Does a car speedometer measure speed, 0j-jir i/x3cb5jd zx y)*b-b rvelocity, or both?

Can an object have a varying speed oi+6r*c wrfe) uqj8)3 lkusj**pg.hw if its velocity is constant? If yes, give examp hj* jeo+q.83)*lwfw)pigkcsur 6 ru *les.

When an object moves with constant velocity, du4)ad;,)yiv d sxr6uqf 7cfw3 6xm4o :a*q dxboes its average velocity during any time interval differ from its instantaneous velocity ab:rxxdau w)7d f xs6vyq3u4*;6 mqcoi da4)f,t any instant?

In drag racing, is it possible for the car with the greatest speed crossingfo : :smq:nu5k;*gosu cw+ ftu.ywuoli8, a/( the finish line to5. +lc:oowy8u f: k m(t/suu u:s,qi ;wgfona* lose the race? Explain.

If one object has a greater speed than a second object, does the first neccjzdz 4 -+fbg w1)2uniessarily have a greater acceleraig jwdbz2z4+fn -1)uction? Explain, using examples.

Compare the acceleration of a.4q kg5ekc;o :m2-eu 3 sxynfl motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to4.mln-u:yke qesxfo2 c5;k 3g 10km/h in the same time.

Can an object have a northwart*vje hh h./((.f24jb cltww zd velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its accehxoa+m-/mlep v ;v)s3lt,x k, ikd8/f leration is positive? What aboutmdl)lk3s/v,ih m kxa+fteo ,-8xpv ; / vice versa?

Give an example where both the velocity and acc)q 7i;jpz 8eyboo2jb1 eleration are negative.

Two cars emerge side by sideut1uueg /ng7/ fnp/ x) from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing geg1n/pu 7fx u/un)t/the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, give u; imzezlok+792nx p 2an example. Imzl pe2nx+zu 2k; 9o7if not, explain.

A baseball player hits a foul ball straight up into1th.yj gs:qo0md2bw 7 frol8) the air. It leaves the bat with a speed of 12 8s wjmo:q1 yfltg7.b0)o2hdr0km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speedsxs a u0j ;c(n+;gnahtnbf3d +l 98xct8 up, what is happening to its acceleration due to gravity — does it increase, dec;nha30xt98+ 8 jcs(tg + nc;ldnafxubrease, or stay the same?

How would you estimate the max9m7 g322.hp)lbfimz ni w2ff vimum height you could throw a ball vertically upward? How would you estimate the maximum speed you bfnfvzw227ih 2l3f) g. pim9mcould give it?

You travel from point7l vid:x t7;r0zs3s uh A to 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 s:dt7 lv0 hr 7z;u3ixsa constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts ti5/*xh3.dhk(k 4nsrslt9mb v ded 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 pl hsx*3(n5m/.s h4k lbdrtdk v9ate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rockaxt (y/3ieyh swv97)wn5( zal falling from a cliff, an elevator moving from the second floor to the fifth flooy( /9n sa5eh7i)az wy3 tlxvw(r making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original positi tc4y acy+ szzzsg5y5fmc5u3 c*h7j+,on 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 always in a direczgys uaz *+, sc75zc5 c 54yjthcy3+fmtion opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same time?-:yzxn 5xjf ew( xs6(b:bjzo xsh0uc,8 iuq 6- Give exampl xoe,-zwsbxci -8 : uh(xjy5(6zfn:sj06bxq ues.

Can an object have zero acceleration and nonzero veloci+syxb4 2l 2rjvjg*)rwty at the same time? Give examlrry 2*wg2 v +sbxjj4)ples.

Describe in words the motion plotted in Figklgmj:-4ii, hsp 5:ukxlxx- (. 2–28 in terms of v, a, etc. [Hint: First try to 4lgpks xmx -xj:lui(5 :,khi-duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the :tkksy+ .zw1ojt ee9 27ib4fw object graphed in Fig. 2–29.

