Does a car speedometer measure speed, velo( ).c7acfvobls 4bndfio( 2i;city, or both?

Can an object have a varying speed if its velonyc:f 7l.w:zrcity is constant? If yes, give example.rl f :7:zncwys.

When an object moves with constant velocity, doexk ns:0um8g8o s its average velocity during any time interval differ from s 8g:8kn0uo mxits instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greavr,d9lsvfj + 7test speed crossing the finish line tofs7 lv+v,djr9 lose the race? Explain.

If one object has a greater speed than a spb tbg0evb5-5uwvcdzd*k +9 +s1e p6uecond object, does the first necessarily have+be5g+k1 6 vswupebdctu 9pvd-0 bz*5 a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerah petx h.e19+htes from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same timet+h9 hxe1.eh p.

Can an object have a northward velocity and a southward ao)q 3 m-sa5chfcceleration? Explain.

Can the velocity of an objej8//um g:wqdj smct*)5 n,ynz ct be negative when its acceleration is positive? What about vice versas,z j:8 wn cmdg5)qt/um /j*ny?

Give an example where both the velocity an+e bfism) .acv1n)q7bd acceleration are negative.

Two cars emerge side by side from a tunnel. Car A isb z 7( 5p:xm1x-5zyz,n wawdcg 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 x: xm(,ybdc1p 57n5g-z zawwzthe other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration kb r))e- gz:shdecreases? If so, give an example. If not, explain :)begkhrzs)- .

A baseball player hits a foul ball straight up into the air. It leaves the bal:f(9xcr a7j4f8nr+dsjsg s2q4 mw- ct with a sp+n j 49c( 4wf -8:2qs cra7fxmjdrsglseed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening thfs 5q18x.rc.if/vop o its acceleration due to gravity — doesoqi f/. hv csp.81fxr5 it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball 6eqn9 y 2nuuhn k7b55i6fi3s v ft:wy-vertically upward? How would yon3yfy:k vw66s t2e595qibnhi- f7uu nu estimate the maximum speed you could give it?

You travel from pointll;ji 0mwl7c/ A to point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constancli;l 7m0 jw/lt 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 ten boltiqc)-aik r -v,s tied to it at equal intervals is dropped from the ceiling of the lecture hall.-qvck-,ra ) ii 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 motions is not at constant acceleration: a rock falling froml;1c +vaf7v*mzderv. a cliff, anz +rl vmeav.71 v*fc;d 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 vertically upward will kzy- hbo(7 ;ucreturn 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 opposity7uh -c zk;(obe to the motion.]

Can an object have zero velocity and noii 4s3opff d56nzero acceleration at the same time? Give exampled p45iffso63is.

Can an object have zero acceleration and nonzero velocity at the samer5cux0o:8 ubsdbw / +t time? Give x:+0bt8ubcw 5d /u rosexamples.

Describe in words the motio;+mgp8)nf idd2h7hq qqwfcy3 qq 5;s 2hvie2, n plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicatechif pqqm2dq d57;qifn,wh3 q;+2hyevs g) 82 the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in Fir)u5d okw(d+e2 ob5er g. 2–29.

  What must be your car’s average spe; balvy ,z5jk7ed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h Hojhx 1 lii+w7xgfo;khqi6clk t:i v67.i7 4l z)w long does it take to fly 15 km?    h

  If you are driving alongtf;o5h l 5y4dl a straight road and you look to the side for 2.0 s, how far do you travel d5 ;4hlofy 5dtluring this inattentive period?    m

