Does a car speedomete p ) zh*:8zf8fsvvafxgd,rw00r measure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yeboddyvxu.3+:f qy )q,s, give examplf qvyx,d y:bd+o ).qu3es.

When an object moves with constant velocity, does its average v j5* cxbe+n2gu -mj6scr0yf *nelocity during any time interval differ from its instantanmcj eys5 nr2f0xu* g6jn*cb -+eous velocity at any instant?

In drag racing, is it possible f c/ev6k7lmu 5dor the car with the greatest speed crossing the finish line cv75d/um elk6to lose the race? Explain.

If one object has a greater speed than a second object, does the first n xmspb/:8 rcq++:k-vr vkz/mwecessarily have a greater acp xs/-b+wkvrqmvm ::ck z+r/8celeration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90km/h feadw;x p;o+ (with the acceleration of ax;doe+;wfp ( a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a nort:kg)j l1bgx6z0dek-j.fiy/ hhward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positiva*0/cfzi p f4re? What about vicp4rffac i 0/z*e versa?

Give an example where both the qak/-a xdcb4wsk97tt,p4fs. velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is travelis /c,) q5zmy/m, upfd b.ynw4jng with a speed of 60km,mqyp.bfjwc)d4 un,m/ s z/y5 /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 tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so9/s aa hqstql.o9(ij+ , give an exasl j+q9otsh/(qi 9 a.ample. If not, explain.

A baseball player hits a foul ball straight up into the airr 8s*g5 ftbi-xmehg eq.g40.y. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fase4-xbeg.*.5hmrgyis f0 q8g tt will the ball be traveling when the catcher catches it?

As a freely falling obje6lo c0 udh0s6ni9k4chct speeds up, what is happening to its acceleration due to gravity — does it increase, decrease, oh09hsc6 d0lni6c o4kur stay the same?

How would you estimate the maximum height you could th9 eh0h:uga )qkrow a ball vertically upward? How would you estimate the maximum gaq):hke9 uh0speed you could give it?

You travel from point A to point B in a car moving at a constant speed ,5keu3b9cundqq(qv8yx(8x :p nae6tof 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 A to C 80km/h ? Expa9bne6( y 3 8qxdnpu,v: t(x8ukqcq5e lain why or why not.

In a lecture demonstration, a 3.0-m-long , 0:jw4 ;pqz pe b4dbt4ktys.bvertical 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 timpbb p0:4zytt4, jbw4s .e; kqde 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( sd5cd.nlgr ole k./z,qk4 :k is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor tod kzln:.res okkq/( .4g,c5ld the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upw 68 u+u6ubbcgz-bk6 kdard 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 so, how? [Hint: The acceleration due to air resistance is alu-68b ck6bzubg+d 6uk ways in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration hz7m) :,w 7gaan84i7e6orm,ejl kkyl at the same time? Give examn7j re lizkm a4me g7w)6 ho7yk:8l,a,ples.

Can an object have zero acceleration and non2:t35 gr2kybf (drkqtzero velocity at the same time? Give ex2k3r(5dr yqbfk:t2g tamples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, k ls* 0ccwshtkx 5m.,g009n ecetc. [Hint: First try to duplicate the motion plotted by walking orsc. k9k5glexhc,t0 m s*00cwn moving your hand.]

Describe in words the motion of ths guq:el7i zx1liet64/8:ses e object graphed in Fig. 2–29.

