Does a car speedometercs0xos 3z:3o q measure speed, velocity, or both?

Can an object have a varying speed if itsh)ki6zbcligu +i5,7 s velocity is constant? If yes, give examliu+ igk,b 6c5z)s 7hiples.

When an object moves with constant velocity, does its average velocity during atzjl(pk;s0qe sn:v c18v (y3lny time interval differ from its instantaneous velocity at any sk ( t18(vp30z;ly: nc eqjslvinstant?

In drag racing, is i,e 9wa : vtwj69w-pgkct possible for the car with the greatest speed crossing the finiswep:,wt6-gaj v9 wc k9h line to lose the race? Explain.

If one object has a greater speed than a seconc9,uqs p k:ht8d object, does the first necessarily have a greater acceleration? Exp,9 qups8t:c khlain, using examples.

Compare the acceleration of a motorcycle that accelerates from 8/jo j3t 7b(mz srrp3x-0km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/j-xprb(z33 rs/7 jo mth in the same time.

Can an object have a northward velocity and a southward acceleration? Explainn09xx2;1vmi /ydjxnr8 gkry7.

Can the velocity of an object be negative when its acceleration is p28/1:o 5)lxcrk tvygzyb( e ndositive? What about vice ver/k1(8 zr :y2e5cgdbnxvt)ol ysa?

Give an example where both tan5c2mz1 6*f./scpic9xj uxhhe velocity and acceleration are negative.

Two cars emerge side 4hhm+dp/fcd )by side from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a spemh /d4phd )+cfed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in spl:n-e*wy.v bg eed as its acceleration decreases? If so, give an example. If not,.*egvn lwy:- b explain.

A baseball player hits a foul ball straight up intt/sm+toe8 f5 )fi.n:rdp mdf5pnt d 14o the air. It leaves the bat with a spen 8t o:tpdpf me .5mnr1+s4ffd )5tid/ed 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 up, what is happening to its . mwhq6j9c7 czheq7kak0+tk3 acceleration due to gravity — does it increase, decke97h+zck ckw3q6aj0m7hq t. rease, or stay the same?

How would you estimate the maximum height you could throw a ball vertic;9jxmr9cc r w-f :1joz h9-neoally upward? How would you estimate the maximum speed you couo jr-fo:9jhn1c r9 m;x-9cezwld give it?

You travel from point A to point B inc5h0r;n7mlv/-8rdj ql+ dqtg a car moving at a constant speed of 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 t d5rvqg/8nl- qld+0ht j7m ;crrip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical strinsm gcrmz9x*: pza5p0k-p 24wfg 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 p*fw0rg makcmzz2 9p-x:4ps5 so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock falsi8n u(fn vxr.6 e2wb6ling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the8u fx v2sren(.i n66bw way, a dish resting on a table?

An object that is thrown vertically upward will return to its (05bny uz*iw 1 ia,kugoriginal position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistancu(y0ubg*k, i 1wz i5nae is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same time.hrd k*8c4fbpluded;1e;zw 1 ? Give examples*.l;fh; 4wzd8 ee 1dupc1kbdr.

Can an object have zero acceleration and nonqd-gfn9 ., yp /pg;phvzero velocity at the same time? Give examples.-/gph ;pf.9y dgq pn,v

Describe in words the motion plotted in Fig. 2–28 in terms of v, tw*8pec1:i4 9jcua vka, etc. [Hint: Fk8 c:p91jatw *4 cueivirst try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed ic df.o5+0:proh-h 2 ufxy:zpp n Fig. 2–29.

  What must be your car’s averaprx+ p0cst0yt(,e t8v ge speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 km? letsr1d z -,m:gh* c)z   h

  If you are driving along *3 g0cniciqcc7pm7 f g+ m0ju92lof1b a straight road and you look to the side for 2.0 s, how far d+lm*n mp9cc qci0f3b17c fjgi u07o2go you travel during this inattentive period?    m

