Does a car speedometer measure speed, v adv0rb5t 41e xngi2+ng+j3 iqi,xl8helocity, or both?

Can an object have a varying speed /8gp da /v2lwn3+jz bfif its velocity is constant? If yes, give examples.pw/ dgb vj8/2lz3+naf

When an object moves with constant velocity, does its average velocity during cd z+iq- :jtoy9*hz+4m9(xg uuq *kqbany time interval differ from its instantaneous velhqu c9uz9*-ybtiozj :qgm(x d4 q++* kocity at any instant?

In drag racing, is it possible for the car with the greatest spe2)x btbgh.ff: ed crossing the finish line to lose the race .)2gtfbx :bhf? Explain.

If one object has a greater speed than a second object, does the first necyy2y/bel 6ry 1essarily have a greater acceleration? Ex2r1 yelby6y /yplain, using examples.

Compare the acceleration ofk 834ihj kp 11)ylemav a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the s31ki)8jvk mh4l1eapyame time.

Can an object have a northward velocity and a southward accto6jdzpn:+.nk esu 90 eleration? Explain.

Can the velocity of an objkz:tv a1(sbmab99(1/76 qa mzsnzn wject be negative when its acceleration is positive? What about vicem(nsjmnbz za v s6k9:t7w/z ba19qa(1 versa?

Give an example where both the i r(hur;-+m3mioiw8 t velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed of 969r v5a llyhb60km/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 . alrvl6h95 b9y Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasinghumm r8nrp 8- w*t8by.z:p 4qr in speed as its acceleration decreases? If so, give an exampleyqz48 wmur*.:rt pbpr8m-hn8. If not, explain.

A baseball player hits a foul ball straight up into the air. It le )av1.y 9b2i e1,mav47jahozvhex3 exaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when 3 ha 27a mvy4x1oh)1e.,9jvxe b vazeithe catcher catches it?

As a freely falling object speeds up, 0tw(wln0n.wuu -ey+ d lbj17y what is happening to its acceleration due to gravity — donb yy07d+wn.le-w(0u t1jwlu es it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball vertgggyall; 8iax 2rqunq,9/7tuy4 )4 zeically upward?4za,l;gi 2 8/xu)947erulqggan qy ty How would you estimate the maximum speed you could give it?

You travel from point A to point cd6z;a, +vbaao/rq7 rB 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 coacrb6/aao;vz,qd+ 7rnstant 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 v:6n o(42tkru cqcb 1snertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the srn b 41n(:co qt6kcu2lecture 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 t 6/ 8y3wd 5xe96 znc 3ewgcz3oruz:vdacceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting onz/v63nzeu o c d59xw3rzcwd3g:e 8y6t a table?

An object that is thrown vertically upward will return to its originapdbben79gj9rdrp 3k :u 4r1t /l position with the same spee9t1:/ ekrjr7npu gb9 drbp3 4dd as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at tes3u uf/mlr 9k3+m0ao he same time? Give examplu m9mse3l/+0ruko 3afes.

Can an object have zero acceleration and nonzero velocity suj qc.w))9 rgat the same time? Give exampg9crs.u)w jq) les.

Describe in words the mot(5nqyxg iezw 8 1i;+pz(lr ta*ion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate (ginpilzqt+a x z(e581;*rw ythe motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in Fig. xt4m0yql3p(j yhsv7x5;9 uv n 2–29.

  What must be your car’s average speed in order -:qth*jl xkq 3to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fl n: qqq84jf,fz6uj8 hly 15 km?    h

  If you are driving alw lvvqx1 dv v+e:*)h p6ap n)nwn:pj(*ong a straight road and you look to the side for 2.0 s, how farn 6wpj(nepvv1a *v*)+ :h :)pvlxdnqw do you travel during this inattentive period?    m

  Convert 35 mi/h to ghs ,wu,0e n j/6aua-dsr0ue6
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves feehd2: 3: 6lmy/tf rkcrom $x_1$ = 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 at1 xf, xloqh-xgk y3 0h,;tz2bd 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive o1lq;hxxzb32dh-y0kf t ,,xg 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, expdtw. mm ngg i*3c*45p,iqj3very five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time i qi*w.3 ppm3 xj4tg nm5cd,*gat all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile trn b,w6o nqnwx73y na-5+x1jvy ack in a total time of 12.5 miq+35n- y wjnaonb ,xnw7yv61x n. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m away p 4f0k j xwn*h:uwbs)+in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calckwpx) s+nufbw*0j 4:h ulate
(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 smsy6dj pk;k 84,sh)cojj-tl,d;ux 4qpeed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach ea,m o;dhc yq;, t4kxslu j4jkjdp)68s-ch other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110qiz f czph/4wl; i;6u,0t ovf+ m behind a truck traveling How long will it take the car to reach the truck?l4 0wih+oict v,/z;6q; ffpzu    s

