Does a car speedometer meiaj.( oaz l9jll9 0vp1asure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, 7hzbh6cn u7;ogive examp huz; b7h7nco6les.

When an object moves with constant velocity, does its average velocity du5h;yyjz uw46y z30gh lring any time interval differ from its instantaney5;wjz03hg6 zyyu lh4ous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crdv kjbcr,:t*6w g7 g(kv 6,nfmossing the finish line to lose the race? Explwkm d6:7vtj(f ,6*cbnv,gk grain.

If one object has a greater speed than a second object, does the s9 x dp+;nsj k8fg x4lz6s0;mrfirst necessarily have a greater accelerat km9 lj6n; sx+4 szd;fr0g8xspion? Explain, using examples.

Compare the acceleration of a motorcx,m0 q t/ulj09bnvw(z ycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates vb(0m,uzqjn w x 90/tlfrom rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleration? Explainffas wdu( 68yu6y;o q6.

Can the velocity of an object be negative when its vs bu) 2*c5dsc54qt69qtg m sij*u.fcacceleration is positive? What about vice versa q56sccqf*ub2) 5mgi.c *u svs4t9 tjd?

Give an example where both the velocity and acceleration are j53 /vasgp 6vp0/axkf negative.

Two cars emerge side by side from a tunnel. Car A is travelin, ( eeh.7n yoa2pz8 wfmf; nnkno6c98hg with a speed of 60km/h and has an accelera9c k7n8hop fz;n oafw8,y6m.nn h (e2etion 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 incre4,9-6j aaab)a+ ifjzq; .rb-e gsd mzeasing in speed as its acceleration decreases? If so, give an eaia9 a-fbmgd-ja46 s.z)ez+ ebj,r ;q xample. If not, explain.

A baseball player hits a foul bac q-cqid;o,5g6aph4 z ll straight up into the air. It leaves the bat with a spdcag o4qhcz qi -6p;,5eed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acceleration due z7e-8-jiutuq to gravity — doe8 jtqe zu-i7u-s it increase, decrease, or stay the same?

How would you estimate the maximum helv1 hm, ms i j-:gkzd7s3he*c:ight you could throw a ball vertically upward? How would you estimate the maxi:dzsk 7-mi 1lm ,3hg*c evh:sjmum speed you could give it?

You travel from point A to point B in a car moving at a con lel0ju c1v72phu/k +vstant speed of Then you travel the same distance from point B to anj1lcuv+hu el2/0vk7 pother 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 3.0-m-long v1z*y7 mtp zw4):ovbnsacbt ./ertical 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 equnzabycz )o 71.4psvb */twm:tal 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 accel war6;t0idtuvr/hg+ 0477 orayar;e d eration: 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 taawa rredah/ri60u7y t; r v+dot70; g4ble?

An object that is thrown vertically upward will return to its ori3bk z15a01iojpy t7(z2 fmefiginal position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to ap0fif7(jb11z ao2kieytm 3 5zir resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same time?5t ic00f st6sg,7p t65qouko s Give examples. s,0c sftgk6oqo50ip56 utst7

Can an object have zero acceleration and nonzero velocity;k9id sreo,.x at the same time? Give exampless rk.,;x oe9id.

Describe in words thkjd9 mkwsvz4x66h p8i 0j,ws*e motion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plottedmw,zk64i0s8jxjws h9v*p k6 d by walking or moving your hand.]

Describe in words the motion of the object gr bj.rilueo;rjhw:(0l5 e ca;t; 6 jea9aphed in Fig. 2–29.

  What must be your car’j 1nj)3wfmfhn : tc2.ns average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/haa4+-yov( ;9uyos / pc xo5wrx 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 svd2uj ; gp-y*s, how far do you travel during this inattentive pyvgd 2p- j;s*ueriod?    m

  Convert 35 mi/h to l bv(zt/,:jld/ t s(hx
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves1 f4 jqs.ia;ob from $x_1$ = 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 thenarua2 2pn x5cgx8pi 74 begins to rain and you slow to 65 km/h You arrive ho2pngruxaa75p x4 82ic me 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, everyj3rs gn/8 b+ljte (y-c.ebsf3 five seconds between a lightning 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, estimate the speed of sound in m/s frc8+ebgsfbyjn ler3t.( s -/3jom this rule.    m/s

