Does a car speedometer measure speed, veloci e5l ixp744uivty, or both?

Can an object have a varying speed if its velocity is rcq798g0*bsi bi5jk c;lg(mm7vs ,ky constant? If yes, give examples0vy, lbqig577cij8 (;sb mmkrg9 *ks c.

When an object moves with constane;4zu5ipfxgwr 3zhd, p4ju2 (t velocity, does its average velocity during any time interval differ from its instantaneou fz;23ug,4xr h pwjid ez45pu(s velocity at any instant?

In drag racing, is it possible for the car with the gr ns2 myz-5 mbkm: gnpef we8tq;115v3peatest speed crossing the finish line to lose the race? 5tg nnsy;mbfmevk:38em1 p1-q 2pzw5Explain.

If one object has a greater speed dipvqq4.s; j 3than a second object, does the first necessarily have a greater acceleration? Explain, using exampp3 s4;i dv.qjqles.

Compare the acceleration of a motorcycoiem4im.ofc,8t/cyn8z9 gik0*am t + le that accelerates from 80km/h to 90km/h with the acceleration of a bi+0z/ty4m fi timecgcoma 98koin, 8.*cycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southww0n.scd7:k l 0res7ayxe-x 5 vard acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positive?t3 cnvvlct. 0/ What about vice vnt t0l 3./cvcversa?

Give an example where both the vely ,:co6pz-w lv 1eutg)ocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A i,re1d8p* lslls+ux30u p kph3j31t oks 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 acceleration of 3h0pl 1p+eld,t83r1o uu k*3xjsspl k60km/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 d6zuzuy (z p/wq gr 1303lk.nwyecreases? If so, give an example. If not, e wu0rw 1pl yzz/(z63nug y3.kqxplain.

A baseball player hits a foul ball straight up into the 73d:goc)8 x8vol hfyiair. It leaves the bat with a speed of 120km/h . In the absence of air resis)g x:o8chvlfdo3 yi87tance, how fast will the ball be traveling when the catcher catches it?

As a freely falling obmk d;pun3 40ibject speeds up, what is happening to its acceleration due to gravity — does it increase,3b kni0;d4pu m decrease, or stay the same?

How would you estimate the maximum height you cohj 5ndp*(awp( jd7z v,uld throw a ball vertically upward? How would you estim5d(j7 *(nphaj, v pwdzate the maximum speed you could give it?

You travel from point A to point B9wc oca4(v0h,bjg9a jlj0 e)e in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip fraa)e0bl v0jjgc4 wh,e 9ojc9( om A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten br e4c v./u4)o eee:mxcolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and theeurmx/4eocv :.cee )4 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 occur at equal intervals?

Which one of these motions is not at constant acceleration: a 9jezs8 hq *gs1rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a tabl z1 gssj9e*hq8e?

An object that is thrownzk pox3xinq61bmopntb ),*;a6 8x0j e vertically upward will return to its original position with the same spbp1z8tmo*x jp)x,qo k6e b3 60n xi;naeed 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 acceleration at wm(h5. w+-vfvjgmua5wab c 8+the same time? Give examplesfwj-b +m vw+w 5cg(8amu5ah .v.

Can an object have zero acceleration and nonzo4cqnq g k.k3(ero velocity at the same time? Give exampkgq4n o q3ck.(les.

Describe in words the motion plotted p2iidg b hzu3 ku -:urfey2(01in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moving yo:dbi3uuuezfg22i1-r0hp k y(ur hand.]

Describe in words the motion of the object graphed in Fig. 2–29 x*hxe)h7 vx(t9ua 9fk.

