Does a car speedometer measure spee.3ln 8 hoi25l9ywsypr d, velocity, or both?

Can an object have a varying speed if its velocity i+ )rj.1wspa mpsd.srp ac w.1.s constant? If yes, give exas s1jaw)dp.+r1p. wmacs ..r pmples.

When an object moves with constant velocity, doe9g 5vcj psz55spbtz0 *s its average velocity during any time interval differ from its inscvg ps5jts b505pz *9ztantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing thev esfn7:*slx 9s,pi+d finish line to lose the race? Explain.:ssxi + lpf,d9 v*7ens

If one object has a greater speed than a second object, does the 2;hf4q t7r*e; jba9dc pib6chfirst necessarily have a greater acceleration?i *j 2qehr49 ap;d6cb;fcbht7 Explain, using examples.

Compare the acceleration o.c/o4ivf5gk3 r2 svc2chz : mqf a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same q 24v2/gcsz5c riv3cmhfk o.:time.

Can an object have a northward cp-5 mblm.6+ lbt 2izeip dzytz ;//.lvelocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its ac d5k*e mjzqf lty+;4t/irl9( cpkx7b2celeration is positive? What about f2k(p/rkz+; etq5*94l 7 yltjm cdibxvice versa?

Give an example where both the velocity and accelerak wu:*0s1t o0fs,uf vation are negative.

Two cars emerge side by side from a tunnbo4pfi t8k+/x qf8 ;k x,j(rpeel. 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 the other as they come out of the tunnel? E8rqpx+k8 o; t(,f i pbkfej/x4xplain your reasoning.

Can an object be increasing in speed as its accel:-cw wy 9rqv0(p wahv(eration decreases? If so, give an example. Ir-w0 yp9(ch(v :wqa wvf not, explain.

A baseball player hits a foul ball straight up in6;pu;ugs x p)uu(/:jqcr+wzqto the air. It leaves the bat with a speed of 120km/h . In the absence of air resip/q puw+ ;6:(qru)xzs cuj ug;stance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happeno4-8alpwy/s+v +nm dzing to its acceleration due to gravity — does it incm ap8ydvz+lo+/ -s4wn rease, decrease, or stay the same?

How would you estimate the maximum h ;uudb 1-nder9eight you could throw a ball vertically upward? How would yo buddre1-9 nu;u estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a comy6ll/a7n x5s7fo3f z xy:8a anstant speed of Then you traves67fxomlz87f5 n3a axal/: yyl 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 why not.

In a lecture demonstration, jn/5n mze wiir)p93 n3a 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal n3p em wnn)35 r/zi9ijintervals?

Which one of these motions is not at constant acceleration: a rock falling fr j,l*mw:b /* , osnykjwhld4a+om a cliff, an elevator moving fk ,*alj,ym* sh4d/ : lnjw+wobrom the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upo.9k6xspgnfz9 j j74tward will return to its original position witf pgt9xnsj zj9k.6o47 h 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 direction opposite to the motion.]

Can an object have zero velocity and nonzero accelera4b3jlta vn7f3 tion at the same time? Give ef4l7n33jtb avxamples.

Can an object have zero acceleration and nonzero +fp7fqiq) *rzvelocity at the same time? Give exa frf+7qziq* )pmples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, 8 gys-+0+h 5r(k8dy fqk wfuj/lmanp0 etc. [Hint: First try to duplicar/ y(0gkmdhjf8sfu+lkq+8 5w -na p0y te the motion plotted by walking or moving your hand.]

Describe in words the motion of the objectd4 bq3to3ky7q2j1 sw r graphed in Fig. 2–29.

  What must be your car’s average speed in order to tra8(u,2iszuh8cjs rjk 1vel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h Howaq3jc cf4) fl( long does it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2 a26be6 eos-xzg*a9e + eqa8jj.0 s, how far do you travel og *e jz+ea8b 9 es2a6-xqaj6eduring this inattentive period?    m

  Convert 35 mi/h to xkfw9vf3uz07
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fr3qom*a0o d knxhn/61jom $x_1$ = 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 9d j.uvbramar3 i ,2,d m9ndjod8vo.8 for 130 km. It then begins to rain and you slow 8.j,or3 2dvmmb9i8don jdaa vu.,r d9to 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-thumb, every j(zf6f*t o i3kfive seconds between a lightning flash and the following thunder gives t o3(ftfzj6 k*ihe 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 arove c( gtm7u0u0ig+ -siund a quarter-mile track in a total time of 12.5 mimg0e -7 tuc gui+is(v0n. 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 116 m afuu rbq /( cq7:cyfz9n.d55jem ehe1+*v-mvpway in 14.0 s. It tjb/vpye5.qh+mre- ed qz7u9 u*fmc f:1nc(v 5hen turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has a speed offe vz4b3: k3ve 95 km/h with respect to the ground. If they are initially 8.5 km apart, how 3k3v fv:ze4e blong will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck tradvy, 9 3;uiwfaveling How long will it take the car to reach the truck?wa9vi ,uyd 3f;    s

