Does a car speedometer measure speed, velt;xdobr1 0f dhcv0o7:ocity, or both?

Can an object have a varyingscr5bud *jj/a 27mjw ( speed if its velocity is constant? If yes, give examples.c27 u jjma(sdj*b5r /w

When an object moves with constant velocity, does its average velocity during 08cta,tbbqtgt v26r2 any time interval differ from its inst,ta2vqctttrb62b 0 g 8antaneous velocity at any instant?

In drag racing, is it possible fo gx5 t9q sva6yvy4 jrnk)v-).qr the car with the greatest speed crossing the finish line to lose the race? Expvv xt6q)-5jy y 9.rq) a4kvgsnlain.

If one object has a greater speed 6k n1y22j oeka5*/ ekodzf jcl x512qcthan a second object, does the first necessarily hd*aj lkq52ck ok62oey 2n1ce1j/x 5zfave a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle4+1(ultdg l-o. )ag o x1clyth that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates frlh) cgy14(+glt-.uaot lx do1 om rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleration?xhq,.sf c4d.m Explain.

Can the velocity of an objecta*4ikhwv (i.y3 ) bddk be negative when its acceleration is positive? What about vic hk da.wi3*v )dk(4byie versa?

Give an example where both the velocity and accelerw82/y-.d qw (y/zm1 xrai syriation are negative.

Two cars emerge side by side from a tunnel. Car A is,b h 88t3c ier5xb;zxc5w:nch 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 i 5c itrc:z58; bhcbh, x8w3nxes passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing x5co y9:5 sif/q 4e+wcb7grw pin speed as its acceleration decreases? If so, give an example. If not, explain5b7x w 9 :rc4fpiq+wsy5oc g/e.

A baseball player hits a foul ball straight up into the air. It leaz/22( y)f 6hc dt-nqtgera3srves the bat with a speed of 120km/h .-(et2tfr 23y dczsg q/hr)n6a In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what isxjdd z un k8*c0)w2v7l happening to its acceleration due to gravity — does it increase, decrease,cwk8 *dx)2 u7dnj0vlz or stay the same?

How would you estimate the maximum hep5:0nih1ux hbight you could throw a ball vertically upward? How would youn h50xuh1pib: estimate the maximum speed you could give it?

You travel from point A to point B r(8tw*6:bqji,wx cim in a car moving at a constant speed of Then you travel thewxci*mwqb 6 ,jtr(8i : 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 why not.

In a lecture demonstration, a 3.0-m-long vertikd.7m uw (dtq+cal string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? W .uwdq+7ktd( mill 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 r4-ii8 l buuclaj3c8.o ock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish rcul.i l8o jui 43c-ba8esting on a table?

An object that is thrown vertically upwmi qa :/opto9:3id4scifg z78ard 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 accelerato8 st:3q9d7ai:icimofg 4p/zion due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acfp137 gb-wn yl*x0hvd5w mjf: celeration at the same time? Give examyb:m 7*wf3d 1x5vhn pl g-fj0wples.

Can an object have zero acceleran, (krh 60pjs1 gx3gnqtion and nonzero velocity at the same time? Give exa,1gpk s0 nj(nghrxq63mples.

Describe in words the motion plotted in Fig. 2–28 in terms w t xukf2u/.fb.9b5:t 7fyj uzir/bt(f z.3rv of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moving yoz/.uf5 ft btw7rykz39xbvj.uuf f .2t/:i r( bur hand.]

Describe in words the motion of the object grayuzun ++nn/k/:aajz4evd/) jphed in Fig. 2–29.

  What must be your car’s average sperb wj2pux v*. ,ar3wxx(yx- 8ted in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/msxjj cxi) ;,kf+x nigu-9 3o1h How long does it take to fly 15 km?    h

  If you are driving along a straight road and you look to 11+:2x8 gm3zc;dts+fnch zoyiotn90x he9xtthe side for 2.0 s, how far do you travel during this inattentivee;h01+fm3y2+c zt1os9oxncdg8thz x9: in tx period?    m

  Convert 35 mi/h to 8m(y gdvq4:jlhs-8ap
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frog03vdk7n74t ii ,.z lxc9wbvdm $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily at 95 km/h forvsf irc7m) zc 9j9cx -,.;hrma 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minu-csm;9v f rc,xha.7 iz)r cmj9tes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb y.u6i,hgp7r krf-h( o, every five seconds between a lightning flash and the following thunder gives the distance t6kgf.o iph-u hrr(,7 yo 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 lapm 7v/5x1rin:5 kvoqcm ls c24ms around a quarter-mile track in a total time of 12.5 min. Caoqcv :1/rxvi scl5m 27 4n5mkmlculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m away in,ulz)4hc re9q ;) , k*xhugmds 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calcu))kuh,cu qhx g*m edl4,z;sr 9late
(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 ounhz/nntn+ed b *x+krjj2117ther on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initinn jr+knt bu2*1/zjx1ed7 + hnally 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 )rhgb-mh(m;ik:spt w0 o+b 1nm behind a truck traveling How long will it take the car to reach the truck? )mghskh0 1r bop+ ;(nw im:tb-   s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters a d,ev*- dnb.b*udsi* ytailwind thatvbdy.dsd*u*e,bn i* - boosts its 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 aq.v+:go6/h gb0*hk 6aj phkjy3a gp)overage velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h6jpok0ghbg :)qh 6aa+/*j og.p y3vkh.    km/h

