Does a car speedometer measure speed, velocitye,j6 k8dm fsc1 /xoj,f, or both?

Can an object have a varying spl/-o u ei/8 shkh:78sqag9kb91jkn nk eed if its velocity is constant? If yes, give exampls le//8 nh 8g -hkik:o9jk1ku7na9sbqes.

When an object moves with constantdsw74vx j.*;,yat jjx velocity, does its average velocity during any time interval differ from its instaj x*xy;, sjwt.vj d4a7ntaneous velocity at any instant?

In drag racing, is it possible for the car with the gc; yu4u 62adbgreatest speed crossing the finish line to lose the race? Explagc2 yuu4 b;d6ain.

If one object has a greater speed -)onpkkopq6 f4 g7w41bcwh :l than a second object, does the first necessarily have a greater acceleration? Exw)k:w1 k6 nh-cgqlp74 b4pfooplain, using examples.

Compare the acceleration of a motorcycle that accelerates from 8 -tfc8zs40qzsjqrp z q6 g+v-20km/h to 90km/h with the acceleration of a bicycle that accelerates 6jz g0-p4qz-vf zts8s2cq+rqfrom rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleration? 3ghw,8ek5eazn;nk4f iz, yt(Explain.

Can the velocity of an object be negative when its accmrx1xy4 g1 cgs c;(i/f eob(7beleration is positive? What about vicx17;c /r(1 fob4s i(cyexbggme versa?

Give an example where both the x3ce/nhsd lo5 4c7ee(velocity and acceleration are negative.

Two cars emerge siden460nxkj3c , m0okp u8o:tmim by side from a tunnel. Car 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 has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnep0i0nj omck6,8omu m x4:n3k tl? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If sahv+enli6 9z/ o, give an examp9/ h nzeiva6l+le. If not, explain.

A baseball player hits a foul ball straight up into the am ae:(;ujz 0s 4btnde(ir. It leaves the bat with a speed of 120km/h . In the absence of air rm(a: e;tn sbdj04e(z uesistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speedxls9 +wxrhxmy b 74 (.m+elk/lsb(x7cs up, what is happening to its acceleration due to gravis rh9m4b( x 7e/x b+xsl7(x+lkylcw .mty — does it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a bxtultv/h n,,- all vertically upward? How would you estimate the maximum speed you could give i,,vnh /utlt-x t?

You travel from point A to point B in af 2o),w84 ma1 jhncdc*hmxtx . car moving at a constant speed of Then you travel thedto 2xm4m8jx,1.cfha )h* wcn 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 from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten boltii0b)7kf v3rp s-:unp.yii p(s tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the0 :b fpvinirpy s(-kp7u3i.i) 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 mot )my4u1z1rgp zions is not at constant acceleration: a rock falling from a cliff, an elevatoz) mugy r14zp1r moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upwa:m ie bj06c9exrd will return 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 0jx6em c:ibe9so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzerog) *.q9o sdxukwvgb2dt8((qw acceleration at the same time? Give ext*qsq2(8 (x.bu9) k vgd wwdogamples.

Can an object have zero acceleration and nonzero velocity at the same time? Givene6r dgp.;;ypbke0n2 nm y.c 3 exndyr3k0bng.n6.2eeppc y m;;amples.

Describe in words the motion plotted in Fig. 2–28 in te lob8suq/m1a,rm q4sb5 4p3bvxha+e8rms of v, a, etc. [Hint: First try to duplicate the motion plotted by ehrlvmb 3omqa5,/sa xu4sq+8pb41b8 walking or moving your hand.]

Describe in words the motion of the object grt,k y pk.-xm,vaphed in Fig. 2–29.

