Does a car speedometer measure spee7 yaq)wx( /vpfd, velocity, or both?

Can an object have a varying speed if its velocity is c65 st* zp;xbrtpz d 0e9u2tmx3onstant? If yes, give exat m zzt2dbt65e*3xr0 9puspx; mples.

When an object moves with constk,kyeppfmv y8g kvgsgh2 :vo5+i n b:/, 1sm)9ant velocity, does its average velocity during any time interval differ from its instantang5b ksvmnepv gk m,h:9y y,1p s)28kfi+:/og veous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossv0l3cjww jf dqih1,v1 yt3 d89ing the finish line , 13f1l yjc wj0d8v9twv3ihqd to lose the race? Explain.

If one object has a greater speed than a second object, m/.cc+w3 zci udoes the first necessarily have a grea +i. u/wm3ccczter acceleration? Explain, using examples.

Compare the acceleration of a motorcycle 2g:hbu 94j+*nhbxn dgiudg/u/v 5rz* that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that acceld5uu b: xnh gv*+hu94i2grbd*g z//nj erates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward accelet s qof a(3v-k;lm2tz,ration? Explain.

Can the velocity of an d4z7p1a 4iystobject be negative when its acceleration is positive? What about vice verss1i 7ty a4pzd4a?

Give an example where both the velocity and acceleration,aq5fr gre-a6 hapz, 8 are negative.

Two cars emerge side by side from a tunnel. Car A is travelg *lnlnt v*2es ;c(h;7kkwua+ing with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of l(n2s*a;gkhk c vwu+*;ne t7l 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, give .:wqco 3v8xzz*rzhl lmc203 a m 3w8l 0z*aqlrzox hc2v.z3c:an example. If not, explain.

A baseball player hits a foul ball straight up into the air. It leaves the baw+xta,y7lcmt5r /)+ h3fz qkst with a speed of 120km/h . In the abt / +smtx flh7q cawr,y)5kz+3sence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds u bx+ngo5k:fjae ..q7a klw:d/p, what is happening to its acceleration due to gwbg:aa q /j5 .:eofl7kn.dkx+ravity — does it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball vertically hr x.ir05vnmxy89u *aldi) 1xupward? How would you estimate the maximum speed you cor18l h xrum*0 dv ai.xyix95n)uld give it?

You travel from pointyt3 ,vv59g h5komwpo; A to point B 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 fro3,phovmt;w55y o 9k gvm A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied o6h*a 99p ka)7abq(aspr qz7jto 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 tapapq *(aj 9kr9 7zaob 7)6shqhe end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is nu/dzbb zl//n(ot at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stoulz /z/b nbd/(ps along the way, a dish resting on a table?

An object that is thrown vertically upward will rr hnltug.ry6,l9p09 h eturn to its original position with the same speed as it had initially if air resistance is negligible.r h9u9yrp60n hl ltg., 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 acceleratrln (pha h-8p2ion at the same time? Give examples.lr( h-2phan8p

Can an object have zero acceleration and nonzero velocity at the same time kdm(s*b7ocuho8*vc;bc3 x6a? Give examplev*m uch(c6a ;b*co s3odx kb87s.

Describe in words the motion plotted iakam l-b f-b7:xl(w5wvj j 84nn Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking o(maj5 wb:wllv4-8nf jbk7x-a r moving your hand.]

Describe in words the motion of the obl( /3psc kohxi,ci99sddb/,9uwc9 utject graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 233*ij5 bqgz2l*oo*vay 5 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it b: -hdqf tm67qtake to fly 15 km?    h

  If you are driving along a straight road and you look to o v6. odh/ izdc,qzi3nf.w;.tthe side for 2.0 s, how far do you travel during this inattentive periodqidv6fzdz w3,oit /o n.h.;.c?    m

  Convert 35 mi/h to gdo(b,w0 7qe8hvxed* ,.axn0pnb e l 0
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from /amw;ur5rp ry i7 ;eq/$x_1$ = 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 95 km/h for 130 km. It then begins 7ml ) mk.jtgr5to rain and you slow to 65g7t5m.jrl k m) km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, 03 fgnmgw ,ikr;1iy )5kqxk8z every five seconds between a lightning flash and the following t3m,fk10ni y)rz kqx85ggkiw ; hunder 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 la7dg-tw.zuvp6y,mg- xps around a quarter-mile track in a total time of 12.5 -v -7gy.x,6zgutmwp d min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, movin1.)6oudu8v: e flgc nfg 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. :d e 8).c vg61ulfuonfCalculate
(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 wdmg*w2q/:t ka speed of 95 km/h with respect to the ground. If th2 wtm*/d qgkw:ey 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/hyopsh3+ n. ao/ is 110 m behind a truck traveling How long will it take the car to reach the truc.h op/nao3sy+k?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters a--x -egilg;n4 5uhsbj tailwind that boosts its speed to 990 km/h for the next 280ug-e x- n;shbglj i5-40 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 vq9b(/c8yx bunelocity of a complete round-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 at 55byc9 8qx/bn(u km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at tl+h- os9hkel e4f47fnhe 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. What is the speed of the ball? The speed of sound is 340 m/fko l7hhn-le 44+fs e9s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its ave7*z f/awfz r/prage accelerarz/wf/a zf*7 ption in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from *:lw27 pkxbu nrest to 10.0 m/s in 1.35 s. What is her acceleration:wbxn up2*kl7
(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 ol.( 5 9oxyf (w1phisfof abouto1 (hfpws fyloix9.(5 $1.6 m/s^2$ 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 tra(+4h,l t z w)uibzfv:evels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accelerati,f4l eb huwzi: zt)v(+on 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, wh ut0 wfsvoo d2.uqje(6-i(tw ayb,-4gich starts from rest at t = 0 and moves in a straight line, is given as a futf2 oi( 0-4uwteb-oqa6 (dwsjv,.uygnction of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25g txuh */nkq (9ugfc6. m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant accelek / th.(u*n6g9ucxgqf ration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a dise+i t(2srp tzu2g 8c4d-v nn0g7crh i :3(rbpdtance of 85 m. What was its acceleration, assume8t pdg bcg27(n:c2 +zu3irr4 nteis-0rhdpv(d constant?    $m/s^2$