  What must be your car’s average speed in order to tbh/7 bxotu9z olh 09o46w-wvx ravel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How7z5rgzn, bpr+ long does it take to fly 15 km?    h

  If you are driving along a straigj,. km+p ri.hnmf s;x0ht road and you look to the side for 2.0 s, how far do you travel durin0+fp i;hkrmm.s.,j nx g this inattentive period?    m

  Convert 35 mi/h to mirh *nw 6+j2d
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frgxj/oz)n9fpwuh8* nb q(j4/c om $x_1$ = 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 kya j gdj 0twl/xf6(1k*m/h for 130 km. It then begins to rain and you slow to 65 km/h You arrivet d1 jy xj*(60fwl/kga 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-thr *mul03f r yjrpx/g9 :eqtex7rt-.*fumb, every 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 at all, estimate the speed of sound in m/s fl.x*tref0*- epfrjg3:/9uxy t7mr rqrom this rule.    m/s

  A person jogs eight complete laps aro2gqv3w5 wh/v hgsfh- .4x-efaund a quarter-mile track in a total time of q5a3f sgfh g.2h/ e-wwh-vxv 412.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its ef3,vyakp w; n42ylf 6hm :uyu71-mottrainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.3, tm 146oya2-heufm;pu7k :lynyfwv8 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 95 k:spn * zhc*5ww;a*cb wm/h with rp5 hz** *:wnbw aswcc;espect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/(f- x8-kcl3v8d vraha h is 110 m behind a truck traveling How long will it take the cavl--aha3f8( k 8dvxrc r to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and thteug 7m: l jlm vc8z3e/tfw 6v naahq)/57y1)aen encounters a tailwind that boosts its speed to 990 km/h for the next 2800 km.m3 8t) an c 7/5ahqyue m)vfwa1jl67vz: gt/el
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 in whijua gtda.f.fa)*+ aq1 ch the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch gf+.d1)jaat f *.aqa ubreak, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant sphxbwo-szr18cohd*t 64sp/v , eed hits the 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 released from his hands*81 ,oc6d zs /hpv4xrwst-o hb. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 9 opf:tx:w ,i1m5 km/h in 6.2 s. What is its average accelerationwxo1m: :fpti, in $m/s^2$ ?    $m/s^2$

  A sprinter acceleratesnrt(x.3s4 ry b from rest to 10.0 m/s in 1.35 s. What is her acceleration r .(xrbn3ys4t
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is cap5lay4h* .x mfqable of an acceleration of aboutql*x5y f4m .ah $1.6 m/s^2$ 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 it then 8k. ,edrk6htmto; ;b lbrakes and comeht8d, ;.etlk; kom br6s to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from res yg5rtfi.m3g6g/ h mf/t at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display eachmt /f. /ygh5mf 3g6rig 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 accele lknhd0:whpy+ xv8qi,0ng n+-ration? How far did it travel in this time? Assume constant acpq+v8g-xnhlin 0w +:k y,h0d nceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a disr -b ss s me,ju2u7h/m8ufv1m7tance of 85 m. What was its acceleratiomev burujsms /m1u- hs, 8727fn, assumed constant?    $m/s^2$

  A light plane must reach a spee. p 2 qdifzk)t59 p71ftmq- k1hxpv3bld of 33 m/s for takeoff. How long a runway is needed if the (consta tx bp5kv hltk9mq2pi. f)13p qf1z7d-nt) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks totnn2ff vrfc1 y/ 290sv essentially top speed (of a n vfv f2sc/9r12fn0ytbout 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uni/yf6 ))ub3u*rdx mful0/io zuformly from a speed of 12.0 m/s to rest in 6.00 s. How far did it traveulz/3ouf m*)6)u rbyu /0fxdil in that time?    m

  In coming to a stop, a car leaves skid m w+;t ) brdwmdo;y2m2x8h6ofwie ml27arks 92 m long on the highway. Assuming a deceleration offw m8o+xieh bwrl627 ytdomw);dm2 ;2 $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h st ;)l bpeqdn 0c77iu1marikes a tree. The front end of the car compresses and the driver comes 7 ci17)budp eq l0am;nto rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stoppia f5/ytf3zn5r x+gmki*uij6vc;v2t3 ng distances for a car with an initial speed of 95 km/h and human reaction time of 1.52+f6mzv *itj;ic n /gfuvrx5k3 aty30 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 dist l.hh5 k6tz( xwg(v*rbance 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 looks fo kw,/0thdir/jr an opportunity to pass, guessing that h/k0jdw/ tirh ,is car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to completeop2jb2am 3 ac. the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then acceleraac ajpo. b3m22te at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car a-2bwd miui9 1kt 45 km/h 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 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 light turns red? The inte-9 kibwmd2 1uirsection 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 ofndw /58+kmdkg a cliff. It hits the ground below after 3.25 s. How high is the cli 5+wkmg8dn/kdff?    m

