Does a car speedometer measure speed, velocity, dd1,h1(( ws5tixsizg68 uzwf or both?

Can an object have a varying speed if its velocityqk xzp :nmkz /u-c*9e; is constant? If yes, give examples.c9*zp;kexuz m nk/-: q

When an object moves with constant velocity, does its average velocvnwfxx7yvgl3y ):6; m ity during any time ;yv:vg)fx763xlnmwy interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crosiw8xmux 10lf 6hu 3wk,sing the finish line wmwx1h3,x lu0k i6u8fto lose the race? Explain.

If one object has a greater spee .ap4-k-xp nbt u4fa/nd than a second object, does the first necessarily have a greater acceleration ./faptuk4 b an-xp4-n? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 904a,g4ke1hii kkm/h with the acceleration of a bicycle tek 4 iki1ahg4,hat accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceler xt gbz5krd8 c,s*xebvcp a6w)v86 m1)ation? Explain.

Can the velocity of an ob5i za+mpt*mo+595r,a*tz*zu pzgc qp ject be negative when its acceleration is positive? What about vice verar,+opm9z i *ct qz* z5+gamp5 pz*t5usa?

Give an example where both the velocity and acceleration ar;2 i 5y4mgm+s,rskhq de negative.

Two cars emerge side by side from a tunnel. Car A is traveling with-ovl 3f0v v20 facs-hnlro9.q a speed of 60km/h and has an acceleration of 40km/h/min . Car B has o.h llvrfnvqso3 -00 2av-9 cfa 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 tib;g ik;d/eh7i 4o1r its acceleration decreases? If so, give an ekh7 igdi1r4;i ;et/o bxample. If not, explain.

A baseball player hits a foul ball st1hx /hg kj :llrs*)y4uraight up into the air. It leaves the bat with a speed of 120km/h . yh j:k4/xusrg1*l)l hIn 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 isoyr;sqc fo :11 happening to its acceleration due to gravity — doq1or:yofs;1c es it increase, decrease, or stay the same?

How would you estimate t+ gv h*-ghp6owhe maximum height you could throw a ball vertically upward? How would you+6vh wo-hgg* p estimate the maximum speed you could give it?

You travel from point A dm()q8pprog -to point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your averag8 -gpq)(mr dpoe speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied tb:; q5ghx.oyc9m,p ii o it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied soi. ipb5,qyxgmc; :oh9 that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock falling f9o wa+ a;h-oqnp.;qz arom a cliff, an elevator moving from the second floor to the fifth floor making -9nz wh+oa; paoqq.a; stops along the way, a dish resting on a table?

An object that is th l n.,d(/4yoa4ngsl1w eadnv4rown vertically upward will return to its original 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 ren/4w (snloy,de144 v.laan g dsistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration/mi ,nfa1w*x qnlay (+ at the same time? Give examplx a*i,nqny(a mlw/+f 1es.

Can an object have zero acceleration and nonze(6a.3 cmuc4qpjaz1 sx ro velocity at the same time? Give examp4cxs.a1(3 z jmap6uqcles.

Describe in words the motio glkw2)cy2j3(-quiyv. at gf/n plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking oj-fygik )y/u.v 2l qw(gat32cr moving your hand.]

Describe in words the motion of the object graphed in F pqy6ip: 5e7t3u+0x ehdjgae6ig. 2–29.

  What must be your car(sdh5lik x-. s’s average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h H, n:tpjy1(/wf dv9gtcys9jg4ow long does it take to fly 15 km?    h

  If you are driving along a straight road and you look to thea 4+ gvy(:htxtu( (eou side for 2.0 s, how far do you travel during thi g tx((y:etha(u4v+ous inattentive period?    m

  Convert 35 mi/h to cyf)zyumuu7 ,5n w*+r
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fro67k;*ipgnmubny 5rx0 soy4p2m $x_1$ = 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 t3o7u7s r 9 n)fsq j4;eir(r8cq dd:cmhhen begins to rain and you slow to 65 km/h You arrive home i u 77dq(c f9rr4c;)s:dhmo3e qsj8n rafter 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-th cf uw(5kyi 8du1yc 0kiz(wk )a0c+qj+umb, every 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 sp5iqac00(y+dckw+uc 8jf ui y kkz)1(w eed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps aro /6q6+yjggv/ jctdoji* :tbt6und a quarter-mile track in a total time of 12.5 min. Calculate c: gytvb+ t /t 6ojjq/j*6idg6
(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 1/ vlb6gl7vz 0(nh b a+eahf4.z16 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calcuh7av4bhn+le6 0az /v( bflzg.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 parallw/6nlp,zvlpp4 9 vpp,el tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 9zvppw6pn/ , lp l4pv,km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long wi b+lkn a7j34vnll it take the car to 3b+lnv4j ka7n reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encohtaaf-tv11g6 rb t d7cv96s0i unters a tailwind that boosts its speed to 990 km/h for the next 280rg0-t96saf badt6hv 1v ci t710 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 compjs qnws4 5i7e:6ey 5ehau7b)mlete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch brm:6nue iheje754)ws aqsyb7 5eak, 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 bowf7y*k z.kem; /4 ljzxlling 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 sound is 340 m/s zx.yekjzmf k/7;4 l*l.    m/s