  A bowling ball traveling with constant 5g8 wrw9 w2*nr2 q(px vtjql.ispeed 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 s2q(l9v. xw t*jn 5 wqwp8r2rgipeed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest tooiuf-s, u5o6 b tempek.*..tfm u 4) retppz49 95 km/h in 6.2 s. What is its average accelebt5. p oto9fzuu-e.pk4r s,.6 up4mft*mi)eeration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.3d/: -kkeato n*5 s. What is her accelerationn d-o*a t:ekk/
(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 a5d3r*z43dxwle ;ldcl 9tjt c7cceleration of abouddt5 j 3e*; rtcl3lzdx9lcw74 t $1.6 m/s^2$ 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-o: )f )tyzuyd in 5.0 s. If it then brakes and comes to a stop in 4.0 s, )u: oy-tz)fyd 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 rest at t = 0 p65cq::zkv 5jwdqur1 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) ic zjwpqu5 q6v ::dr1k5ts velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleratan jlhpk/ )+h2ion? How far )al+nkj/hh2p did it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 8-,u 0k yswd;hh5 m. What was its acceleratiw sk;h-,dy uh0on, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runway is ne mp1-ub +y9h;zd mm 3p:a9nssqeded if mdmqzpbyh1 a+ s;:m u 9p9-ns3the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed (of cwk4ya;, 1bo habout 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprib4a, 1oc;k wyhnter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to restr jr 93kv,; u4t)fwlry in 6.00 s. How far did it travel in that tiwuv; r4 k ltj,r3)fy9rme?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Ahcr+ 5a3n3 bcwssuming a decelera w+3r5hcnbc3a tion of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car comxax-gg)bs-/7z3 ,r p m,(rjko +oamoipresses and the driz-a7)mro jmabxsx,-o, /3og p(+rikgver 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 = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances nvcmc2 9vw02eeof(t 8for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for a2c0t89cf 2no we(evmvn acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stoppingy hj5;hvte (:ab8p. nzga05qs 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 goingiugxql99 b5;/jfq:w l 25 m/s on the highway. The car’s driver looks for an opportunity to passl: j 5wlqbg9x if9q;u/, 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 10,000-m run in less than 3tbzlr8k 2a5k *0.0 min. After exactly 27.0 min, there are still 1100 m *ltk85r b k2zato go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h aw yq1rj8n*xw 0pproaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before tu8 w1 qnryw*xj0rning 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 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 below after 3.25 wb /y*gz4g -i+vvw7vg s. How high is the cliff? wvg b 7v*vg-ywzig 4/+   m

  If a car rolls gently ;/cdfd8s )cz2)vw k i7qvq1ks($v_0\,=\,0$) 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 straihs 0jvntb/7 1/(a jsbrbd)y ,cght 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 m dt.rs(m3su c(g9e8zwhy7-r+ 9pbrr vertically upward. With what speed did he throw it, and what height did pwt+(yhrur(m3zr9d.- 9 srems 87 gbc it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the inm) p a dtdb/)r7x/z j7wf/bl z92m2ijvfluence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t 7j/dl zj 7bvda/tmp/x2mb)i 9zr )fw2= 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a qh+mja;be5 7 uheight of 125 m above the E5qm;7jhb u+ae arth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance tr */2ib(u rpeoraveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc. e r*/p(oibur2). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglectf/b4)yqloalrv::l:w we*i+ i2s f gy;ed, show (algebraically) that a ball thrown vertically upward with a speedifw:l:/)l qo:f24 +sy v*; gireb wyla $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertical(y:6ytcorc d5 prn7+aly upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of thnn)u ujkcc 6f 7n.4v/oe apple in Fig. 2–18 (or number of photoflashes per seconk6jnuf./n uc) co4 7vnd). 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 travel past a window 2.2 m tall (Fig. 2–3j* lqcot1 dc:- 06qzz1z; axra2). From what height above the top of the windad1zoj -aq10 rqc*6 zc:x tz;low did the stone fall?    m

  A rock is dropped from a sea cliff, and trzxs6xs t 7s6)he sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how s)s xtzrs676xhigh is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for c6vr)+z-h;-bj m e ffaa hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. z)mjfch ;b+ef v-a-6rWhat 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 thdcyxjheb. b: /40i2wd j a*e/he edge of a cli /j0dj*he4d2 .bchw/exabyi : ff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pas z9cbk (:0bncws upward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the street, c:(wbb n0 9zkc
(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 ak8ll6krh2gl:apj. :a s 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 accele rl:pl2jlkak:8 ah6. gration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a funco4nwagh, f:l ; q8ybg.tion of time is plotted in Fig. 2–28. What is its instantaneous veloloy fwq,8.;n g:4gbhacity
(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 automobis c6 ;9d8eoki yb3ea wjuenb*2,b24ql dq15j ble can accelerate approximately as shown in the velocity–tij;dn ebd blw*e2qbk1a6s38joq4 i9eu5b c,2yme graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Pr;u qfozd) ;y;uoblem (Fig. 2–35)fz ;yq;o ;ud)u when it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object traveled dutj m)zxbk7d 18,i kxkk2zl r/8c0qm w*ring
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t gra s yk8xgxx2vi* ah7p31uq7 x3wph for the object whose displacement as a function of time is given by Fig1is2k gqx38xxp v3y a7 x*whu7. 2–28.