  A light plane must r-(i m8i y;kyvd4 s moi3y)3dyaeach a speed of 33 m/s for takeoff. How long a runway is needed if the (conay-(y ymdi)ody8k4si3v;3im stant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to esse3a0fe:s ,r zwjntially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprine0wzf3 a:jr ,ster, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to *lwy ;:rha)j8 cohl 8ijzt;5 qrest in 6.00 s. How far did it travel in that timiw aj;y58);ltr joqh:l* 8hzc e?    m

  In coming to a stop, a car leaves skid mar2j+)f w0 y(ouyd7fowx ks 92 m long on the highway. Assuming a deceleratio2j0 x7w(dofy) owy +ufn of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car comh;kqet/ob m2.2a4foa8k- l nrpresses 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 1.00 ;amrkba to/. 8nekh42f2-lqo g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping ub2p3v)i;y ll9x8hktdistances for a car with an initial speed of 95 km/h and human reactioklpv yu9xti 2hb 38;l)n 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 c6c-/0pzc.g vw x8x(lijvl6ythe stopping distance 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 goingof5y t rop1-y/ 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that hio yt5p-ry1of/s car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 mink:;j id ugy-u elmd v5hr,dg2/ i-ov/7. After exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at 0.20joe2, id7lm5h/iu -:v;ug-vrkd ygd / $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approachsuj nuaj(l +myv/)hx)*;a k h)es 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 cross the intersection before txa/vj (); a+*u)y sml)jnkhu hhe 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 t,8god1*m u s5ofi *iwuhe top of a cliff. It hits the ground below after 3.25 s. How high is the1f58*d mi,uus*wooi g cliff?    m

  If a car rolls gently 2s+ lhra okv7n54 3a4w8zrbku ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

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

  A baseball is hit nearly straight up into the air with a speed of 22b3 ge,*dwce0fe0t;mq m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches ac9onceux )d+2 ball 3.0 s after throwing it vertically upward. With what s9 d2n)xeoc+u cpeed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw graphsi 0p+xc ;nk*lm of (a) its speed and (b) the diki 0 cn;xplm*+stance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending verti;.-vlr6 f psw8dmz9rg cally with a speed of 5.20 m/s. At a height of 125 m above the -l rrfp; z.8d9wm6 gsvEarth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest,(q) yqemcr,4 v show that the distance traveled during each successive second increases in the ratio of successive odd integq)(qe4rm v, cyers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is ne0lg-*rzjh1zf how(a5 4 uw3uzglected, show (algebraically) that a ball thrown vertically upward wiowjh*1u lwga5(rf z3u-0 zhz4th a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertihv9 p)b -+b e.xa4idtqcally 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 beeyh)qa18he- s-x4gys tween each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). g84shq-x-y 1saeyh)e Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2tjk5a+5 lme:7 n, n)gcmz:a9ntne h qc:k1ft/ m tall (Fig. 2–32). From what height above the top of the window did the stt h)n,m :17atat5+n 5k jq:nnc l kgz/e9mef:cone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking thezx(rv c)bfx qr:m65p: b-u9 aw ocean is heard 3.x m69: b)rv zxa5 burwpfcq-:(2 s later. If the speed of sound 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 po0mod u-2 0fd;4yzhue uint the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to;u0m0d2duf-zyeuo h4 you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s f o8 :6*cofxr z,w .me w69 ipz+qmxfp-fara9/vrom the edge of a cliff 70.0 m high (Fig. 2 wwr*cp/zvafx6mep-8z.oi f9mxa +f9 q :6,ro–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 tou)m9v. yz1c1wnp:7 , yx)iq wtrd-pcu pass upward by a window 28 m above the street with a vertical speed of 13 m/s vzcyw,y7i - x). 11numwtrd u9pp)cq :If the ball 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 velo)owjaut.n6p7p k/ )xeqz,20nnum j 3zcity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) D .,z a/xonz0k 73nup)6uqp )je wtmjn2uring what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit alonv)sd0wmaqp):, r7hv ng a straight tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneous velocidhpv m 7:wv,)q0arn)sty
(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 automom.-wp+h sn x(ee4t,7zytzw 3x2f sgb /bile can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The .w4 2xzw3s-m x,nz/( ft+hptsb7g yeeshort 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 -k f7la0,usfgh +oxk3Problem (Fig. 2–35) when it is in x3k f7kfhu, 0a-s+glo
(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 them;r91k xd t4lu distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for :h qdcn.oxs: 3the object whose displacement as a function of time is giv3 d.cqh:s:n oxen by Fig. 2–28.

