Does a car speedometer me-vk iph/ 8dig7;sitljo/ )t :aasure speed, velocity, or both?

Can an object have a varying speegwe62 5f73iyfp fjc2p d if its velocity is constant? If yes, give examples. cjp7i3gpwf fe652f2y

When an object moves with constant velocity, does its average veloit hjq+, /dp.ocity during any time interval differ from its in,qid+./ thpjo stantaneous velocity at any instant?

In drag racing, is it possible for the car with the x6x ;*geq.vgt greatest speed crossing the finish line to lose the racev 6.xeq;xggt *? Explain.

If one object has a greater speed than a second object, does the*xc,s(p* auqrm)kfe; first necessarily have a cx) *m,qr*(pkfe s;u agreater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates.u fq1xg8c6t5-veya*e gt ar p+,)sfs4a q*wq from 80km/h to 90km/h with the acceleration of a bicycltga ,ta qe8qsx1p* efgu5.fcr)6+y q4aw* -vse that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward accelerats7 yrwgx e80hhb,4eil ;ek/k-ion? Explain.

Can the velocity of an object be negative when its ac g ;+p,4i1az,xucgv tdceleration is positive? What about vuzv dix+gt4 1g;,,acpice versa?

Give an example where both the velocity and acceleration are ne. .9df;s ffr0dzda2swgative.

Two cars emerge side by side from a lba x09fa)ih xc:l3 c/tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has bcax0lilf9):3ha / cxan 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 speed as izxyif,ok q f,uk111fb3a )-jkts acceleration decreases? If so, give an example1-u b,i,qkfkzkja1)f1 xoyf3. If not, explain.

A baseball player hits a foul balzo gnto1s28q p co5n-*l straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcsoz 1o8o nq p5-2gn*cther catches it?

As a freely falling object speeds up xdtgery/6-n 2, what is happening to its acceleration due to gravity — does it increase, decrease,6y dtr2x /-gen or stay the same?

How would you estimate t0yc8 sa +uav1zhe maximum height you could throw a ball vertically upward? How would you estimate thcuaa8+ y0z1sv e maximum speed you could give it?

You travel from point A to point B in a,pff+ac p0hdc-ec.0 m hf+7tx car moving at a constant speed of Then you travel the same distance from pocftfpcefph d.+a,0 0-m+c h x7int 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 verticalmzt5vrh)r(d2 e1h s ue03/sz-af;vm k string with ten bolts tied to it at equal intervals is dropped from the ceiling of the le5;f u2)tvz(mv eskd h0err3-z1 s/hamcture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these mkg-x:e,2xna2 bm0 y)u +tlt llp+2gpk*5p tj wotions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fift- 2wgatmtek lx0,pp lkub+y+)lg*nj52p:2t xh floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to suny.xwjht ,*vj)) q 4its original position with the same speedsnq *vw t)ujxh,.4jy ) 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 acceleration at the. kx2q6wk (zpx same time? Give exzpx 2w 6.k(qkxamples.

Can an object have zero acceleration and nonzero velocity at the samec .muo*2q 2bc1uq7mzq time? Give examplesoc.*umq1c22z q7bqmu .

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [Hintf2,a 7glcz dd9: First try toz,d92 gadf 7lc duplicate the motion plotted by walking or moving your hand.]

Describe in words thf2uth2/llz vg(zov0e2 4 2pqye motion of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in y(fb c/y2px s3.yih5j3.25 h?    km/h

  A bird can fly 25 km/h How long d+d4i(b t jlfjtxag:b* p3o cb +6ua19poes it take to fly 15 km?    h

  If you are driving along5 +jlar25vc 1mzn-;e73 xrda kwt:o pv a straight road and you look to the side for 2.0 s, how far do you travel during th7 + n1rzv2kaa35 re-ot;5vcw:lj xdmpis inattentive period?    m

  Convert 35 mi/h to 50rwoicf : 0ih)x).34idem lps z7a rq
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frogp.r(v8*u ei/ cd.rwe m $x_1$ = 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 then begoa,z7szrn e8-n-o n*gins to rain and you slow to 65 km/h You arrive home after dgaroon nz*nez- ,s8-7riving 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-thumgeu pv(d 4st73b, every five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuminupe4t(g 3v7sdg 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-mrhk9 e2v9d z(gile track in a total time of 12.5 mi9 kr9(g2 hevdzn. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a strai,ynqu: leh 29hght line, moving 116 m away in 14.0 s. It then turns abruptly and galloy l e:q2u,h9nhps 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 -o agvcrxh7:f:/n2r qeach 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 lon x /q:2ranrh fg:cvo7-g will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a n 3v4 ov0ihg2dtruck traveling How long will it take the car to reach the t4 0vvo2 3nghdiruck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters su w,pma(u8:g a tailwind that boosts its speed to 990 km/h for the next 2800 km.w8apg: u m,(su
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 rig4f xa:r3 icx o213vin which the outgoing 25oc4ra vx3 fi231gxi r:0 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/h.    km/h

