Does a car speedometer measure speed, velocity qaojc:/9 wye) fk ;)dhsx36dl, or both?

Can an object have a varying speed if its velocity is constant? If yes, givl30 mg+ llx-qcay(+p le examples.yl(a0+llml g px-qc+3

When an object moves with constan1mi5qr.x72yeb *q8 f cxv6megt velocity, does its average velocity during any time interval dmv1 q5qcm 28byf6x7ie*ex.g riffer from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greateyj 6l ,ygo;1i ;9qilddst speed crossing the finish line to lose o,d;y id9i1gjy; ql l6the race? Explain.

If one object has a greater speex: b8;fn7hercd than a second object, does the first necessaric;rfbn: h x87ely have a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 9e+0 i)bb+ azgnf io-e80km/h to 90km/h with the acceleration of a09fe+agibn)zib- o + e bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a norkumm7 0 viano a7-l)c:thward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is e3eok l. : yco 6.9rlv6abo.vxpositive? What about vice versoe y.xr9ac .3 ko6:lol6v.vb ea?

Give an example where both the vr 2v0y olfoh7vh ql/x5p. 17juelocity and acceleration are negative.

Two cars emerge side by side from a tunnel. C)jo)8-(b*fk+pyawfu b,y tfc ar 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 8*+fu -wa p,k jyfboy)()fcbthas an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration8z rkmdp m3r3tf j+k/2 decreases? If so, give an example. If n m/ptm3 j+fr8rkdz32k ot, explain.

A baseball player hits a foul ball straight up into the air. It leavesk c lr;v+wah3722vl;d+urw p k the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catchevu7hlwr2p;wl k + ;3+dcv2kars it?

As a freely falling objesxv)al 2 6lh-wmg+ xm0ct speeds up, what is happening to its acceleration due to gravity — does it increase, decrease, or stay the same?m l6lamvx) x-+sh w2g0

How would you estimate the maximum heeaj4p qq a 3xk x2+n::)qj)cbkight you could throw a ball vertically upward? How would you estimate thq nbk2)x3+x: )akjqa ecq j4p:e maximum speed you could give it?

You travel from point A to point B in a c ccq00 7miqsdx4 d3sj+ar moving at a constant speed of Then you travel the sa7qjx4 cciss0qd0+m d3me distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonst*jefd y e-0fv7ih6l;sration, a 3.0-m-long 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 e7;6d-h0f*v sfly i ejtied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock falling dg(e iz.p 3d-dfrom a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish restinei.dz3d(d pg -g on a table?

An object that is thrown vertically upward will returnv-d6+/g14pn9vg nt dcvy jp( n 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, t4g9np ddny p(gvv+ -1c vjn/6how? [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 th 6ybi5p:ry5vp e same time? Give exib 5vpy56yr p:amples.

Can an object have zero acceleration and nonzero velocity at the sa lgin1;o;eusdk6skud: 4kx:8me time? Give examples1:gd:u4;nslke;doksx 68 kiu.

Describe in words the motion plotted in Fig. 2–28 in terms ofc :m w3.d.ipkh v, a, etc. [Hint: First t w:dm ci.pkh3.ry to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motizn1l+hb9nci -k8m kfc8v,b 6don of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order ( l; runyiz26 zt;cpk35izw; wto travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly;uvm.w w)v 3 zizcv41u 15 km?    h

  If you are driving along a straight road and you look to the side foss.8z jt z*idc0*ulp4csi3 g, r 2.0 s, how far do you travel during zsciz *cs3,ud.l8jpi4* tsg0this inattentive period?    m

  Convert 35 mi/h to i qbxw* u;2t4+ mn l)+fkd)uwki;t+fj
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves gn c f f67:by8hjmt)0*lxcv/e from $x_1$ = 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 steadilyuadl5 whrc vu(/ja7we*(r k45 at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive ho u rc45d/*ka5he(7lu (wa wrjvme 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, evncc 2n ge9+08nez ook;* 7ulyfery five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of+gu8;nfo oz0 kcen9e7 yl2cn* 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 la to8j ng./ovkcpx:.0t ps around a quarter-mile track in a total time of 12.5 migtp tn. jc8o0 vk/xo:.n. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line,wuujjs;n-b rm+ e84v8 moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4. ;mws+u e884n ujrvb-j8 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 parad7fpniog/ is5eb0; 8wllel tracks. Each has a speed of 95 km/h wi0s57inoegw;8bf/p di th respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a p0pe- vzv a)4ltruck traveling How long will it take the car a z )l0-evp4vpto reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters7ci3v :i,mh 3zxnev0/ y qtuptb; 1c+m a tailwind pnm37,yz ;c :iuc+qvmx 0b1e3/tvtihthat 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 of a complete rouzd))v+hgu/ yamk706 c b5ewqhnd-trip in which tgea zq k y+)whdu7/h06c v)b5mhe outgoing 250 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 hits the pins at*ac-pe+j*ptb5wqp7/.z xpb ee)dk y/ 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. e-ky +)d7ze.je*c*w/atbp /bp q xp5pWhat 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 aveq1uylyeno9 8yd .-j 9urage acceleration in l- u ueoyyy9.n19dq8j$m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in3zjd1 2duz6cs j;x+hr 1.35 s. What is her acceleration 3d6j2cdh ;xrsu1zzj+
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particularr/)/uijfg / i) coom2x automobile is capable of an acceleration of abou i//cm i2o/ougr j))xft $1.6 m/s^2$ 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 constanmx, 9gk9sf 2c*ciioj /t speed travels 110 m in 5.0 s. If it then brakes and comes to a st2 k j*99gsoxmc i,/fciop 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, 7(g 7x.iadc 5fp uets)2uly2jwhich starts from rest at t = 0 and moves in a straight line, ix 7cfl 22)u.gayi5dts 7e(p ujs 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 Table and on a graph.

