Does a car speedometer measuptc/y3 ) -oey/ 3thitore speed, velocity, or both?

Can an object have a varying speed if its velocitv dek( w.)d4ssz/t7 wmy is constant? If yes, give exam4 /st7wsd(z mw)v. edkples.

When an object moves with constant velocity,;e3 c,gv-iyui (kuv3 a does its average velocity during any time interval differ from its instantaneous v3 (ki ug,eucy3;- aivvelocity at any instant?

In drag racing, is it possible for the car with,kpfm/b5 bp;f5 r5rgc the greatest speed crossing the finish line to lose the race?p/grpfr kb 5c, 5m;5bf Explain.

If one object has a grst9-*3je vm5n/dd xrcd ix8z2 v9q s.deater speed than a second object, does the first necessarily have a greater acceleration? Explain, using exampter3/9- js.d*qxd8n cv5dvxi mzd 92s les.

Compare the acceleratim-ln - jfl:;xsr8/ta c87cpuhon of a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from lj;cu- ha:spm8n 7rl 8x -ft/crest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleratio ecxbdnyv1l9)+ ew;7a . mq4a5j0jxmjn? Explain.

Can the velocity of an object be negative when its acceleration is positivbgt+-zsm 6 xzc;qek-y *4 q:mqe? What about *k+: m-;qzg6xsb-t eyc4qmz qvice versa?

Give an example where both the velocitydg87vlr fnn7 d5w:kvj ;a41s r and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A 6j3b -ljq2s; /d/bddnml.tcuis 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 -s;jntqjddcb/ b23lmd.lu6/ 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increg2+2x yk:cw1dau* uwi )nnt-k asing in speed as its acceleration decreases? If so, give and :ui )+1w xwc2u*n2-kgtk yan example. If not, explain.

A baseball player hits a 3, yy vamnxu;8foul ball straight up into the air. It leaves the bat with a speed of 120km/h . In thy3vn;a 8u xym,e absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what57zncb/6m* u * wam3ca3lgolf is happening to its acceleration due to gravity — does it756 *g a*blc3 nmloz3mu/ca wf increase, decrease, or stay the same?

How would you estimate the maximum heig /0a5p kqmv..ja-6h;aqn pl csht you could throw a ball vertically upward? How would you estimate the maximum pk5m.s-a 6qpvhlq .; j0/cna aspeed you could give it?

You travel from point A tz:e xz :,qok8uo point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C,:,8ko xqzzeu: 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 vertical string with 2ha,kj eqih qcjz,-p8 w m3a)a.9wj:s 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 betweh w j3-98 wej,m,:kac.aiz q)a2hspjqen clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock falling frobrk e5zul4s)p p1n 9f6pir ptl(r 45aef,dq8, m a cliff p6uf r8pa ,bri d4nkl9q) ppez5r1stf(4, 5el, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertica:*; :ac, ruvrkk.9d tcx6tc 8t x+cicflly upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction oppositfkc,d;rax 6+crc ki ctv*9:u ttx:8.c e to the motion.]

Can an object have zero velocity and nonzero acceleration at7q*h nw3b ws,q the same time? Give ,n7*h wbsqw q3examples.

Can an object have zero acceleration and nonzero veloci-pdfr d8o+ p;nty at the same time? Give examplpr -fn+ o8p;ddes.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etz9nnds9g4m* ec. [Hint: First try to duplicate the motion plotted by walking or moving your mg nd9*9znse4 hand.]

Describe in words the motion of uietss: 0otihtg 9x4,4h+n4 p the object graphed in Fig. 2–29.

  What must be your car’s average speed in ordpy l id+;8h3edy9 7yever to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h H jsl +m /zf*gnci *ghr3:l-fqh9hm9q;ow long does it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s * 7-odwmveuzrmj9h ss6* ;r6u, how far do you travel durin* 97zsrhw -m6rms;d evu*o6jug this inattentive period?    m

  Convert 35 mi/h to :rru esq3li-jr : d2:*mu/eds
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fgi:.,rjoe.y 6g a +rrdrom $x_1$ = 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 stbn h aexb585e1/b cs1acy1dk1eadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive hom1xhck58nyeb 1 a /5cb1sdeb a1e after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lighnf7v pxl6f8t )tning flash and the following thunder gives the distance to the flash in mile6flt7v pn) f8xs. 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 cofzie yptn5 579mplete laps around a quarter-mile track in a total time of 12.5 7it5f5 pyzn9 emin. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m away;v mhk7)j mqe6 in 14.0m7) h kvm6jq;e s. It then turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks.(z2 )(ipy cgclsk: a*o Each has a speed of 95 km/h with respect to the ground. If they arep(zliya)sc* (: 2c kog initially 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/yj6eg xyx 85j a truck traveling How long will it take the car to reach the truck?/x5j86 gxyey j    s