  A bowling ball traveling with constant sxxun*cz 0 1q)speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What n1 *xzu 0cxq)sis the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its aver,:y2y5 cp mbtaim- yq)age acceleration i, my2 y5-ic:ybm) tpqan $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest tv.jz ;parz7)mdk-pj,o 10.0 m/s in 1.35 s. What is her accelerationpk)za; -m rj d,pzv.j7
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automog3 h hib ;p;v/g1su3hybile is capable of an acceleration of abou1h gp sh3g/b3 uv;y;hit $1.6 m/s^2$ 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 trar 1vo)lfzfuxfjo dz f (:.-4x2vels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accelera zlof 42-(r:u)djxx1fo .ffzvtion 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 tzp pp/,fd+x;dy:( ixn = 0 and moves in a straight line, is given as a funcx+, fndd/ xz ppip;(y:tion of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s8j r2nt,ovgt:0x enk, in 6.0 s. What was its acceleration? How far did it travel in this xkvo2 r,t n8t:eg,0njtime? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. Whn(:ab+( pn -ah* fgpteat was its acceleration, assum(n :b+ *nap t-agfhe(ped constant?    $m/s^2$

  A light plane must reach a speed of gt qy0 2;vl(awvos88l33 m/s for takeoff. How long a runway is needed if the (co8sy0;2 lla q8tgw(vv onstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinte71r r rgdxna z9wm3r)b8xf9t +r can burst out of the blocks to 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? 17xgrarzdx f 9t9wbrn+ )83 mr$\approx$ =    $m/s^2$ (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 fa h g x-5bag22d- fzrxjxd-+k(xr did it travel 2 f-bx5j g-hk+xd ra(gd-x2zxin that time?    m

  In coming to a stop, a car leaves skid marks 92 m los3wqh7o to.7 f);dltqng on the highway. Assuming f.woodqq )t3tl; 77h sa deceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car compr .p6 ypkp6o nq*t8.acbdjg r/0esses 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 yn/tc p8pa.go0kp.6q6 r*dbj of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 km/h a-h7o0 s:tovgsm6 qy /ynd human reaction time of 1.0 s, for an accs- mto:yy706hgsoqv /eleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance ofh/l.tz jub *m;dpcw8qfsrxr9;2* fjq2 w4bi) 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 drivyof*5/*g ji kuer looks for an opportunity to pass, guessing that his car cako/*j 5fgi*yun 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 10,3+ h6 krf + ytz1uygk8z5wpp2q000-m run in less than 30.0 min. After exactly 27.0 min, th+p+fhw uyz tkk1y g5pqr628z3ere are still 1100 m to 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 approaches an intersection just as thamj/b*g vpop 07b2ky- ef 61jys-vz8 de 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 ipj8mb1j0sfbo/ - zdyp 6-v v2g7a* ykentersection (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 p5l ) : 2t6lmo/jzffftcliff. It hits the ground below after 3.25 s. How high is6llf5ftjfpo) /m2zt : the cliff?    m

  If a car rolls gentllalqk7qkx1y8t. 1 h.v y ($v_0\,=\,0$) 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 nqr)j f. e3,oxwith 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 vertically upward. With wua/ixson8k):,ga s t 64vlr t;hat speed did he throw it, and what height did )ktlan4gxus/oa :6vt,ri;8 s it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influerarqtky cffv:m)31w q)x) 64pnce of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time f3f) m1 )r6c pvtawyqf:r kxq)4rom t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height 5j;mj xrvy-f/f mi+y+ of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the grymfm+jx -jf / +vyir;5ound? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance tra-8sl :l p9cad:cqi1d)p; ear iveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.)d8s cip:pc- :l91ae ia;lqdr). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a balz3e b hr t.d3:ke;:xqvl thrown vertically upward with a s:veq hrzkd3.3b;e:xt peed $v_0$ 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 :y,b 6l1 jl ljk mb hgfnfb/2v7-lxo3+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 appl9i/o dhz x6 2swv5i1jde in Fig. 2–18 (or number of photoflashes p9/oiwjxv25di6 h sz1der second). 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 sh6m xa1( t:adsc o fze57nae m*1e7;owindow 2.2 m tall (Fig. 2–32). From what height above tt*ehac snam 71dfe mxo: oz(5 e1sa;76he top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of ih2m,2vgc( 0 8qqp zhegt striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is8( mh qq0vgz2 2hepcg, the cliff? H =    m

  Suppose you adjust your garden h*.* i 5va.onp1l d bb4plb+xkqose nozzle 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 next to 5x4pobl* +l1d*b a.p. binkvq you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the ebfy xi5-75qk)ww .atsdge of a cliff 7 ysi7ax t.-qb5fk) 5ww0.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the street with a vert,ro. fbc at q:9rzg fc3d )ir/t888rgyical speed of 13 m/s If the 8qic9g :bofty )rfra/rz8g8trd3,c.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 o4.jt;u4 d18 vhg tvu*ryaycd3f a train as a function of time. (a) At what time was its velocity gdv.j3t; hu4 vgt4uaryy*8 1cd reatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time hss)bll:r7j sv;nl (( is plotted in Fign;l7hv(s(lsj)br: s l. 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 approximr3jm 8ec* mg*mately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the8e*mm c3rmg*j 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 averageg -zou90dmit7 acceleration of the car in the previous Problem (Fig. 2–35) wh0dmtuig79 -o zen 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 ;j 9w n3ny0xrgthe distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for thef kwoxqa ;803 hx.bpd8 object whose displacement as a function of time is given by Figo3b pwqa x80kx;d.h 8f. 2–28.