Figure 2–36 is a position versu g,:xctc0l (hu wvh(5g ah9q0r a:28wag(alf qs time graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E.vhr(,c h(gxg2 aq wf580u( waq lt:h0:glac a9 (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s sbeh bggwx3: .-afety net. The survivor stretches the n: gbh3g-.w ebxet 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on 4ta*ta/zxww1jc7t8h;3q:uncz r ev+ Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on E1hcwt/wqne ;48+uztx aa*zr 3t:vc7jarth, assuming the same initial velocity?

  A person who is properly constrained by an gmrbfja8(4 4p over-the-shoulder seat belt has a good chance of survima8 b4( 4pfrgjving 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 his purs rs5y1+t g8l9+cxvil7 dt;l n8x u8xyycm1fc;uers 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 bt ;1 i88xdrx; 75y s8cvymc1ntcfgx ++l9ul lye when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions ba8s9eda*r3h09 - ) rhhsaaochy hauling them 8ac0*hhe sda- )sr 9a ah39rhoup 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 about qe9vaemfqa l1o d94ot+wp-4( $10^9\,km$ 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 rjqnqng35*y , ;p xt/mrest. 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? (See gnmp;5 jyrtqxq3/* ,nFig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m aboveoe05/5h bxtp6s;w qcjo 4y3ph the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the wateox654/cso3hjq e bp5ht p y0w;r. 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 trada7*v b5sfe3a nsit system, it is necessary to balance the average speed of a train against the distance between stes*af7 adv3 5bops. 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 fall straight down when diving for fish. S f0nuu c b49i50a- jcv2:jegxmuppose 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 spot the2v4cgjmx ju -bi0 u n0c9a:5ef 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 plan :h+z2z jho c coj(;wo;*xel4rned 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. 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 particw cjj(zxhho; o42;zo c+e: lr*ular 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 travelingv/6 ho c3fc4egrol oj3aj2m0 5 at a constant speed of 6.0 m/s Just as an empty box car passes him, the fu 5 vr2oha4fe33goj0/mc 6lojcgitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stonn+r z8 a0dn(e hjj(3iae is dropped 1.50 s later. How far apar e38h0(dj +(jnainzar t are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial lastiwprc82tx ls2gqtm .iuyhx 151;q:us, ng ten laps. If the first nine laps were done at 198.0 km/h . what average speed:tsm q x5 xwr.cls u2u 1q821yt;gi,ph must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he mon1fvh r ,fs21 inqp91xves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his averrq219,xvni h fsfp1n 1age acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two tramp,mu4lk(tm n8folines. The first child can bounce up one-and-a-half times higher than the second child. 8mf4 mlnk(, tuThe 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 1.10-km-long train traveli 7( :ov3jxzuskng 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 caku3: jxz(o7svr 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 throws7lr 4lxycxar4hf:*bi n 9/-wl a baseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3cwn 44b9-ll hi*rry/a 7 l:xxf.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 an accel0poph p+/:hztkl 3c 1seration 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 patt :; tk(bn1l2jvohw/imern shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. Whekowl i(tb:1/ ; j2mhnvn 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, passebzcqnwk6, g*nf x4.iy9 :gw1q d by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The po*1zwbg:9q 4y ki6., gxfqnnw clice officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s after thbrjr vbt-vmig9(w 5dl/gpm 0hj54c +0 :fgst3at, a second stone is thrown straight down with an initiagg +v0i0 pb4jtr3 d5f5t/ljmrb-w(m :c9gsvhl speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time.z,xb/x4qs.pn .u0 icj 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,czx0 nqbsuj./i4x.p 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 t7,ooxmtbx 43n sfgy 50ake a free-falling parachutist to fall from a plane at 32sto4 nx xy0m75gfbo3,00 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+ df3(2tfuwn d 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 travelfd+3nd( 2ufwt? 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 verticalln 7au6j +eu6nx(g/oxi y at a speed 1.5 times faster than Joe can. How manyxn67u g+eao( j/iux6n times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your a a rs66ae d2putatua 5,f 6upx-g438sfriend 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,a3a4ap6ts r8a2e gaf5-u6tx pd s6uu, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find o4:r3h 9ictol the height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estim3tr 4oi:lch9oates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two b 54khgfb,7 eqdjme./z icycles, 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) Whd. /4eb ,km7hfzqje 5gich bicycle has the higher average velocity?