Does a car speedometer measu)lz3q;qm s/bdre speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give exag cp8k m9af 7ax9q7,yfmplm8cq gff9yka79 7,xapes.

When an object moves with constant velocity, does1:gvoy5l.0gfac g t5x its average velocity during any txg1f 50g .o5cv gtay:lime interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatek ha0+dv n*w*mst speed crossing the finish line to lose the race? Explain.dnkw*0+*m vah

If one object has a grx ac-io0e 32kxeater speed than a second object, does the first necessarily have a greater acceleration? Explain, using examples c3xo2 -kaie0x.

Compare the acceleration of a motorcycle that accelerat j d-5fhif2,p uej,eq,es from 80km/h to 90km/h with the acceleratiofjpd-hjfe uie ,q 2,5,n of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northwar1eu9je;ygm (q5yzxa o1 i 0i:fd velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceler ,)hia/ cqc6qk x- mnbcs)t40 of7du7lation is positive? What about vice verfk no-i6asqm 4 7ql)bu cd0xt/c c)7h,sa?

Give an example where both 0ey:wzasc-my ; qyr,.the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with bb3zfhed-s 4f:aleho1*m w21 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 passind zm2l:a1h-e ffs3h1b*bow 4eg 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, g0imq n9u )rd/-* q5k.yuwkohcive an exa 5qh0r9./cwy udiknuk-q) om*mple. If not, explain.

A baseball player hits a foul ball stxj9be;ecz0 )(r, rcqqg/w y.zraight up into the air. It leaves the bat wcrq)jez/y, x zbrg(0cwe .q9;ith a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds upp8 smath*2m )fcu)w4ozr0an 1.nf. kv, what is happening to its acceleration due to gravity — does it increase, decrewmmn8rtua)okz*h. v 2cff)a1 4 sp0.nase, or stay the same?

How would you estimate the maximum height you could throw a ball vyef.o,(j o+n gertically upward? How would you estimate the maximum spee y,oonf(je g.+d you could give it?

You travel from point A to point B in a car moving at a constant speed of *ah 4qx 133w)kmomvae 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 ? Explain why or whya k3q)h4oe mvxma3 w*1 not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts . kh*ai bsjtkr ;d ns40zil80/tied to it at eqs0t.zh8 s n/i0akrjdb; lk4 i*ual 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 clinks occur at equal intervals?

Which one of these motpaoxyp2( tt-* ions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish restxap p(to2 y-t*ing on a table?

An object that is thrown vertically upward will xa; -nv. :uyms,qyuoj;zc: j,xm)zt6 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 bu:6:tmxsujaz ;z)-y jmynxvqo;,,c .e altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zeroew403tr6a 0v )j ma/d)ezzzyw velocity and nonzero acceleration at the same time? Give)vj)3w 0ez 6rw0 tyez4zmada/ examples.

Can an object have zero acceleration and nonzero velocio gyu1r)hcl4 q0nny9:ty at the same time? Give examplen n1c) ry4yo qlh0:9ugs.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [Hw(o oi(8j(wfs )zvos8int: First try to duplicate tho(sjo wvfwo8 zsi) (8(e motion plotted by walking or moving your hand.]

Describe in words the motion of s yys*mh(2h v5the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to trv :)(zy (ah me.:sg9eat mjwu3avel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 nd+;l6/*nnbb7 uawyikmq 14skm?    h

  If you are driving along a straight road and you look to fc( j x:a:(2fcy )wovmthe side for 2.0 s, how faw: jx v:)( y2cmofcf(ar do you travel during this inattentive period?    m

  Convert 35 mi/h to . sk)db3 :r8zi tloc74rz. ujt
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fromi0qf)kv j.y* l crsde.f3c gk w)*:j.e $x_1$ = 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 steadiz). xm.sw8ye ely at 95 km/h for 130 km. It then begins to rain sz.e w8ey )x.mand you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thu:3-*2 )ee qpwgkvcnkumb, 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 c2eu:) pq-gk nwe3kv* 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 .dfr w58mf8zux/2 *)atgy.ogi4tz uc a total time of 12.5 min.zfi*xt854rzgm wty .2.a o)uc/ 8ufdg Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away fro v5xozs8 n2;pom its trainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calcuxo5 v2ps8nz; olate
(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 tracl+3js sd6 +/:s k3wtmnjycdq6ks. 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 befor /dnq+:yjw3 ms3skdj6ctl s6+e they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will it nndhe/ n)5kbdxw2rc) :wi x4 6take the car to reach the trucx26dxw))hi wbk4/rnn:5d cnek?    s

  An airplane travels 3100 km at a speed of 790 kn,9)iib9xcsh +j;my sm/h , and then encounters a tailwind that boosts its speed x)hi,;yi s+9j cnms9 bto 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 of a complete round-trip in w )3 ii8r:zlnpbhich the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered rizib8p)n3 l :at 55 km/h.    km/h

