Does a car speedometer measure speoc i:t )uqtgf:00rwc (ed, velocity, or both?

Can an object have a varying spee m c8f+or,5qz6ft unv(d if its velocity is constant? If yes, give examfcq f+rmon5vut,z6 (8 ples.

When an object moves wit1xq 6)4pwwrp i1j*j lph constant velocity, does its average velocity during any ti)6 pipx* 1l1rjw4p wjqme interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed cril7i . wxg3 mfi yehy8**l(5rkossing the finish f * ige7yl(m i8yx5rihk.w* l3line to lose the race? Explain.

If one object has a greater speed than a second object, does the first necess6jc6sq;0 gnvibot p*67tu /w harily have a greater at/nsu t7;qihov*g6j 6cb06 wpcceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80 :kyf t*8+fc. ucwpnj-km/h to 90km/h with the acceleration of a bifpjk.*nyu f-w:+c 8t ccycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward ake+:c:5ru j mb-ex 9cicceleration? Explain.

Can the velocity of an object be negative when it s gjag8m;a0:bs acceleration is positive? What about vice jas 8g0;m :abgversa?

Give an example where both the velocit2p8 :aa rddnv7y and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is travelrp- o6xhp1(-z0acjv fup-p d6ing with a speed 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 car is passing the other as they come out of the tunnel? Expl6x orp6ahj-ppu - 0(1d- pfcvzain your reasoning.

Can an object be increasing in speed as its accelerw(mwohd b0g /,ation decreases? If so, give an examgm,dhbww0( o /ple. If not, explain.

A baseball player hits a foul ball straight up into3,lvj +i pztd- ded+vv4.yce3 the air. It leaves the bat with a speed of 120km/h . In the absence ofv4p le3,3+-d+j.ie y vtcdzd v air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what o(o fr,7ttl3ris happening to its acceleration due to gravity — does it increase, d , tr3f7tr(oloecrease, or stay the same?

How would you estimate the maximum height you cod4 as- pwnw04yjv;8lpdluq)61n 4 azw uld throw a ball vertically upward? How would you estimate the maxnp4nlq4udsy p;wl z)v6a1wa 0wd-4j 8imum speed you could give it?

You travel from point A to point B in a car moving at a constan ry8/w2dui3i)n gckxpmn 1(v-m ag4x,t speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip fromxumpr1/,agkng4 xn-m ycd8w)2( i3 v i A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten q0ce0vhtwmm8w x- :;qbolts 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? Willq:v0mcmh-wxwq;e8t 0 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 no /1o jcql0ut0wt at constant acceleration: a rock falling from a cliff, an elevator moving fr 0/tjq uo0cwl1om the second floor to 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 utag+yl*opk b vu- s1 9;qbp41l2x/jcoriginal 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 air resistance is always in a direction opposite to the motion.]9tax;vqsjp *yub-+o c4/ku 2lgp1b1l

Can an object have zero velocity and nonzero ji -/ns8abj4iacceleration at the same time? Give exampl-jj ib4/8iasnes.

Can an object have zero acceleration aw 38kwt-f2 y,q-*ksr sxeu kxhv.2dy4nd nonzero velocity at the same time? Give exampl-v2k3e48k2 d wt w shkyrfu-*, xx.ysqes.

Describe in words the motion plotted in Fig. 2–2rwir-*4 ::ltyq ueu 9pd l7m-v8 in terms of v, a, etc. [Hint: First try to duplitim :ye *rwq updrl9u7-l:-4vcate the motion plotted by walking or moving your hand.]

Describe in words the w-mjg v6 2t4)whgqa+kmotion of the object graphed in Fig. 2–29.