  A person jogs eight complete laps around a quartwv /l6z4qtzi6u 544iyj,ka4h 3evgoeer-mile track in a total time of 12.5 min. Calculate 4q eztva uvy6,h64 3z4ilewoi4/ kjg5
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in amfm d ar0,d+*mx tb-w5 straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calcuft0 +*mmrdm5d-wba x ,late
(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 qmdwb z ;;35c/olpr- sspeed of 95 km/h with loqdrc;5/p b- 3wmz;srespect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 67oc2lxp ;mqk m behind a truck traveling How long will it take the car to reach the truck?6;xq7pkl m2 co    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encast4l,*:yf mw 0:g qm y .edsqn axv:e(9nkl7)ounters a tailwind that boosts its speed to 9) k9ylym: avwa:q m.tnn 4qxsse(,7d*lf g:e 090 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 ave 8 nq;u. wyk7)4klmq;fly;d birage velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-8ny;qlkl; qmu 47b)fik d.yw ;hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end of a- ** s+dgd(xuge*4 0uq9pn rs-oftvlb 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 of soundb-uoqr+ldd -s tvf *9 e0*x* p4gn(sug is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. Wh+(a3gtbfyja :at is its average acceleration inj(faybt + 3:ga $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceleru dq4xh* )9dvsinm qw/.i-u f8ation /)sm.iv * n-q8xi4dduhq9wuf
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular autng3qydv+ mag 9 ,vui0+omobile is capable of an acceleration of about uqav+m,i n y0v 9gg3d+$1.6 m/s^2$ 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 travels 110 m in 5.0 +26c-,kjyl1 sgbpvx h 1 wv ei-tpwm7*s. If it then brakes and comes to a stop in 4.0 s, what is its aceh--m6cskgx1vt2iw ,j* pwy l+v1b 7pceleration 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 starts7*15hs fady 6haya1 ew 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 tihya61ydfe* 5 h1wa 7same. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its d-, ,m*k .fwxrhw7 +3.yyuo;c ovilpcacceleration? How far did it travel in this time? Assume.;mrwykfiph +oc-, ld3yc7w ,.u xo*v constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its accelefd/;t ijjlm( )ration,jfi;dl(mjt/ ) assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for take6po *. u f3qayimh7:icoff. How long a runway is needed if the (conuicqpo7 *fiam :.3y6hstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of tnw.gt6yxx9c fx v*/o +he blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average ax fg+.twy x*9v/6 nxcocceleration 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 ft* de xc56bb4iar did it travelxtib 5 cde*64b in that time?    m

  In coming to a stop, a carz4d q.1 * oknpmvr5bc. leaves skid marks 92 m long on the highway. Assuming a deceleration ofqp1.*nbrv5k dz4o mc. $7.00 m/s^2$ 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 .z4awkmvdh t .3 2/ jefef+mp0and the drivwm.fed fjht.mezva+ 4 k230 p/er 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 = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95zf zn58iqc0e.*gxh ht, coyw;)uno to93u28o km/h and human reat3x o og.85 )ihonecw9yth ,u0noquczf*;2z8 ction time of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car is-f 3kdg -p-lbeiaqx 11 $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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.m 4o2(ssao iat; hb-:c The car’s driver looks for an opportunity too:a;s( astb-c 4h2m oi pass, guessing that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to completeiy. t k,h9xmdr))g*a x the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at 0a ) tgyixh9.rxd,k) *m.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h a.lp.7e9n 6jnq) 35d 8sm uaw gkrva)ykpproaches an intersection just as the traffic light turns yellow. She know9. l8kqyu) nj7 kwa63sp).mg5 eavd nrs that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The 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 bjl6 kkni,12z felow after 3.25 s. How high is t1klj ,f2k z6inhe cliff?    m

  If a car rolls gently.o(mt 1vn2r k /dln7jx ($v_0\,=\,0$) 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 spe lt 6h,idyd s+- a0ier1dk/7deed 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 thr(( h4uj om+zbsq4 s jq.nw:+r55y.e8lse hs djowing it vertically upward. With what speed did he throw it, and what height did it reach? n458o q:um+yhd ( ze4je s.j5jrhsbw.(lsq+ s   m/s (Round to the nearest integer)    m

An object starts from rest aq / k0l9hmha1ynd falls 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 1a0y/l hk9mqhto t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20.x(fzbg z. -: c8key93sqdgp z m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals 8qc9z-kep gsd zg.( y3xbz:f.the helicopter’s.] t =__ s

For an object falling freely foa9v9,fud/83km(vs, i )u immii -jfsrom rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, d ,i8 9asm)v,u39ij -uviis(kmf o/m f3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, showdwm:4ltc*4rb-d brltk4 +2dq (algebraically) that a ball thrown vertically upward with a speed*bqck t- lt+w4 4:lbdd4r rmd2 $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speexm lj5i i5w;;ld 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 (or 8/hhx se/ pz8b(h ox,tnumber of photoflasheh ,( 8s8/hb/xopehtxzs per second). Assume the 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–h86g :1t)vgpqme* v6fv rw 4dy32). From what height above the top of the wind 4vf 8w:vgmye)r6t6g* 1qd vhpow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound xomr e/.80wq iof it striking the ocean is heard 3.2 s later. If the speed er0m wq8x./ oiof sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garip5,a(-n bk9 mily jq6den hose nozzle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m abi9bnmj(6i5k-,p yqa l ove the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0w)/0d dsy0dgb m/s from the edge of a cliff/ y0sb)ddg dw0 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 above thet(1qq)q8z+ *fs+wz nj/caq:p opxx7 m street with a vertical *qznqq7/xw 1z mp(stp ca:+jf)+o qx8speed of 13 m/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 veupk2y,tu4n 54/44pf pwdyogt r x*qr9locity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, w4uprtu pg52 4y4pn9xrfkq4y /o dw*,t as 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 straight tunnel as a function 9hkn 9yktfsgny.35s29t5 i ut of time is plotted in Fig. 2–28. What is itsfny593 nuh5g 9ssy9tk. iktt 2 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 approximwzs.2(ar d 5nxately as shown in the velocity–time graph of Fig. 2–35wnd2sx5(a .rz. (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 accelera+;iqfp63 l vyd,0uswation of the car in the previous Problem (Fig. 2–35) when it is in w6p,a ds ifyl3u;+vq0
(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 theze 6 9wzts:g7d :mal5p distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a funct2cij 8 6zhrji4ion of time ijicz6 jh4 ri28s given by Fig. 2–28.

