Does a car speedometer mr3eqafw z9t; ,easure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? Ivbpp0 9a elmfm 1s e1tj)6c-ccy;+ bg(f yes, give example( ag p-61m )+mb;s 9cp0te1cfclebjyvs.

When an object moves with constant velocity, does its av4f9,pks 2 jb0d(bezg oerage velocity during any time interval differ from its instantaneous velocity at a,dg(fpe 2b0 j49oksbz ny instant?

In drag racing, is it possible for izwvae fry7z; l ,kn 1k-/t(y 6(rf:rfthe car with the greatest speed crossing the finish line (f:,(ir6r1 yn kzyf7ewzk- tr/l;a vfto lose the race? Explain.

If one object has a greater speed thanuqv60m7y2 fwjmlj5x( 5tol6w a second object, does the first necessarily have a greater acceler2 5olj0q66 7mf5u vxywmw(ltjation? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 8rwv k:78-2z; fszgqq n0km/h to 90km/h with the acceleration of fk:s v-zz r8q gn27w;qa bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acwm5 - c4zn *gltz5n9x,n :yffdz)n a4sceleration? Explain.

Can the velocity of an objecn3c v (dvd-rd2t be negative when its acceleration is positive? What about2ddn 3v(-dr vc vice versa?

Give an example where both t6lobd q8 g6 )c6nl/s+0p txujqhe velocity and acceleration are negative.

Two cars emerge side by side fro*xfa c,4k fjb)m 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 ha4f),baf * kxjcs an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration diiix69 ymde)9: f(1h rw*ul vuecreases? If so, give an examplehx 6ev9 iyuliwf*1 dr):9ui(m. If not, explain.

A baseball player hits a foulsd(nshu cqh8/m-kxlb+-j k1y4 tj78t n+hem. ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of q n hjshjxueyms+8 kt4 1c(-b + dh8m.n7ktl/-air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its accejs8l*7x oi:b cleration due to gravity — does it increase, decrease, or stay the samelsi7cojb:*8x ?

How would you estimate the maximum height you could throw a ball vertically uje 474v(oi-hjso,oha pward? How would yooh(i ja,j-v e7h4o 4sou estimate the maximum speed you could give it?

You travel from point A qcn7gtr9 w; 8hto point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from An7hw ;gt9cqr 8 to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertix+jlh/bq 2 js+cal string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinksl/hbj +x+qj2s occur at equal intervals?

Which one of these motions is not at constant a3 ,om2ps7e ;dx2r 5hkitc5 ncrcceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops alonx2kd5;ros ipreh,5 t7c 23mn cg the way, a dish resting on a table?

An object that is thrown vertically upward will return to its or3h,83dqqk ,der;g-i5 so rrh tiginal position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hid 5g,sdk3irr o,hqrhq8-;e3tnt: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocit3x t73mln.kr oy and nonzero acceleration at the same time? Give ex.lotk3 mr7n 3xamples.

Can an object have zero acceleration and nonzero velse1h(nna1-yis k)z a+ st7 sa6ocity at the same time? Give examplesnsata 7) a6y+hzek1 sis(1n-s.

Describe in words the motion00u-y+9h t;ee kvbkc r plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walkvbk hku;09ety cr0e-+ing or moving your hand.]

Describe in words the motion of the object graphed in Fig. 2–dhlq)gxs fm10xji / f/rk3f0( 29.