Figure 2–36 is a position ve r4i12nlqu 3m.:qwsqzrsus time graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negzq:4m1u2 s 3rlq i.nqwative? 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 aj( b81u9; xe/kvpjhrt fourth-story window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest xk9j1vbrephu8(;/ j t, 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 toc;8z-q5brou)xi p5 xl gravity on the Moon is about one-sixth what it is on Earth. If an object is throwq-rxb p5x iz5ulo)c;8 n vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an cphug(rgrgpd4dy e;7k 4c0 c*+(ec0 c over-the-shoulder seat belt has a good chance of surviving a carygcpucpc0(; kc h07 r +4cdrd (gge4e* 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,9z4qnl l2-0t-xdm dnr 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bon 4r-x zlldqdt n9-n2m0d 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 collisions b; j1dwp2dxd (by hauling them up on a crane and dropping them from a ce p2 ddxd;bj(w1rtain 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 tra27gdpsgd) /g o7tv7fmvels 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. The a : jkfdmqwvg-hpt -5m5 h ;5(+fhtp8qfront 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 carahfqw v5 :t g mp;h-pd58f(qk -m+hjt5 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 into7wdl q v7ad/2 1f*o ar2qwqq3y a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration 7ql f*3o v w7qaqa/rdyd2 1q2wof the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it isuq ua e6x;i0p4 necessary to balance the average speed of a train against the distance between stops. Tpueia0xq4u6 ;he more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-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 i 1 u;lz*xszjv .d,0;ne-ihamdown when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fisvldz n;. u0ei ,a1;*mjx-shiz h 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is plannea6 :cnjse t(jl-ac 59vd 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. 5ea-9tn6vj a :l jcc(sTo 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 traveling at a constant speed ou ,c,jkze s1mjiu 1n4z 5dm6r:ygu 3:af 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accelerates akej sid63 ,c,mrzmjuuz:y4: 1 ga1u5nt $a\,=\,4.0 m/s^2$ 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 roiub)fq 2/p( wiof of a high building. A second stone is dropped 1.50 s later. How far /w2ip if(uqb) 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 oj7iwcfdhk e*5:s7)cx ver the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap? j*ch e)w7 5ci:fdxsk7   km/h

  A bicyclist in the Tour he,dkk(uy5f f ,r/+-e.pb wluwc0 9fjde France crests a mountain pass as he moves at 18 km/h . At the bottom u-w(kbel,ydfj ,5 /u. cwe0fk+r ph9f, 4.0 km farther, 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 first child canr+1qu,e yg xk1r. :m (0xhhmhm bounce up one-and-a-half times higher than the se(r.hgq1m k1xm:m+ hyue,r x 0hcond 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 triu.g05 1ujb u5a adv.zain 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 traveiz.uuva dg5 b10j.u5a led in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball hm3y(9dpqoja)+mf5t with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from 9ft5 )ymd(poh+j q3ma 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, c79ndfpb g3c 5with 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. Eac +93jv rxiv(h w zg:nlp+bd)3zh intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed+zd(b)h3i+vv n 3l :zrjgwp 9x 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, pax9p0e)2 y5qv g-q jhznssed by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder ingv2 )qx5q0ehyz 9j-p n 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building;(h ,u 7rz)peq::vg9*xakoftrz d9 c2 j 2.00 s after that, a second stone is thrown straighacdvxje 9 zr u 7qz)ok(9:gtp,hf:*2rt down with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same ti /q 9+jnnok2f(y0.0pkc1z hic7jnydr me. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-f0z9.kcqndnf +7op2jck(0yi n rj1 h /yloor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-falling parachutinhj/gjo+fv a0wh 4 7vvql)7z-st to fall from a plane at 3200 m to an 0/j n7v lw )j4 f+-vgozhqh7vaaltitude 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 stytnr.zt+bj8 (f 7v09 rx aqr yn89)ahend the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burge9nn+.f 8rv0t7 qj ab)9zaxhr( t8t yryr production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.. fnm; pkudiunl/wx2 22r*5 vq5 times faster than Joe can. How many times higher 25u 2*xdnn.ivukqp w/;r 2 mlfwill Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend standscwdvo 7(2wbq1 on the ground below you. You drop a ball from rest and see that i2v co 1dqw7(wbt 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 the speed with which your friend threw the ball?    m/s

  Two students are asked to find thholwym r3+.-j e height of a particular building using a barometer. Instead of using the barometer as an altitude-measwh3y.mr -+ ljouring 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 tlyo:cp/a yka. d2n0bm8. m,uvs. time 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) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instant u .n.t,mp 2 8ca:0d/oaykylbmaneous velocity? (e) Which bicycle has the higher average velocity?