  What must be your car’s average speed in order to travel 235 km in 3.25o6 vj ggcen: 6*+,ccbtis6kl3 h?    km/h

  A bird can fly 25 km/h How long do(uw;qxx/xqy zh:+7z oes it take to fly 15 km?    h

  If you are driving along a str6g 3 2izhv13xzfzx5t baight road and you look to the side for 2.0 s, how far do you travel dt3z hb2i1x6zgzfx v35 uring this inattentive period?    m

  Convert 35 mi/h to mfai j t,i -o6xw0*0cd
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fo8x2a9af7 ,eorbch ;rrom $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily at 9t-06h ugzq 0nkq-im;d5 km/h for 130 km. It then begins to rain and you slow to 65 km/h Yo-60 ;d - nu0hzqmgtqkiu 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, every five second dx8fu 0ba9b;is between a lightning flash and the following thunder gives the distance to the flash in miles. Assaix; f90dbb 8uuming 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 lapsc.-bfn(1b nknc- - kjt around a quarter-mile track in a total time of 12.5 m nbbc--1ncnkfj-t (k. in. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a stra);i8oq4ci:pop zw4si ight line, moving 116 m away in 14.0 s. It th8;ii wcpz)ip:4osoq4 en 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 tracks. Each has a speed of 9q8 5ph29 qdtege su;3s5 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 F2g98tp3e; sd shequq 5ig. 2–30).    min

  A car traveling 88 kcjd pn0b/*l:ck/f 1 (+df wfxym/h is 110 m behind a truck traveling How long will it take the car to reach tdf:/0+ckff c*1 xy( dwp/jnblhe truck?    s

  An airplane travels 3100 km at a speed of 790 km/hgfqb o2 (1vh7v , and then encounters a tailwin7hvfq 1go2v( bd that boosts its speed to 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 a3ix y/y 2mh2 eq3g ay54voha8of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour luoya 2yy g3 vi3a4h8eqxhm 52/anch 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 end of a s+6tza8wmky + bowlin8 yazkw m6++stg lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its average acce*+2 g;u pnya9dtsw*meleramug* dy+npa s*w 9e2t;tion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Wh4d l9tq8/34h 5q iizgo:oi wriat is her acceleration t 5lq9:r8z iio4dgihq/o4i w3
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acceleration of ag8kxt l6pyik1 ks)3/mbout gpi s8x/m31lk)k6 ykt $1.6 m/s^2$ 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 cons2 7;8zvka d5b dh0xpjjtant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s,8dbhvd;a2z p0x7k jj5 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 at t = 0 and mov2jjqfuth n8 *ef1;zxiu4 he7 +v 3ng5mes in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration 84 qujx mzgn2e7ff+1njh3;hi t*e 5vuas 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 aqo2 ahz1 .mzs*cceleration? How far did it travel in this hqm a*1 zszo2.time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance ojrn *cj:vtsxk l/) 0p.f 85 m. What was its acceleration, ass *rj0vlx ptkc/s).nj :umed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for tak0- a5f;lxbk7m i.8auqedw0u hwjp-c3 eoff. How long a runway is needed if the (constant) acceleration is m xaf3lp.wcek;5 u8j i07-- au0wdhqb$3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed erghom k)*15 a n(;u8wovtvoh;r5jb5(of about 11.5 m/s) in the first 15.0 m of the race. W5nhokobu( er rvj*81 ) v5 m5o;thw;aghat 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 m/s quib(vi;butj + 2ze+9to rest in 6.00 s. How far did it travel in that+jqti9 bu2 ;b e(viu+z time?    m

  In coming to a stop, a c+9louk) vxrf; ar leaves skid marks 92 m long on the highway. Assuming a dkxofrv)u9 ; l+eceleration 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 ezsd;a8 pf 0tg(nd of the car compresses and the driver comes to rest after traveling 0.; tzspd0 afg(880 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stoppi)rc, vadz(f ,qng distances for a car with an initial speed of 95 km/h and human reactiona )v, cz(,dqrf 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 of a cary mzx( *:gupd:*ekm(;psrgopy7e9 g 4 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 t9im;cs v n0hcpgpy cs*6y3) 0 udjlm850peim :he highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate3clsp0 ym*pcpyvmeh86 u9s0;0 g)ni i:jcm5d 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 inlaig op1jw0z/qk, +6h less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. Thqg+ho0 6pzl1 /,ikajwe 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 *wupi sg3yfzn (h t4/4approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turninzw4ishygf/* 3 pn(4tug 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 cliff. It hits the groun:j*2 bt*k u(zc:pc sqvd below after 3.25 s. How high is the z:: *ubp tvcks*q(2jccliff?    m

