmg6,k+q-f ript.em c n*3be3pesz tion: a rock falling from a cliff, an elevator moving from the second floor to5-c.n sktq, 3*rp e ph6mm/e efig3+bz the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original posaxnwe -0ofuy9-3 cvdou(cf/al7vo 92ition with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, willaf(ae3uvoy 9w uxvnol c-29o-/d7c0 f 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 time?nsh93m8 ;gbrf Giveg; s3rhbn8f 9m examples.

Can an object have zero acceleration and nonz 4xxuh;jq/h0s ero velocity at the same time? Give examplesj/4xuhs x0 hq;.

Describe in words the motion plott;qc vo(cqf i(g ez:i).ed in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion pc;)cev o qi:i.gzf(q( lotted by walking or moving your hand.]

Describe in words the motion ofmgp(y cu-6s h9j n0r 2h:emth- the object graphed in Fig. 2–29.

  What must be your car’s average spe q:xd 9sox*u*ted in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h5 4nmjc, lz,o swa(bl/ How long does it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s,7cskgb 5eq1 0h how far do you travel durin17k sgb5ce0qh g this inattentive period?    m

  Convert 35 mi/h to bzm-s vy1/h0a.tgr 6)o9 juqm
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves froayytbu u(2 ;;nm $x_1$ = 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 130 km. It dukg g,. ss6(wl) u(uqthen begins to rain and you slow to 65 km/h You arrive home afuu.qsg(dk us6l )( g,wter 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 lightrntvp1 :pc29 ,mkykv 9ning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, esti cktpny,:vm91r92 vkpmate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total time ok2xpz,g d5x-c f 12.5 min. Calkzdx-gx p ,c52culate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, mfws5;./ td+dn kw+cmnoving 116 m away in 14.0 s. It then turns abruptly and gallopsmnw5 dcs ;+.+ dwkt/nf 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 approa8j3f7u wcop p0ch each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If f07jpwu8poc3 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 o: zu t f* i7/j-9a2r.hrxdmqztruck traveling How long will it take theqa m9i7: zfh*ud.zx2o-/trrj car to reach the truck?    s

  An airplane travels 3100 ks1vl/xty -s r1m at a speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the lv/ -xstsr1y1 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 spe7sy-t2at q3ji ed and average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lq273a-tj syitunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with cha9l (l 3okffjo9e49qonstant 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 lhl9ofq949ako(j fe3 speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s.l 0x uz-;mp,bh What is its average acceleration zupx0ml -,h b;in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.mx y8*rc*k1jd35 s. What is her acceleration 8*r1 * jycxkdm
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particumwk fb z)a qgmr./)sk6f 1) 6.db *pj6)gespewlar automobile is capable of an acceleration of abou.s* )p1j wr kfkp6fz)wgb/g.q6eabm e dm)s)6t $1.6 m/s^2$ 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 con)d 0ma1g .) yi0dlqnqx,lfd r1stant speed travels 110 m in 5.0 s. If it then brakes and comes trn)iaq,. l md)l1dxd1y00f gqo 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 raci w podw55:spkx)rg*li4. ( knlzj k:7zng car, which starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Tablwjw r 5zli5(xonz pd4:k):p.kl7s *kge and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceler ph54lxei 80wvation? How far did it travel in this time? 4ilph0e8wx5v Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance ofzj5gphm+7:miqtj h ** 85 m. What was its acceleration, assumeqh t*mhiz* 75+:pj jmgd constant?    $m/s^2$

  A light plane must re,yl.nuhapc2 :ach a speed of 33 m/s for takeoff. How long a runway is needed ucayh l,pn:.2 if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of thel 3 v6ab.locr7o ,y5tn blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does ioat 5b,yl637vr.olnc t 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 t lpzvh3gh,3* do rest in 6.00 s. How far did it travehgv*hl,zd3 3pl in that time?    m

