Does a car speedometer measure speed, veloc oyw,h 1;7z hl55hrsho j6a.(gy6 sjucity, or both?

Can an object have a varying) 9gu5d-n .vt* cppihnlyv. *nbsi3j/ speed if its velocity is constant? If yes, give examn*5j9lpsyv /g .)c uvnnt.- hb d*3iipples.

When an object moves with constant velocity, does its averagr/u+v3t avo4he velocity during any time interval differ from its instantanevah+or3t uv 4/ous velocity at any instant?

In drag racing, is it possible for the car with the gre5vdc +o:ms0n*u yk.1i+y0nrixn 0qvfatest speed crossing the finish line to lose the race? Ex +s+ cfqi m k*n :y0d.n10uyin0xvv5orplain.

If one object has a greater 60c qt2 r,k+aj azm /bty -moiqj( c.b/0t(fbgspeed than a second object, does the first necessarily have a greater accelerab/i qga2ftj z6 ,(qo.a+-tmbj0t c 0kybc/( rmtion? Explain, using examples.

Compare the acceleration of a mokni 1j2d:58g qff9kvttorcycle that accelerates from 80km/h to 90km/h with tn1f2tqf5k: d vi8g j9khe acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a nortv38ee0+z olrtjmq b(8vw)j 5rhward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its accelerzbl7r ek.0no))vj z -zation is positive? What about vice versa?zl k0 .)ob-njrv) ze7z

Give an example where both aswuq/4.l hvcz8hz f(;z7y + fthe velocity and acceleration are negative.

Two cars emerge side byuu +e7ii9arl xj0e; 8;-um coe side 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 40 km/h and has an ac+a- m7iurexeuu ;j eo9ic 08l;celeration 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 n 6qjwsx 1x ./6k2cu 4s*fs)whe uy.utas its acceleration decreases? If so, give /weq6h.x.jux uusfs t6 4s2k)nwy 1* can example. If not, explain.

A baseball player hits a foul baddmt2wa52b (ag e 2m8jll straight up into the air. It leaves the bat with a speed of 120km/h . In the abmddatb(gmj 85w ea222sence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds y wb7pe1bnt6kyc .+ s42zhl*n up, what is happening to its acceleration due to gravity — does it inc4h.nb71 bs *ye 2n+kl tpwzc6yrease, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball verticallyfw7mf4 uujad/7j(u gr+1.i c ti*v0gu upward? How would you estimate the maug/c.d41ui+ gva*t i0j(r ff7mj7uwu ximum speed you could give it?

You travel from point A to point B in a car moving at a con8tk93 he fa7zwogg4tshf,vh d*6 o )q5stant 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 th h t 6ov7,*fh8qf stok)3da5hg9ez g4we entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-longzsr8vxw q0:fy -omxsqa 55 ++y vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks qs w8-mzvay fyo :0xrs q5++x5occur at equal intervals?

Which one of these motions is not at constant acceleration:a;: o ;zaiy9us8sv-*qwhwch ) a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making scy; - owa8*i)qsav: shh9;w uztops along the way, a dish resting on a table?

An object that is thrown vertically upward a g jmc5upc756will 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 resistance is always6j75a pccmug5 in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same tr l f-l(aaxjc 8mpz)s7w p(y4.ime? Give example ysm (78p az)(-awrjllcp4f. xs.

Can an object have zero acceleratioj, +h)7wc boihsu 1bak8t5a:tn and nonzero velocity at the same time? Give examjahk,)bci7o1 : bt+ hu5 wtas8ples.

Describe in words the j;pf2r/av7nv:g ,bin motion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the mpia:j;,g/2rnv7v nfbotion plotted by walking or moving your hand.]