  An airplane travels 3100 km at a speed of 790 km/h , and then enc bf5)9jvd+ cn-bd2kl g(v 5-hxasgzz:ounters a tailwind that boosts its sp9afd)jbv vb h5 5 -d:2c-ls (zgzxkgn+eed 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 s06zd.(f,xwsw (lske q peed and average velocity of a complete round-trip in which the outgoing 250 km is,se w0.zq( xds6f(k wl 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 ;u g k61iq+k4 zf;oxpqof 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 of the ball? The speed of sound1 gpo ;kfu6x4z+iqkq; is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in )/, 0 2xphu./gv su l n7 sti+jgwl7z1ttn7yyz6.2 s. What is its average acceleration it/zt 1ztg7vu yh7nxnj)yi0 .s2g lp/7 ,u +lswn $m/s^2$ ?    $m/s^2$

  A sprinter accelerates frot *cizw2qh)3f2 vijh jbent :2/k.c o3m rest to 10.0 m/s in 1.35 s. What is her accelerationikvj .fj w:3 3qi t 2co2c)thn/*bh2ez
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular 2 *7 5pwtjs7gnbcntj*automobile is capable of an acceleration of about jjw ng c25tb*7stpn*7$1.6 m/s^2$ 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 u9r3)b iz 5,nteyy.yh travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleray.e5 )zt,9rh uy3iybntion 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 moves i-gdw6kxh 0e:tj5 tqrdu 91wd- n a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a functiontd d wj:u d-qr5-hx 69etw1k0g of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 mfy 73lrjio 1su/yo(1sj n )rh8/s in 6.0 s. What was its acceleration? How far did it )1/( yji7nus8 3jor 1oyrsflhtravel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85twy: b;.oowe. m. What was its acceleration, assumed ctw o.y;:w.o beonstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. Ho,) j g,rze;nmyw long a runway is needed if the (constangz,;y ) rj,ment) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essefb42o,o iod,uuy)-we4 * xacn ntially 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 x*fnbwoicu,)d42 4oa e-ou,y 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 mw/4 wj2ibp5jg /s to rest in 6.00 s. How far did it travel in that tijbpi54/wg2wj me?    m

  In coming to a stop, a car leaves skid marks 92 m l(py6 vevwfm3)g+ hc;68 eck ciong on the highway. Assuming a deceleration ofhc cc)(8g 6k6me v3e;yw+ vifp $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikx v bb435gub0qes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 4 bvq0b5ugx3b m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping dlyt8 /m5zu+a ;uz) y2y wby.ftistances for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an acce2 )t+ yzbum5yytf;yl 8u w/z.aleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equati(dk:ilhqr 6x:;0bh : 5rw enioon 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 highwa2a*u gldx .2i5(qczfn: kt ,spy. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate2,zdg2kq p au(.s5:nlxc i*ft 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 themzp ,2-,lfikmzuv9zhf- zq4 z8,9n*b wkqn2z 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runw zv2zlm bpzk mzn8 4f, z -qnhf,i2,99z-*kuqner 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 approachebg bw*sp,/ h(ts 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 intersecti pbh(,*btws /gon (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hit0tzgi,u +uja4(p +)bkg lrid2s the ground below after 3.25 s. )agilu0d upt+2kbirg j4+z(,How high is the cliff?    m

  If a car rolls gently ( vqfd6.h26k eq: djjw.$v_0\,=\,0$) 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 ip6u w k6g2l(dbh gm(-unto 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 ba qcw-9h(zs(m mll 3.0 s after throwing it vertically upward. With what speed did he throw it, mcs-(q9zh wm( and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence )r-kxuki-9 oayu-- in of gravity. Draw graphs of (a) its speed and -krkn9)i -iy-x au-ou(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 speedhzxf , )upyd. f-f;g5s of 5.20 m/s. At a height of 125 m abov;5-gdfu.hx ), pzysf fe the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, sho5+x fj;ioqlu 3w that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5l;o+jx53 f uiq, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) thawwvev-z:oi2 ;t a ball thrown vertically upward wi2v -iwz:;voweth a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticalbcl )d w;w.w2lg4d7gf1mn nk6ly upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each 0j chnt1*(qhfphotoflash of the apple in Fig. 2–18 (or number of phot0( jchqfth n1*oflashes 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 past a window 2.2 m tats.zf k bz+nk: e*q1/rll (Fig. 2–32). From what height above the top of the windon/r1ezzb:k*s +tf . qkw did the stone fall?    m