  In coming to a stop, inf+qf n ;3-jca car leaves skid marks 92 m long on the highway. Assuming a deceleration3 +cn f;fqnji- 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 jm(ww(0p e2y)c g,bk,knpt8ncompresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express t t kkwj) nb(pc2 ,8(0pywm,enghe 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 stoppingq5l nblbrfy;,jh*1x92 (qs xg distances for a car with an initial speed of 95 km/h and human reaction timh,*(j5n flxs yqbg1b ;rq l9x2e of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distawhh3*/ u 5fg2ji9jiqsnce 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 tckd-xu+ w eoe*4v j7 c3vi t sh2au884fix1wl:he highway. The car’s driver looks for an opportunity to pass, guessing that hif 34kde+v81clxi7a4 w-j 8t wcus:oxvh2ie u* s 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 complemc9t g ns rbu+ey3ouixrh2 :0q (95.39t awoyvte the 10,000-m run in less than 30.0 min. After exactly 27.e v. yr3 99giutqayxs(rum o25w39+0ohnt:cb0 min, there are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection justqyw 4; 7gba vg1+.s0w, ro1vwe8y extw 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 beforexw;ve1+ bvw w.87gy1et rqao ys0, 4gw the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below after 3.2of+83 l /*lbekf5xzz g5 s. How high is the clifzofx llke8b3 *+fg/5zf?    m

  If a car rolls gentl;,p8t96b4lnbxnr6.cka a swq y ($v_0\,=\,0$) 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 uimbse-uenw9p9d79wrc, :cx( 8 :r uqjp into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after th-ngr(diqq9 jzb q giiy,2h.:;rowing it vertically upward. With what speed did he throw ijgn ;(i- hgi9rzb.qq ,y 2i:dqt, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and fall*l:ya 6y90d 9qftq)bbfvepsj gt-.c0s under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallenc bqp-fj9bf:y s 6 )qav.lge t*9dt0y0, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with 63.dui x(tg /i*vx8l r +-vghl2cmyk; n8dsuz a speed 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 igr8yvuzmgs3tdlcx8 h+ 2/(x.6ldn ; *k uiv- 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, s(wj2q4f)x zszr, h l8mhow that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–(q8mwx2)ls 4z hrf, zj21.

If air resistance is neglected, show (algebraically) that ek7 /:wnrt tnuy) y9w:6w 0uyta ball thrown vertically upwarty/uy6w t n9w)0nyw ue:7 r:ktd with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticall3hww8a-n k0 6e zh+prdy 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 thh/tq ps5f n02dqdw 4gb.t mz/)e apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is abou/204/tndg) h.fqtds wzbpqm 5t 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 evah(;mc. ) exa window 2.2 m tall (Fig. 2–32). From what height above the top of the window di(cmhe.)xv a;e d the stone fall?    m

  A rock is dropped from a sf: n+ww 97sa 3adcpjz0ea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , ans3f z0d79wj :ca +pwhow high is the cliff? H =    m

  Suppose you adjust y zhg5x2y+. y2f m3sj6vph dn4jour garden hose 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 yojfzhh63jdpvx + gm42y2y5 sn.u quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from4fmfz 0v1xcl ;yfix4h7u9s -u the edge of a cliff 70.0 m high (Fig. 4lvyhz 0xffi xu41 9fs7mu-c;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 upw,ot pswil 75:dard by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the st5tol7: p ,diwsreet,
(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 ej27328tsil:ub1 z hiwiolo,el/ ,fla function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (coutwl i l2,eof,7 b l3jz: le8i/2ihs1) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight rj*z thh9 ltn9yr *k:9tunnel as a function of time is plotted in Fig. 2–28. What isk t*l:j*nryr9 9h9 zth 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 automwxdf -,qno58 07s8isn usyy 3: iwy6epobile can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve repyw6so:-s yfnw3i7q0i5 dy 8x,s uen8present 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 accelerat 6u7r/ xp):jbhub3 ociion of the car in the previous Problem (Fig. 2–35) when it is inp63xohbb7j :/ruu) ic
(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 disttc. -q-vi x5wyk zv5e+ance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as yuz y/ 0vae:g51yrp k6a function of time6yvzr yy/:ke5g0p a 1u is given by Fig. 2–28.