  What must be your cazhnf oaizw a sdl+u, ou,+ ;)6+23tehor’s average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does i sp +9um3eq bn y.4mi1byl5ok.t take to fly 15 km?    h

  If you are driving along a straight road and you look to tcs pzexp 8w.-9he side for 2.0 s, how far dwes-.8 cpp9zxo you travel during this inattentive period?    m

  Convert 35 mi/h to .f5w2h6u+l0s6 9y+. pb zyzpeshy rue
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fromxxkgyi( o* *chw u-(x5 $x_1$ = 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 kcy-b;k 5nviopy os6y0nz 3h)3 m. It then begins to ra cn-oy0k6i3n h yby3os5);pz vin and you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, evx8 4prx ;mnd9xery five seconds between a lightning flash and the following thunder gives th rxpn8xd 9x;m4e 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 from this rule.    m/s

  A person jogs eight complete laps around a quarter-mr xc 2ee/nv5 iv:qb1hh+mgu*(ile track in a total time of 12.5 min. Calculat n*bg/5vrceqhvx (e m:h1+iu2e
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m awayy: n /x0 9yf-x-g:xoiwbazxo,rkne v)a; an+1 in 14.0 s. It then turns abruptly and gallonbang1:kw- 9in,x/a-x0) o+ :r;yyxe fo zxavps 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 i, v7apvq,fm 9y a4ate9yxjx8t u9p34parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, howaxe,t4a mta 8yu3y i9pvfq9pv 7j 49x, 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 tal cn:.kf(i4 hxke the car t kch.( ifl:n4xo reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and xcjt33ma 4:bv8 l*a:g;baygtv, kvp8then encounters a tailwind that boosts its speed to 990 km/h for the nextv g c8t3;mg:al va4,3:j*bat8xy vpkb 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete round-t(lbb-o0rj4h v rip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 5-or( 4 h0bjvbl5 km/h.    km/h

  A bowling ball traveling with constant speed hits the pi d,a),mkx;w6e t2oeghns 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 bkxodee gmt6,w ; 2)ah,all? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from /b5ngwe v: 2qe9xl y6urest to 95 km/h in 6.2 s. What is its average accel5 g 69q2nu/y vx:beewleration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s;ihuwd -gigudn+*n .7 in 1.35 s. What is her acceleration 7di-u;gd unw.in*hg +
(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 accel/dxh+ fz d8- 8ltyyfw4eration of aboulwyh-8 x4+zft8 /y fddt $1.6 m/s^2$ 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 s. If it5 -hy dyc)pvb- then brakes and comes to a stop in 4.0 s, whaydbh cp-v -y5)t is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at te s2iry gqd02fa u/8xba,:q(t = 0 and moves in a straight line, is given as a function of time in the folf u0a ieqsytrg2x8/:(,dba2qlowing Table. 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 quc*jus 4/vf5s. What was its acceleration? How far did it travel in this t squfj/* vcu54ime? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 7dnr7-p hgz e 6dnc0u p9aqo*323 m/s to rest in a distance of 85 m. What was its acceleratio e*ng3d7 q dap9ponhz7r60 c-un, assumed constant?    $m/s^2$

  A light plane must reach a spiiadyso31.v yla 72 9zeed of 33 m/s for takeoff. How long a runway is needed if the (constant) aciy lza. dos137iv a92yceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed ggd.:m nksdveh9 ufz5v 522; r(of about 11.5 m/s) in the first 15.0 m of the race. What is the average :nk5h9z.u 5regv2;mdfd gs2v acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest inmjnwf7( x(1t55wa lfa)d, yio 6.00 s. How far did 7) dmo (yj,ltwnfx5fa1iaw5(it travel in that time?    m

