Does a car speedometer measow y7;way ;btl7a wz*(ure speed, velocity, or both?

Can an object have a varying speeded5zp *zt:3o0b5ia:om8 mjmn if its velocity is constant? If yes, give exa55 :0 *apoj 3m8dzboe i:nzmmtmples.

When an object moves with constant velocity, does its average *+gs(h ownm eoj (23drvelocity during any time interval differ from its instantaneous velw2 *r(3mshngo(eodj+ocity at any instant?

In drag racing, is it possiblz335f w1spjh1utq.ju+ 5ucuhwu +zy7e for the car with the greatest speed crossing the finish line to lose the race? Exp3yfu+ .tj5zwwuu 1u z53uc h1jpqh7s+lain.

If one object has a greater speerqp2 qzt2hy *k.tk5s9d than a second object, does the first necessarily have a greater acctt 2h.k ryqsk9*zqp5 2eleration? Explain, using examples.

Compare the acceleratiok ,b z bxeuv3j(,vlyt*vf6 .i.g)7pfin of a motorcycle that accelerates from 80km/h to 90km/h with th ,vzyb3jvgxu6kif* .,f(b)ve.lt7 ipe acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward achr-rurp (vs-+celeration? Explain.

Can the velocity of an object be negative when its acceleration ib,24s/u d7 f;rh()q tu t5pjzjzc p9cvs positive? What about vq2ru(tp,s c7h9)d4j/z v uc ;pzj5f tbice versa?

Give an example where both the velocity and acceleration are negat),9kd; w2htwiw.a hl oive.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed of 6g* hsvb.yk1 s bac)7b:0km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an accelerats h sygvb7.* :back1)bion 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 its acceleration decreases? If.tzk (y2zcb)ug* jy*q-zu,ln so, give an exampleb .)jgy, kzyl(uzn*z2q *ct-u. If not, explain.

A baseball player hits a foul ball straight up into the air rl rr88j6rc 9zmfrc2;. It leaves the bat with a speed of 120km/h . In the absence of air26j cr;z9rmrf lcr r88 resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling objyn)o v0,fb)o- r lgd0pect speeds up, what is happening to its acceleration due to gravity — does it increao0py0b-v,ln ) o)f dgrse, decrease, or stay the same?

How would you estimate the maximum height you could throw a bal-(kkrn k- j9i 5oadpt;l vertically upward?oj-pkt- ;rk(d ka9n5i How would you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at,yah/enbp/q1yt:ue(k: n0 py 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 ://y: 1bheq(unpe, 0 tkayypn . 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 szm 8,lvxrlh/n hp( gi6lwk0-3tring 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. r(xzk-gpm/8lwvl 6h 30 i,nlh 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 occur at equal intervals?

Which one of these motions is not at constant acceleration: a ri:5 +cbw*bnl mock falling from ancbmi:l+b w*5 cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upw3 po;5sgfn,y2g7s wsj ard will return to its original position with thgj; s7, os5yp2nwg 3fse same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero awglnwi/z6ifp4:. rd(cceleration at the same time? Give e(/d zig 6iwlfw4:.r npxamples.

Can an object have zero acceleratipq+1klqe0s 17tf qs j:on and nonzero velocity at the same time? Give :tel0kj +fqqss1q1 7p examples.

Describe in words the motion plottedla), q2idrk8v in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or2dkri ,a8lv)q moving your hand.]

Describe in words the motion of the object grap00r1 d5fmdyjm hed in Fig. 2–29.

  What must be your car’s avi+c w93: liys, 5lhzbp - dt42ie1kxdjerage speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How 8qcba56atn3x7omd y.long does it take to fly 15 km?    h

  If you are driving along a str4*k.8+)gr h+wj+cav bxp sj dmaight road and you look to the side for 2.0 s, how far do you travel during this inattentive*8gcadjjb v+s +k)wx+rm4h. p period?    m

  Convert 35 mi/h to 2euy 3ish623 l 0ajshc
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from 2bq/ ;i :qqai:- pd yt-5cgykd$x_1$ = 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 sy /b 0yux/( tplvf0 yx4)rim5wchool steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours ayix l r)0mypbwy/u4 f/v50x(tnd 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,z i niqsny 0. -k00v(gph9aya lightning flash and the followina(i0 9vh iq-0gp,ys 0z .kaynng 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 g d6s+dxf;ugd/m5, lw-mile track in a total time of 12.5 min. Calculat,dl w;d6g/dsf gum5+xe
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away f(sh3cw1 gu/c nrom its trainer in a straight line, moving 116 m away in 14.0 s. It sh3/cc1ng ( wuthen turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel trak+ rlnk hbhqj-**q6 u8cks. Each 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 before they reach eak+lrbn6ukh*-* q j8hq ch other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a trucs9s yw ))km6cbk traveling How long will it take the car to reach the truc cwsbsky 9))6mk?    s

  An airplane travels 38siporc( y 5/q h)1sxcx-/k8t:k qvbx4mvrx,100 km at a speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for txps5)tyxbm /x:c8v xrv, -hkk 8i1c/sq(4o q rhe 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*cl +pxjb7aqy0 s*qq/-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered*+p*c sj7 l/qa0y qbxq at 55 km/h.    km/h

