Does a car speedometer measure speed, velo;d tn( xzgt+.vo1.qwzcity, or both?

Can an object have a varying speed if its velocity is constant? If yes, gr*eoapz- 1f v:flrtjbaq:1 20ive examla1:j0 e:b*aqzfrtvo f p1r-2ples.

When an object moves with constant velocity, does its avev;gc:x0j p :36 llbe:xl*qcccph: jk-rage velocity during any time ikg 0hv:c clje;*j:-q3 xb:6lclp:xp c nterval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing the q 0asbjte7d6u )+*iev finish l s7at) ive6*bq0eudj+ine to lose the race? Explain.

If one object has a greater speed than a second object, does the first nep6o 0pli1x mxdq1/) plcessarily have a greater acceleration? Explain, using examples. 1 pi/0x6omllxpp)dq1

Compare the acceleration 0v e8n( rte7pxof a motorcycle that accelerates from 80km/h to 90km/h with thee (vt7rp8x0n e acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a n4c8 d y54yr 6vsn(x6nbxkx 0unorthward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is 0k-hntdcpc.agjmq 3f/+pc66w k wbhdyy0.4 1positive? What about vice yp/hfhcdb6cw +j-tg .m001dk.4cp3ywa qk6 nversa?

Give an example where both the velocity and accelerah i fb8eq0 kw0*ac-4ustion are negative.

Two cars emerge side by side from a tunnel. Car A is trabb +9 j9ypfzd4(,poab veling with a speed of 60km/h and has an accelerata9zf,4 (pbbobyp+ 9 jdion of 40km/h/min . Car B has a speed of 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 uxoxz4 rg;+g33 ra7voin speed as its acceleration decreases? If so, give an o+3oxg743; r rzgvaxu example. If not, explain.

A baseball player hiksugk n5s24ic(4u5af gjq6 . its a foul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of ainssgukq5u44 (c.j k56a 2ifgir resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening t zn(ukyus s72-o its acceleration due to gravity — does kz-nyusu2( 7sit increase, decrease, or stay the same?

How would you estimate the maxiyv(4isr21ql nt/ce3 omum height you could throw a ball vertically upward? How would you estimate the maximum speed you (o4vsq / cy nl312rteicould give it?

You travel from point A to poix ndv 8u9py7r15d:z7+ojx lr cnt B in a car moving at a constant speed of Then you travel the same distance from point 7:ljvu1o58dr7r zxynp+9xdc 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 demonstration, a 3.0-m-l qn6azxn-0acu1,1/cz mevg( song vertical string with ten bolts tied to it at equal intervals is dropped x q6mn1-e, 1cacsau(g/0zzv n from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock fallbf(n70ta -1oc7jf)ww.udl vwing from a cliff, an elevator moving from the second floor to the fifth o1b(v-t 0nd7l)uc . 7wajffww floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original positio6hg+ jj7pu*ii1 ybkr 5n with the same speed as it had initially if air resistanchky61ib57j* u+ipgj re 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 nonzero0m-iz u q0hum. kxc0x1 v3sav1 acceleration at the same time? Give 11su. 0xv0 chuk- mzx amq3v0iexamples.

Can an object have ze elgx. .xjo8;cro acceleration and nonzero velocity at the same time? Give examples.ejlxx c8 ;go..

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [H0nvf4*2c3yua j+ xhygc ;qr0uint: First try to duplicate the motion plotted by walking or mov2r*j+xyg uncq0c 4;f 0uvh3ya ing your hand.]