  An airplane travels 3100 km at a speed of 790 km/h , g8 (1 mgt+xfol9/lp uiand then encounters a tailwind th(iu +m1f lgot/9lgpx8at 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 average ro6f;0huyi * 9lfe;et .7hzz wvelocity 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 9.* e07hfw6;z e;fziyoltrh u55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end ofl*drh97 j.rjh9)tz vm+ /mlyc a bowling lane 16.5 m long. The llv/rd 9yjz +mjm)7 h.hr9ct*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.    m/s

  A sports car accelerates from rest to 95 km/h inklak ;c;kt+ ;od n+q8f 6.2 s. What is its average acceleration idl8aq k+; n;f ct+kk;on $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceleratioau- wzp 02/yzlbyg7r;h k yol)f8.w- zngkh8yr; wyol--l2/z. w0pzab)7ufz y
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile i4)2yipree2asni8 n:y s capable of an acceleration of aboutira42 e)iep n8ysn: y2 $1.6 m/s^2$ 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 tb nqt.y ,o9u 3i0f91.sbh wdhlravels 110 m in 5.0 s. If it then brakes and comes 0b huqf3 tbh.n .wo91yidls,9to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which stqxqfd w-mxaom+4*,53 l.komjarts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) x ml,q4f.xo w*5+a-jq3m kom dits 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 acceleration? Ho.nori;a qku6xw18bj7 w far did it travel in this time? i7bnr;8x1wa u.qk6oj Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a 4q5j8hi7(cl 55jp w w(u8suroce wfx5distance of 85 m. What was its acceleration, assumed constanoj54(5l8 s ixpjce78(rwuwuwq5fc 5ht?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeofqg+gn fl,3j0 uf. How long a runway is needed i j g,ugfl03q+nf the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to 3tl*fr7wfrv 0 vx y+yqux*t05 essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? *v*3txl q 7xwuyrfr+y 050vft$\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformlyl c-u uuon)l (+w)2rb)wa3 wlx h40kyy from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in tha)u b4h) ay)k u y- 2wc0ruln3(w+lxwolt time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. As xw:v3jecka/yym*9n fs4 xox jl77 i7i+wg6c .suming a deinyc9ymcve xsoa w*+ 3gkx4 j.w x7/:lfj77i6celeration 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 compresse9m8d,spbymshbz 61 y 4-do(jx s 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,h y4s9myob-m1(bpdj8 6 xzd s “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 initial j z3yuzqi li-d1m9pei-rn9l73b74ccspeed of 95 km/h and human reaction time of 1.0 s, for an accelera 7cd-l1lci43zqzu7 mib-n9rye 9p3 ijtion
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a ;o:4s 2:ddzhdpd m+zun r:x*p car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s dyx*zyy+w xm,3j hur(* river looks for an opportunity to pass, guessing that his car can acmy, 3jx(rzy* *wh uy+xcelerate 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 compl rcgoy0ln: y85ete the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. T cyrl :yg5o80nhe 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 bpj+i 1sib2tlm /c ,3f(/eijvat 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wil p2mft,sjib i/b (/ev1+c3jide. 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 vng-kr kcy.ytu/:)n.d1b*bt a cliff. It hits the ground below after 3.25 sd) /.u-ctbrky.vntb gk y1n*:. How high is the cliff?    m

  If a car rolls gently pbp-xm 542bnw 0q(hjr($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

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

  A baseball is hit nearly straight up into the air with a speed of 22 m/s f9 0ss/s6 yb6 mj.a6ymu6jd wg
(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 vertica0tftw1(c:s telly upward. With what speed did s tectf(w0: t1he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influencypr; oy: wf6q:p:w .uie of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s wpop i:r;y6y::q u.wf. Ignore air resistance.

A helicopter is ascendte (dhi:j.4ivpa6+xtpo / ok *ing vertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a pa+ oie.:j*k6htpdtv 4o (pax i/ckage 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 thep1byr(:0 :,lamr wbrpcua2t ( distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first rtl1rmy:c(au(bw:pbr2 ap , 0shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball throb s,ygki-1 6stwn vertically upward withk sgt, s1i6y-b 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 ozuu yyjo*lce: hmsstv2n ni 14./* /o7f 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 the apps+fh:lp12m 2grnq5 pm8ovz .cle in Fig. 2–18 (or number of photoflashes per second). Assume the apple f1 clg nm5228pmo+.:qszpv hris 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 bwl4xfy hfie*:+4p 3km tall (Fig. 2–32). From whbw +4 lixfyp3 k4:hef*at height above the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking tio f wks.+,fa0* p3msjhe ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =3p,om*faj0 .sf iswk +    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. Ye e6p/4pcj ch7ou 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 /pceh 6 pj47cefrom 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 nyxb r+n ,v;:bspeed of 12.0 m/s from the edge of a cl;n+bn br,yx:viff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m abovx,, 8zn rby a6ae74;cfja 0xvie the street with a vertical speed of 134cbj,axe x8zn7ar ,;a06y fvi 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 trayg5o,iuro):7d t8 y0nsell g1in 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 wassiu1g7yngdt) leyr o85:o,0l the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a/w: xl7 )biq,cvake( o function of time is plotted in Fig. 2–28. What is ibw ilk,qac /)7evxo(: ts 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 approximately ase70t egjum7z8y lvw( )l4y;p*gfvcd0 shown in the velocity–7vgyzv0)04e 7t g(pw fy*m;8lucjel dtime graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Problem (Fig. 2–3 rlrm-u5 )2z6hfmqi o/5) when it is in r5)/mmq rz u-2iohfl6
(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 , 1cxvlo8 aecy*ycn2 gr +ak:9distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t gra50 p1z n 3c-h2* rumtkzedwfw0ph for the object whose displacement as a function of time is given by Fig. 2–28. e-2zu0h1kz5t3df0c *rm wpn w