  What must be your car’s averab2crbybcxbc4 x g:443e26c izge speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it tvpjdvxk :27m9 d n)ja9ake to fly 15 km?    h

  If you are driving along a straifkl5h- uk)5q 4 8h+,n2qhm)swt4ihtwjm zm /x ght road and you look to the side for 2.0 s, how far do you travel during this inattentive perio 4h8m h5whn- xiz2q+/wj , qk5)h4utts mlkfm)d?    m

  Convert 35 mi/h to i;26ff gxn lf;
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves c3r5kcz16an5x qpx, -j f3qvpfrom $x_1$ = 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 i h*c5xuvt-:t-d0z y vto rain and you slow v:d h-ytx*tvcui-z05 to 65 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, every five seconds between a lightning y * j,q8by.wj)5uwncaflash and the following thunder gives the distance to the flash in miles. Assuming that the flash of la q.jw ,ny8buyc5 j)*wight 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 quarterky1(rdwc sq 0ur(/yj- -mile track in a total time ofykdc (s(1 -qw0yj/ru r 12.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its traiiry*g ,) 9nfmgyws1 q-ner in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back min,1)ysrq9y -g fw*gin 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has a speed of ju tqq/+ gj5mv0;3h 4zcl iod;95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before theygz+ ;h5dqlm;v3tujcoji0 4 /q reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind adaei21d d skd-:o 34op truck traveling How long will it take tdo1i - sdaope24:3kdd he car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then ea+vbwubo5) p5.5u nhancounters a tailwind that boosts its speed to 990 km/h for the nex) nav+5 huop5b bw.u5at 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 rounv 6p9-dqwhl.rd-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 co-ph69 w dq.vrlvered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins atay111 t as0la32la :fqrpir3 a the end of a bowling lane 16.5 m long. The 1apq l3tralr3 s0iaa1:21a fybowler 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 averagevq/j tvxt(cj vt7,.8f acceleratiot v,/ft vvjc7t x(.q8jn in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accelerathghed7i *1fl4ion dgh47 he*li1f
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a parwc u;i 8x8gk;2 is k pzm3;)g/hn)lrzpticular automobile is capable of an acceleration of about 2i /l;;u3i kpwzs)rhg88pk;)xn zcmg $1.6 m/s^2$ 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 rqw kas.-99a ftravels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is itr9-qa fk w.a9ss 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 starm;8 bmw+ k1 mf.kfi(eets from rest at t = 0 and moves in a straight line, k(ik fe + wme1bfmm.;8is 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 m/s7o *z+j8bh;y x qsne7k.+ zzop to 25 m/s in 6.0 s. What was its acceleration? How far didn *kozo 7e.+jxsh78q+y;bzpz it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s tpaive7szq961o4,kfz cnn8 9io rest in a distance of 85 m. What was its acceleration, ap k f7qe1nz4 on9vai8 is,6z9cssumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff)g qmx,tby+ +yl j8cs*. How long a runway is needed if the (constant) ac + )cgjl,ymt8+*ysbxqceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top6 z 9oaln;3pid speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and ;9dlo6n3piaz 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 hye f6 /adrhq+o4)j c)12.0 m/s to rest in 6.00 s. How far did it r4jfch )/hyqea6od)+ travel in that time?    m

  In coming to a stop, a car leky2 f*s2fgc7 naves skid marks 92 m long on the highway. Assuming a dece*7n2kgfy c2sf leration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 kmme)92h*:hcnen h (uwi/h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of(h)9i mnh c2u wen*e:h 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 initial speed of 95 km/k zw-jx ,lk*dl a4f7;t:ojoa.h and human reaction time of 1.0xawdfja7:ktl.olz,*k-j4o ; 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 hp,* rew39vksbp0 3sca car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. b,4sr-8b,;ftcpvhmh8 t48wdp .nxqp The car’s driver looks for an opportunity to pass, guessing that his car can acv,t;pp8 s4 .bcxfh m,dnp8h - wtqr4b8celerate 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 min. After e*j3lmw egspp78sh( 7r xactly 27.0 min, there are still 1 (7jhspp 8ges7m3wrl* 100 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 intersect(kd2b:feq l,b ion 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 the li (d,:eqkbbl f2ght turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the grouxj asu0oe2vhw/ (9tm5nd below after 3.25 s. How hi (ujv9x/o5 w2sm0th eagh is the cliff?    m