  An airplane travels 3100 km at a s).-nxgo -3sd ioliz0b peed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 2800 zb.i-3gn0 o- ds)liox 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 round-trip ix j7)a4dk vh4 090u mmwg9pjhpn which pj4xaj 0)0km uv9ghw7 dhm 9p4the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits th( u/xcz0wn o0 qexst9/e pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is r q0es/0/tcx9(nouz xweleased 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.eb+7t,iw4 zdgpn3 tu;2 s. What is its average accelert id3;u wbn4zg7 e,+tpation in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceptb. .(jy jvk.leration p. jk y(bj..vt
(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 acceleration1tot u3fnew 9/3q0ml2-pcbja of about ejolc 3/p9mbwq23 uf1tnt0 -a$1.6 m/s^2$ 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 travels 110.gcei yf6ncad6(e8 ,vss7/ez m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleration ezs c 8.c,n6vifa(/s6dyg7 e ein $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t = 0,b1ba4yud lw- rp)o t2 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) idua-p21rwb,)tyl 4bots 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 in 6.0 s. What was its acceleratinuv.37 fv0qae on? How far did it travvvafue q0n. 73el in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to0gd/zjqi 5 l;u rest in a distance of 85 m. What was its acceleration, assumed conu5 0q/j dilg;zstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a run lba9;ou()ye dzgt99lx e26y dway is needed if the (constant) acceleration is(b z6 9eyd9 x2g9;oyatdlul) e $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of cpfd/6y 2asm (*heyb(the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this ba h *y((fpmsy/de26csprinter, 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 3wpcg8mb j t5+y* s/j)v jwqq4a speed of 12.0 m/s to rest in 6.00 s. How far did i qy)5 + j/mbwcwq3 *j8gtpjvs4t travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the 0kpa/u ts0)/)sc( xfxd bfa/chighway. Assuming a decd)a/)a0fxkc/xut ( f0 /psbs celeration 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 compr ui78d 4 6dvfk5+ultmhesses and the driver comes to rest after traveling 0.80 m. What was the average acceleration hk 486di5d tulf v+7muof 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 9)-.nsw t:o/j m ;bkbtc5 km/h and human reaction ti- ;tt/o)s:bnj.wcb m kme 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 foh7f c5 wmtd58xr the 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 going 25 m/s on the h tgxz ab.g+nxp;)7 +pcighway. The car’s driver looks for an opportunity to pass, guessing that his car canbpg)atx ++pnz.x;g 7 c 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 th 2zwbvclp5 vvy:-ayc 9 8h/m(han 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at 0.2/5(l9hyh8zvcv vy- wb:mp2 ca 0 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection j3eootrao88 xzn*m3 ) dust 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 tda3nrx*otz oemo)88 3o cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the grog )qk .fwpd )(ldce7 v(vh nb8k3p.ir0und below after 3.25 s. How high is the 3gw7e)nc(p8)v ddvqkh(0 l.i krb p .fcliff?    m

  If a car rolls gently t3 syk 289qf;ny1i cjmr:c+tq($v_0\,=\,0$) 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 stmqy k/z evhql8)-1hhy1g,c f: ,hyd.zraight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it verticallytaz r 0d+. t-ygmtf*2fo*hs0h upward. With what spet t ff0zyrg dh* m+oth20-.a*sed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rr(sk6agypxc* k5i *q8est and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fall * (58kay sxgp6*rqckien, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertic7* ixm+;m5 q;9whmqdvwyme a c2n5j0sally with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window+w5mx*q m w2ic05smhy;qem7 jd ;n9 va. 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 the distance traveled d u()8rvs39kh k+upwezuring each successive second increases in the ratio of successive odd integers (1 9)epwzr3ukh(k8 us +v, 3, 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 x9z4 ecnc,ay4thrown vertically upward with ye,c4 4na9cxz a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticwmw unmw) vox9;73 -jkally upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in Fig. 2–18 vn u,-zh -r4vl(or number of photoflashes per second). Assume -nrh,-vvu z l4the 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 tall (Fiibs-:x7 vy h50s)uouxg. 2–32). From whato7xuu) 0vi-sxy hs5:b height above the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the0u b) )h3kfejd sound of it striking the ocean is heard 3.2 s later. If the speed o) fb03 jkdeu)hf sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzledvl08r; kg: anucsj6: pws.q1 for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it j s d1pk68cq;g lr.w:v:as u0nleaves the nozzle?    m/s

  A stone is thrown vertically upward with a spee f 5zs ggz6rf1p) 1;ofjs0j-fhd of 12.0 m/s from the edge of a clifggf-fj sjp161 ;f0s5zfzh r)of 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the street with0/rpwyw*kpns- kz) p+vbj)9ed u;0ow a vertical speed of 13 m/s If the ball was thrown fp+ w-0nbrp/*y;w9se) zuwv pd k o0k)jrom 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 ascvc- bi0z ohzc1nelmc :4;u6*-vg8qi a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration conl:1m zqh*oic -6ivg b z0-c4en;uv8ccstant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel a33ay .pw 1js nlm(cs, (9ri km1pgi4vbs a function of time is plotted in Fig. 2–28. What is its instantaneous velocity s3ca.ykgjv pbi ,r (3m9n11 l4sp(wim
(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 the p e13z*l9ftzivelocity–time graph of Fig. 2–35. (The short flat spots in the curve representze l9*1fipt3z 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 thp o3 feyk,;5bme car in the previous Problem (Fig. 2–35) bf5e y,k;po3mwhen it 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 traveledkgtvu /3h+te 7 during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph fora6f 8/*fi swro)hek+67 f kvzh the object whose displacement as a function of time is given by Fig. 2–28/ *ffe hizh+k6vr s)wfaok786.