  Convert 35 mi/h to j9bi 5ciui5 d r8mwf01
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves )tow2khl kqgk 1-2 q;hfrom $x_1$ = 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 schoo+l(dprs4jx 3(mp2 t. kfe q:yo7b+ujvl steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after djypuf.7mdlo s xv 2qjt:+(k (+br34periving 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 secondsf28k 3smr hwh,mya(r- e)prz5 between a lightning flash and the following thunder gives the distance to the r(8mmfk r) 2yaw- hsp3r5e zh,flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a qt it4/pkfrh36tpt rwbgn5 w+s(,,b2o uarter-mile track in a total time of 12.5 min. Calculate h,/ pn35 4tbg iwtb(wr2tok+,sfpr 6t
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straigh:g;g*+l fqxtdv,i 7dwt line, moving 116 m away in 14.0 s. It th dit:+; 7wv dql,fggx*en 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 paran.hfd(j (qz/:c+kj pz llel tracks. Each has a speed of 95 km/h with rhdjk( + qf n:zjp/.cz(espect to the ground. If they are 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 a truoe6bg y15, aavoih 3e5ck traveling How long will it take the car to reach the1a ,e5h6a5gbiy o ve3o truck?    s

  An airplane travels 3100 km at a speedv4sb:ud a.vc+0qz s9x of 790 km/h , and then encounters a tailwind that boosts its ssv:a0vbx4u q .9c+dszpeed 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 apc */ e1 xnsqzoq21sl(v- gi.dxde7o9nd average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch-q( l* /os nsc9vqdgx1oe7eizd21p x . break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pinsg2)t9wt 0csw- iw,lz h at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speeci 0,whg)9t2z wl-ts wd 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. yut0 s17)3uesrhnwef8 ni6 j u30x7bmWhat is its average accelerati fuxr0yesm) t3jhi7w7n1eus0u8 36 n bon in $m/s^2$ ?    $m/s^2$

  A sprinter accelerateofd6 y5068::ucj*x px uvnque s from rest to 10.0 m/s in 1.35 s. What is her acceleration euu:86cq60nyv pd5 uxjoxf*:
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a pag k;a*c03 40 lj s1di:wpwt-neb:y qgfrticular automobile is capable of an acceleration of aboug ayk*-sdfin41wc3w0t; :b eplj:g0 q 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 4vm v4qngc iu:g;fpe+zqf :5;speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 sq4pn5uv+gq m fecg:z:;v ;i4 f, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t 2gg po7(ux5p xv7*v;oxlzye . = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) itsozxy7exp2 o v5*v.(u7pl x gg; 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 accelerl0;0dpgugdu;d 6s57es bialpa6 fv -1ation? How far did it travel in thisbp6ui;uv0 7p ddlsal gs10a- 5e df;6g time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 mu2bcr- u9.o/vk 9( l4+q itmiclm(xwn/s to rest in a distance of 85 m. What was its acceleration, assumerw9 m vitl(29. uicob4kxmn(-u c/q+ld constant?    $m/s^2$

  A light plane must reach a speed4ww xpjqevrgts 209o3el- 5 *j of 33 m/s for takeoff. How long a runway is needed if the (constant) acceleration is 3 j*9wlrp2oe4q 0jest g 5wv-x$3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speedv9fava4f:pmj : ;a5ef (of about 11.5 m/s) in the first 15.0 m of the race. What ;: m4vpaafa9fe :5vjfis 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 fr-t)ax+ )ddp1su: vbg;fa8 de zom a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in that t+):x dv-d 1tfe;apazg8) usdbime?    m

  In coming to a stop, a car leaves skid marks 92 m long on sb khg5ijonev8od/h,91l 4s n+se 0. jthe highway. Assuming a deceleration 0j.neejd85kh/ osbo9 ss lig4 h n1+v,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 compvn )ghc39z2kxot-k- 7nlzo7 i resses and the driver comes to rest after traveling 0zoivncz gkk--x7t3 h2lon)97.80 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 distances for a car with an initial speed of 9rxjcc23 6 /5nvg eu)xz5 km/h and human reaction time of 1.0 s, forc3jzcg62r/e5)xn xvu an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the sw ld/8es*6kpf topping 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 truc kvs(uwvib2m. 0ia)l :ejy7 m.k going 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessinslmb:(w. 0uaiv.7eiv jm2)k yg that his car can 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 complehwq8 xg9s( sk 7 s92m dydtpks8:jbq(3te the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then acceqs 3 bs(s7(9 w9kmgkq: dh2 ty8jsxp8dlerate 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 intersectioz4:zklnjmcrh -w1 7xh.9 f-t hn 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 nm9 zfcx-1:k4zthhhl7 -.r nwj ear side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m 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 frg sf dw7c4p z-wt(v5wfib)q4 m5cq5;*ipgln : om the top of a cliff. It hits the ground below after 3.25 s. How high is the cligpw 5 );i4m5f*dqvc(cftgbi7 qzl: pww-4sn5ff?    m