Describe in words the motion of the o96tgnvici3bniek5f u c q4fk:f18 )g 7zh24uabject graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 kmfo :hj+ 2.4wc yl3drza in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 km?jah )b: /t cofcy-p;z5    h

  If you are driving along a straight rln../e5en sfp -o* usfoad and you look to the side for 2.0 s, how far do you travel /lf -e. .efpss5* nunoduring this inattentive period?    m

  Convert 35 mi/h to h8xo*)go*urx
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from ic5ta; bcym *k u4*u:r$x_1$ = 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 sch4*smulmpeb8pm p+um 6u(p h2: ool steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You am+up4 p b8mpu( s*muelh :m2p6rrive 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, every five seconds between a lightning f .+iv7xs-r 3 i0jmlvp2udepg0lash and tgdi x+.im2sj70 p0pev v3-lruhe following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a tot.u hce .kc ig;ys5;* k3kf9gosal time of 12.;.9f5gucyo s3sgikeckh* k ;.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in 1 z )znulompe z k2g (,rf3.2eft44zwaa straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Cal u)m4a3wgfzt4 o nrz(2k,f 21 ezepzl.culate
(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 g.*e/siyh/y c wlj;1 )nrf,yx has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be bef*x,) fhn;/ly w/yiys er.cg1jore they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a u6d(uj j)ag c2 ch3sg8kcc3xw;5ygq 6truck traveling How long will it take the car to reach 68kayc;2 5jh3cdsx (quggcg3)c uwj6the truck?    s

  An airplane travels 3100 km at a speed ok enqnj1o 2xx(xn0-y2f 790 km/h , and then encounters a tailwind that boosts its speed to-yxnx 0nq2(knx 1e2 jo 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete round-trimllb m0*9ja 04 k90umqrd5vn ep in which the outgoing 25vmr kmadu04b5* n99ll0qm je00 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hitt(ok(ah :wk x/q*:5aymy )xqus the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands.h(au:yt yk/ o()m:q5xk xq*aw What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its avrz8ax5c2 gmyx-v ;1zgxx4u 2jy bo(3perage accelpj x (zr15gvx2a;zb34o2x -gxyu8 ymceration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Wha;:jdnb+/y 8wvhp wi)6aro 1uet is her accelerationaoy/ dwuhi np e:w6+1jrv); b8
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile isa1+,yco)jszmsymcq0 7*f r t 5 capable of an acceleration of abouofz 7m*m 1)y5s,t+ascyqrc j 0t $1.6 m/s^2$ 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 /bpdowyzkkwg1c p 6ms-lc9l )+o9 b/8.0 s. If it then brakes andz) 9wl61goycwkdopsb9c8pmk/ +b-l / comes to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest 9vf px u.:7fyzat t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and7: f9u.vfzpyx (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. What was its accele3nf 6wt.wdkv4 ration? How far did it travel in this time? Assume constant acceleration. .wv 4kf6twn3 d   $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What wa :fa ):oq .:c;cpxtdjas its acceleratid:caco qft.a ;j ):px:on, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a ruy:jt+e 6lxroz2g/ vi4nway is needil6etr2 /zyxj :4 ogv+ed if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter om fh2xz 7xlk;k955m xcan burst out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is fx o l2m95mzxk5;hk7x 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 m/s to rest in 6.00 kzwn4gpbgk/ / h;uq3* s. How far did it travel in thpk4 ggw; kn/ hbq*3u/zat time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. psgaqo4s1 6..jq) li gAssuming a decelsja1g.) .p6qg4olqi seration 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 cotulx4*7fbu 4t h b8/oi8i 5, lra/ug oeyl8k7gmpresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the co*4//lg77ofk8ituero h84l,li5u x ga bb 8 yutllisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 kn8x + lwj o/ka/34 15 tnmir0ntneoga*m/h and human reaction tiawl3 n04x /81tig*k /mar +ne5njootnme of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car sf4rpm q: gx 3bsmp/-)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 carv4agap/yg ln34 x4eh3 ’s driver looks for an opportunity to pass, guessing that hi l4x pgaae44nghv/y3 3s 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. After egj. 79 ti0j emtzl;aqyhc5(3 ,c /fumrxactly 27.0 min, there are still 1100 m to go. The runner must then agq 0r le;t/.ca(fctz,j7um h 9i53jymccelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 k;1 1uqobw fxw2d vy;n/m/h approaches an intersection just as the traffic light turns yellow. nu1dvwx/;qy2fw ;bo1She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection 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 clif:xd xjxs4gzj.b) 4r6vf. It hits the ground below after 3.25 s. How high is the cliff? 6x4zgx. 4:j)bd r jvxs   m