  What must be your car’s average speed in order to travelqb. .+juz/we a 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it taked,.e8tsbcav9 n1 okcb7uq5 e, to fly 15 km?    h

  If you are driving along a straight road and you lo;o0j k+ 093vh ad*kwh(fmznkbok to the side for 2.0 s, how far do you trb 0k a dh9 kj+0;zo*m(hnk3fwvavel during this inattentive period?    m

  Convert 35 mi/h to f0k/ 7zhh c(lu
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves f7v z2ci(kn6k ox1mh:urom $x_1$ = 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 tp)7zo(g9yah ha hm3g21:i pyat6 ll2ehen begins to rain and you slow to 65 km/2y a1 72ap)gim:tp lhyaho9 zg3(lh6e 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 betweenude/6l.q mjx* a lightning flash and the following thundmu 6e*lqxj/.der 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 total time ofv 7v5p a hpn)88kh1ooi 12.5 min. Cav8pa)kpovh8hi1n o 75lculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a stk 1ealum0iq (k l6qh67raight line, moving 116 m away in 14.0 s. It thkl ueh61a6i70qm(qk l en 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 parallel tracks. Eaxque-g/)d x,y 09xcdfch has a speed of 95 km/h with respect to the ground. If they are in-u dc,f9g0exx/x yq)ditially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck trav (cugvx 6x,)dheling How long will it take the car to ) gvchdx x(u6,reach the truck?    s

  An airplane travels 3100 km at a speewut4dlgn8lz d: o gr54dq 2/4td of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 2800 km. d dg8ow 54ld gz4n2r:ut4q t/l
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 averagesat.vi-,;+ zb pr- *ejovs+lq speed and average velocity 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 svvbil,j*s+o;q z rp.-te+-a the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the enq gx dn2j.f1;fd of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of2gdq njf.1fx ; the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from res btlhv8xkb 8pb6/.1vdt to 95 km/h in 6.2 s. What is its average acce /8.1hdxtblkv pvb68b leration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates fro(uq ap/2dl7- cngt+t sm rest to 10.0 m/s in 1.35 s. What is her accelerationas-n ct/d2l7tuq+pg(
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is cas .uvr juc7; rj:9w1m3mq:pek pable of an acceleration of aboutmj; v.e1p:u3u9q:rswjc 7rkm $1.6 m/s^2$ 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 m in 5.0 s. If iq(/g:jdk cnoa, lw:: vt then brakes and comes to a stop in 4.0 s, what i/k,wo (lqdj:c ng:a :vs 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, which4erh fu1g+ kj,q q/*uh starts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity ah qk,*4rqfh1 ueju+/g nd (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 acce iihv,jzx f18m- xr0j*3 dxm*42y xchwal *2cdleration? How far did it traveld0 a cfcxjv4mij 1h x28i*wlr-3,ydx m2*h x*z in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/svhot ;f 4r:k8bd1i ok: to rest in a distance of 85 m. What was its acceleration, assumed constbh;:4krdv fo o8kt:i 1ant?    $m/s^2$

  A light plane must reach a speed of 33 mn myddyp,68-m/s for takeoff. How long a runway is needed if the (constany6d npy,8m-md t) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the z9u -.uqw7js yac+sc:x7q5 ws 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 sprinter, and how swcuw xj9 s.a75-zy+qs:qc7ulong 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 1z/ibt/ *cb u9erl* (ej2.0 m/s to rest in 6.00 s. How far did it travel in z(j b* /cibeu rel*9/tthat time?    m

  In coming to a stop,f6 + xzj:j9 5og (r4vx -huff;x*iomrm a car leaves skid marks 92 m long on the highway. Assuming a decelg; zj4fm9 *u6+rjh(riox5-o:mxfxvferation 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 fron;p+gjwzb( ngg,fu 8n4royn5m (vd( .st 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 “ dmg8;j4nr.wo(+nspug(yz( f,n 5v bg 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+czlrz 2yf ;h- a car with an initial speed of 95 km/h and human reaction time of f-2y+zcrh zl ;1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stoppingbiq7zp fd )xb -(nyg80 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 highway. The car’s driver lo+ rn yj8:uex(+gjm b7ek1:wf soks for an opportunity to pass, guessing that his carj( kbn1 :ruw+7:xyj+8egfsm e can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. Afterxwo o qbk./4 idx9p:*qjtwtu-(qm9 0e exactly 27.0 min, there are still:wmwdx .pq 4q9buox( e*iktqo0j 9- /t 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/ w1y l6y1 c.lofjpo,.dh approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away frompwo lyy. f1,1l6djo.c 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 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 thrj73lnt 4n5j zluzkkj3di*-) 35 qpzbyaf :s5 e top of a cliff. It hits the ground below after 3.25 s. How high is the cliff55nyk :z djf3 j*p -47)s3lk 3qbzzlnr5atiuj?    m