Figure 2–36 is a position versus timev ;oo9sf 2*(9rltt/gdtfchm * 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 movin dsf r*;o29tl(tt9g cfmvoh*/g 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-st g6-wxq4vfg9hb 6l.lzh ;,g qvg gd(d*ory window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–36lhgd(vdf vx9*qggh4 ;6gg.bw, lqz-7.
(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 iny oh unf*n/ 1 k-cx:fd,)v+rx+p2vibs about one-sixth what it is on Earth. If an object is thrown vertically 1fhp+*,io k-)xxvf2 n:d/uycnvbr+n 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-shoulder seat belt has a gooxtpq8*uk ,ya 72 6y o+a;bdfcvpo8n9sd chance of surviving a car collision if thaqoydak9 b pf+o6s2 n;8x* py,uc7tv8e 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 ro/71q kw:d(b lcq 4btghad 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 passhkq:w4bd cqb(/ t17lging 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 cars for front-end co3v2kndm s;lrh* u6bp6 errofok o-b// k+yr:,llisions by hauling them up on a crane and dropping them from a certain height:o3lfrnm,dos+y rp k h; uk r/e6r b-obk2v6*/.
(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 aboun vledj,5;dip p+4qx.- r 9vtyt $10^9\,km$ 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 front of e4e;q; ksh ni0the train has a speed of 25 m/s when it passes a railway worke s 4ieq0hne;k;r who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.6p)60. j iaes+-bzo9t 9nutzkkutnb(0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while)ukn6u i- ozb90ttjbat+e s9nkp( .z6 under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, ik-yey/ b,sj x2t 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 tims ke/ -xyyb,2je 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 fish+wmrv p7ka v4;. Suppose a pelican starts its dive from k4vv prwa m+;7a 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 wi) ;prg,re exy72 mtqh uqyt/a715dcx9th which a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 17 gy,m)5x7ud;ar 2t9 eh /qt rq1ycpxe.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling ag3sa1yv vnx3 d;tjk7)/4 sbppt a constant speed of 6.0 m/s Just as an empty box car pdanyv1;/37sj gvb4pp3stk x )asses 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 b4y1x(xu k(;ea 5lgoj* qbe-dduilding. A second stone is dropped 1.50 s later. How far apart are the stonlx xbe je*5 kya-oqdd4ug(1;(es when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.vq 47ujnnc fi-h1)pq30 km/h 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 maintaiivq-hfj4 17pnn 3q)cuned for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass a*ubcmm( yqw1)6v8 sja3ct/r w s he moves at 18 km/h . At the bottom, 4.0 km farther, his a31rwjcwy q bv6*ts)c(/8 mumspeed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can b:a1ps3t 3)vhchs g7gg ounce up one-and-a-half times higher than the second child. The initial speed up of the se g1t)g:37schp3ah vgscond 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-ln4 ,l kbz-;ichong train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results lc iz4; -nk,bhif 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 sss.elhko oa2ifmi+; 2j7(p 0speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a dis io h0s+af l2m;p(7 kosj2ei.splacement 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 acceleratio(t*8hsizlg n8 b dx)(cn 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 xugy 6civ;30:ayhp 4vl((nlo shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. Whenu gpac0 yl ;4hlv6yo3( xn(:iv you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km/h take.lzl(waigxe4n.c6 cx06t-q( +sov j rs off in hot 4g(zxt(vlca-jn lc i.+esrx66 oq. w 0pursuit. The 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 after that, pd(z exzw 01 cown* ,nx5v5)kka second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the zp1x ecwkwoxv5nd, kz*)n5( 0same 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 sor: t :w)cc m:7r yhz5a.c4jmlame time. The first stone is thrown with an initial velocity )c wm:j oh:yr54r ltm:cac7.z of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take aunt9hcoc 98, ox1s; eld0r: ek free-falling parachutist to fall from a;cxnt:eh0 ose1 99kc l8u,odr 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)z;vydz 1q uo0 t6y132zike ar grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If theudyqz v1ty123i)o0zk ; ear6z 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 acvvlou 1j5rq;x-z 3p3 speed 1.5 times faster than Joe can. How many times higher will Bill’s ball go than r1 - zjpv3cvx3;luq5o Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your fri(r9l0b qmplx /)p nj1fend 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 plflpx1)j9(r0mbp qn /icks 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 tyt8 bg5;xab co1 tg1)+mc4iml o 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. 1a+48ib t;gcoc 5bm)g xl1tmy0 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 B. (ax.mw+fz 5 d18vqco+;2dbls ag ) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which io d;ax z15 s2dmgcvf. qb+8wl+nstant(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?