  If a car rolls gently (z- /zv6-flpbbzabr 7v8vz-5o$v_0\,=\,0$) 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 ),uy vn7 qdif;.fz;pgthe 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 bqx 645d2w rjph n,,gcuall 3.0 s after throwing it vertically upward. With what speed did he throw it, and what height did it reach? uwgc2 d5jr x,,46npq h   m/s (Round to the nearest integer)    m

An object starts from rest and falls underqdxu. scpap u++-4s:erv90k n the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s .cnau vr+qdesp+0u4ks9:. p x- Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a 1 dzk/ w:ojx ;mjiq,p-n)lg*nheight 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 ground? [Hint: Thw*,:z1di mg/kxjp nj ;-lnqo )e package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the di,w u+pde2/b,z w;uzn ustance traveled during each successive second increases in the ratio of successive odd u/+uw zne,w bp2zu,;d integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) j vml(m j*9rll(lhr*, wt5g4fthat a ball thrown vertically ul(gml*j*wf9(t4llhr5 v r j,mpward with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a spe ;e*r3c t;qwnfed 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 appleh1zn 4+yje8bx in Fig. 2–18 (or number of photoflashes per second). Assume the apple njxb4+e81h yzis 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 treusof)gp//e g4 2ebkp ;2z3aaavel past a window 2.2 m tall (Fig. 2–32). From what height ab) uegb4o;gkee as /f3a2pz/2pove the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sounb, -an0(b)dqco ivo46q, fqn sd of it striking the ocean is hear0 q-oo qa4b6icnq,v)fsd(bn,d 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 nozzle for a hard stream of water. You poiny3dua8kw b4 o(t 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 verticad4ykub83 o (wal, 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 qhj/iq;f b/wdw/ a wv5gh)r2 7upward with a speed of 12.0 m/s from the edge of a clifr)/ //5 2ihgdaqv;hw jfwwqb7 f 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a windown1)*wtdtj5dh i 1y vs) 28 m above the street with a vertical speed of 13 m/s If the ball was thrown1j )vdt*1)shdwit5ny 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 thz i1.bnsu:u, ue velocity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what 1.u :nuzb,siu periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along p ,mr3vh 0,xf:bmjih1a 2yc9v;7e d cha straight tunnel as a function of time is plotted in Fig. 2–28. What is its i:v bpr ,;ah 19cihm jxh,72dycvem3f0nstantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accelerate approximately aoob1 t4gtvbe-+-vy3 es shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gee3+ -vbegot- tv1oby4ars.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car 3 k *1 h)wfdz2dv5lfivin the previous Problem (Fig. 2–35) v5 f*zwvdlk3h)d 1 if2when 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 the distance the object traveled dut v9i k7v4v8esring
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t z)cl-p3q w 2ckl(9old,n vx8f6im9 sn graph for the object whose displacement as a function of time is given by Figk n 6olv( 9)ficlls8m zw9xq2c ,p-dn3. 2–28.