  A car accelerates from 13 1z1yd 0cqc*uu3t id7 mvd*e(dm/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant acced1duev*m0d iy7t31q (duc*c zleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distuwk4/ dkk71kku 0y br6ance of 85 m. What was its acceleration, as7yk1dw/ kb0 ur4uk6k ksumed constant?    $m/s^2$

  A light plane must reach a speed of 3cqe d3vck o,vu8v.4 0w3 m/s for takeoff. How long a runway is needed if the (constant) a0q.ovcu 3 8cw4ev k,dvcceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed (of h*98j e3g-zl mgyl3kwabout 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how lk zelm9-j lh3wy8g *3gong 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 s. f l-g4 swsc5t*How far did it travel in tc-l4f 5sswg* that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the* skd,p+s fst6nw ;ch- highway. Assuming ak- *ws 6,snhtpfds; c+ deceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strike no) h,/dbcty;z8zuo 2s a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. Whao,;y oz2c uzd8/)nbh tt 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 stopping distances for a car with an i2r enc dl:pq* )a1d0o(tlrbl2 nitial speed of 95 km/h and human reaction time of 1treac:qld)2n0d(12lp br *ol .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 dii1q4j6 yx pjtupvz-2g l62o9 pstance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck 6moeld i71rj4:ug 7 kzgoing 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car cao jdiel 77 r61umk4z:gn 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 10,0v0 ol;av3k ji93kwoa 100-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. Tkoki1v09la33;w jav ohe 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 ca6xanu1upk m1 hugzcuy6881. ar at 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to crosah 1uuupk.66cz gu n18axm8y1s 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 cliff7zaf+ oxulo pu.0/5ri. It hits the ground below after 3.25 s. How high is the cliff+7.ofpx/alru0 u5ioz ?    m

  If a car rolls gently qvrulw1sn0t ;* 6z g2j43qagw($v_0\,=\,0$) 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 up0zsbx(hr 1 uu: into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward. zgz:f s5-i hx6sn ,;nyWith what speed did he f6;n5ghzn-:xiz sys ,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 infk;wjrn1x6+o)8m yjf2 sgb7trs5du o4 luence of gravity. Draw graphs of (a) its speed and (b) the distanjrbo)2j sdk8g7tnr54u61y wo+mxs f; ce it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending cnu7+7 bw;k uoytb75hvertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. Ho tbun7cb5h7 w ok7+u;yw 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 restw/xfozz7)6 et 8ip s7e, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. S7o pz 7swf/e 6et8zix)ee Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) u8acgo.5nip k f5mp0 pf;i, hd)67b cwthat a ball thrown vertically upward with .ukmi;f)7 h0ndfbpc,a55g8p p6io w ca 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 wit9b 4.+o 4sjfqvng7u7dupn9ich 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 photoflah :xl+s1 l tqznlq,9k3sh of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple pos3,:x ktl +qh1 qln9zlsitions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 d(q5k9t5rks7vb/a*mmb. j+ js5yeqxm tall (Fig. 2–32). From what height above the top of the wie axk7qs+9 (qyrs bm5d*k tj v/mjb55.ndow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean is z n*/ ha0zaer2jz;jm1 heard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? r1/ez jaz*z 0n2ma;h jH =    m

  Suppose you adjust your gardeu55kbu8 hxf2k l0 90rxrl:ll /ttdmm.n hose nozzle for a hard stream of water. You point the nozzle vlkxtk0/x:m0 l r 5.h5 u8dr2u ftlm9lbertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown ve :)cp vb/xymz(,q.x- uk n7yenrtically upward with a speed of 12.0 m/s from the edge of a cliff 70.0 m 7pk :-.b(z,unmx/)e vxqc yynhigh (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the strep t6l,w5gdr,eet with a vertical speed of 13 m/s If the ball lp,tr,e 5gw6d was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velockl)*3x nlc-nofwh8f9k 77kn oity of a train as a function of time. (a) At what time was its velocikk- 9how)7fcf8nn3k7o lx n*l ty 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 ayb7 -eldv9(ma s a function of time is plotted in Fig. 2–28. What is-y bav79 m(dle 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 approximat z(1 fnup(sh(u6khjn; ely as shown in the velocity–time graun sk p1;((u (hh6jznfph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Problem pkrt 1vfd86;jnh+b; j(Fig. 2–35) when it is in ;tp6jd8b rvkh1;f j n+
(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 distan h-+kr+u clze.u8 di9ece the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object wl(gg of r .n)arx.4.bkhose displacement as a function of time is given by Fig. 2–28.rb).ol( .g4 k.g xrafn