Figure 2–36 is a positipm6v 623u7q z )navmkto u 2uegy6g*n3on versus time graph for the motion of an object along the x axis. Consider the time interval from A to B.yvnm)3u6 *7q m3 k 2gguap6u 2oznet6v (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story wibc9qqgo8plw xt8 i), 6ndow 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–37.c,w8 )96qgbo lixtq p8
(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 .b-g ,+*gfu1pvuckgj 7 y7.kdvz 4puuabout one-sixth what it is on Earth. If an object is thrown verticaly+ p4gjvk pugg d7*u1,u. z.bkfc v7u-ly upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat belt hac vbev)+l ps0jdi3v*/s a good chance of surviving a car collision if the deceleration does not exceed aboutie3/ j d)0*vv+ sbcplv 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, lbz)u2wl01vg j.ar + w12 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 the truck should be whenzlvw g)r.2+ uw0albj1 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 hauling .0l5ifaum.emsoxb06) p ud,w them up on a crane and dropping them from a certain heiodmfw ,0.em u5xsb0)lu6 p.aight.
(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 traver3w 2xhmqk;wkgr 9aat6x)(5 fls 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 from rest. Thu f7 +iuijsi(:e front of the train has a speed of 25 m/s when iti:uui+fj7 i(s 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 t ydn;:, q(a4roi3i gzxuyi.9 che water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the s:q.;9 nxiir ,doy4ag cyz3 ui(urface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the af cogjjl,zc uc.9+mcs+*m:x-verage 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 promm +jcxc9+:ljs* oz c -.ugc,fblem, 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 straight down when diving for fish.o sx)5y0 :ixwh Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assxowy s:)5i0hx ume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is 9xi 3 6hj(1 pztgu;nhjplanned 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 difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constanh i16xjg(hzn j9upt ;3tly 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 tra-.i f3.xb *a:a hbwocbveling at a constant speed of 6.0 m/s x-hcwoi* 3ba.fbb. :a Just as an empty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high bu1*;kzoxamg t5 w/ a8z.wmm)ccilding. A second stone is dropped 1.50 s later. How far apart are the stones when the second km c.zw;awt1 gcz8 /xm m*)oa5one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h z:93la4p wqesover the course of a time trial lasting epsq4 9 az:3wlten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour ssw4/6ci6 sf6hksz9 vqm* 6ps de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his vsc46wsk66sm*6f /qi9 hspzsspeed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounce uhm/d48xuanxqv42qls 5s s3 ) up one-and-a-half times higher than the second child. The initial speed up of the second child is xxal m5svnhd3q8 u2s qu4)/4s $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/hb--6tz*7qprzn si0 9rc ;tdff overtakes a 1.10-km-long train traveling 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; zf*-d bpr if70s9qt6nztc-r 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 thrq1luirursv2k6g(v . y,*p 9zdows a baseball with a speed of 44 m/s In throwing the baseball, the1visrz y(u r.udg,l 2q*k6 p9v pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an ac4mx )+*shy uc (2 +lbrvwr(smeceleration 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 tra/i lx7wl+4 rgbffic 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 intersection, all the lights turn g4r/bi x+w7g llreen. 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, passex1bg()w3lad- 7 ekji i0i4p yxcwk*-td by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maix-p iex0 wc) kl 3iydt-*(14bj7giakwntaining 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 buic/u1/fbs o ob8s0a4yclding; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones labcfo sa81ys c4/bu/o0nd 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 sam)rz0*g2+):t7 c5hw is fxb ctjh2qhuie time. The first stone is thrown wix2+)c ) q0th2f 7 *gsjhzcwhtiibru5:th an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resjzqraw3h4x., ;ybg, iv86pc tistance, how long would it take a free-falling parachutist,.pbi 8q6t,wvxgrj4 cyz 3a;h to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a gril6y e0sb5b 2 3l7tkc*a1 fyvind7(tvyu s6,lujling 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 6 ( *uvys60bi yl lfn127bydc etv5a,js7 ktu3the 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.pv a jiwnp7560c tr7i than Joe can. How many times higher will Bill’s w6inrpaiv77 0p5t c .jball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground be92qh e sotq1m/r8l n1g .tco+ylow 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 upel 8oyt 1mgoq+ 1rc snq/.t92h the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular buildingiw94kjv 3bd4 tbol8-y using a barometer. Instead of using the d3ito8 y9kb-j4 lwv 4bbarometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time)9j m(hyjondua10.w h graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) 9jay10)uhh.nodm wj ( 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?