Figure 2–36 is a position versus time graph for the motion of an obbw;kmva 3 3s-jject 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 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) m3 -jw; v3sabkIs 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 e+u j w-r 8c28/a)xvfij m,u(sxkzif(firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest,)u-fjs,((xi w2f8z e8 kjr+xm v/iuc a 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 goc 3k1l2x 1iwtravity on the Moon is about one-sixth what it is on Earth. If an object is thr3 xotk i1lc1w2own 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 constv m.a3gfzv (kdy:3)et rained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does n(3.)z :df3avyvg mkteot 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 standinn(j-p ,v7jo e;9ivz xgg ve0s6g on a bridge, 12 m above the road below, and his pursuers are getting too close for comfort. He spo onxg iev(ge;v,p-j6v07sz9jts 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 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 fr)/qdj7 qs:nxiont-end collisions by hauling them up on a crane and drop:qn7 i )dxqsj/ping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels a;d w 0u:/mm tspv kcod0 /msd(/ok.b-obout $10^9\,km$ 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 acceleratiky (e*gv8.ymoo f 0t(woc;6fion from rest. The front of the train has a speed of 25 m/s when it passes a railway worket(wf8;*. 6ifcoekyom gov(y0r who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface iszk 8ij *fah)* z3usc:nto a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deces afs *83)huzij*:cz kleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the averaz78b o9v ck ;zjcj-teaw.pua 7e*f a*(ge speed of a train against the distance between stops. The juveaa* (z *apfj 9.b8-;co ec7z7 tkwmore 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 diving fo/n p6, k)nncr.vs hq 14bxvu.wr fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path oncen6x q v1,ph.cubs ) wnrv4/nk. committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is plann fpk/mf ksa(p;y38 r3ned so that the ball will stop within some small distance of the cu;/s kf yfnrpk 3p(83amp, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates 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 trainspj aaa7sp hm5jajos; puv::-1 x:14u traveling at a constant speed of 6.0 m/s Just as an emptpajp :mjhpo:4 -ja7uxs:5uss11 ;v aa y box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is droppedmf( k7 7o8rfhpqt w;/qmq25b n 1.50 s later. How far apart are the stones when the second one has reached a speed of 12.0 m7mwq5 2hkn/p m8; fotbqr7(q f/s ?    m

  A race car driver must average 200.0 km/h over the cous0p q;fo c / smdlbr(r(txbk.pr/h;*(rse of a time trial lasting ten laps. If the first nine laps were done at 198.0 co*s//;;p 0hkflsqx r (trmbd b((pr .km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a s.kk3wy ,1pbs mountain pass as he moves at 18 km/h . At3 w.spsk1 ,kby 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 playin9uhoy/q cq96t72vjqk g on two trampolines. The first child can bounce up one-and-a-half times higher than the2y9jqtq6h9vk u7 co /q second 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 o(2e hb9ag9ofchk* 5xyvertakes 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 hava5xb ck 9 hg29eyh(f*oe 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 a speed of 44 m/myb e nw e)gd4js xy(.*hdq.(6s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point wheds.x)eb hy d*(6q4j . emwgyn(re 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 acceleration omp 3enhk( z7z:f $3.2 m/s^2$ 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 patterzs209ec8qsov2eyv;9eb yl wfe 1) rw;n shown in Fig. 2–42. Each intersection 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, aeyrf2s9e byecvw)zw2o ;1 v0s8 ;9leqll 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 6 i3b9qxm0mrfby a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to m90 xmfbr63qi 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 ror66oon rai vy*hc; .-;gnavp4of of a building; 2.00 s after that, a second stone is thrown straight down with -ay rvprv oaon. *h n6g46ci;;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 verticallyylwib 3)++d.8 eu+3edle rn d/de.fcv up at the same time. The first stone is thrown with an initial velocityd+.ei u +bd)fc./+w8een3rvdy l 3 dle 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 airah8n(g bck mjj8mq mia 92-;+2mdihj, resistance, how long would it take 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 hjkaa ;cjmi9 b-28mm(d82h,gmij n+qher speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the) 5kjrr-1y4kd ngjrv* burgers through a grilling machine. If the grilling machine is 1.1 m nk*)g yj4 - rrdrj1k5vlong 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 verticalpku *ei8y* uz8ly at a speed 1.5 times faster than Joe can. How many *u8 yzk8u pe*itimes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff whileldixi a79llz9fku*y;7b6r05g ru j (n your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to r u9( d5zuf l g0;*l96ly77rnaxjibr kiest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to fin iwxsv6f4dp nop)21k q/-e7tad 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 fall. Oneas1tk vo7)-wxfi6d/2 p pqne4 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 for two bicycles, A andp yd)-5bga82vr2m .vf o.jiuj 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 rvfa.juyo-i52mjdv. 2) gb p8 the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?