Figure 2–36 is a position versus time graph for the motion r *hh1sg8 fi3vof an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in f 3h8vsrh*gi 1the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a5 .o6h+00-p-8m mrns cw*3 )mdfrzz ww weflhz fourth-story window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1n 6s.rrzz d0wlm)3p o wh8*+m-0 ffw -em5whcz.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 itbrk2cq r 11ld: is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assumr drlck2:1q1b ing the same initial velocity?

  A person who is properly constrained by an over-the-s8 mzrxw/h7q -shoulder seat belt has a good wz7xrq/ -m8s hchance of surviving a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his ppoed h0b,9x1.k1z gex aiicf r)-n7h 4ursuers 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 man0frnb1ee-7x9ikxio c g1z.ha d4p),h y 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 manufacturerp5wc / :hmg68 mggoe1kd o-dq7 tested its cars for front-end collisions by hauling them up on a crane and dropping 7egw m/o5 :1qg kp6oh-gddmc 8them 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 aboy0 ( z5 ucf20-bqyydzvt4 -bzdut $10^9\,km$ 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 rest. The front ofritm5r n r.32z 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 passrz3r 5 mnri2t.es the worker? (See Fig. 2–38.)    m/s

  A person jumps off a div9*qng8;xdd(d zfiekh-- j7qyq2fd p -ing board 4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the - q7exjyq-g kqd2fd9di8d hf n*p-;z(water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to s;9qo rjce8 4ybalance 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 of this problem, calculate the time it takes a train to m8 ;cro9qejsy4 ake 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 strai,9wgnt bc+ vazu xhn/c4lt8d zt5r ()*ght 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 pelican to escape? Assume the fish*ugn+c9 c4wt/ltbzvdr n zx(8 a5t h), is at the surface of the water.    m

  In putting, the force with which a golfer 4,6 va y)bzosostrikes a ball is planned so that the ball will stop within some small distance of the cu,4)by vso z6aop, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train tra/ si h2a(m ic:qdl*sg/ /vs*mi6 ;pgzqveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and acceler*c lgs;mqq:/d*gi s/h/v6im2p( isaz ates 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)*t2 zkizckp8 building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a speed of 12.0 m/s ? kkz zpi*)tc 28   m

  A race car driver must average 200.0 km/h over the course of awb2+uy u m6ra. time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must bew6a m+buyur2. maintained for the last lap?    km/h

  A bicyclist in the Tour de France cr8nr/yu wje;t+0ln c:vests a mountain pass as he moves at 18 km/h . At the rcuenl+w8nt 0;v:y/ j 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 trampolin h;5jtilr.-lmwn+ij n-4 onm9es. The first child can bounce up one-and-a-half times higher than the second c9 l-- no+rj ni t4mw.mjh5ln;ihild. 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/pvqta aa 5ku)b ya/2+ 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 traveledab +)p52ayaaku//tvq 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 sprd7bvm7b8 as +kz/ 8uuv.-ba seed of 44 m/s In throwing the baseball, the pitcher accelerates the ball thr kzmb8vbrd7buusa. - va /s7+8ough a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerate+yq*3hy6 cjl ion 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 shomx -hjpawl sni/3: *6wwn 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 6hsa-m3pjwxi * l: w/nspeed limit. When 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, passed by a speeder traveling at a constant 120 km/h pssp2;:vr/r7dk ylh)i4 2 imntakes off in hot pursuit. The police officer catche ns;dpymrsh2i2 k 7il)pr:4v/s 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 that, a seconrh,re8*m y/bd:p4tbbx+ .lcv d stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time. * btrp4+hb,ce :drxlm/ .8yvb
(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 h,5qcirk r2/-0./rjmpuhc) r: zdwmm at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground afczdmmuhk5.2 q ri , j/cr0r-hpr:)m/ wter 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resisto.1 vt z90nde.fm6cxtance, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pulle9t ox 6.d0f 1nctzmv. 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 througojku6. l1d 8nth a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 ml kjdnuo.t61 8in 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 1.5o .h1uxugz.bs+ i 4co) times faster than Joe can. How many times higher will Bill’s ball go than Joe’s?xu1io u.zhs .+)4ocbg $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your fr.oz5 cyj6fiyq1p ;l b/iend stands on the ground below you. You drop a ball from rest and see that it 6boi/p y .ql1fc jy;5ztakes 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 ball?    m/s

  Two students are asked to find the height of a dyoo8sqs:)7 1g*gs sfparticular 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 differensg:8)o 1 syodg q*s7fsce does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the positk axt8i33e7qo .x0mgcion vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicyclkmxe g8 q 7.xti03a3oce is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?