Describe in words the motion of the object 2s/n4s n+y)n o7xmxyp i x8.yvgraphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.i.h1bml y g,j025 h?    km/h

  A bird can fly 25 km/h How long does it takehoo fy(kj(kws1w5( r+ to fly 15 km?    h

  If you are driving along a straight road an5fdj:ejdz3 p( v3 e)qwd you look to the side for 2.0 s, how far3:j)pe3q v( wzdfjd5e do you travel during this inattentive period?    m

  Convert 35 mi/h to 0 ujmu z(*ss,ryff:7n
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves -+:l5 agj3pwo7jzvdn 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 steadily atl y-* y2 mf ihom4w0a*it)hhy5 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after drivin*aw0itf5m)ly h myioy-h4 h2* g 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightni1 +0a*k/ ,zjg 4 vcrweheol(bzng flash and the following thun g0ze*+h1wzl/j4rv( eabc ,koder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a dg /fyfw97z ;.r puu3arv2x +qtotal time of 12.5 fqz7w+ rxpy92 fu a ;vrd.u/3gmin. 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, moving 116 m away:jpi76o-x95eycw1 frzp; kz qoh+ 7bu in 14.0 s. I 7h5zq uwo:pi;je 9y-rxz7pf co+k6b1t then 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 para/)m9ed*swco : z.5dxzjw 5mhxllel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how lonmc.dxojw mhd )s: 5e zwx/5*9zg will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h x(e*0 e n t*-u;bsfyx.xpkl4cis 110 m behind a truck traveling How long will it take the car kn*yx(4f c exltx0 -.bup*e;sto reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then7)gr3e8vovar l fkr ;9 encounters a tailwind that boosts i g lf3ro)aevrkr87;9 vts 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 velocity8hr 6yibynbw*s .1-sour a;+ y 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 + n.bsi*r-8ao;61brw uyyyh sthe return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constanz60hwfk ,fpf n;z b:u/ ;wec a7q31xwegzgx+-t speed hits the pins at the end of a bowling lane 16.5 6,3wngbf k; / fwafq07x:wx 1 ;ezezc+gh-p uzm 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 averaft/bqa+s7v8v vg) y d:ge acce ) adf:b v+tvvsqgy/87leration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Whoya o0 9tka 3xv-vjuby-(05av25wxhtat is her acceleration hvuatj -xkv -(0ya359y0to5wb2xa ov
(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 ni4-o tt1.gn/hh+nas ;/hoo owm+m v ;acceleration of about ;ms1 t;nogvo/o.mnhhi/ot+ -+nw4 ha$1.6 m/s^2$ 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 tr6 w:k t67jdvycavels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0tkyc:jv7w d66 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which start( p6jtyjewj9-s from rest at t = 0 and moves in a straight line, is given as a function of time in the jt pjy6(9- ewjfollowing 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 25 m/s :g b-2tb4zt7mgok: bain 6.0 s. What was its acceleration? How far did it tra 7-kzbg :og:a2b bm4ttvel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. Wv 1j 4p2wdel6q/fz xg*k jxpyp7:w59ghat was its acceleration, assumed kjxy69vwfd5pgg 2x/zje: 7w 1q l*4ppconstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runway is n4f -m k v7yo6d;l(vtdbeeded if the (consta4 t7 bmdkov;lfdy(v-6nt) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can bu5iy 7ls fx5havp+c12crst out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m ofalx2+ 5h 57vysc1pcf i the race. What 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 12.0xoh1d rzfw*t-g, 9z2b m/s to rest in 6.00 s. How far did itrg, 9w1 z2-ohbd *fxtz travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 q4 l7ae+kmmm5 m long on the highway. Assuming a deceleratiol+mq a5m k4em7n 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 f/bm6h m5e:w3 wju(vecront end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.0v5w:m6b3 hcujee(wm/0 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping tu5azusk+ .e (distances for a car with an initial speed of 95 km/h and human reaction time of 1.0sauzt+ 5. k(eu s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car o, up*mp3 d:eyts ll53is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. Thelf0.. abhg wz( .p t+ 7v-i5apdles3rx car’s driver looks for an opporel( -5gvsa7..f hi3bpz0trda.l x w p+tunity to pass, guessing that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 1a;/gc k 4;sm vn23ul/t sdufio4lu5 v*0,000-m run in less than 30.0 min. After exactly 27.0 min, there are sticl*/iv5av uu o ug;2; st44/n3kmfsdlll 1100 m to go. The 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 approaches an intersection just as the traffjpj;28k2 m(fa47gaj0 ei 43 rcsdgbqaic 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 spe sagiq2ecag 404; pfd3jka2b8jr7m(jed 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. 0ot: lv4806wfi,r6y kbg8 b a9bjangnIt hits the ground below after 3.25 s. How hn,bbf4tn9gl o 8gvjaya0:r6i8wb0 k6 igh is the cliff?    m