  A bowling ball traveling yp1un7 ,d,ufvnr vc;9with constant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of 9, rdfnpnvvy,;7c u 1uthe 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.    m/s

  A sports car accelerates from rest to 95 km/hx,w6-hqaw:h 9 hw 0s bq1yd5jk in 6.2 s. What is its average accele q01j9whb5 h -w:h6xws,ydakqration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Wju0 t3rda9 ( )4laftghhat is her acceleration 3f4r jtaua)lgdht0(9
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is cnv/1i*byf/ uok;(x 2by i.zwpapable of an acceleration of about biz 2;/yxw o*yb f./vnpku1(i$1.6 m/s^2$ 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 brapkf koap5,1y 2cwg6zpy3 vp 5;kes and comes to a stop in 4. w p p2z3aykk56pcpy,;1 o5gvf0 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 h:)28forrsc e 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) its velocity and (b) its acceleration as a function of time. Display each in a Taof2h)re s 8cr:ble and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. ny.5 wrn(oi; wWhat was its acceleration? How far did it trave w.;no(y5wri nl in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 d0jqkw; om;w v-ry.s+ m. What was its acceleration, assumed+-vdm.ws;0;jqoky r w constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runwayyrfg.0w09dncym 1 a41ytffd 9 is needed if the (constant) acceleratioyd1cwfm1y00 grf af9 nd94 t.yn is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to es f-y-g4fa kyp2sentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What isafp g-42ykyf- 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 spee/i d+v;fi-* e pzfpb8cd of 12.0 m/s to rest in 6.00 s. How far did it travel in that timbp/ideipfc 8-zvf* ;+e?    m

  In coming to a stop, a car leaves skid marmq/5r ).:j9z ga b l qgkj5u;mnmm4iy0ks 92 m long on the highway. Assuming a deceleration uzmg4:;95qkmaril gqmy0j./5)jbmn of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strik-yq+ 3hrkip,bnr 0rt.es a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.000tp3.r-yrb,hkinq+ r g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a a2o(yeer m18i car with an initial speed of 95 km/h and hume28er aomi(1 yan reaction time of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance op-iu(v 645vewa:fvp ff 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 (enb;x 5tfff* car’s driver looks for an opportunity to pass, guessing ;(fbf* 5xftnethat 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 r 2dolo pglsr g,rr+07-un in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at -gsr+prllr0 o 2,o gd70.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as the tr2 2 mql9*wfbewvl+kj- affic light turns yellow. She knows that the yellow light lasts only 2.0 s befq2b2wl+em 9wfkv *l-jore 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 -edtx6hh 99cm cliff. It hits the ground below after 3.25 s. How high is the cliff?- emtx c6d9h9h    m

  If a car rolls gentl rz q(k- 55kr1u ;s5r+ba1ze5v rmacway ($v_0\,=\,0$) 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 speoces nw-x+kvu (5- o6led of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward. With wha(1h 21vorhjwu73y mibt speed did he throw it, uohrh(3vb7y mw21 ji1and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and fb0vz 0z -sfd,palls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function ofz -d0vbsfp ,z0 time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 ug3zel)h z 1c9m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =_gzl9h3c)1ze u_ s