  What must be your car’s average speed iy xwxz7lh;6idm(l h o14uw y+1n order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does ith6(x0je0 rdbh9/ u7c8w:yh-s eupn ln take to fly 15 km?    h

  If you are driving along a straight road and you look to the sid*tgy2ls /fz 1a+c4awbe for 2.0 s, how far do fw a+*lc142 szat/yb gyou travel during this inattentive period?    m

  Convert 35 mi/h to rf6y ,* 3j7 hlwujdg3y
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from 3h l0i y0t27f,f wwwf( )hzhcp$x_1$ = 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 ste+fvseupr* k,(fs zf* 9adily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after drik p(+ *r*vs9,use zfffving 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-orh-2u.kq g .lvf-thumb, every five seconds between a lightning flash and the following thunder givhu.l.g2 -kr qves 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 afgb2mu k2 l1.w total time of 12.5wg. 1l2kbfm2u min. 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 zu2;*gzs a/i 3qjv;ja yynp zx4e,q49116 m away in 14.0 s. It then turns abruptly and gz4 sg2i; uvap y4;jxazznqy/, *ej39q allops 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 tracka-dm6g tes+z0 s. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they rt0z s6 g-amd+eeach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How loph)1w8c+szmr4 wix k+241boj j2k pycng will it take the car to reach the truck? mspc+iohw +kyx28brkjz4 4j p2cw11)    s

  An airplane travels 3100 ivs,ryx*zg iel.d5 2+km at a speed of 790 km/h , and then encounters a tailwind that boosts i5lveg2 *z r,xis.y+idts speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity 7:f+ ium2zzbv of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch2 mbvzz7+u :fi break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with co8wuj-vye 4ru/cu: ql +d3 qir(nstant speed 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. What is the speed of the ball? The speed of sound is 340 m/s. ujq uqw8erv 4dl:uy-/ri3c( +   m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its average acce)s(x yqfkwjj *r q.)j;ls) wjfk(yrxq q)j; *.jeration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her a x.g wsuok7))tcceleration kw) otxs).7g u
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a partqn;np0t*mrb(7a gnu)k6 7ldgicular automobile is capable of an acceleration of about aqn)*nt6n m u d(0pbg7;k7 glr$1.6 m/s^2$ 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 le1odsu;0a .zsggs d*+vsc8/ speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what iss evu* a8/c g+g1o0dsl dz;s.s 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 rest at t lp hq::*bgo,vgvzc, ,= 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (bc z*bpovvgl,: h:,gq,) 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 acceleration? Ho n7 ivhvdi,p3. d*mv7yw far did it travel in thish v 3mvvyinid.7*dp7 , time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What wasawvw +a. vn54r its acceleration, assumed c4wn .wvvr+5 aaonstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How l5yxvf3tq wz q8 c+d2x:ong a runway is needex3fxd:5ty 8q2 z+wcqvd if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of p y6u-mt5z4tk the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m oftzt-m up6y 54k 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 unif kw6jte g,ln24ormly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in that 2n 6wt,jkl4g etime?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway.+k qu,7jug y8o Assuming ay ku+ujo7g ,8q deceleration 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. e itnh yjm+*ki3c h/c7oqh,0* 3* manhThe front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g =kh0em yi oqca* 7h +t*j,nhhic *33nm/ 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping diz0kp/ja8 - vszstances for a car with an initial speed of 95 km/h and human reack- jpzvsa z/08tion time 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 for the stopc)zs o/ugdn l7b/:k9pv hpz -9ping 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 ca8vef-myz qd1qe3(r i -r’s driver looks for an opportunity to pass, guessi 3z-r i8eeyv f1-dqmq(ng that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. After exa/4 y7m rfh.qb2hejj/h ctly 27.0 min, there are still 1100 m to go. The runner must then r/j7b.h yjhhm q /fe24accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h apxpio4i:m0.gu6yb4 m9r*4 * ucvmqvhaproaches 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 m6yvva04pu*mgix 4cr9 qo h.4ib:*mu 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 the top of a cliff. It hits the ground betm dc2 3 ;ygm78ivty;flow after 3.25 s. How high is thiyy3mtgc vm2d;f8t ;7 e cliff?    m