  If a car rolls gently ( k3jn,t1z 6 wk/rng7li$v_0\,=\,0$) 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)z u0pobg/wn( 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. With wha uujsw-k7i ,q5mht;i ssj.1/q t speed did he throw it, and what hi ts-1mjjs,.qskuq57huwi / ;eight did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls und u + ixtnilccv*(+adil+gm0-,er the influence of gravity. Draw graphs of (a) its speed and (b) the distance it n+ a-m*d,t +cic(g0+v ui lilxhas fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vevsq,dn868tqp,a u ia8rtically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dro68,u , 88 pdvqistnaaqpped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that thhlt;/ .i(. giikt;apgcf 9/u d.j 3mcoe distance traveled during each successive second increases in the ratio of successive odd integers (1, mkdi tiagfcljg.ou(. /.;t/ 39h ci; p3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball throf4n1ws , fh-pewn vertically upward with a speed 4nf fp,1se-hw $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed of 18.0 m/s l08 pl2:ddcxjy8rd g(
(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 appjwbtznm3 -s/ 0ht9ly( le in Fig. 2–18 (or number of photoflashes per secohytb wt j9n0l-s3mz (/nd). 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 2.2 m yrgd86k qv8( dwv kt9w9p1rx , 7-ublatall (Fig. 2–32). From what height above the top of the window did the stone fallbadx ,y gwpuw vqk6-rk7l18v9tr (d 89?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean is hwp70kvp(0q 5 www urq,)*/sswb0no mseard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? w)w/ pb5w7k0qv*oswqsr, 0(smwpn0u H =    m

  Suppose you adjust your garden hose nozzle for a hard strearhy0 bjl2:rc:nb z, (om of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). z,lrbhryc: job2 (:0n 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 vertiy vwf8 u/mz i p3zkwes2042rl;cally upward with a speed of 12.0 m/s from the edge of a cliff 70.0 m high (Figl2uy zm240wkprs38wie zv;f / . 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 /2b4bdg ups8eg0l w,v window 28 m above the street with a vertical speed of 13 m/s I8pdwg b g0u2,b elsv4/f 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 velocity of a train as a func.ac t8o+ - zgnouknh*5tion of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? ( +n.ou*-t noak5hg8 czc) 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 (qyu7mb. znr: hbn9id (zx58x straight tunnel as a function of time is plotted in Fig. 2–28. What is its inbzqu 9r7nh.bdny mz( :(x5i8xstantaneous 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 ca xsk n5) b1tfm zrfzkrna*9*48n accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The r5x4kfab*8z9 kz *ntr sm1fn)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 previousbv4tr5 v3g;pxu pz,-x Problem (Fig. 2–35) when i3-t pbvx,u4p;z5 vrxgt 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 travel(xi0:dgps ps 0x2*q *gqirr*ned during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the obt5 hxom57e1i b* sn4ulmd+q.hject whose displacement as a function of ti+ 7n5s.5ul qti h1bh4xmoed m*me is given by Fig. 2–28.