For an object falling freely from rest, show that the distance trpvu6/3 clgl kdkmi5kxee5;ah*4 b, 9xaveled during each successive second increases in the ratio of successive odd ik4plxkeiu a5,x c3b9/vhk5 6* dgem;l ntegers (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 c9(jij6-8n byb/zhie thrown vertically upward wi9 j(cnz8hy6eb-/ij bith a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with eic/u,(kr1n aa speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple inbun 3)*l9gqi 4mds nz1p nd6+0rmbew; 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 ones at th) r; mlb*nzi0qsg bu9pw43+d6 nd1emne top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a wev(;6*l7)8cf rthihl s2c szoindow 2.2 m tall (Fig. 2–32). From what height above the top of ;irl)hcz f s8t o2chv6( 7*lsethe window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound o2s4nl 6tvoj z,othz jqe9)orej8s.+l : *g0nef it striking the ocean is heard 3.2 s later. If the speed of s s29,q:*ezool4 lozvj.nh n0jr8e)tts+ e gj6ound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You p0knqm la zeoxm gwbf;y:w:0;) z-)/w86ox pmaoint the nozzle vertically upward at a height of 1.5 m ablbxm;q z)wmm ga )0: pn e y;kf/:o0aw8xow6z-ove the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown verticalulodq4f0h h(y 6df qzw0, +/tyly upward with a speed of 12.0 m/s from the edge of a cliff 70.0 m hi uz6d0y0 , yh4/qlf+owtqdf (hgh (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 28k9ioibv9)a13ush f2-8pn lme(,ssm l m above the street with a vertical speed of 13 m/s If the ball was thinspb,8 ( -sm lfl)1ivhe2 9umao3k9srown 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 timrzd/o9p3sg :- iths ,-.ngfwv e. (a) At what time was its velocitn/g -9,owdt3:ss .h-ivz rfpgy greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as rev 1n: t qciu.520+ ypeex g:;nsfc0rwt5(xu a function of time is plotted in Fig. 2–28. What is its instantaneous ve;0n+gny c s vex:i uu r5(2et5terf.01pcwqx: locity
(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 shown inhkxp-y4tt;exm .gh6 8 the velocity–time graph of Fig. 2–35. (The shorem.;8gyhx xk46 thp-tt 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 the previous Problem hqb6bl68-*. mg6 fv kgjlbi +i(Fig. 2–35) wh6lhf8 kg6bi.+mg *jib-bv q 6len it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object cfuscz8vc: s8,1ng b z4v9g hkz:;2m ctraveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function wk(e, wcp,de xw:ej19of time is given by Figp(ewd,kjcw :,ex9w1 e. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object 46oq ix drcsx+6w m9d0along 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 objectx xomics+r9qwd60d4 6 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.wl(kr4/;0bx eou8bfxt(hgs(v z fv250 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–37. /eg20z (o5tv(bk;f8s lx(xh u vwbr4f
(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-sixtg9zb)u p)7.2xv ye belh what it is on Earth. If an object is thrown vertically upward on the Moon, how many tim)xy v9bp )2belgz 7.uees 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 zx48u j d1gmsw3 fqd085jsxls2 9*oapbelt has a good chance of surviving a car collision if thgxsxaw8d*4 jzsp5j q2lm8fu o19s3 d0e deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and hi65o4wmtv m8m.gh0 kttp8n1m b s 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.mvoktt 85 410 n thpmmb6wmg8 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 carsjojv 23,4hwno for front-end collisions by hauling them up on a crane and droppinj3vh4oj2nw , og 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 tr3a9k aruie.0 bavels 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 the train c :ebc4* oybs2has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the lab4y*so: c2e cbst car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving 6t(p* qjw gj-ul) iimol:3fw*board 4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of thqw:- ()lwjf *u opg*j36imlite 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 necess 8,q/svxh3wqb** ci c j9ry2ioary 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 make a 9.0-km trip in twojorshi*yxwb 8 ,vq i3q29 */cc 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 mlp )fhp p-ind56 8dm,wings and free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once cip-m8h)mflnd 5pd p,6ommitted. 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 planjgus07zs o8c1 0gpn1qned 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. Accomplishp 80gsjq01u osc 71znging 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 fr3oq fb700nxht77qe*:z cqg gdeight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and acc0 f7dbz qhtg:ox* c3n77qeq0gelerates 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 uei9+ kjrj0*j mckj3)high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second onekiju) +j *3krmjc0j9 e has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 kmmux63sfz:;,2 ;one rf o*ncjp/h over the course of a time trial lasting ten laps. njf:p 6;s3;zx on*r2ue cm,of 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/wq2)2peob x7vqvfbkp 4lf:h9n32v a at 18 km/h . At the2l 9bpwhvo23qkv)v f 72ea4:qpbx/ fn bottom, 4.0 km farther, 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 c.p kt8o 5;5qc)gcaes child can bounce up one-and-a-hkg; c5ac 5.t)8csopeqalf times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.mlg2c z9 f,x/r10-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–z/gm2,r 9lcf x40. 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 4nw*p;rx t5t ek 0gz3hspeed of 44 m/s In throwing the baseball, the pitcher accelerates the bwp 0txkr3z;e 5thn *4gall through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, 8kak e:fuje0 .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 intersectio:gtxhb9bmp 3-ou j4y (tkq x87n has a traffic signal, and the speed limit is 50 km/s . Suppose yothj7(8x b:9tkypqgbxo4- 3u m u 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 120 km/h takdkn c/cpg7.,gvgc 5;hes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acc5;,cc/ g.ggndp kvch7 eleration.
(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.e.vp7e pxhg (vu;u l-200 s after that, a second stone is thrown sv-hvl7x;ueu.p( e g2 ptraight 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 veqe k7l2w*w r-atg)cx:rtically up at the same time. The first stone is thrown with an inikcwg xw2:l ta-r7e)q*tial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be 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 s-.gug0e 1u v oya3 q4aa9ql,q+isd0d-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the a+ ssau q 9g q0oy-.1,ava0 l4udegqid3ir resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send 3g9be9 3lqssjxb :sr* mp/:vdthe 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 belt travel? If the burgers are spaced es/p:j93gvxdblrmb9 3*s:qs 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. How -2f j ox:-w 98qksqkcumany times higher will2xwk c8-fqjouk9 :q-s Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top 9k /7yjuu *co3of ahy-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 throws it up to you, such that it just comes to rest in your c7y*yahu9ukf j3 o-/ ohand. 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 uso-*-hp+6 sq8oeq0n z cn rho8cing a barometer. Instead of cznno +8*6qcer 0phh qs-8o -ousing 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.2 yhbyae66 17ls mxcp(+ ojz3v time graph for two bicycles, A and 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? Whicha3b6z(ejc1ls o 6xh2y+ v 7mpy bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?