  If a car rolls gentl*sbsus )mk zej 5ue+*4y ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up into the air with a speed g5zq i7ywc()ipj ; rl7of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward. Wvvr3/(-qjzvu9ue / jdith what speedjdve/v u/3 - urzj9vq( did he throw 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. Draw gra nnso,s,nm63.;a kklbphs of (a) its spe,, 3k.6mskb;lnnano sed 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 315e2lt wr.jqifl xcj9 ;jkj /a height of 125 m above the Earth, a package is droppejf5c jj1;x tw 9jleq3l/rk i.2d 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 from rest, show that th bawf2zmy70zjw96p l9 e distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etcfb0p9jw zylw m962za7.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown verjl gqm2i;ut- /; i pzzm,9if+atically upward with a -uptim, + az/jl9if m;;qg2 izspeed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward w + -sjd;+rkyfdith 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 apxub:: zmcrlw:1.b(hn ple 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 notzb:(.:u1 nlcxmwbhr : the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–322vfhe otni7 q+v/i8a 9). From 7qahvio n/et 9 v2+8ifwhat height above the top of the window did the stone fall?    m

  A rock is dropped from rkof,c-xf 9 b4a sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 mf 4oxk9f- ,brc/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a h; yq7fy;qii0iard stream of water. You point the nozzle vertically upward at a height of 1.5 m abovei qiy 0y;i;7qf 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 fro/aay )/ ka5 kh,e2tyq2 fi)wbrm the edge of a cliff y iyk2 a),thaa 5rq/b/w2)ek f70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to fmr3.uecj,k* pass upward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the s. *c jkf,u3remtreet,
(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 a7 ;p/wc8,z 6jc,jvzsnxw 7bj9in4qvz function of time. (a) At what time was its velocity greatest? 7 4 pvbzs9njj/w7ic6, zjqx;n,8vc wz(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 straight tunnel as a function of time is p6keovs2nrczt9k,:(ve ha(( wlotted in Fig. 2–28. Whn2vr 9 hvc(ekseta6,( zowk( :at 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 accelerate approximately as shownkr.8xfgaw lo. 8:e,dg ouo8v2maz1 5i in the velocity–time graph of Fig. 2–3. 8ko8ovxi1l rg2,a5: wezfogm8d.au 5. (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 n on;c44 h2 rpd-i2knf*pec) lof the car in the previous Problem (Fig. 2–35) when it i nhe4;in -c n2lpko4pfr2 d)c*s 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*jcexpy+.b 9 i distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose dispd32iq7dp 2vn4w2 l ncolacement as a function of time i2 vd2lin on3wq2 d7c4ps given by Fig. 2–28.