Figure 2–36 is a position versus time graph fot-yl smer (6z g0icwp-ti0w2 6r 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 directr2iztmys(c twig l 60w-0-pe6ion? (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 x60mmh0y gh+ tz66vxq-story window 15.0 m above a firefighter’s safety net. The survi6 x 6 x0qyvmgt6mzhh+0vor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is abouhs72tg:36lxkw 9 ly8htcv c:qt one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many tim chlqt76cvth9k8lw :gx y:2 s3es higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the :n udsdobjs6y*g-go+ :5zx-d-shoulder seat belt has a good chance of surviving a car collision if the de g:+6*-s:- dj dsobugy5zdno xceleration 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 br 7gehbo v4m34;dmyvl(idge, 12 m above the road below, and his 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 be when he jumps down from the bridge onto the truck to make his getaway. How many poles i;o 4vde7(h ybmmgvl3 4s it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by haulil k):bwpcz4q6l 9 /jocng them up on a crane akl:j / cq4lbz cow)p96nd 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 travezd*f;,ncmf,+ bl og -hls 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 unifordqc25+) 7f *ev)m/ esq auccamm acceleration from rest. The front of the train has a speed of 25 m/s when it pas/*asvcqu7cm 5) a+d) cmfqe 2eses 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 Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surf0mp 5 a*, 8b7gvma/l, qkrwymvace into a deep pool. The person’s downward motion stops 2.0 m below the surwm ,rm q7b8vpvg*mka, l5a0/yface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the aver uyo*s9v7:ec 05l;rr ic:mn pjage speed of a train vnriylj :9mouc7 *p 05cesr;: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 wingr 7zk6ofqb t9j2u)e c,s and free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelekub,67t c)o9q2 fzrj ican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with whi y/jh57y)xno n5mok g*ch a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case hj5g m yo75y*xnk) on/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 of d)jwv1be,xttnk z q o12+sh 0-6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and acceleratesh w+1-,ds b etk0jq1zt2x)vo n 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 buildtgaq bw7s +9t(ing. A second stone is dropped 1.50 s later. How far apart are the stones gqs 7awb(t9 t+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 time1ft9h nnu 8au9kak135xq m c0h trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lapn 1q kan9tu9u8f1xa h ckh503m?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 km/h xa*ss yrx;)q hc0l- t1. At the bottom, 4.0 km r ;xhsl-*a)qxsty 1c0 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 u he+9xh 8kbf.child can bounce up one-and-a-half times higher than the second child. The initial speed up of the second child is h.uxh98 kf +be$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-lo (wa;85tlcfal/ s,kyfng train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results ifa fasc(fk /y8tlw5l;, 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 o4h+timcnt-3 5yh m3ih f 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is -43n5htm m3ic yhh +itreleased (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with v(7 rlet8co4q mxc2ex92bkd 6an 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 intea ;ip,yuw2 ajaqir7,9 rsection 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 griwa,i y97,a jru qap;2een 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 tne3;ojex)-s0:t z ub kraveling at a constant 120 km/h takes off in hot pursuit. The polue) x0;3ko jns: ez-tbice 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 to8;vsj l +a,jn7l*kqmhe roof of a building; 2.00 s after that, a second stone ol8n lsm7;,a j*kjq+v is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the sa 4calk 5b nxb79fa1q6fme time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. Wi aaf7b 64b l9cn5kxf1qth 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, how5 q6ahh srf2zg8r 4-rl long would it take a free-falling parachutist to fall from a plane at6f r h5-a4g2 8hlrrzsq 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 conv fk2:w ,r*a jh9zdjbb2eyor belt to send the burgers through a grillingjwb:j*rf d2h9,k zba2 machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 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 spee7; sy-00thr - gklh6i aqfbkkw88-mpwq; kc l(d 1.5 times faster than Joe can. How many times higher will Bill’s ba - qk pr-;8 t8s0g l;ymhfk06h7klikbaw (q-wcll go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend sk pdr aiov3 pli.49e+1 c7efm:tands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the f+d 37:e 9ca1lek ip pmri4o.vball?    m/s

  Two students are asked to find the height of a particular building using a bark;i pn0xok+eyvns:i(:c l a (5ometer. Instead of using the barometer as an altitude-measuring device, they take it to the rooaix0 ;k5 y ln:+knoci(pe (:svf of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a)0 jqgg9uwc uok l85yj7qbe,:/ 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 biuy5: ucebl ,/7k0wqo9jj8g gqcycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?