  A sports car accelerates from rest to 95 km/h inp0 bn1c w tl5-wf)0rku 6.2 s. What is its average acceleratiu0)5tw0nk-fbw clr1p on in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 y/m9s*) mfuqim/s in 1.35 s. What is her acceleration i9 mmfqy /)u*s
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a parti4 i4 saj1n ri6psg3k 8)ernnm-cular automobile is capable of an acceleration of about rin 6s -a1ksp8 ) 4nnm4ij3erg$1.6 m/s^2$ 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 it theny c2n) 8-qmv7amb .dxe brakes and comes to a stop in q2 y7eb 8 m.-cn)avxdm4.0 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 rago ybw6342oa 5:t 2cj cigvtw6cing 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) itcitcwt oy j32vo5:gg6a24wb 6s 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 . )aodfm/t; my25 m/s in 6.0 s. What was its acceleration? How far ma.d o) fty/m;did it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of h;nu6 s;ro,pj6d( i co85 m. What was its acceleration, assumed constant? r du;hi6o p(so ;nc6,j   $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. Hok 3)gbm4;tz6nud) akf w long a runway is needed if the (const)k6dt ubm4n;3fzg)k aant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentia/ e+e:vut6 puilly 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 howp/uue:e i +t6v 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 spe ncq :4igmrp6b ,5)7hytxhkc 7sj5 ,sbed of 12.0 m/s to rest in 6.00 s. How far di y ,6577gm:ksi bn sh5ctp4jx)rhbq ,cd it travel in that time?    m

  In coming to a stop, a ca i4df3bh m9)bs mam))sr leaves skid marks 92 m long on the highway. Assuming a decelf bmd am3sis4)b)9h )meration 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 frl,eh7i 71pawy* -z:ufmb q;k5bj5 jv lont end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleraze7p-,;a hbblfkiu 5*j 1wv7q:m yj5ltion 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 stoppinh8::rmtqf u3i0q j9 tzg distances for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an afhq:0j 9 :tt3zm uqri8cceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping t3gh( yo gw9t6cz)k -u /ozw+qfn2)xo 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 car’s driver looks febo hl8l m2u4 sow.6k;or an opportunity to pass, guessing th.lukhl8s we m26ob4o;at his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. .fjwmm- w +el:al.)cl After exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at 0.20 -wme f :al+..cw)lmjl$m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h - t5 c*ds3hphxapproaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and shehd*p5h x- 3stc 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 belowpj6 /,4u ubzdl after 3.25 s. How h6j,dulzu4 /bpigh is the cliff?    m

  If a car rolls gently (bl(jkh;6 9/ idrbtc e6$v_0\,=\,0$) 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 a7ftxkys:jbq 0-b 5d 2up 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 o0w tg96,hc g u00tkhhafter throwing it vertically upward. With what speed did he t0tto 0c9 6 gw0guh,hkhhrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rb/t acxzj,1y/dj: sb,,ka-qi 1q9dy i est and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it kai9/1qyd:basj,,x1 tcqdz-y b ,i/j 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 (+l8uv l owdsoya2r61e6u (pz of 125 m above the Earth, a package is dropped from a window. How much tims8 (o reypwo +ll(uz66v2d 1aue does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from/uu+0y ,cj m1;z d;8bmyujqs s rest, show that the distance traveled during each s0/, ubcm 8dqjs+ ju;yyu1 zsm;uccessive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown :qrifv :hq)-ivertically r:qvfh):q -ii upward 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 vein96y r o ( rn+bogk:ap5iei5*rtically 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 applh5zd b*. 8jrkxdgy k60e in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear onerjk0zy6 k x g5d.b*d8hs at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel pat,lr+ap :5m :8n(dyubeunrb:xun ,l(st a window 2.2 m tall (Fig. 2–32). From what height above the top of the w t(d:,lr5n :nb:l,ue( +pr u umnab8xyindow did the stone fall?    m

  A rock is dropped from aq0ok)* 0 x1dx0 h,d4svmatech sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the clifxdkxth 01sa*q40, )c 0mvo hdef? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of d0)z xzg; 8nokg .)bjf vcc0 n+ws8n9xwater. You point the nozzle vertica0f980xzcdg +)vgx)bkoj8.nz wc n;nslly 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?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of a d eb/usqtgs 9,qv+9a(cliff 70.0 e/, +b 9gvdaqs(uts9qm 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 the street txa;)j oh.r nqv3ta+ab, x-- zwith a vertical speed of 13 m/s If the bbjarxz,+;3h )-. tav ntao- qxall was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a) At what 8y 53j7 ed8vqzmn ;rrctime was its velocity great8e873vnzm qd5cj rry;est? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straiu ml7a p)o g);;zk4dzmgg1p uj8z1je6 ght tunnel as a function of time is plotted in g k)j z) p 4p7oj;glzmzg86u1u1adem; Fig. 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accele2 fo dh5wy:9pmdy6r 0fmduy p0 --xhk-rate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve repp0dmu- 5fwdy rh 9 ymk:xp06yh-d-fo2 resent 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 accelerakyis w1u(*xjkn zi+xjj8jq897 /shhse6v9d 5tion of the car in the previous Problem (Fig. 2–35) when it is in iw5hks z9 uqj8hyx j 98(se67sjjv+i/dxnk* 1
(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 iq7ep)a.7 l4nzk qcp5 traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the objec04qyj;p j: eeet whose displacement as a function of time is gi ejep 4q:eyj0;ven by Fig. 2–28.