  In coming to a stop, a car leaves skid marks 92)cs ;*cjxxhd*-xyeg0sj/ x(t m long on the highway. Assuming a decelerat yjgs;s/hc 0jt*ex xx-d*(x)cion of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strg7x(j0tp,uknt9v mz2ww8d t.iwg 87 yikes a tree. The front end of the car compresses and the driver comes to rest j ty8(t 8dk9pm 2x07v twnzg.uw7,igw 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 distanuh0x9,nv 5burs-ax 4a7gown (ces for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an accelera vwbruonusg n,4hxa957(a- x0tion
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation d:, sukq6 a t.(gpmqfe7td.k* for the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The cd9 4v- cf,iqyjh6(ficar’s driver looks for an opportunity to pass, guessing that his car can a49yh- j(fq, fcvi6cdiccelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in ltz+q yxti1 n8ao2ir)2ess than 30.0 min. After exactly 27.0 min, there are still 118ty2ri2q )1niax ot+z00 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 c)k tm)j/pe5ryar at 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light l5tp)y r)je/km asts 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 ozl64g7n3bkm* )cqqftkv4 vt3f a cliff. It hits the ground below after 3.25 s. How high is t3tb 74t* zq) kvncvgf3 6kqlm4he cliff?    m

  If a car rolls gentl0w 9)aln q9f7s4xk ezoy ($v_0\,=\,0$) 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/6 efqg-n,f ed 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 bab z2rhee8zph4r .2v y*ll 3.0 s after throwing it vertically upward. With what speed did he t rz4 e 2y82.ez*vphhbrhrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. v28e3 f;r ; y,b+fssqll- hdtbDraw graphs of (a) itfbvlr32h;+ ytf 8 qe;d,sbs l-s speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height 537s hf6ydy ztof 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 the helicopter’stf 376dysz 5yh.] t =__ s

For an object falling freely from rest, std.w, dsj6 aip4o p0( vi/kz*ghow that the distance traveled during each successive second increases in the ratio of successive odd intedzs(/ iv,.w0pgdk * 4tjiapo6gers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown ve(6w5k x srw3a7,idwg zrtically upward with a spksrag3(d w ixwz567w,eed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vert,j cp8uflmv m)nzw hn9-4v-8j ically 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 Fig. 2–18 (ot+uaivt 4/: ehr number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.+/ uit :ehvt4a]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tal9f.m iw g)5izuls0q+0u i)oi ll (Fig. 2–32). From what height above the top of the wind+) isll.im quzifw0g )0uo9 i5ow did the stone fall?    m

  A rock is dropped from a sea cliff, -ry- v5 hf;xw:a nx0aiand the sound of it striking the ocean is heard 3.2 sy:nra xwif xv5-0ah;- later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzojh f(ch y63*zle 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 water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?6yh ch (*j3fzo    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the :x 9 m-rhrpckm60sj3bedge of a cliff 70.0 m high (Fig. 2:9schb p-6xkm3rm0rj –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 upwe+jlcwcmxp( j/b/8:g c8rc nd1q/p 9card by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the streetcq j e /j8xcnl/1c8/9+(r pcmpg:d bwc,
(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 a8+k / n a.tsja9,.seufv7onyd train as a function of time. (a) At what time was its velocity ktos a,n7v.a d/.9ynfe+jus8 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 ra.a ( 7jmsq7wkafk(7i( (la: rtck ,vgobbit along a straight tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneokoq7v7 wkrlf(a mi, j a7((.skgt(ac:us 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 caqhnyy9 3j/v k8n accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the cu /v9qnh8yj3y krve 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 acceleration of the car in the previous Problem (Fig. efel;m (n.mw* 2–35) (l .m eemfw*n;when it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object kun 1k0a-p5currujdm 8s01zhjn64o ;traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose di/7h*k:tk8 z)km aqgeqsplacement as a function of time is given by Figq)kkt/zmk 8 e7hq: ga*. 2–28.