  A bowling ball traveling with cwb 5d-sz2xvrao7rm 6jjz+e, ,onstant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting td,z- we7ra+rjo mjsb6xv, 5z 2he pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is i-v zqt/fc0kn3ts average accel-vtfz3c /q0nk eration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/,y 3c(z *ayjiks in 1.35 s. What is her acceleration y3*ikj(yc a,z
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acceleratia1:xcs8 mr**odp12u65lsztap o qg 5son of abouz:otsu5p8 oxd1gal 5pq 1 2rc**ms6 ast $1.6 m/s^2$ 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 constm2flhnk b+1h6 ant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleration inh n1l26 kmh+fb $m/s^2$ ? 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 ca.do 03wrmo*,9,dykak: ylvcctey06 c8b bz7wr, which 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 and (b) its acceleration as a function of time. Display each in a Table and on a graw0 6bk ym. *l0v:kzdc7yrat3e8wc bo ,d 9yc,oph.

  A car accelerates from 13 m/s to 25 m/s++h ppgmn v ,:g(qkb7u in 6.0 s. What was its acceleration? How far did it travel in thisnm(p7+bp +,: vqugghk time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85f.e(9 4ybzjdylq x;b; m. What was its acceleration, assumed constfdb;eb4. z;y (9qjyxlant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runwy g++x:fuz 9xkay is needed if the (constanx9x+ g +u:zkfyt) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed (ofnomp5e.vr ir7s ks) ;. about 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 takersn7m )ri;.k o.s p5ev her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/ssc ky85ri b)u: pq.+sj to rest in 6.00 s. How far did it)yr pqbk. scs5+iuj 8: travel in that time?    m

  In coming to a stop, a car leaves skvg c)no4,u)i aw)vrp5 id marks 92 m long on the highway. Assuming a dec5p,)wv vou4 )cg i)rnaeleration 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 treepo(legk kp8-6qnp.*wsw6il: zr 9r - i. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the aveq-g *r pppikn8ls w6io(. l-k:wz6e9rrage 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 stopping distances for a car with an igwwuoopr )mo9,;. w*cnitial speed of 95 km/h and humaom,ur* ;o)gw. o wp9wcn reaction 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 stopping distance ohtew 0 83 z: stsvijj44y8lvq6f 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 goig.lxt3i 5x m5nng 25 m/s on the highway. The car’s driver looks for an opportunity to pasn5lxgmt5 ix3 .s, guessing 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 2;apf)w,vyy1f4 z b6plz5o xn10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The2pbo15)zzx l fvf6;p, 4nayw y runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches and* lnl:6)g m /4pxh+d6vyleky 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 intersection is 1d6 : ymyd6hlx+ l*e)kg/nl4vp5 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 n9hfztk8usmhel4 rzl 8 5p-o((e 9s8chits the ground below after 3.25 s. How high is the clf t(4zeom5ls9lz8e prh 8-k9 u( sn8hciff?    m

  If a car rolls gently ( f1uj0q) *qiub$v_0\,=\,0$) 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 awh3ae5n-w wjgk: 11pb ir 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 t60x;qwu4 hp3 qtf:m cyhrowing it vertically upward. With what speed did he throw it, and what height did it ret3xmh 4wu0q: p6 ;cyqfach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. wxjkc0. 5gq y lpy.rzi0u+*/qDraw graphs of (a) its speed and (b) the distance it has fall0qw 0qpk+z*x yi5/ry..gc jluen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed ogkv (g wsds,h62p 6:d+ qfppmt.sto., f 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How (2.t+d:hd gks pgv, p6stmf6s, p.oqwmuch 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 distanjj/ars+jss dle +8+4 cce traveled during each successive seconjcja8s4 /srlds++je + d increases 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 neglected, s6dqkylq+7 ow(5ptgisa5n 6hq.s) -wb how (algebraically) that a ball thrown vertically 6hi.-q sqw(p+l g65ay k)do 5st7wnqbupward 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 m2ow+2z k4euqm/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 betw: pwhg: hmis effm.8u-nl32c y +mnm+;een each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assumnmhp :+fh:um+g2f.8 w;mi ymcl -nse3e 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 travel past a window 2 ;,mqmhtna9 1b.2 m tall (Fig. 2–32). From what height above the top of the window did the stonqa 1hnm;b9 mt,e fall?    m