Figure 2–36 is a position versus time graphm/heq:ranvigih*d: )zt6h f9-l t;(b for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negatil ba:i;tn :r 6h-/vm tiqedzhg(9f*h) ve? (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 firefighter’s safety nep*w jcdua c( /f/ves,/t. The survivor stretches the net 1.0 m befored*/cea (s j/ /,fupcwv 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 g30f( eabgg3 lyravity on the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go ta(y3 b03 lefgghan it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat - smx5bx- ti7a;tc8d+*shpae belt has a good chance of survivingm;ih a7*tsd-tx+ pbc5sxa 8e- a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridg0) t6 lu fd6k t.i88hfgug/mgze, 12 m above the road below, and his pursuers are getting/. zlut6tgdi 80fu 6gfgm 8)hk 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 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 c xrt 4tbh--ksh;evz9oy).ns6ollisions by hauling them up on a crane and dropping them from a c.nv6h4t-tz-xokh) ryes b9 s ;ertain 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 wo;y nyc6h ii :icsdr;sa.a+3 bk,4b9travels about $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform s6( 8udym n7-wvp-gwfcm o 9b3acceleration 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 tov ydw -7n6(mcb -38mpgfuw9she last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the watejm l2)jyfq lrk):ug61e.in (yr’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 thnu1yr : e 6jgylk)ji2m f)q(.le person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system,+ exwy8) .xyny it is necessary to balance the average speed of a train against the exyn)8+y yx.wdistance between stops. The more stops there are, the slower 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 4e9xixlo2pa aa b;c3*free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and can a9c3ali*b2aope; xx4 not 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 with which a golfer strikes a ball is planneyb v4rov+i ;*)is b;8:vi:vs nt1t mlbd 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, putting downhill, see Fig. 2–39) is8vv)imib* t;b 14i ::vlsy +o;trvsbn 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 travelz6/a 1yvfn md+t2io t7ing at a constant speed of 6.0 m/s Just as an empty box car passes him, tho1t+d i/yfv2 t6 an7mze fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is drn tb ;kjnap1:8opped 1.50 s later. How far apart are the stones whe1ntpa;bn8: jk n the 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 t +wjjr o:izvwk +t3k15ime trial lasting ten lav :o +ji5wj+wkk13 rtzps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 kmuj9-uf3 gl v0x/h . At the bottom, 4.0 km far ugl x93-0vfjuther, 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 two trampolines. The first child c* 8(xqgg 5kw8gl t)bqdan bounce up one-and-a-half times higher than the second child. The initial speed up of the seco dx*85wkqgglq b t)(g8nd 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 overtakesd/ tb85 di9jhy a 1.10-km-long 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 t 8di5t/9jyhd bhe 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 with a speed of 44 m/s In thron c9yt pf3 ;,-4ngrkdxwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the p 4t,;9 gfnkxrp-yndc3oint 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, k9 8t)k gcet;wfrom rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each id 60:v ii:dazsntersection has a traffic signal, and the speed limit is 50 km/s . Suppossdd :6 vz:i0aie you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a spee a5o31(mghh bjder traveling at a constant 120 km/h takes off in hot pursuit. The police off hgjohm1ab53( icer 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, a second szfu5ms9 kty( 4o-4 g yr-sku;.j: bhq(qhban0tone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at tro.byu-ka4nut 50y :fz ksq9(; -j m ghs4bq(hhe 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 timv.spd(i w5cyp4zn-wd1) d wy.e. The first stone is thrown with an initial velocity of 11.0 m/s fromid(4z s1cp wvdn .. wd-p5yyw) 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 wouldphi 5qyrhi c9o7 w5p65 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 q c965ywio7ip5r 5hhp reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyo k. 3 noge/ ksu6wpiv9(x*8svrr belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and thk pskre/*sxw v8.vi63 u 9ngo(e 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 spea ),8umm30 l7x(n) gc.v9wqur zwk sesed 1.5 times faster than Joe can. How many times high7 .l kw, sva9uc wn80(zm))3xseqrgm uer will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top jrqyz02n+ q7 dof a cliff while your friend stands on the ground below you. You drop a ball f+n7q2 rjyq0z drom rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest 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 particular building using a bk)wtk 58 tkeyk 1k6jt(q2v/oaarometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s)2ja5kv (y 6to1ke w q/tk8tkk. 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 B6de h6bxx il8g n8jaiq/ ,i9l(. (a) Is there any instant at which the two bicyclel66 li ,ibdnx a9hq(eix j8/8gs 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?