Does a car speedometer measure speed, velor ;n7wnuh7mgj x 0y*+ys-p.*n* uhzeccity, or both?

Can an object have a varying speed if its velocity is cog6d; ngek7cdy 0a ,uireo* 70nnstant? If yes, give examg *,0i;g e77 duko6are yn0cndples.

When an object moves with conrh/ 7cde3vx 0nstant velocity, does its average velocity during any time interval differ from its c 03e7/v hnxdrinstantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossinhr lptl rov.7e+h uc 92fk.52kg the finish line to lose the race? h 7lr5h p.ckul2 r.efk9v+to2Explain.

If one object has a greater speed than a second object, does the first necessar,+or1yj+)ue0pqh,g t q ur mr3ily have a greater acceleration? Explain,tm+ rrre3u ,o, uq yph1q+0)gj using examples.

Compare the acceleration of a motorcycle that r.vt ik(-e bn6f(- 7la im+rujaccelerates from 80km/h to 90km/h with the acceleration of a bicycle thu nm-li7k evfra i((bj 6t-r+.at accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity an rid7:rneec1( d a southward acceleration? Explain.

Can the velocity of an object be negative when its aco+ cm7x x mh2-mlyw81j8+d(zyju o(o gceleration is positive? What aboutdj yz +l-+hu72o1(8x8mmmjco g( xwyo vice versa?

Give an example where both the velocity and acceleration are negativepjqk5n b* :2f-mzl6mgv:6n la.

Two cars emerge side by sioh9aqj a,q/ td2f m:c33zwcs8de from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 4aj9:smq z,acq /d833tf2 woc h0 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 ne4rvm 4i *pz-in speed as its acceleration decreases? If so, give an example. If not, rez4vn4- pi m*explain.

A baseball player hits a foul b ;altu5. /hsekall straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be 5.u se;khat/l traveling when the catcher catches it?

As a freely falling object spv6rd9 t3p/d+g7pvk oki( u3taeeds up, what is happening to its acceleration due to gravity — does it increase, decuaovkr+t96k3 gtpdi /7dv3( prease, or stay the same?

How would you estimate the maximum height you could throw a ball verticallymg h0ln6d.ql- q4 gfo3 upward? How w-6hfq gnl 0m.ldgo43 qould you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant di8vw+fc. +uz: 6hifj speed of Then you travel the same distance from point B to another point C, moving at a constant speezfdf++ i vh6ujw:ic8.d 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 vertical string with ten bolkoy 2vcpzb*, (ts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the tv* zk(2pcoyb,ime 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 acceleration:18gz 9a (pvdo(pm pz6v a rock falling from a cliff, an elevator moving fr1(pz9( aov dgv pz8p6mom the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vts ytm 5j81nm5f0- +a1qh*-gga tjlxmertically 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 accelerammg1 g0qst-a 5m-lxfjt ty5a* jh+ 81ntion due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleratiohg uebl/+;7z.h g e8pyn at the same time? Give e /g;lh+.beph zy7gu8examples.

Can an object have zero acceleration and nonzero velocity at thelf5nlim vk9 ()(wa3(yfj t8ipvuh )f7 same time? Give exl7)tlff kvva)8f h p(3ymjiwni5 u( (9amples.

Describe in words the motion plotted in Fig. 2–28 in terms of ,z 0n *ufcy*q47 b56(wu -vklvpganlfv, a, etc. [Hint: First try to duplicate the motion plown * v7apqlcnlg*fk0 uvf uz-,465 (bytted by walking or moving your hand.]

Describe in words the motion of the object graphed i03c f .kbir0, qzh xzw.,nj5kyn Fig. 2–29.

