Does a car speedometer mg5q. :ypce*x measure speed, velocity, or both?

Can an object have a varying speed if its vell5* 0f y1p8icki(t a4gmtcj b9ocity is constant? If yes, give exampl41( f9bjcliyttgkpm *iac5 80 es.

When an object moves with constant velocitytoy,7koofa 7 ,pu c:w,, does its average velocity during any time interval dif7 o cyo7, kaut,:fpwo,fer from its instantaneous velocity at any instant?

In drag racing, is it possible fo o2fi la+h;ap;r the car with the greatest speed crossing the finish line to lose thflaip h+;2o;a e race? Explain.

If one object has a greater speed than a second object: iiqh f;t, 9c2es t)7oqqrjg3, does the first necessarily have a greater9q cs je;gtq3qf)2t,7o:ii hr acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that a( taxdi fjq+y0y52q1yccelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same ti0t+5xqyqia2 1fjy dy( me.

Can an object have a northward velocity and a southward acceleration? En /yadgd(s*. axplain.

Can the velocity of an object be ne)1r9ut yzjx((4gsc eigative when its acceleration is positive? What about vice versa?1iux4egc9 j ys()r(tz

Give an example where both the velocity and acceb c0lin;07 cgcnnwg 77leration are negative.

Two cars emerge side by side from a cq; d8 xc;mq z81bawd/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 an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasonincm dq ;b1 aqw8zxd/c8;g.

Can an object be increasin +5rut/uu jroq.eop8+ g in speed as its acceleration decreases? If so, give an qut/jp8reuro5o+ .+ uexample. If not, explain.

A baseball player hits a foulvyam ;bq,nu-z wl-+e uh2(c1n ball straight up into the air. It leaves the bat with a speed of 120km/h . I,bv-lh(wuen m zqy -u 1nc;+a2n 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 ac, 632r hdhizjoceleration due to gravity ioz6j23d,rh h — does it increase, decrease, or stay the same?

How would you estimate the maximum height you could thro2ogn;whg9 d909 ibbfvvhs1h x88 oe3rw a ball vertically upward? How would you estimate the maximum speed you could give 8oh3;vi9 w ne 28hfo9s 1r9xg 0vbbgdhit?

You travel from point A to point B in a car moving at a constant speed of phhv h3cw ,/8im 6pur:Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your averageh/p8 pmvw, 3hrc6uhi : 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 vertical string with ten bolts tie/ m8: da./ag.tpnn vond 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/tad v.mgpn 8na:on/ . 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 motions is not at constant a(p (0d6u4 sh(pemjzd pcceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor (4zu mp(p6d 0 j(dphesmaking stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its or5zio y q3cr38yiginal position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, andq3cyo 3 yr5iz8 if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero ve)-+vzuzs -kgu98.a 8 aztwxkzlocity and nonzero acceleration at the same time? Give example88k kz9vz gaa-u xw.-+ z)zusts.

Can an object have zero acceleration and nonz g(nq. +ksp*vg1vmsb/ ero velocity at the same time? Give exams*pkbn.(+1/vgqsv m g ples.

Describe in words the motn8hnx:5mrqmk ( nz 3e+end5p5ion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motionn5+ n5h:3drenmnq 5 em(pk8zx plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in u j)/bm9y9kjwc vo7py7k)l9y Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.25 h?0(u1hsvq(-dez dffm z 9yp6f*    km/h

  A bird can fly 25 km/h How +hp wvzf2je-(x t/lq6 long does it take to fly 15 km?    h

  If you are driving along a straig /a sbb, sw2tuba6f+e,ht road and you look to the side for 2.0 s, how far do you travel during this inat/b62b,ws,afateu bs + tentive period?    m

  Convert 35 mi/h to l24hg cvhw g:ce :4welm8v./d
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball movesmc8- c(k0m jdx from $x_1$ = 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 pbjbv2.7 gl ,nkm/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3j,p2 bglb.v n7 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 five seconds between aj4hz-f9rlg6qr .go i; lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the rr4q ;o h-j6ggl.fiz 9speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a toe0/np s afnz0ji7 (h7y6kvrm /tal time of 12.5 min. Calculate emn(i/has /7yvp0z6n0 j7f kr
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its tv;-g11w din ;9jjd. g(msdixxrainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in ;i(vg g;jnd1s -jm9dxdx.w 1i 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 t3s fb3rht d/ yqds;x4(racks. Each has a speed of 95 km/h with respect to the ground. If they are initiashs 4/3;x y3rft(dbdq lly 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling H2 qa)wk t*l n- r dxpo4pmgcub-1c8(v;ow long will it take the )-;gu4 p218-*drkclxtaq(omw bvp cncar to reach the truck?    s