Figure 2–36 is a position versus txnol/s6 p ;(up v+gqo+ime graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? No;pl ouvo(+ /x 6gs+qpnw 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 above a firefighterewrf 0*r2pl: k hf/2dz2hk:la b2ma;geeq k*7’s safety net. T2*r2d hlm2aebqklhf2zkew g:e/fp;: a7rk*0 he survivor stretches 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 pg)a53 ntpogu02 j7wlit is on Earth.jw5nt ug g0o app72)3l If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat belt has a goo8u7ypbj(pa2 - sxdd ;bd chance of surviving a car collision if the deceleration does not exceed about 30 “gpp -j8axuyb 2; (bs7dd’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his pur:i c(p-.x :6uk p3hduas pxy6tsuers 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 ucpy.ixs(xpup6- thd:3ak: 6 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 collisions bt f*cujilj8t i5zqo9 96 h9y/of6 wj2cy hauling them up on a crane and dropping them from a certain w6j52*jhu j cfilt q8cz9f/it69 yo9oheight.
(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 about +jzs- jy70y qn txi(56onuq+w$10^9\,km$ 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 q,ei k.l+ u)eha*kkm9front of the train has a speed of 25 m/s when it passes a railway worker who k, +e hli m9*eka.q)ukis standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above t-; v7 miv9mw3lq;hm b7drkg4b he 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 undergkdm 3- vw7q bih9 vm;lr47mb; the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, iu. ( zfst+yayj1 h7ds3t 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 time it takes a train to mauyztj syshdf1 .3+a( 7ke 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 win7y6l2cz8hvfwb7zvk 7e 29bt pgs and free fall straight down when diving for fish. Suppose a pelican starts7wt6e f7pbvcbkzyh 72z29v l 8 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 the fish is at the surface of the water.    m

  In putting, the force with whirlci 5t p8e:gnf3.6q:h9vgtm ch a golfer strikes a ball is planned so that the ball will stop within so.56m pn gc8let:qft: r3 i9vhgme 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 o rwpjl 3acobf++tp-47 f 6.0 m/s Just as an empty box car passes tc-r f7jpp4 a+wbl+o3 him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is m,hz,ij/.-tz (d8aj ver x:ft dropped 1.50 s later. How far apart are the stones. r(:fthz8jzj /edx,v-, mait when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average t4rv mj,si zjw05no66.yyb:b200.0 km/h over the course of a time trial lasting ten laps. If the ,vyj.w 6n4t:jmb56y rsob 0izfirst 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 atuipuix64g*5p2)mi ti 18 km/h . At the bottom, 4.0 km farthm xu64it5pg u2 )iip*ier, 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 .mn*o-tue rz2wb2 u, od3flg0first child can bounce up one-and-a-half times higher than the second child. The initial speed up of the second child-t0g 3.dmnr2uz obw e*,olf2u 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 travelii,mfwhd0 *xey;bco, he vx(a,f ;;t*gng 95 km/h overtakes 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 the results if the car and train are traveling in opposite dirx* ( wh cf;ydf;e,ob mg,t,ha* 0vix;eections? 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 throwx:song,sk7t qct5 y4w f:,7ocing the baseball, the pitcher accelerates the ball through a displacement of about 3.no c:77 fstcts5:o,xq g,wy 4k5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, witr01vrk 9 l12pnouyb*sh 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 iclr z/g;d ln1vs6f4)jc z.1osn Fig. 2–42. Each intersection has a traffic signal, and the speed lif ;/zolnj) gv.szcr6d11 cs4lmit 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 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 bh0xq g k9ko(pmsx:9; 120 km/h takes off in hot pursuit. The police officer catcskxq(0hg b9:kp 9xom;hes 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 from0o) tcoxz5su/ (pd)nitdy a(0 the roof of a building; 2.00 s after that, a second stone is oo5(di)(0a nd/u0pxts tczy )thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up su0 jzi* tnu6z a*,al6at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground aau,* i 06utans*l j6zzfter 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-falling k751plz*g om0d n)fztparachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? ozg l*tzkdm)0 15fpn7 What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a 7x6 ci**zl gzuconveyor belt to send the burgers 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 bex*il* z7z6gc ult travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe can. Hay x5/c rjkp/8ow many times higher willa/5ky rxp8cj/ Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top 8h-uhc9saijg( 88x ds of 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 thrh sg8x-asc id8uj8h9( ows 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 orendzh ud1.4 qez631gf a particular building using a barometer. Instead of u1 4r qdug3zzhd1 en.e6sing 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 the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A anp l+fvm.7/zdkycgcgi qa8(8 s90*vsod2 -yha d B. (a) 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 bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle h.a8qcgla +-sg (kzvm/d*o ifpvcy h2897syd0 as the higher average velocity?