  What must be your car’s2dy7uo+3 x s6xti; etg average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 km? owo3 7-vgo ),5ptbcvd c*u -st   h

  If you are driving along a straight road and you look to ty :f ;))o,umeeeew -inhe side for 2.0 s, how far do you travel during this inattentive -moene;e )y) u,: eifwperiod?    m

  Convert 35 mi/h to 08hgbwwp)xi+
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frojhth--bm 6 ljl5s*9 rim $x_1$ = 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 ,a, l i5prtqxwbs*v3+steadily at 95 km/h for 130 km. It then begins to rain and y,a3qilbstpr* ,+xvw5 ou 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, eveh0ti,i suq/x 4e :xlq5ry five seconds between a lightning flash and the following thunder gives t/4,qxselit ih5:0q u xhe 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 l9n3obor vt ,(aaps around a quarter-mile track in a total time of 12.5rbvto, na9(o3 min. Calculate
(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 away hzv4)ygf .ssq(-a +al in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calch-)qag zlfvasy.s4+ ( ulate
(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 speed of 95r hj 0qouop 51/j.k4jj km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See F0j u/.ok p45q1jjhjor ig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a tru(9cjr 5k8( mzd+asw3 amc 1gdcck traveling How long will it take the car to reach the truck?mgcw(rz9 3 5skcd 8(1jadam+c    s

  An airplane travels 3100 km at a spee2b4q(o*1uf* oa3lb yohdazh .d of 790 km/h , and then encounters a tailwind that boosts its speed to 990 lby zhb23f o4.a *(oo1 *qaudhkm/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a compk )4 7h*-bji jzzhga9plete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour hzhj kab 4gip-*7)9 zjlunch 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 endsru zfk*j( ) *5:*u:3v+ yv xsqqcndvb of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340:yf s:ckux *5r+v 3*qbsvd*q)u(jv zn m/s.    m/s

  A sports car accelerates frunb 52 i,lxx,aom rest to 95 km/h in 6.2 s. What is its average acceleration ,n,x 5ixb2lauin $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 kw8d9gke3 v39x *yi xks. What is her acceleration dx*kxyv3 ig 8e3k99wk
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capami46koo e /yh:ble of an acceleration of aboutoh:e im4/ yk6o $1.6 m/s^2$ 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 then br u2kmsi(hs0z 6akes and comes to a stop imsh(ks0iz6u2 n 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which startsonka5y /bwd-6 from rest at t = 0 and moves in a straight line, is okwb- ay56n/ dgiven as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. Whatu+ll5*da j9f p was its acceleration? How far did it travel in this+ p9ajf5du*l l time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distan,fd)xz8 , rwjsd33whsce of 85 m. What was its acceleration, assumed constant? )8dw3fs3, rj hxzwd ,s   $m/s^2$

  A light plane must reach a speed t/u/b0f 8 mjkkof 33 m/s for takeoff. How long a runway is needed if the (constm8kkf/0t ju b/ant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter czx 2l(+pemck 1an burst out of the blocks to essentially top speed (of about 11.5 m/s) in the+ ck 2xpe1m(zl first 15.0 m of the race. What is the average 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 mw*wb 4 /ojc+,(kakc*5khrng b )yx s:g/s to rest in 6.00 s. How far did it 5w*4/a)*:,g+ xkjwyhobcgnksc(rkb travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assumingctv+ +k.lhp q.*x*y ev3 m1g+b7c;za wtdrpc) a dyvwp7c.k +d *;)1cva rh .qt3+pmb*t gelz+ cxeceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car compressestkyur/lj ;gntab-9 -2 and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Expressgur n k2j -t;9t/b-aly 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 wiuc (cmha 4qt;97yhl*) /ivffmth an initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleraiamc hy; cf/*l4fu9)(7hv mq ttion
(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 i e-a )xoa*k:efl7ta m,s $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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 .g*tzezat5 6 s5ptqc-dy 2eg6driver looks for an opportunity to pass, guessing that his car can accelerategzcsp5a.et2e g-t 5*tzd6 qy 6 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 10,0007 (p0dmlalvhb,r. ) at-m run in less than 30.0 min. After exactly 27.0 min, thereh adpv.r7l(,m bl 0at) are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an inte5/7atooqjbpt) qx,l8e*okm ; rsection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to s)be l o,jx o7t* m;qkaotq8p/5top, 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 smh;,n lg6o*bd gky10the top of a cliff. It hits the ground below after 3.25 s. How hisohg0y m*6n;k gb,1ldgh is the cliff?    m