  An airplane travels 3100 km at a speed of 7gxxdz0i5 :i;jw r2n;m 90 km/h , and then encounters a tailwind that boosts its speedgxdjnxz;m r5;0ii: w2 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 velocity of a comp( m s yocdz-pfp7p0jrw7 qw1e p,/th)*lete round-trip in which the outgoing-(17w0 oy,)qp w * /jphdrpzm7pefstc 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end of a i3z+g 1og1+x+l617r gvnf o zmpzmrs9bowling 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 of the ball? gx m11 g1lr o+7inp+vfrzm9g+6zzs3o The speed of sound is 340 m/s.    m/s

  A sports car accelerates from +la- a) s/ixvqg3 h+qk20lntnrest to 95 km/h in 6.2 s. What is its average accel+v+ 3sxqt0iq -na l2glh)k/n aeration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Wpny 1 veh0l42rhat is her acceleration 2nv1 el phr4y0
(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 acceleration of abou *wj.z(cu ; jiuni2;crcc(ju;*zu;j2iiwr. n t $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110 m in 5.0 s. If it the:b4(ortvh.a hn brakes and comes to a stop in 4.0 s, what i:.rothah 4(v bs its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t = 0 and move* :0f7uy .k hzrz/cgku-zzz1g s in a straight line, is given as a function of time in the*-yh zgz0:z/uzg .k17cfur kz 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/s in 6.0 s. What was its accelidjxgjf0 174mnf-aq wcn ,3 9peration? How far did it travel in this time? Assume constant acceleratio0p,njc-mf fnd x w4193iq agj7n.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What vor:v(kw2 hr1c/2t fq0agb k r(ymn+5 was its acceleration, assumed consrf rn:20gv 2m(hotqa +y/ b v5cwrk(1ktant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How lon4 mbnzgmet-ir4.veu / 6 rfo(9g a runway is needed if the (constant) acceleratb 4fmtr9/4 gunr o i.mzv(-e6eion is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essob)c8y zw g4;7 4xeyztentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. Whabzcw egzo7 8t;4x4yy)t is 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 far04)m raazh d9.x+uw:d+*ye j7r yfmif did it travel in that xarmd7y:m 4h0+a*fi zwf9j uey+rd.)time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assu;f) ,y vwsutxc34v k65 uyjri/ming ajvwry 3fy6/ x4s , ;)ktvicu5u 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 compresses ande uwp/4kwtp2z pm( +8o 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 “g’zw 8u e+2tp(p4kp/mo ws,” 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 initiad )x .5iycmzfe9uk5-a l speed of 95 km/h and human reaction time of 1.0 s, for an acceleratio)5k.-fz duxicyae9 m 5n
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equatie 1,m)7 ibd jhzj8,kiqon for the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver looks forur;vn2wq7o d/clr ;9 r an opportunity to pass, guessing that his car can accelerate at 1.0l;n2v9d 7rcq wr; or/u $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. Aftechvc/9 63ovddr exactly 27.0 min, th3hv9/dd co6cv ere 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 gy y0*8 lyzze9a-+re9m*umz ikm/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 urlmy 9iz yzgay *- e8mu9*z+e0p 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 cl bef:l4c,2x gbiff. It hits the ground below after 3.25 s. How high is t2l:4gfxc ebb,he cliff?    m

  If a car rolls gently (c5ymthc i95d14 ;lau6k/wa im $v_0\,=\,0$) 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 se g hs ob f69ly;t.+y1q+dq6imtraight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward.5od*,2 jceg gq With what speed did he tcge ,g2dq*j5ohrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls uy p(5qa0pe-pb8hfp 8snder the influence of gravity. Draw graphs of sp(8fb-h 5 q ppa0yp8e(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 resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height oq7a r 2 vu8lfqie*/w g75gl*hwf 125 m above the Earth, a package is dropped from a windg 28 5w/qai7rv lhewfgq*u*l7ow. 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 thelthh(h3:ka ,-d v0zj z distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. tjkhhvz-zadl , 0(3h: 2–18 and 2–21.

If air resistance is neglected, show (algebraicallys/suj/7j srltpl9p o+2zb* q 1) that a ball thrown vertically upward with olj/ *+ps jpu9 rs1ztb2 lq7/sa speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically ut ,2hce e*d. n weut6c:yuhx()pward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the app.k 82m( 0tbm3rg xzouele in Fig. 2–18 (or number of u (tr2me83okx0 .zm gbphotoflashes per 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 pas0-jr lyv j.nm/t a window 2.2 m tall (Fig. 2–32). From what height ab. -j v0ml/rynjove the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of ittscj wou 44y/ j(-l4pw striking the ocean is heard 3.2 s later. If the speedc4ujosw/ ( jt w4lpy-4 of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust yourm,ztex5u30zr;x urca23c n j) garden hose nozzle for a hard stream of water. You point the nozzle vertically upward at a heighnx0r,3a3 ;m zxu)j 5tzercc u2t of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s f5+pyu/ udmq0 krom the edge of a cliff 70.0 m high (Fig. 2–p quyu0md5k/+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 stree g lvkg8eil9t4t b75(jt with a vertical spkvi5l4e9tb8g tjlg7 (eed of 13 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 train as a functionls m,9b,th- mt ugf uq::w);lp 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 was the magnitude of the-9tl ,qlb,sm t f;g::uph)mwu acceleration greatest?