  If a car rolls gently q))vt 4(hlgxt ;g 8nfy,5(mfvagb/ gz($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

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

  A baseball is hit nearly straight up into the air with a speei +8li)y3g9msjj)ra dtdy18o 9a rz0 vd 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 throwx .pbad 6yg6 +tns.--gxm(o4z gytsp+ ing it vertically upward. With what speed 4gox.(6y6atmd s+b g .yg-p ntxp-sz+did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from reslw hc5yzlaovc383,63 jm0vket and falls under the 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 = 5.00 s . Ignore aiy3 wvcmc3zjh v053 l,6ke8ola r resistance.

A helicopter is ascendim2wfu 1 s2npm8a,t(osc xs .9fng vertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package 2 u8,1p.s sms(am xfnc 9ow2tfis dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distancs07yg(n t: wwxgt(lh2k*x/ tje traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first sho/ lwt *gst 27:wxjygx (h(t0knwn by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrownfhh20wb6 hu: r ,vim) un.kqj9k2z7rm vertical7q02m)j,6.khkmr h nb uvuzr9: wi2hfly upward with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed of 18.0 m/s ewcz8kz252 c; k/j2fq; iv 4awaye tw6
(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 photoflashre zv z ga.:77-ilw+gd of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, g7-rgzl:+di w7 a ez.vbut not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.2sw eb3o7vn) e48 s to travel past a window 2.2 m tall (Fig. 2–32). From 37nv) swo4b eewhat height above the top of the window did the stone fall?    m

  A rock is dropped from a sea clineb1kr 3 db4mf)gv( ,; ejzoj,ff, and the sound of it striking the ocean is heard 3.2 s later. If tzve 1;rjkbjd,g n )om,3e4 b(fhe speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. Youn 1. y7ozmbg7g 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 wate71bg. nmzg7yo r speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of azn bl )uxn)jku.vv lo,b 3,90j cli)bukl9ul0,.bnjv,z o n)j3 v xff 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 woj 1paxg44jv zul7 2,dith a vertical speed of 13 m/s If the ball was 4vu42,d7 1pxogljj zathrown 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 th1yd2vu ;do)l re velocity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During w1ru)ld ; vo2dyhat periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tuncgnfy s hl h3g+qvu*r54c6 i2.nel as a function of time is plotted in Fig. 2–28. What 6h3 yr*ugq v+si g fhc5lc.n42is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can accelerate approximatt(xsyd9i3 5qlj(uy* *5 bypwo ely as shown in the velocity–tilsu5ytyqyxd iwj* o*p5b(93 (me graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Problem (Fig. 2–35:xi- +xg:dgt i)gt+g-ix:xdi : when 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 traveled dur8kv0vao4yj s3ing
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement asg:ujj(4chpowj 7b:kt1 n l9d6 a function of time is given by Fig. dj (9: u:ckl pgw1jot74 n6jhb2–28.