  A rock is dropped from a sea cliff, and the6 3mkr7et imj trc,-a4 sound of it striking the ocean is heard64r k ,ttm3c7eir-jma 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzlm-yog3kb9,r ; e ysr+qe 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 you for another 2.qm+ery k3g-, b9ry;o s0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward.lx/f.7ze pq d with a speed of 12.0 m/s from the edge of a cliff 70.0 f qp.z .7de/lxm 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 9 d(wuqrdnh. 1oac 9w,pass upward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from t.h 1dc9w (uwoan9dr, qhe 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 a : 1/iu 0 iax1z..qpzn3divdkus a function of time. (a) At what time was its velocity greatest? (b) Dur:knqa011/ixi3 v dz u.uzdpi.ing 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 tiqavqizp(n6:i- u . f:n)dy 7zame is plotted :( .zdyani:vzn-u6pq) qai7fin 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 c*q/ arwya(r-5qrhxf g,z . qckw95g1nan accelerate approximately as shown in the velociaqg c 5,z9n w.h/-rqaf 1rk5x y*qrwg(ty–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the rvxc f 7ewhin2j*m8*h1)/l becar in the previous Problem (Fig. 2–35) when it is in j )7fm2xw8*i*1hbvlere h /nc
(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, estimattkbsl4 c+/bmsh7/v(y e the distance 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 functio 6tfqa.1 6ca bxdmgto6/w5xn*n of time is givexa.bo/6 adt w x6*c1 m6t5fngqn by Fig. 2–28.

Figure 2–36 is a position versus time graph for : xm m6g:rka9cthe 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 posr:gc:m 6k9axmitive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a fc3uxtw3lr1 .sxkpw t)v9i450tyyazp4v)a 3 wirefighter’s safety net. The t alwkprcv p3zv 04t yu9)ayw xs3t54i.w)3x1survivor 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 abo5/a itaco,l9d gwtun fi 586jr+ 10xarut one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go thanit5f r +co/uaw nd a5ijg1 r0,a96lxt8 it would on Earth, assuming the same initial velocity?

  A person who is properly gbh 3rb j2f2l8constrained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the decelb28jg r lfh3b2eration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m a x0 73wn,w0l ltcjjim3bove the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be 3 ,n7j0liml c0jtx3wwwhen 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 mw* o/s f2 6nmmqevx1vwja681collisions by hauling them up on a crane and dropping them from a certainmwvs nxe2w6fv q1j a6*/m18 mo 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 travels abqh31ic p*a -i. xsjun0out $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begivrqs;dcmge/j ai/ 8wzgs4d7 ;6 gf *c8ns uniform acceleration 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 train6a*/ m4f ci8 ;;dw /verdc8zg7sg jsgq started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a deeq20cx p clt5(a5hfq. ap pool. The person’s downward motion sto.aqa0 cpfhqc2x 55l( tps 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is u9 y8b :ohmuviy9;gi) necessary to balance the average 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 9.0-km trip in two situations:y y;bui9oig8hv: m)u9
(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 str9fu r7o 51kg0ahpqcr5aight down 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 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 waterok p01ar9hucqg557r f.    m

  In putting, the force with which a golfera rko*5xv eo,8.4rc8)awbcn j strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than fromoce ba5 ,o4.wxrr *kj 8v)anc8 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 traveling at a constano x:sinqi/)bz c);;kxt speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest anqok:z; i; nibsx)xc)/ d 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 -*dvhe6vnyy*high building. A second stone is dropped 1.50 s later. How far apart are the stones when hdv y*y6*-n vethe second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the cour17d9grvs .t5.iue4 talzzt f6se of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what avera74zl. zt1e d.usrfttvg596a ige speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves atn+0dqnzpt gd0btcm hg+j3sw39f( ) l; 18 km/h . Afgq;wpd 3 (z+)gn0 l9m+ ht0js3dctn bt the bottom, 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 chi,x jrl+ly9xhb mf5 h m90pu48vld can bounce up one-and-a-half times higher than the second,p95 uhmrb 0x l8f x+my4jhvl9 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 az-)nqdr :zq3apcz8 * r 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 longz*q dnzcrz3-rq8:)a p 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 baseball with a4 e r3wbzm8qu l1*j9ij 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 body to the point where it is released (Fig. 2–41). Estimatwuq bj rjl8z9e1mi 4*3e the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with vkgjit bp fmgk:3k/ ab5) s9; iio/5(tan 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. kfmclr- .k -j82–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are drivingklr--j8cf m.k 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 sp4pav *;qf 7flveeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer ;*vf 7fql 4apvcatches 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 th g-2kniqb7 o*ge 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 stones land at the-iok *q nbg2g7 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 verticall tu;oe pusue8348.8w9oxlan cy up at the same time. The first stone is thrown ww 4uo8p8aueo9ne us .x c8;tl3ith an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-s e,jznd,+z7( ;x il(qaun1ebfalling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pnas,,n(1(z;iex7bdl +eu qzjull 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 xb;elwf7 ao*b0c*z (oto send the burgers through a grilling machine. If xzl(;*ocfeb*b0 a wo7 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 vertically at a slnnivz40kb ky*+a 6s ,peed 1.5 times faster than Joe can. How many times higher will Bill’s ball go th6,y vlnik4 ba+z0ns k*an Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your frictrds*g.3dbco0 9 8 eiend stands on the ground below you. You drop ecg*id t3 8 brcods0.9a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are aske+disp;o3j2n4o2i 1wrs ujsa6slsb8 4d to find the height 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 2ds8ls j b on; o442+sauisriswj63p1fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph fxh108e q74yo 7fqpf6yy; lgfror 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 ot40f ry8;eh7l1fpy go 7q6fxyq her? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?