  If a car rolls gentlym. vvp8*bnys 9 ($v_0\,=\,0$) 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 straigz* +caf0 5+8 rh h9hp-cyhcukeht 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 am ;8 kd5pyq*6j n2prevertically upward. With what smpk5 da ey qp62;*j8nrpeed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts froao1o6f dt ( af:sw6h)gm rest and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the doh ostw61)f6 :aagf( distance 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. At i7 +f y ft11r:h;juhj.bd mso8a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s init fhbjt11:h+m r8o jud.fiy7s; ial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the 5ym0j mroa-*-ui; + zbp* lfdsdistance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo pmd+;-o u*ljriyb0a5m -fzs*. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown vertico. d-w. a+8d kqajw/d bx*lc0kally upward with dc. .+ j/kb8xad* 0wadk-q lowa speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically 4tro:.5 tbk wezol u*4upward 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 piz0ma)jjswd cr k)qdalj/+ 6l8u )d(,hotoflash 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, but not the unclearz)ddjr wc8 ) /dika+0)al ,u(qjm 6ljs ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m ta.fz2 m6vynua03on(yg ll (Fig. 2–32). From what height above the top of the window did ton ( 0ynzuy2vm63f ag.he stone fall?    m

  A rock is dropped from a sd:jw p:s)x( l3oaej*ywbi 1e, g5c,csea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is wa5ej::y* cis3d,sg, o xp(e1)lbc wj340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard streaxce .xd:q97ud m 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 f:xx.cuedd7 q 9or 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 12.0hkwf 9/g,mmwnvxc /,* m/s from the edge of a cliff 70.0 fk*/wcgmv /,nxmh ,9wm 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 etp43heo acop9/8: suwith a vertical speed o4ptohe3os e : ap/98ucf 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 ly + p0-l*ilbktrain 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 what periods, if any, was the acceleration constant? (d) When was the mag -*lb+lkly0i pnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnem.vj8 zj-6ll ll cn),gl as a function of time is plotted in Fig. 2–l8l- 6 .gjvcl,l)njmz28. What is 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 apnojmp2) ; rtt:proximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve repret)2o;rmjt:n psent 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 (Fiblm 4qi n00eqwcp2(2w-x r l /+6taxkxg. 2–35) when it k ltx0qexcl a0rwq 4w+6xim/b-p(2n2is 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 distayru s v,nkom/02ca3hl, n(1wjnce the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph (.*lu (sekqd+h-igorfor the object whose displacement as a function of time is g.dhreig k(*(ulq os+-iven by Fig. 2–28.

Figure 2–36 is a posito)zyy3(py- 5ddi ) qfsion versus time graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative 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 positi 3- (d)iyf)pqzodys5y ve 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 15.0 m above a firefighter’s safehv -ejai/wgsezgze-ob+ 37k7)j p;z)ty net. The survivor stretches the net 1.0 m bzzgewa bvg ei+) -s3k o)ph;7e- j/7zjefore 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 Monse9-y( b7dh4 * qx,.v 6qjdkkm wqgo-a,g)fmon is about one-sixth what it is on Earth. If an object is thrown vertically upward .k,g6 ayq-x7-q gw*k ndosjm 9,h fe( m)db4qvon 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 seatyisz- gf1 4,dq,mn 3rjewkv( 2 belt has a good chance oz1gdive43 r2(y k, -nfq,sw jmf 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 bridgrfs8d (81gbvj- iwrny yl(3,we, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away tvg8yibf swl(3rd,1rwn8-( yj he truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by haulin 9w e.0.cj0c0cpq yly4 ag9 uctt,8rcqdcj8; ng them up onuc q8te a cd0 ncgq9pc4y.t.80;j,jl9y0ccwr a crane and dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth tral*bk) iqg0i ltr-j 0)evels 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 beginghtu(e7x5il48ee-) z mlyz6 qs uniform acceleration from rest. The front of the train has a speed of 25 m/s when it passes q867)xu5 t il4hem( yze-legza railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board .+c2514us nn;9q ezvp lhuzvk4.0 m above the water’s surface into a deep pool. The person’s downward motion stqe.p n1zvshu; k94cluz2 v+ n5ops 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 balayy9 xpz :1mo +ze(.ndkz;sak o:u-1kunce 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 make a 9.0-ku:zxaodnezz.o 1s:-( kp+9 y1kmyuk; m 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 straig+qu6+8pkj fv fht down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once commit++6 qvujpff8k ted. 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 is at the surface of the water.    m