  If a car rolls gently +qgh3 8/yv/rpf9;no;n4;mqdn wmwvq ($v_0\,=\,0$) 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 p7 j7uof8tbm gsy*2r8v*6o ik5.z vpd 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 my5hd y67d i5eball 3.0 s after throwing it vertically upward. With what speed did he throw it, and what height diy ei65 7hdm5dyd it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and f4yk) h;-elgd 1qnb r;jalls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ign;l)yk;g-h1 4r je bdqnore air resistance.

A helicopter is ascending ve+:g ia.cr0 vkqgkjl701/cs kn rtically with a speed of 5.20 m/s. At a height of 125 m ab.si0:k/ajcr7g cg l+kn01kq v ove 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’s.] t =__ s

For an object falling freely u:h q+mob6 ,gm :uv,yjqk ci60from rest, show that the distance traveled during each successive second bhm6,cuyu goqi:mjv0, +kq:6 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 negle c9o 55sx n9v4b9bghxfcted, show (algebraically) that a ball thrown vertically upward with a spehx c9b49b vgns95ofx 5ed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed pcqzphynhyrq4h 909 ow7 cn* 4a5+: bkof 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 Fi5tu*l o2z6 pcig. 2–18 (or number of photoflashes per second). Assume the apple* ui6cz2p lo5t 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 xm*w8z9 n(5ndli5/kx n ffm9 p(Fig. 2–32). From what height above the top of th znfd5x59*9p(mn8fnxm / klwie window did the stone fall?    m

  A rock is dropped from a sea cliff, and o6k+ 1 cc0zxqtm;u /glb* 2mvbthe sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how higl mvkmb *+ut0z; qc6 c2ob/1xgh is the cliff? H =    m

  Suppose you adjust your garden hose nozzle form2z jjd197ge+ u.lieg 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 tgzug 2d7mj el+9jei1.he water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s fx/uqc vw5ytb c35u* m07fog ,trom the edge of a cliff 70.0 m high (Fig. 2tw,fcq m7x 53cu/gb0o5vu*yt –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 (uy .tijvvjjg60o5- b by a window 28 m above the street with a vertical speed of 13 m/s If the ball wat .y-jb5jvoj gvi0u6(s 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 wok2 ,a7.w ofkuhat time was its velocity 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 gre,w7o2oa fkuk.atest?

  The position of a rabbit along a straight tunnel as a func+3 .oqsi ::w s k-kkzajk+yfx;tion of time is plotted in Fig. 2–28. What is its instantaneous:- y ja:k.sk fqw3z;+o+sik xk 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 accelervy 3 *dd.k is99k dk-ac4dn bn;dh44xaate approximately as shown in the velocity–timcs.3 i yd kba;4ddk9*d9hdvk4n a-nx4e graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in 51thc7 f2je-yh5ak+w kk vv.0x flrx, the previous Problem (Fig. 2–35) when it isxk cywe 1jx l vfkhrv+t,k5f h207.a-5 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 distanc 85lnjk p18wpye the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the ou:g5s6 gs0z(huo*axhbk0rj )bject whose displacement as a function of time is given* gus a0 ukjors)hbz506:(xgh by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an v),;p/wtdbh lobject 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 pvdbw)ht;l/, ) 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 fourth-story window 15.0 m dtk).:yg.f wf above a firefighter’s safety net. The survivor stretches the net 1.0 m be..f ykt gfw:d)fore 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 Eau 4uhwizcb64kwsy.m vp /vdi5 f.:+i8 rth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it woul/yi+vm68i:c.hdk5.iws 4 uw4 zfuvbpd on Earth, assuming the same initial velocity?