  The position of a rabbit along a straight s.cs8,sg -bn 63,kez pcka0rx tunnel as a function of time is plotted inn es0-,8 p.cg3c sabx6zsrk, k Fig. 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 cawx84il elutj4er ; /d 1 txwe:ikbdm9.z **s*xn accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.lelx4*die1i*e*mws r4:.8 tdu tw/k9x;j bxz)
(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 accelerat3 nr*omf0 4*a mfmxe0o*n* opj0 h2yoxion of the car in the previous Problem (Fig. 2–35) when it iomon 00nxj*4of20afm o3 eh*rpx**yms 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 *p :+m srdpg8wdistance 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 function of t/ y:opkukbx:(*5 zuwvime is g z5:xwy: vopuu(k/*b kiven by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an objectuvexn 7a;.p+g along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Ipg+n7ve; ax.u s 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 window 15.0 m above abjo7n jp+o: y5ezj:,v firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. eo7n: z+jv bjp:,5oy j2–37.
(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 ony v 1v; nrr.m :mk.az4qupic9. the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher r4 u ..rz1my9p v;n:aq.v kmicwill it go than it would on Earth, assuming the same initial velocity?

  A person who is properly v x9;-d;azzzr constrained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceez-x;v9 a d;zzrd 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 bq1*fo2nwjus 6/7hqb40 jyyj n elow, and his pursuers are getting too close for comfort. He spots a flatbed tj6 *hsy 4j /qyobnuqjf2071nwruck 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 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 i2ut v65dbcp*o ts cars for front-end collisions by hauling them up on a crane and dropping them from a ce5b*dutp v co62rtain 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 toqw 08*ffeup+x)e -cojsgi.ligr5s, *j:1vp ravels 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 un,a dao4qjqi 57m-, uksiform acceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who 7 ,,siukja4q ado 5-mqis 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 boar;rs7ccr h*v q1l)ljp ;d 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. Estimate the average decelecvj p srr;lc1l7h)*q;ration 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 njt hs uh(m6y, :2uf0edecessary to balance the average speed of a train against the di0fth u6, he2 jmsyu(d:stance 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 9.0-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 azy vb4x )h:fv fu*p/(scx.c ;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 t: u y;fphf.vz(x s cx)4ac/*vbakes 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 forcqn +ygawq,-8se with which a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (th8, + -ynqawsgqat is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train jbp*b3wlarw 45 4zms4traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugja 4smw3b z p*b45r4wlitive 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 thia 4xxah/( vbbt nz(79e roof of a high building. A second stone is dropped 1.50 s laterza9n/ (vb (4axbhxt7i . How far 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 course of a time ktfy7g,*dh5w ibc6n00vf4pz trial lasting ten laps. If the first niw7c4ft*05inpfg z6b h0k yd,vne 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 de France crests a mountai6 pk;2 mefdguc-cq)zmjn v/p8( :3ncj n pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What wasndz)pfc2 /;cm6 v g(kjpe-q:n3mucj8 his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two tragwx6mm .xwy/er)odr )+ 9lj+wmpolines. The first child can bounce up one-and-a-half times higher than the second child. The initial sp +)m+)rj er9dw/wogyxm l.wx 6eed 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 95a*xzm 1hs s:px5( d1ml km/h 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 the car and train are traveling in opposite directions? td*1( m a:xmspzx 1sh5l =    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 throcnwc wdwm0go69: / vbj.-;uj9orbw86wa; r qi ws a baseball 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 behind the bodyodwwc:j;nug j 6bw;6qcamrob/rw0vw .9-8i9 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 a8xx /oyo )31w0v0h ms, pfiwbacceleration 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 intersecti br+*pas+i no3on has a traffic 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 green. The lights are g+nir*abp+3 os reen for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km/h take0,bb2vx eun e/7xdo3ss off inoeen d73,0 u b2xvs/xb 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 from the ro j.kja:4ul8)y8saikf,:xa tx of 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 stones land at the same time. :. 8kk8)a if:jtslau,xx y aj4
(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 ve3hwqz(u(cjj+do b-/4a negi 7rtically 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 building and hits the grou74c q3zu-onj/+h e wig(jbda (nd 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 5k +velxyy72l a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 5yx7+ly k2lve km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through kchmgj,b / b*t,j+f4ka 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 burg,gk mc,/*+tbjhjf kb 4ers 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 times7 67e6a5 in yzvwzs)ttiml7 j2 faster than Joe can. How many tim6 az67ltyei7tz)v5inj27ws m es higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friendbc5o- dqh,x9k7 vru-q sep,q* stands on the ground below you. You drop a ball from rest and q*bc5- 7rq x-9quksh, ,evpodsee that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height ofh z 89fgyho9i5+sxh 6r 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 9o6is8yhhgh 5x9+f rz 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 wukl2iu18tx(i- 5l gn vs. 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 eac(wi2 uuxlk g-8lt1i 5nh other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?