  Convert 35 mi/h to u:g p9 adz3(6c lj2xis
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves g)cy6h/b3cf;o6 elz ofrom $x_1$ = 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 for 130 km. It ;xg8bfd-t2 9ha4s okm then begins to rain and you slow to 65 km/h You arrive home after driv o-kg 482db9sfxta;m hing 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-th go(:fnzf ,(1ohd1rvv kkf*a7umb, every five seconds between a lightning flash and the following thunder gives the distanrko ,7gohv zf1(1a nk*v(d :ffce to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mkni),lt b8zmoy9yok-iz5;) lile track in a total time of 12.5 min. Calb)zkiolky, 8 i9m)ytnlz- ;o5culate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its tracl *33q cfd1p-xc2ozt iner in a straight line, moving 116 m away in 14.0 s. It then turnso3f* l3 tpdqc-zxc1c2 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 e,6m:ppoys8qc5 )z,hgaoe m t)ach other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach eachcas mtz,)o p : ygq,)h5p6m8oe other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck trpi*:x)q 5xctp aveling How long will it take the car to reach tt:p5*xqi x)pc he truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters aew ,6l+qi+cts tailwind that boosts its speed to 990 km/h for the next 2800 kmi+t,c6 l+eqw s.
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 i5 :e5k1-+ l lgwkhcuiin which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km iu5+k :hl5g lic wki-1es covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hitsj)ws,ws-kq2 vds+j:z the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed )w: 2+jsssjzdq ,vw-kof the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6bw c/nznqn( x9ri py(x/2a)a6.2 s. What is its average acceleratiox nw ac 6pzai 2/nryq9)xb((/nn in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s i ::2g v,1j/vhddypcc doy9fj5n 1.35 s. What is her accelerationvjcj d5vh:/pg :d, c9yd1yof2
(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 z23vb objgm z3z *j:s3acceleration of aboutj3zj3: sbb*gz 2 oz3mv $1.6 m/s^2$ 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 consta93 gnkuv3 3s- 1xhwvpent speed travels 110 m in 5.0 s. If it then brakes and comes to a 3k-n xp vv1w3e3g9uhsstop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from w1wbfdfj 6t.,..6 dlld 3d eohrest at t = 0 and moves in a straight line, is given as a function of time in the following Table.bw lj..,1hl6e dd63 wf.todfd Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 1c ndmo q.jbq-ggcuioir-(2-:p : .yd03 m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant accg.: bgr jm (co.qnyp -dcdi0-qo2:-uieleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its act )puh( j,d2khceleration, assumed duk (t)h ,jhp2constant?    $m/s^2$

  A light plane must r l8)pcrqdl/, (5bofvn each a speed of 33 m/s for takeoff. How long a runway is needed if the (constant) acceleration 5d( pfbc loqr/,v8 nl)is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks ha e+ut327ja,ep o86 sbm0bta to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What ishb a8tpbms7at,0je 2 o 3a+ue6 the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How far(b:5h bhhs;vf did it travel in that timvs:5bhb hfh (;e?    m

  In coming to a stop, a car leaves skid marks ;g2(w:6k1yrr jxmofs 92 m long on the highway. Assuming a deceleration of j:sy16o gw ;mrr 2xf(k$7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h striku c4vf0l nfn vh/z68r*es a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. nl 8vf4hnvzrf c/06*uWhat 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 distanthh g2h-hl(o 80m+g elces for a car with an initial speed of 95 km/h and human reaction time of ( g0 glm+8-olthe hh2h1.0 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 distc3xtl,l nu 6w2p r9)alance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s drivega5ib p07:tdfr looks for an opportunity to pass, guessing that his car can accelerf:gi5da b0t p7ate 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-mo,6 oxty(fm m 5qz au0fpql(4gu6q5m- run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runa q(6y mq mx0 5-4q f(loum5ftgzp,uo6ner 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 approac+y9p5q6i *opn jkz; sghes 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 s6+;qy*jnp skip o9z g5peed 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 o/ c1/7hcg hfsbf a cliff. It hits the ground below after 3.25 s. How high is theb sg/ch1c7 /fh cliff?    m

  If a car rolls gentlxv z7 h 3nr3gisa0h3ql18u un4y ($v_0\,=\,0$) 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 airalu-.4g:yb dr4ida/ b 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 aftelnb iudxh8/ (0r throwing it vertically upward. With what speed dlhxb 0du 8n(i/id he 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 inflo ) 2,eoego:hkhw5c ,kuence 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 . Ignore air r2g,5whc:ehoo),ke k o esistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height o ll.qgdc9kw)nrn0;/b+/cn1ht aj im.f 125 m above the Earth, a package is dropped from a window. How much time does it take for qminw.;/htla+n)j 9bd 1k0g nc.r lc/ the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely oqz0wf ui1kl1fy9l db i6v -9)from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.).69)l-zd 1y9 0ukqo ififlb1 vw This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thpdedcy7(5zt-q 5kr0s rown vertically upwar55qtde dsr-pz cy( k07d 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 m/s t;si :sm.e gctyf:1/a
(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 photoflaba o6+4lz-egzm2x 9 eush of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the zza+e 2 bl6mox u49-egapple 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 (F25j0 nu9q6fkf 1itawveq*1s/jh . kuu ig. 2–32). From what height above the top of thqfv ej 1wfu6qhi2/n 5*aj s.u1kk90ut e window did the stone fall?    m

  A rock is dropped frs4 +niae wugk :9mgn4p9dq. wv(5g:ar om a sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high gngu9m :d.wa skq a4+:e4rw9g 5( nipvis the cliff? H =    m