  A person who is properly constrainedd wthc./ihn)a k7 .gv+t(x 6gus.d/uz by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 30 “hgwvuux6)z d/h.sn( i./ cd+kt ag7t.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 brid7i jm cutu-;e)ge, 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 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 ieuj mtu7 -c);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 collisions by; ;bjwr,u7sj/uqb wh 5usq;x + hauling them up on a qjs quj5s7; uxburw; +hb,w/; 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 t27s /:aoubyh;u:jbb9g 3 c+a+otc 7 ;nzkauhx ravels about $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of y3 2gj) wubxf;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 trai 2bw)xfy u;g3jn started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surfa u ;z q6 7inkrekxm+m:0lf. 2fbgmqa-.ce into a deep pool. kn- m6: + mm b2e7ul; 0f.zkra.iqqxfgThe person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance tmx2-syn k.1rt/ q.g i(-gw ld km6zv/vhe average speed of a train against the distance between stops. The more wmm2-tg .6/v -1 /xzgskrvlky(.qndi 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 free fall strai5l.)9f1 ilba;l zwlh rght down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and can59i. hfl rbllw)z;a 1lnot 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 striylbwaz,5f.m 4:m6b vwkes a ball is planned so that the ball will stop within sofa:w ym,w lmzv 56.bb4me 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 constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a constant speed offo:apkq 69bn+w2t 6yg 6.0 m/s Just as an empty box car passes him, the fugitive start+ypn6 2:f kbo awtq69gs 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 sgx:su 06fu;lljw+n fodc1f. 89w3nehf1o9yztone is dropped 1.50 s later. How far apart are the stones when the second one has reached awd1njo :ffux3l l .s fyo1n; 9g9cwh 6+0efzu8 speed of 12.0 m/s ?    m

  A race car driver must aveua)yk6 zo3dp9y1b p4)iga s7erage 200.0 km/h over the course of a time trial lasting ten laps. If the first nine 9p1sako3) 4yd)egpza6i7 uyblaps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour deh;ggmlkw,6( at . p4xh France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h ..m4lhgx(h;tka , pg 6w 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 firj t e1:anplly/65cho rp;j *q.fj -*umst child can bounce up one-and-a-half times higher than the second child. The initial speed up -6lc .j *eryojjuflppt15*mhq/n: ; aof 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 1l g25crrrz- cl3wqb-/.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 th-l3 lr rz5r/c- wbgq2ce 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 with a speed of 44 m/s In throwing the b:nts-y,bpgomo.zuex)y y*c(v 09 g /8ck1gv caseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is0g,:bv(*tgc.v x/)k-u o ysnz1 gp8cmoe yy9c released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from resm wd.1,l-2y f*fopthtt, 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 patn 2 fn+;zgbdr0.3qm an hi9p)ptern 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 10 m from the first intersection, all the lights turn green. The lights 2dq3;. rfzn9)b man npph0i+g 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 ba7*ep+5. ovl pbus5 dtraveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the d op b.p55ue7l+sbva*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 l/eoi13i xa 0c jp7+a )(keebt hw(v:mthat, a second stone is thrown straight down with an initial speede eii :lc ha)+(t1w7jvep30 bko(mx/a 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 s0 g 1njnc c62jhc+; 1ziue,pdstone 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 vel2czui pn1 ; g+dcn01ejsjh,6cocity 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 longnsh d h))xy*6vd6d zu5 would 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 a 6h)* x6z)v sydn5duhdt 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through n7 ,m b;isa s*h)ugl66dd0f lza grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the 0 mbfl 6uslg*zd 6,dah7)ni;sconveyor 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 vz :p3k3 smsivts5r0l5zzu5w pi9 ef29ertically at a speed 1.5 times faster than Joe can. How many 5tvi3s5zwmu k p9l 90 35fsis2z pzr:etimes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top oscfl s /;cy;er3(i/g8e5aub rf 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 t;ubs e rg;5/ea/(s 3ycfrli8 co 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 height5se4expu: -d a of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for thee 5:du-pxse a4 estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a*3uuaqyu f9e hov1i y *u*wp,3) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicyclefypa 3h vwyiuu* q19e,3o**uus 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?