  If a car rolls gently 47vcm-fk y1dep1xz8 r ($v_0\,=\,0$) 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 i;obh5j69p 6zobflbz* xwhtzt1*6 eb3nto 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 ug9 tdc9,35 4wl k-li,;gbj i bsqhxk7i*bcs -a ball 3.0 s after throwing it vertically upward. With what speed did he throw it, and what c bwdi ,x9-cklulk, *5t7b4g si -jbg;39sqhiheight did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw gr7mye9 8if d q4b1y-znaaphs of (a) its speed and (b) the distanczfq m1i 7d 4bay-98yene it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s.m *v2xz:d ehig)fq.p 5 At a 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? [ fx zm)vqh:*i 5gedp2.Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distans-8p+omi b *wzce traveled during each successive second incrbsp8+ ziw-*omeases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is 4 s +. lzkkk/kxj83/yl bxc9z: j:fdsjneglected, show (algebraically) that a ball thrown vertically upward k9j:y+3kl/jxs d/b .z lx: ckjs84kfzwith a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertica q 0nk*.jzr hm:0n1ho.)xtgedepu :9 zlly 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 epu 5gxr(of2 x,ach photoflash of the apple in Fig. 2–18 (or number of photoflashes per se, 2pgx5(ou fxrcond). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to traveha.c0 xl-a 4l1m4 v9rhcojdk 4l past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fall? xc.04-1ahk 4 rolj4acmhdl v9   m