Figure 2–36 is a position versus time graph for u7gv;bs 6ldp+ dk1d1o the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving ikg bv1ou s +p16l7d;ddn the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fouri9gg (s;-wrcvr mori( 3ti70sth-story window 15.0 m above a firefighter’s safety net. The survivor stre0 9 wo srvicr g;gr3is-m7(it(tches 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 it is on Earsum6i2 g/mwp3th. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assumium3s iwpmg26/ng the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat belt has a goo bt ;a9p8:ntsdd chance of surviving a car collision if the deceleration does not exceed about 30 “g’s;98pa:tt sb nd” $(1.0 g\,=\,9.8\,m/s^2)$. 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 brido /w;hsi2,f5qgp cip1 6omr/sge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by sp/ 51 ir omohip/6g,fw;scq 2knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-eni;xw*ru(yw 4k( dnn+c79dqp cd collisions by hauling them up on a crane and dropping them from a certain heiwcuykc;n(+x 9 d7pnrw4q(d *ight.
(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 abofibvi sjcxok ,:v.738 ut $10^9\,km$ 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 frontjyfs;jz*lialq,0n /+ 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 willa;lj+il,f 0sj* n zy/q 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 gwb. 9w1 n2i)b xsg7kim 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 under the watw.b wbik29)sn1 x7i gger. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit sy4ap3 gfw . *r;nneaco8stem, 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 timgw;nf 3a8*.oc4anpre e 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 f/ee*3tk(d 7h jftoj4ulj75bfor fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume b45du ( l77ktj/fetjjohfe* 3the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planned so th hm5okcsd.+: bat the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates cons5s.kbh :cd+motantly 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 at a co +v,q; +ageoiwnstant speed of 6.0 m/s Just as an empty box car passes him, t,oq ;we gv+i+ahe 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 ;damf p+t kx7ip-r ief7 3z8z)the roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the 3 f- zpxk7dm;t a+ifp7i) zre8second one has reached a speed of 12.0 m/s ?    m

  A race car driver must ave *nafe 9,6fqhjrage 200.0 km/h over the course of a time trial lasting ten laps.f,*q9anejf6h 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 Tourk .qsta,k; o0z ;vslouti: yozc :.1t; de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed 0kol oso zkq;acvt;tuit::;. ,yz1 s.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 o+7 ulvotwz1 rmd/3,ee .o(wu two trampolines. The first child can bounce up one-and-a-half times higher 3 uvlw romo.7+w1o /ee dz(ut,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-long train83(netyn ua1x9)ba qh traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h .na ab nq8 9ux13yt(h)e 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 thrjk ,funhi ahf 1lo37+z2aaf(bq;k 9r.ows a baseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates thuk.+ijakq;1 h2h a3,lfb79rnf zo (afe ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertical,)j+dx slrc1gp1m 7 ea 6q-iqcly, from 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 p2n vux.. t 8p:raapfrey:0 of9attern 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. When you are p2vxanfu f:.: tr8rpa0 y.9oe10 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 p7p-.)x;ti cr :fptda 120 km/h takes off in hot pursuit. The pp-pxdtfp;7a :) tcri.olice 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 ax kv rj0m2/4l asvb.w* rd,b)ruxb8u1 building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same tvmb vk2*du lx0 /b84sbjwa rx,.ur )1rime.
(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 s8spn ;0jnmi c:tone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be throm8psj n 0c;n:iwn 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 wz o 1 htu3 jr+(b;c(ouxgc82y0mxsp r/ould 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?xo/ 1r (s2x3pjtuob m8( z+0rccug;yh (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 urx r:h5,:l dlburgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If th, ld r5:xulrh:e 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 Joe can. Howgu dyx3d (aun5i4o4ao*gg - 5u many times higher will Bill’s ball go than Joe’ogu5dg n uo a 34iagydux*-54(s? $\approx$ =    (retain one decimal places)

  You stand at the top a y ib8oshn,)3l .-l6ssef;hxp+j v/jof a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, suchlvo.njpeh)a,s /i38-6lbs; hf+ j yxs 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 p9o 66zs l-sk tvis,u:sarticular 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 osv6-u6kli,os z 9 sts:ff, 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 thec2srw9yt, ,f hgkgj1 rjp1 j)s*3,m hf position vs. time graph for two bicycles, A and B. (a) Is there anymp2hj y ,r1gtws,f c *j,3gj)hr9sf k1 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?