  If a car rolls gently, +so:8yobfyfx s1xbs h/e/6l ($v_0\,=\,0$) 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 t9f*i1dc ezwog o+ho5-he 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 upwarh x y z,ec8,zool cz2.8 t/o8f8is5t+j2vrl spd. With what speed did he throw it, and what height dihxc8.+ plzz s5ie o8fsz8tj,/,r22ty 8c oovld it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under th mn smng1orw7/;vvh9 i0f; 6io+lp7ape influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.0o76fgh vs /o0 lwrm1iani p;;v+7mpn90 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At at(28 4hkb )n9.(qxh . ojyoyzvmc sq*t height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ q9hy (.( 8jvy2 *zq xhb.)stonkc4mt os

For an object falling freely fro,)) fedi euzhd9at 7t))po/l uw 6;ai5zfiyb*m rest, 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 Ga tewaz9;e uodu75f,ziti/py bhd)a)6 il ))f*lileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraicalmk v xxtys5 6*xr)7rj/* 5dxu5*oqobmly) that a ball thrown vertically upward with a spv rxt xms*oy75jk)qu6m rx5d5/ **bo xeed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertic+* qbkm8q3fr+fm79nnb 9t nqx ally upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of thecptcd vh0v,xp/k;dd9j9 of 04 apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. cdp9tvpkf/dh90 j,c0 4;oxdv[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 windtyz 7ja roj:8 sh/8.. ov39;uumzv brhow 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fall? /mroo jv s t.z78bhj8;:ya93 vhruzu.    m

  A rock is dropped from a sea cliff, and the sound of it striking the oa8 5ct)irgay,cean is heard 3.2 s later. If the speed of sound is 340 m/s , how high iag,8)5 c yraits the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard strer1aidh01e:hx 55gkwy b uj/t;am of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed h:ywjabiuek0/5r 51 xhtd ;1gas it leaves the nozzle?    m/s

  A stone is thrown veroox79ljq-u 7 ftically upward with a speed of 12.0 m/s from the edge of a cliff 70.0 m high (Figou7fx jl-q 97o. 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 j nlm69rb: jy0rkqv*1 the street with a vertical speed of 13 m/s If rkq rny01b m lj96:jv*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 function of time. (a)vj;juh0u hs 7( ;i/ogs At what time wa/(7s;jj;g hoshu 0vi us its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along 1xc w) q4ego/ua straight tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneous velux q4oe1cw)g/ocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accelerate approximately as shown in th.zt,jjl9n xae gryry+3hesdtmbk4 2;z 37h35e velocity–time graph js,l de73y.ytbkt53xjz 3m4; 29gn+ezhahr r 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 accelerd6veuo ji ;qi dsuq *::,a,(jration of the car in the previous Problem (Fig. 2–35) when iq6, dru ov ;jud(a:q:,ii*sj et is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object traveled duringglwp g8n-pi,wa *u- 3*aa d7 me1eh6lk
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement md9hq /+cyw4:: 6ms7fhewy klas a function of time is given by /46mk:e :9m w wh+7fydq lhyscFig. 2–28.