  If a car rolls gently zj(ee c* p7 c2crv(z45b5lscy($v_0\,=\,0$) 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 withtz :ao(fvy1m8 s3 :o,tyzz9yv a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3 isn:z rx1i(z*.0 s after throwing it vertically upward. With what speed did he throw it, and what height did itxziri1 (z*:ns reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity.n8/iw*gqpic ri, j **ko5ld:y Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 t 5nc/l*ig *yq:wip 8 d*ir,kjoo t = 5.00 s . Ignore air resistance.

A helicopter is ascend5dpwpu;f u r3/ing vertically with a speed of 5.20 m/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? [Hintp /wuu3 d5p;rf: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling fr2rebqb3i ve 1r,9r chpk hh(3)eely from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers e9qhhe r )h2pvibb,(r31rk3c(1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraical4 r/mv6bb6aj yly) that a ball thrown vertically upwardbyr6/bjm va64 with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticall4ai/pm. b6pt4o )gqt xy upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the appg9hmlq5p7x u7 ml+27 / nstt /s3uekfzle in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top5 7ge 7+p 93qs tm7 /umxlszl2/thknfu.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past agsw :(2jeo 7wu2i h1+iqul1 tu window 2.2 m tall (Fig. 2–32). From what height above tw(t7uihu oe+jug 11w q:22sl ihe top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the soui y7mtu3y r/mw:hs h5/i,zt,tnd of it striking the ocean is heard 3.2 s later. If the speed of sou753sy ztt,,tym ui/h/ wrmhi:nd is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hieybm.73r vd7 /va 2gmard 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 verticmda. y7v3eb72 grvmi/al, 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 vertic9ibl1y4zcn0o ss :y6w ally upward with a speed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. osc9i l0nbw1y 6:zsy42–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m rs7ruuogl wku:k /84 z5sh2p0above the street with a vertical speed of 13 m/s If the ball was thrown from the strrh:ruzlp/su8k7wso k0 425gu eet,
(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 of83 vmo57db z7fc sfgte b/5oa8 time. (a) At what 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 greatest?obd/o aff8vg3s7 5cbemt78z5

  The position of a rabbit along a straight tunnel as a function b x(y+o/is ly.tf 8*quof time is plotted in Fig. 2–28. What is its instantaneous veloci+/o t (bu*8i lsf.yqxyty
(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 auk,v4s (pdlvi ;-iz.y3ffz kk1tomobile can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represe 34k-(,f .lvz ;kkyv1pif iszdnt 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 prb::* a9r /xcz(leugi52ync pjevious Problem (Fig. 2–35) when it:rp/2ay5cjzcul n xg*b9i e(: 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 traveled durix5 goqq -qje8)ng
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a functi)15 yg b-a4jhgyr8fiq on of time is 4ygbfr1q8ah5jgy ) -i given by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of p,u:u-ja-uma an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object s ,-aa u:j-pumupeeding 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 a6tsl. k2h)xph;c76-0 2 n ymlnzjjm twbove a firefighter’s safety net. The survivor stretches the net 1.0 m before com)yk6-.2jhcpnjs ;txn06l 7ztl2mmhwing 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 whaihswkivk 1; cbe1h ;/r0g1 av:t it is on Earth. If an object is thrown vertically upward on the Moon, how many ti1vh1/ 1hiv ;wr;gcei:k0 bkas mes higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrainesvda8,c(jrf- dg0( k f6wz(p id by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed abofk-s0(j c(pa (8vw6rfz, iddg ut 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 his pursuers ilm.u 8b :4a r;1rhpldare getting too close for comfort. H l a4rr:db. u8i1mhl;pe spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer testedvwi 3b6ol hj o,,q+y(z its cars for front-end collisions by hauling theloq v(6,+,y3 ihzwobj m up on a 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 travels abb8.k kaec:uy nkk q; c4e0g 58m+q/gwlout $10^9\,km$ 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 restg96+ 5mw :j4h v )eyglifcp u9vv:zwu7. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? wmivl9:juf7 5gw g94ecu+6:y v)h pvz(See Fig. 2–38.)    m/s