Figure 2–36 is a position versus * ijtbovh. e*u as+3)utime graph for the motion of an object along thebuh.*3au tieo)* js+v x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window,(jft s.v a7wb 15.0 m above a firefighter’s safety net. The jfasbt(w., 7v survivor 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 gb*;mrq fm-nrf) d5ufy ; sq1/iravity on the Moon is about one-sixth what it is on Earth. ;rquf5f* ; bdm s1r fq)/iym-nIf an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly co()8tb ohd0cnx , vm(sonstrained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceedv8 dx (sn0)thm(bo,oc 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 belowsvc6,.ms/ej1 fpd p n 3l:ifm9, 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:s9ipjs1vd 3ce,m lf p./m6fn from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars-zvqbm 9na; bb:xep.5 0vdl/ k for front-end collisions by hauling them up on a crane and dropping them from a certain he . m/nzk5eb-a;v vbb9px dl0:qight.
(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 trav2zpl0tadyupw, mbrcm8sf7e+q84 3 0 cels 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 begivk xce q7/gqev )* d in:i+ms66)bz-ttns uniform 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 started. What will be the speed of the last car as it passes the worker? (See Fig. qm-/xb)ec) k iv 6tze it6dgqv+ns:7 *2–38.)    m/s

  A person jumps off a diving board 4.0 m abova xdlt1.k e:,je the water’s surface into a deep pool. The person t.axek, dl1:j’s downward 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 balance the avertas04a2c2ri page speed of a trainr2 ia02p4cs ta against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fwa 15rbdy4l/ tall 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 to4b y51rtd/wa l perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force withghk6t 1q 9 vc6gudgz-, which a golfer strikes a ball is planned so that the ball will stop within some z61t -vuqgd9gkg,6hcsmall distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a constant speed of 6.0 k 7hq/l aqkp7l,-q+ts m/s Just as an empty box c 7l7q,l h+kpaskq q/t-ar passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. 7tqq3ydux :b;A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a : u qt7b3qy;dxspeed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h ove6,ei6( itcc 7v6xix pqr the course of a time trial lasting tet 66q (ci 76e,iixcxpvn laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crestsskj4c db* uv4- a mountain pass as he moves at 18 km/h . At the b4 -cj su4kv*dbottom, 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 child can bounce uu*a(mj6 )buy52. hdeilhup;vp one-and-a-half times him6uby avdhuh5j2p u).e; il (*gher 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 trpehj0/ vedla i-f2(rs0lb 93sain traveling in the same directio ee as frbp2ji(lvh039s0-l /dn on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with aiwt;i6uws 5 sfj )g7)myfsrfhwr5 o:bd) o1*4 speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behin7yr4 5 buom)sd )gi*6ws5:f ;twr1oi)h fswfjd 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 verticall- zygcibo96mg5b5xp1 4cd q7vy, from rest, with an 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 inter7nca 0e32zjk0login0z7um y:*lv3refd ,ex; section 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 interkg,erzc 2v 0e da3fe;7o z:lx7m iuyl0j0nn*3section, 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 speeuu k sg7,9.hklder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant a.9gk u lu,7shkcceleration.
(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.n zw5e-1:+ r2rrvhqhf00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the sam1+z rr-5 nfvwre:qh2h e 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 upjn exw l9pq6v48(kv *36y zwmd at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balconpv6w86lwnq* 4k (x 3z 9edmyjvy of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how lmvjkjr8 bdveot:*pyyvmy9;1b73 6 j, ong would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrivb8d yej7t; v vk1 r:o,6m*jjmpb 93yyct her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conv 4x 77k6y hbctehu8d+su.o0r6nhv ic n6:tx) teyor belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm467 d+hu.vbiucy80 xht tr6 shxkt7 :cn6eo)n apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertic l.n+vv6 ungk*k 2nfz1ally at a speed 1.5 times faster than Joe can. How many times higher will Bill’s ball go thavunkl6g .n1+vn2 zk*f n Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground below you3els1bs9soj7n .1e lw. You drop a ball from rest and see that it tak.w7ssnoe le1l j b3s19es 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 particular building using a baroh . ;7a* nraq/f ,fe4iuexluu0meter. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates q a ;u4 nua0rui.7f x/lhee,*fof the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) g:p 6dl;0 ;;titef (hrwg r0m i6vr8adb4m5sz Is t04:er6iv; dr58 ifhdsa 0gb(l;mt6twp;gz rm here any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?