  A rock is dropped from a sea cliff, and thooa q8j42w /hee sound of it striking the ocean is heard 3.2 s later. If the speed of sound hjawo2o q/48eis 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden ckcjoq 6e f.hb zk,wu1h6u1 2.hose nozzle for a hard stream of water. You point the nozzlek.q6,2 ccohjubkw . f h61uze1 vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/dlg8ww,7,gc8 e */ xafy:gani s from the edge of a cliff 7gi g/*d:e ,,wlwa 78cfy gx8na0.0 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 s6(kvak ,)f;sm;t wym the street with a vertical speed of 13 m/s If the ball was 6;;) k,tmysvk(smwfa 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 veloc.mbg53 nx,v)xn e -hwf:pl5sdity 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 what periods, if any, was the acceleration constant? (d) Whenw n:mx - s5xfp n.5g)le,dv3bh was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time is pdb t4 :;c+wrmd4qmv qk;r/cg2lotted in Figqm v; dt4d2cbckr4:+; qrm/wg. 2–28. 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 automob+q*80qgf fvl pile can accelerate approximately as shown in the velocity–time graph of Fig. v+lg0q *fpf8 q2–35. (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 -;43kc9-p;h fi) glzzhy+pp3i csuy vthe previous Problem (Fig. 2–35) when is9h+vy pl4) -;pg3 zicczi-;yku3fph t 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 distahb:)*t pg 44ryzb2+v. bswqlnnce the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as obu 4/:hn/mcmu)ir e 5a function of time is gi:5u/ /4nb eu)cirom mhven by Fig. 2–28.

Figure 2–36 is a position versus time graph w k;yjkwv8- zq5.0rta 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 posit.r w5y-;0a qzk kjtw8vive 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 saftn gk 7yi,t *-2no -.mc5luymcety net. The survivor stretches the ny,unkt 5c 72lg-tm-* oi. ycmnet 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon2fiba7dl t g g)4ld5i )pw9v/v is about one-sixth what it is on Earth. If an object is t9wi )i5tdb72f v)a /g4dvl lgphrown 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-shgqm 48 qpbbr6(oulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 30 rb84q (pbm6qg“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 pursuerssp*, eih;i knzd ca4xj8,ck(.i7lh7 p are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , wh(e. k8cs iick7pz li 7pd,;*h hx4n,ajich 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 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 collistlqok1bzs46-(3wx6dm jqsc 3ions by hauling them up on s6w3 zs(q1oxbk 43- q6dltcjma 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 travels abou ;agwlq 1wbm:dg 445tqt $10^9\,km$ 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 s 1z-r zldbv(02x 0dgracceleration from rest. The front of the train has a speed of 25 mdv01drzxzlrg -(2s 0b/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. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s suq8p6 rjoa2ms2rface into a deep pool. The person’s downward motion stops 2.0 m below th j286qmrposa 2e 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/lrufj08 gf 0h to balance 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 9.0l hj0/urfgf80-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight down when diving for fct190)+bd etk p f3jfaish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committ kced9abp0j1 +ftf t3)ed. 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 balltpdr wx /3h)*b 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. A)* bptr3dxhw /ccomplishing 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 freighq3*uwxn-nj( m6s a(wct train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accelerates - w6ns3uaqwn(x(*cmj 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. A second stone is dropped 1(cv zyrw ft12u n/lwu4n tiv4ck5l4;8.50 s later. How far apart are tf wt8vu2( 4yc ll;tvku/n1w z45 4icrnhe 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 /k1ze 9/jaly-sza/pyof a time trial lasting ten laps. If the first nine lap19y/p jalek/ zz-/says 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 crests a mountain pass as o-8 ye+lh brsa( 92qs6 p3abkhhe moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average ac rq8k bs a y-9(pbahl+s632oheceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first ; flxlh)lmazw/ h cl- k*1c:5cchild can bounce up one-and-a-half times higher than the second child.lll*hfh/l c:k cw1z5c )x;a-m 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 n xm) m:ydr*g9km/h overtakes a 1.10-km-long train traveling in the xyg*:)mnmd r9 same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have 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 0n nfscw8+*ma with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behi+ *mnf can0ws8nd 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, n5p6uy -jmty8(qx t 4g(ac1( uwhf+zvwith 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 intersection has a m 8a ne+as gm,m/x2ma-traffic signal, and the speed limit is 50 km/s . Suppose you as /ma n8,meaa+mmx-g 2re driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km/h takegu6l/ /y-kqj+ d lf9vz5lk:yj s off in hot pursuit. The polldkyv/g/l -j:5uz9+ klyf qj6 ice officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s after that, a secov ri+ jm8m apxn+u,(l3nd stone is thrown straight down with an initial speed of 25.0 m/s and the two stone(3xjv+m lruma p,+ni8 s 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 filef 4u eqb:4du;dt 4z7rst stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initia44ulfbzde7;et4: dqu l 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-falop3q(6m 4 becpling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where sh po m(4qeb36cpe will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers througp3 2az 4bb yyiynqa./(h 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 npy2ayzqa3i y./(bb4 burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe can. Ho( ix;txcept96ofyg9 6e *gw*l w many times higher wgxow9; xt g*t(e 6eipl69*ycfill Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your fribsr 4w9 dne8:9q g gxna-x2/pnend 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 w /rn9q: e2px9sa gd4 g-8nbxnyou, 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 pail ;suacl :9wnyhqwl15)6y+ articular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the bua l 9wa1)ync ; ullwysq:h+5i6ilding 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 position vs. time graph for two bicycles, A andobr v1y:t*7jm B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle h7: mb1yovtjr *as 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?