  A person jumps off a diving bg59b /kkz kaq*owt-:s oard 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 the water. Estimate the average deceleration of the person while un t5aq9bk*soz/: -kkwgder the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the a2bg yn8+p(g 0o 0sb ulxxlds3+verage speed of a tral s(8p3 0l+ +bxnxb2gyso g0duin 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 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 s j:g* 8hpy5oyqy/82 g vtpa;kv..jovfall 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 committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it / k.h vaqoyj ;2tovgppy.8 *8:j5vysgspot 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 planned s8m cb/hubxv+2o that the ball will stop within some small dishb c/x+ bvm2u8tance 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 afy-ninn7ipd**/xg)b e0,hyf 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and acc dp,hxnyn 7 **n/)-yefib0gia elerates 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 ,pu /1xu; gm3;c hnlhbof a high building. A second stone is dropped 1.50 s later. How far apart are the stones ; x3ghu1cblnu; p,m/h when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 2nzgnk-+ mr8e 700.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for thn em7n rkg8-+ze last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 km/hpum 5frwap0pn2q7tk41ykyu k nk3xuc1)/ .9i . At t )/ypukn.nq0p2 x3kwpym1ac t7 1ui4fk rk5u 9he 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 child can boun/f/4uxc8 u1 ,:b df7e eqsclgvce up one-and-a-half times higher than the second child. The initial speed up of q/ seu1xl,/4 7f c8 cb:gfdvuethe second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train travelinlk1x+ t,yv8y lgmllh*qs b035 g 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,l 1y *lk+b8 ls,gtyqxh53ml0v and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speerx+6yj nzvm+ 2qq+/0nvqn dh 9xb -uo2d of 44 m/s In throwing the baseball, the pitcher acceleratem2x+rq +2zbvnqxoq v 9n0/-dj6u nh+y s the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with awr hiu3u/ ff5ki4 *hlfic 6;qe9:u1fm n 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 inter pm0 /l:bw/b9zdw nsw-section 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 greendnzb ws/b pm0/l 9w-:w. 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/h7xj2k b sx2: yfv7tos zpo3)j1 takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintainin2t7y1zx3p)jk: sxo sfjbv o72 g a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s after that, a second stonyw.uj8 h xtunb8l 3*(fe is thrown straight down with an initial speed of 25.0 m/s and the twnx(*uf yuhj3tw 8lb.8o 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 ti8avz.,/;xe a(wh2l/qn uwq +.ec kc bime. 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 after 4.5 s. With what i,zca u h/x(;. i.aqc8e/+blveqw wn2knitial 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 para.+z 9 5h ae 2/u:ag-xyrqryynuchutist tu.9g/q2aa+rynhzu-e x5 y :ryo 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 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 burgers5h8r:y5jg m63f6ivcmhr2 o gefle-6i through a grilling machine. If the grilling machio:ei e fh6 2f3vm hr58ylg6rgcmi5-j6ne 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 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 titve4*v vyni;cf*oo) ,j98qx97 wsdibmes faster than Joe can. How many txnd;ti84 7v9oy i9)os*q vjbwf,evc* imes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a clif8q6olz1f d cbmo vm:6*f 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 b*oo6 d 1mmc8q6 lf:vzcomes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular buv7p rtaod x:ss .au75mh*4pj :ilding 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 :*ras 5ha7.udm:p7xjvps4toother, 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 p5+x 5rzy(6rdk8 su tq(w3ovjbicycles, 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? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle(56xrpsy+koujz3v58w qt(dr has the higher average velocity?