Figure 2–36 is a position versus time gftj 1j+);k/hofgu.o xpss 9k b8.+vflraph 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 slowingj81sujvf9fg b+. )kf; lh.o/po +xtks down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s saftyor5 uxq, 5tq4r08chety net. The survivor stretches the net 1.0 m before tx,o8t uqr 5qh4 0yr5ccoming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixthf4err+ ef7:fjag82zme,9 grp1gaq 4z what it is on Earth. If an object is thrown vertically upward on the Moon, how many z89ge 2, rapgzg f1m4 f7ar +frqje:4etimes higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly 5ws/ck.k(s n7bw3fu bv/ q5*oz zec2kconstrained by an over-the-shoulder seat belt has a goo.vw7kzoksc/uwz bckf 5*/q(n sbe35 2d chance of surviving a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road bel043ag8 .rbuk g9m co o*yygjp+ow, and his pursuers are getting too close for comfort. He spots a flatbed truck approp*8g9 .yy u3obog0j gk+carm4aching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufac8ymg r kn838vpturer tested its cars for front-end collisions by hauling them up 83nmryp8kg v 8on 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 travel+wv9)4 ktolvf s 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 acceleration fi) dn sbg yz6h:gdbp;u+if+h znk5 .7-rom 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 .dp kbzy 5nii :d +7+gfhnzhgu6b;s)-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 surface into a jk73b5gzkha8 wa59d 3uym9 ow deep pool. The person’s downward motion stops 2.z5g 59938 b7kjwmuhoaa kwyd 30 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 xh5rik1 xm/5ba6 *mc yis necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower thbm rx6hy x5c/im5k 1*ae train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall i,fqpfliv:uaz* (pus b8)6k 4straight down when diving for fish. Suppose a pi:su4i lfb akq)fzpp6v,u(*8elican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the forcwhz7 8e1s 2(o ef+ho f0ksr4xwe with which a golfer strikes a 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 missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more diffic h7f(w4e sx1 zsh ok8oew2fr0+ult 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 trave*p17fu zws )enyg/eki59tl )g ling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive)yi)peewku1ng s*/ 5z f9ltg 7 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 oz uo9q dqslu1 5w)/ks,f a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has lw1 zusq/9o5k,s qdu) reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial lastfx45rx - ac0qm9qcb; aqd95mfing ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for thf9df4 m5qax9bm0ax 5qqc;r-c e last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he movsd9;,tmaj mh( es at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . jm ,da9hsm(; tWhat was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing or2,l.t .*g k5x 3ovpbd6 emygf *8ytenn two trampolines. The first child can bounce up one-and-a-half timg 3f.8geyv , y6tdr5nm2.*l*x oektb pes 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 trave /ynh:e *m1yl;bf59bpe3clriling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directio nb;y:9 fb/e3hceimply5l r1*ns? 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 throwing jgfi*l k/0h ,dd 2.yh n7v:cms 3--un+xnzkh othe 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 average acceleratu+h0 3dgmcyx2,:fz sk-v-*. ldihj /n 7onhnkion of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from ;5sldkmp b s85x,:asc rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a trafs16-i zy-jn)ppnscr7fic signal, and the speed limit is 50 km/s . Suppose you are drini 1 prs7 -6c)-npzysjving 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 speedeh 083bdttx+ dyr traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, m+3xdtyb 8d0h taintaining 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 fromngom,7xi n,jgmua4ol0 (3 s f0 the roof of a building; 2.00 s after that, a second stone is thrown straight 0m4n0,f7igagooj n(, msl3ux 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 i:q;k dc3a9 avsame time. The first stone is thrown with an initial velocity ofvq:kci 3 ;aa9d 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 resistanu3k ;n ov*jb5uce, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistanuu *v5n;b jo3kce will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers throug9zak+imjr1 9 uh a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to kma991ji u zr+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 faster tl+ fms ,tsz/7bhan Joe can. How many times higher will Bill’s ball go m+s/flzb,7 st than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff whilmsqb0y4 p) zt/e your 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 ys0mbzp)4q t /the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height 3hvai u75xix1 of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does tix3h x15aui7v he 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph f. rfica.6la br +3nl-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 passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) +afr .bncl-lr6f3i.aWhich bicycle has the higher average velocity?