Figure 2–36 is a position ve(w0 4 j3dc:x;vihi*yb)xlu0 c msazp;rsus time graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the objec:0p dbsux xjca0zl y;*w4m ivi )3h(c;t moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15ngg5 b: qdhd-..0 m above a firefighter’s safety net. The survivor stretches .gg5 - hq:bdndthe 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 Mooeh r6.8:mzhi3xj add gl4v -b9n is about one-sixth what it is on Earth. If an object is thrown vertically h:3mhdd6xbzi8-ea. l v j9rg4 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 u 5uy)pakwmzjgnw; -/z 44*mk7uhq) wan over-the-shoulder seat belt has a good chanzknuwhw4-jgau 4w7pum/ q5y)*) m ;zk ce of surviving a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and hip6 kbwoj3-iq78t46we i fvde3s pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should bko peitw6 vw37ed8 j64bfq i-3e 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 fqfrzcr1e 88)hor front-end collisions by hauling them up on a crane and dropping them from a certain hecr)er8z hfq1 8ight.
(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 trav n9ddatsm vd5-.,nb 3aels 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 5 kkgf,swj/7zfrom rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front ojfws/kg ,7 kz5f 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 the wat5n.n5 b jn1glz2wtn ,ber’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate thg25jwbbtn. n 5,1 lnnze average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid tramyvozsh/.lc/oi kz-0 9p8 d-lnsit system, it is necessary to balance the average speed of a trai/0 shvlozo-.z/ -dl9mc ip8yk n 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 f lod5f(kuu+d1u4 bv:fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot chal b kd(+4o vfu1:fuu5dnge 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 whichf7 ra6wv9ty7htp3p-u a golfer strikes a ball is planned so that the ball w-9 yupv73ahp7rtwft 6ill stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) 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/qeonybh i.w95tk1z 1 t:jmk / constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accelerates zkb./1qwky:hj ite o/9t n1m5 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 o2ejpiysi7-duq 0) hr)f a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reachedydjpuq ) r0sh2i-) ie7 a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/7a; 3,k:nbrt:/xkou.ge6ep+rvkar t h over the course of a time trial lasting ten laps. If the fka,7ut.: 6pr3a +krtbr eegvo;k n :x/irst 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 ssd,n qa );u)dat 18 km/h . At the bottom, 4.0 km farther, his speed is 75 usn;) )qdads,km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playingqw 7*j ,hm(/pqwbcl( a0:rab k on two trampolines. The first child can bounce up one-and-a-half times highew 7(jkc :b awq(h,0alr* qmpb/r 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 overtaken+ z hn7 s6zn9jg.cv x3eor0g.s a 1.10-km-long train traveling in the same din cnn.z r+ov90sx.g3jgh67 zerection 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 directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/s In throwing the btlh(w3eya :(;n3rxi xy)rrx/aseball, the pitcher accelerates 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 ae ( i(xnya rl)33rhr:wy t;xx/verage acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an aomg : mc8(im/tcceleration 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 show4nge0umjdw8gq 8fq9h x;xwe9i jn39+n in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each. g9 +h q9q8ux40xiw j;3e8ejm9fd ngwn
(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 talk,o7k 8pqex. ls7o-lkes off in hot pursuit. The police officer catches up to the speeder in 750l,7k.qel 7 losp8x ok- 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 fr p4qkzt )j:rk;c 8ggk8b8mr 6xom the roof of a building; 2.00 s after that, a second stone is:mbk k8rxj z8tkp4 );c6gr gq8 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 ver yasbt76)iayoqt;,y; tically up at 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 hit) 7 iq,yaybtso6a; y;ts 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-falling parachut-g1 y1q: yai vv:tql9tist 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 air resistance 11 y vitq:-v:tq9 yglawill restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurafugeh 7s+dx.;l4rj- z/ vpnz2nt uses a conveyor 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 belt travel? If the burgers are spac+r.hvpn sxz/dg7 2;f 4juzel -ed 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 h q:zsu1v la0jh,b0, fthan Joe can. How many times higher will Bill’s ball go thas0:f j,, l0zahh1vuqb n Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliffdlv f 5hgkj *6fup l7;;bhm;b+ 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 thal*pbhf +f b 5;jl;k;6vugdm h7t it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using af oqy(.u t)eove7g8 ;n barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the buileqt;(evo .yg fo7u8n) ding 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 posigtw9a r r0u4w*tion vs. 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 l9*r0aw gur tw4arger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?