Figure 2–36 is a position versuscn s/kae:(2s4(hwm td sqca50 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 direction? (e) Is the object speeding up or slowing down? (2s5en 0q(/smht (cad w: c4askf) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefig0bgu - t8 spj.qnz)pk7hter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Finj80pp )t g. usk7bq-zg. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on v5eve:eudv 9x+xb+j 9Earth. If an object++ve 9exuxevv b j:9d5 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 ecj+ypjb4 5mz)e 3kr/over-the-shoulder seat belt has a good chance of surviving a car collik5rey +zbmc 3pj e4/j)sion 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 puf vha0fv7q:t0 rsuers 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 truck is 1.5 m above the road, and Bo0:vv0taff qh7nd 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 testu+btamq hx/9e,7af 2yv*4 gt r4 4joeied its cars for front-end collisions by hauling them up on a ux7tgj*4fae+ /9ovh maiqyer b44t2 ,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 travels abou- wy5z,ek/efc-vod m1wtl ,1i t $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins0.bsh( x6 aw5il7u +9:0pdcaebqey hx uniform acceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38 :0y.x0 ihsbweb+qc (a pead57u9l6xh.)    m/s

  A person jumps off a diving board 4.0 m above the water’s fqp3lpxf;p-4 surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the pqfpxf4 -;lp3water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, qljs6e nyfp)0. mz u;+it is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slow ufn+jp.l qzy);0 sme6er the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall stm5oif -iq -uu(raight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once c u-5if(mou qi-ommitted. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with w hr52koy,jfnrv.i- (rhich a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, hi -jn,y5r(fr2r.vok 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 f)b; 2xdh,z lqoreight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive stz2b,d)l qh;x oarts 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 droppe8,jx t yfcy( rgv(gw,2d 1.50 s later. How far apart are the stones when the (,w2crygj(y8 ,f xtvg second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial la3dem3lyn, mejl* ;mwn b1d:s*sting ten laps. If the first niym3d3;*ew n1:,*db ljs emlnm ne 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 France crests a mountain pass as he moves at 18 kmic4*pi)y9o9d t8 ee am/h . At the bottom, 4.0 km farth)i 989p4 moe*eaicy tder, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on twoj/*g. 3vghr vl trampolines. The first child can bounce up one-and-a-half times higg.* jglrv/hv 3her 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-lo;m9cr-t ogkxhim1 -c3 ng train traveling in the same direction on a track parallel to the road. If the train’sohc3 kx9; ct-r-1m mgi 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 baseball wx*1eq2i+ 0lfe)xr m1je9 l tdgith a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41).lxmx) 92g l1t de10ejif+ *erq Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerationo 0x dk;hx2bnd2bpk69 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 intersec 8k(hr6hyq 9mltion has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 1 lh(q8rm9k 6hy0 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, passedpjibnka m;pl6) h2m)j.i5da 0 by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police office)p6m0. pb 5 k)alamijj2nid; hr 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/r6f0t: y)e .wgxc cma/h1vn k; 2.00 s after that, a second stone is thrown straight downw/f6m1gkt0 h :r )/.ecn acvyx with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The first stone * sn)5:v rse5y+ffeg6 l as*owis thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a snswyof velsfa56+ er*:)* g5building 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 woul ro n0neph ;g0:(nk3xyd it 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 would her speed be at 350 m? (In reality, the air resistance will restricg(p n;:0ynx3knh 0eo rt her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a con 3,),(xpimi2 t/oq tjoj x8vyeveyor belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and83(m)i,oy/ etiqp ,t 2jj vxxo the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joyuoroi* a3 zkwcly (l1:7t0f/ e can. How many times hi k(liuor3ta/ylf: z y7co01 *wgher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground below w:rep/ds cnb3awt2*8 you. You drop a ball from rest and see that it takes :8 wsp*wcnr t 3e2bad/1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particulapc40 )gu( gwvar building using a barometer. Instead of using the barometer as anuc 4)wg va0g(p altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the positio-uv 3q4nnvk (sn vs. time graph for two bicycles, A and B. (a) Is there an s-nuqvnk3v4( y instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?