Figure 2–36 is a position versus time graph for the motion of 06wmwa f3 15gad8h2z+bgsf u kan 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 thwgff m6 uhazd8g0a2w53s1kb+ e 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 fourgzoz8y9r( p(x th-story window 15.0 m above a firefighter’s safety net. The survivor stretches the y(z8 g9(xpzro 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 cuc:/o o .-. e8d kug,tbn- iep,fto,nabout one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how ,p g/,t 8b o .-ut.ci -coe,kdno:uenfmany times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constra: wp9:jfj m9g xpj4lv5ined by an over-the-shoulder seat belt has a good chance of surviving 5j jg9 fxvp wljm::4p9a 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 ab(5 w,wqm4n*q9s ub cbbove 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 knou45nbcw q9 (qm s*,wbbwing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars forhh).c46bdbiqu dd do5,nxo /s+p+1us front-end collisions by hauling them+/ c4bp+ddx,ousbdu q) 1 h d6osn.5ih up on a crane and dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth yr,8u2rtc 3fx travels 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,o e o8g)h9m:mif:nukzi*.xdp i z o26 acceleration from 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 of the train startein,iuozk zi )eo:.6g: pd*289mm x fohd. 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 surface intog)6w s )ei.ha3 57ykmzij gnzpl e41/e a deep pool. The person’s downwarda ip)sj 4n)lie6ghe w17z.3mkgez5/ y motion stops 2.0 m below the surface 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 bagcj+ 7j tn:(bt(q ;zwalance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea og:w7;+(j (a tqjtzbcnf 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 divin9kd wb0df, p:r;i2rzkxjv173-x xg smg 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 minimum19xirv xs,07k: gbdk j ;dr-z3pfxmw2 height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a gos5u/cd6lh6x b, nga -blfer 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 the putt is missed. Accomplishing this from an uphill lie (that is, aux,6gd bbhcn5-s/ 6lputting 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 frx0oo/ sz0(ji;dtt3ru ( zr cv:eight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accelerates vr0/io z0 (co;duj r3(zs t:xtat $a\,=\,4.0 m/s^2$ 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 stone is dropped goy:x vh6*f:8d +ndtivly3d2 1.50 s later. How far apart are the stones wh3l+f di: 8y y2tgo x6nvhdvd*:en 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 lastin7l+f1p4g n)dlztvf 1ag ten laps. If the first nine laps were done atdl7afp+t4 1 1gn)l zvf 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de Francejtvq.o5 pg ,wt0kao8dd t. tqka):2e7 crests a mountain pass as he moves at 18 km/h qd), j8vtgw.adt k2o 7 5ta:q tpeo0k.. At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first chil *uswh(4xva7ikqgf:,la1 s1 n* c9ro ld can bounce up one-and-a-half times highl,vc**1a7uos: 91 lr(iwafqk g s4hn xer than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train traveling in thevyawo0wg9 -n,u) zo cmeh9)-u same direction on a track p9)uan-ouw, oe)cz y-w vmh9g 0arallel 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 t8uydy :6 ;8p* isitm96qlfoa34 ixrcdhrowing 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 released (Fig. 2–41). Estimate the average acceleration of the ball during the4fyx9qcrty6 m:id;pa 3o*s u8 6d8iil throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accetqa+an 7-ixmbzkd d9g 0-:g( aleration 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 pat*;n7:x*;een q gt wqxktern 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. When you are n7;wx ;* kq x:*eqtnge10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a cons5 f6rh82wdg o4lh0j(4aart ay tant 120 km/h takes off in hot pursuit. Theara6jl(oyh 0r8h adw4g 5tf42 police 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 f9, .;ya y x+vfvn +uky+1jdeytrom the roof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and tj9vy ; dy y. +te1+fvn,ayku+xhe 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. The br2p:x u37jps 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 xrp2 bjp:us73initial 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, h /qg* t wb0yc(jc-o gnp;m96szow long would it take a free-falling parachutist to fall from a plane at 3200 m to an ap-g6jsc(w*nyob z c9/0m q; gtltitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a grillobuwv/gi)g *0 /gv xj3b 5dsr/ gdpz88ing machine. I*8 5 /0g8bgzd3vwoxir gdb/psgj) uv /f 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 speed 1.5 times faster than Jo/,9i iu/xlldme can. How many times highe/lm/i xiul, 9dr will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend st1-2g+y0n;ek oj q;c/ khigwo g6fu8ukands 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, fk+/; ;1uykgecigjkn20ohow q-6g8 usuch 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 the heig8onw kohx/,h3k 2jo-o/vcy 0 tht 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 2.30kyok8h j/ /vnotohw,co 2-x0 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 posit(gsml q: (i *dfw0q;rqion 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 thew; lq(drq i *0m(:qfsg larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?