  Suppose you adjust your garden hose na+-qmt-/7 ptmsl,ww(l o ijt (ozzle for a 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 ne lm(sla(-t/wtw-o +m qij7pt, xt 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 a,wk/,gtx*it *vx, le of 12.0 m/s from the edge of a clika*lw, *etxxit,v ,/g 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 pass upward by a window 28 m s-oah)p.ozx 33eky z 1above the street with a vertical speed of 13 m/s If the ball was thrown from the stre.p1hk) ea- y3xzs3ozoet,
(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 a 5i6fh bq2j(onc *smk,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 acceleration constant? (d) When w2s*oc65ihnf ( qkm,bjas the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time kz,lcxw4(q4:t,k x oeis plotted in Fig.kc e4,(wx,l4zqto:kx 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 automobile can accelerate approximately as shown-), u1e;em zcbv4ydr e in the velocity–time graph of Figby, reed1v- u )cez;4m. 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 averageqhsp/ nek3abt46 w1v, acceleration of the car in the previous Problem (Fig. 2–35) when ist 4h wbp6a31 /nvek,qt 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 distancaas5)i6;ox5-ykvcbc w13n b ue0io e3e the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a x7t5ypwws9r3f24hf i ng( )zqfunction of time is given )p xr93 4 fg7qtzw5h s(2wfyniby Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object al.z0uoia 1mz7nong the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negat nauo. 017zzimive 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 jfd(xpi )j+oe* 4gmi;.0 m above a firefighter’s safety net. T;(po fim jjg4e+xd*)i he survivor stretches the net 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 Moon is about o35zn+ i192m-)rwi bgd jjqmppne-sixth what it is on Earth. If an object is thrown vertically 5qpgiz pj 9w3rm )mdi -b1+nj2upward 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 h9 u( / ed6ni brhk99u9ld*pfsjas a good chance of surviving a car collision if the deceleration does notj /*9fhi(r dp b9knu 9udes69l exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and hif0 neq*cai e51s pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , whicefe c0a5in q1*h 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 collir 1lcxj3*f c4tsions by hauling them up on a crane 1clr*xt4cf 3jand 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 travel6 +mqqoeq u1s ;s39 gv/jalu*ls 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 awr *)d7 j ednamp3jh3:cceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. j3n)jh dw 7pr3:made*2–38.)    m/s

  A person jumps off a divingy;cqb6hyb2 i+pg*l.c7 t hjwk;a7 8zf board 4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estlyzg6*c7ytqhh+2 wja;b7. pc8 fbki; imate 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 nl:r9 8c hn4b,givfibb+j, ,2v8escbaverage 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 9.0bshc+ 898l:vr,b4bcij,g, f v enbn2i-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 f3qm tqgb+9w p,all straight down when diving for fish. Suppose a pelican starts its qw3gq9 m ,pbt+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 force with which a golfer striked7do oe,y0upo /e )nym.c -ki;s 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 difficult than from a downhill lie. To see why, assume that on a particular green the ball deuoo- , mcd/7ke iy0.n)p e;dyocelerates 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 frl7vco9iz .c6leight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest an6zicc. 7 ll9ovd 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 buildingvu qe (1nqnp21. A second stone is dropped 1.50 s later. How f 2qq1nnpe1(uv ar apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the colcc7 a leokv:iys/.76-r , vdkjf/ya7urse of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . f.c/7k7avj-ro si ,dcy7v ey/l 6: lkawhat average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves a cht,ht).d 09ikncyka xc91 u5t 18 km/h . At the bottom, 4.0 km fart.k1x 9ad) 59c0h,kcht yucnit her, his speed 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 fi +gvp+v3x2: zdtx6 osprst child can bounce up one-and-a-half times higher than the second child. The initial speed up 6+ xpo: g3vs+vxzp 2tdof 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 pk cfw :y0+-(xt mj,m/wp; owks(jhx7 train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h x;mw,jh pk7- kxmwcf(oj 0/sypw:(t+. 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 baseball1jwrwevcvtw:+vk *s (idq2,+ with a speed of 44 m/s In throwing the baseball, the pitcher acceleratewid*rww1:+ ,q e vs(tv+kc2jvs 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 verti:hxs6mqeqi8 6cally, from 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+ fcuc;1hk2eku:lnp 6 traffic signal, and the speed limit is 50 km/s . Suppose you are drivingu+pn:u k2lhckf 1;e6c 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 atz:7wxs n:u8b ul.s v.t a constant 120 km/h takes off .uwut xz7sn8s.v bl:: in hot pursuit. The police 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 fro o:*ep:juv g7gtvgpb/w 5x0m3m the roof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two st7u 03g m/:o xje5bgtw*:vvgpp ones 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 vertically1 vxo,yxqbh y ,544s:ba fy uj oe+9d2i.frmw; up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a ;oabdw :4o5hj2xvrs,,1bqy+uf 4 m . fyeiyx9building 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 resistancerr8o jcjv1*6c+ni vz /, how long would it take a free-falling parachutist to fall from a plane at 3200 m to ann +1v ijo/* zvrrcj86c 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 xhjsf 2wp-9 k(send the burgers through a grilling machine.j2hwp9x k f-s( If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertical7/zfrj(ta7yy9l hj;j ly at a speed 1.5 times faster than Joe can. How many times higher will Bill’s ball go than Joe’s?j9 ryaj;l7j y(ht/ f7z $\approx$ =    (retain one decimal places)

  You stand at the top of a cyj3x 6o xnf,1gz k)nr::q .bqjliff while 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 throwsrb,j6gn:j1 z .xn 3 y:oqfxqk) 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 height8ca 1lk8k wvacn,v5m* 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 ol*wk8mk1 nc8v 5avca, ther, 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 and B. (a) I l(8zhx3gz*ee s 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 o(e zghe83zl *xther? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?