  In putting, the force with which a golfer strikes a bp-j8txe fnw fnye-p;:mx 8 /9kall is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (t8feyx 9fknw/:;m -pt-np8 jex hat 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 travel2jwf c.2d 6shhing at a constant speed of 6.0 m/s Just as an empty box car passes h6f 2cw2 hsjhd.im, 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 bui zcww0dsic 5uz m4n9.voh- uh0ff:o1;lding. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a speed c.91wvu di0ocuz0m h:o; wfnf sh- 54zof 12.0 m/s ?    m

  A race car driver must average 200.0 km/h o*9 vk6hs r 0jkmucq8:jver the course of a time trial lasting ten laps. If the first nine laps wer*hq :69jk8m vkrsj0cue done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de4-k)+ e 9ynzdjc odwr1)bj ixv,tlw (0 France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (i ,0v4bdek1w dl-(yion)9)cjrwjxtz+n $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first .hw-4 uqz cn4jchild can bounce up one-and-a-halfz-qh4.n4j uc w times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train traveling in teyzbzq y1:3cs17 vuj6p zx+n6ci06lfhe same direction on a track parallel to the road. If the train’s spb xe1lpzc616s:iju nq7+f zy yvc6z03eed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/s In throwppk*e; 0uur w-ing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the averagp0rwkup ;u -e*e acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from t2 7g 8jm26*jc 8tiua k.vu+w bkc8hjlrest, 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 pattk30ro (f1mgsf )q/wqq ern shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersectiofgs o)fm01/rwkq q(3qn, 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 128w iz xhnph9/zy( 6fm90 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintan9z9ix (hh mzfy8 pw6/ining 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 roopzt6b-j3ln3c u1 9ipvf of a building; 2.00 s after that, a second stone is thrown straightpb9-z 3lv3p i1 6ntjcu down with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The first stonymm ukwj 6a-ur*d1/ lt 8;qhv3e is thrown with an initial velocity of 11.0 m/s from a 12th-fll-j8/ahdm1;k*yq tur6v 3 mwuoor 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 take a free-falli 7-puo) rsz,gph0 me,2c3ai:kx+2 i rmnsku0 ang parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she willse0+7cn,pk)a0xpu2zah: usii kmo gr32r,m - pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a pe nrlcq00)f4:enq,g t ww l0(,9qsyngrilling macs 0n0ref wqg (y,ltnnl0:qeq,9wc )p4hine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times fastr vja-r4)t-k az +ym3uer than Joe can. How m3+rramv-u4-) z jt ykaany times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while yefd(;knsl*-)m6j 0t wfd yxpy8l.u p4 our friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is*l 4utesf)d-x j0y86 nylpfmd ;p. wk( the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using5wl00yck7eg /f7ylf r lg-z(qgd4x/ t 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 difference does the 0.3 s make for ef/rlx q4f(lzy05 cd -l g7w0ggt7k/ythe estimates of the building’s height?    m

Figure 2–43 shows the position vs. time h 3*qcon x0 y3uwqga7d arq3w ,u89qa3graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same veloc9haqy wqa3cxguw nur 3,7 3qd0oq*3a8ity? (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?