  A rock is dropped from a qs cadv,.:tw7jj26 on sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how sc:27 jdo ,q 6aw.ntvjhigh is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You point*cvej6p 2frt kd 6irjn.9vd8v :d.0ox 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 t0f6 96odicj : v8*..vnrk rjtpddx e2vhe vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from tf xx :.z4roxg9he edge of a cliff 70.0 m high (Fig. 2–34). .zrf og:4x9xx
(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 with a vertl:vkr;it k(j)3e( qikical spjk qt:)re(iklv3;i(k eed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train 8rf9s,3rlt/ dr )t6uf(s sjfu as a function of time. (a) At what time was its velocity greatest? (b) Duringd)u3tf,jf ( r t98sls rsu/6fr 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 a straight tunnel as a function of time i8gouf8uqq3sz (k-ae x5l8r*uxu +,j as plotted in Fig. 2–28. What is its inst k,zl8ogu*5 3 f8uaxue-8+j(sa q urxqantaneous 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 approximately as shown in the veloci xx3ckbz6(tb cd u(3fm4:)bydty–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.) )x:myb(udb43fx3 db kc6(ztc
(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) rhp +irzz2*wb;k-zw)xj 1-ts when it is itr;zbj-k* s zwzh2)w+1 -pirxn
(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 objemk.lq,d,2 zhr ct traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object wpc 5x3-(y,vlwowm*/whm y :fphose displacement as a function of time is given by/w5hw,3fomxp clypv: (*-m yw Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion oo1ewrl7ath /:+ iw /jtf an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or tt/ar 1:+jhw we7 oi/lnegative 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 fomo/o2l5 p/ 7yn8es ;gg8k7vuxh.j brm urth-story window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2n5o/g sokuemv 8 l2 8mbpjrg7y.;x7/ h–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it inq 9v /a/lkyhl5+ q,irs on Eart+v ,la9h rqnl5kqyi//h. If 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 constrained by an over-the-shoulder seat belt has a 1d87ple atquqs0 fc;)yr 33ix+ jelb;good chance of surviving a ca;c83;qjeetpa+bl s1fud )l7qy 3 x0i rr 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 phpd7k+xbb044r j d ur/c0 uzc-ursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he meas kubzuhcp0+4-/d0xdj 4 rb7rcures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacczm(kvc 5tz7jr9 - q6ds13tihturer tested its cars for front-end collisions by hauling them up on a crane and dropping them from a c6vkjit1z9- cr( shcqt5mdz73ertain 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 ty./ f4 /rm2*jaq ivcl+,cqrxyravels 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 acceleratiya/snxl)5e02 ren pu +ljl7f)on 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. 2jelfnu0rael )pl) y sx/75+nWhat 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 abof /;f gqlo)/u*pow4 ef12og iove the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water1; wo ffloug 4p*e//ofoi)2g q. 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 necesi2 xcl qwtzqa4oy (ef9:st5 25sary to balance the average sptlfz2y24s9q:c(5 eat 5ioxqw eed 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 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 f8tzf, :ex9 vyygm yjj56;lc) ,gt/ canree fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, a:cyt9l6v,) jfy ,5x;j cgz8t /yamegnt 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 with which a golfer strikes apl )wg p*6yjltd+wxx2 m9x44 s 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 missexjd 4p*gp6+4 wxx 2tm )lw9syld. 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 spk4f prqplh5ep l +29w7eed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accelerates atl h5l792pfp4qp+wr e k $a\,=\,4.0 m/s^2$ 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 thejmddom y,zk *l z-mvkkzkq8/8 )x z8-0 roof of a high building. A second stone is dropped 1.50 s later. How far apa-mmz y kdx k-8vkljmzo8q d z/z08*)k,rt are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a timvdt/)e ;.zq7bw lwe:me trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lmql vezb/ 7d .)w:e;twap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves kxgu v*5;o )kkuwzatm75 .wh 6at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in 5o7) *z 6ukxhw.mwk vaut;k5g$m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. Ty -far 8l7kw,sc1mm(s he first child can bounce up one-and-a-half times higher than the second child. Th,r7 -ya81w(cmlssmk fe 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 ovcz5/4ns )jkq9hqwj 5dertakes a 1.10-km-long train traveling in the same direckzj)5q4n s9qdh5jcw/tion 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 a speed ofzfs*o65 dv9 vq 44 m/s In throwing the baseball96sqvv*zfod 5, 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 the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accem3 roldk3 e1i3leration 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 intersection hankv800qd5.l mth:tip s a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speep 8.ktm :h5tli00n dvqd 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 cos 755zjv6 w,g+fw9a,: p4sxzhfk hjdlnstant 120 km/h takes off in hot pursuit. The police os,hw76lhp9j+vw k g5fz4 5sd,j z:fxafficer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from dd1 8 zv:tsi:,fw lad)n7mok0the 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 the two stones land at the ai d)n,sk7 0vdl1twdzo8 :f:msame 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 t vjmki .v-gc46ime. The first stone is thrown c 6k4vjig -m.vwith 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 initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it targ. mg6)ksk0s2ic*pvver 1 6 h8jj-cwke a free-falling parachutis8h2js rgw ce0p1gm cjvk)6*ivks r-.6t 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 restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send jbm r(ght1op668,ybo lfon;; 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 cm apart, what is the rate of burger production (in burgers/8 y6p;(b,no;lgo fm jh1r bto6min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 tim3sg 7t*npnojm2yp68jhiyt 2(es faster than Joe can. How many times h*yyo(nitm7sp6jp83tg j2 2 hn igher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of aon c85f7q, tys0fl /gw cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s forgqsn0w75/t,cf lf oy8 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 usirm()g p cb-p7p:zlsv8ng a barometer. Instead of using the barometer as an altitude-meas z)c-r8mglpv ( p7:pbsuring 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 of the building’s height?    m

Figure 2–43 shows the p;ofh +ht9 jg2mosition 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 bicycle is p2g+;f9mhhotj assing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?