Does a car speedometer measure speed, velocity, or both?61,m6z .ficgmsc:n aw ;gl6u)y aajf6

Can an object have a varying speed if its velocit.tic.-lzxu-ols rtbh *j36k*r l82nsy is constant? If yes, give exampl*lzs2rko s*j 86ux.l-inrbhtc l3.- tes.

When an object moves with conspe bh /6e49hy49jvwzktant velocity, does its average velocity during any time interval differ from its inyh/jk4z6h 4w9 e9 vbepstantaneous velocity at any instant?

In drag racing, is it possible for the car wi8;b czoqz *8db::wc erth the greatest speed crossing the finish line to losezrqwc cb8ob *d:;e8z: the race? Explain.

If one object has a greater speed than ammw-sjyh q+(n 2asb: 0 second object, does the first necessarily have a greater acceleration? Explain, using exa+wm njqsabh0( :-2 smymples.

Compare the acceleration of a,oe4 0nn3:lv ce5bsxri4pk h: motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h inr:hps,veonbn4x0il c:e35k4 the same time.

Can an object have a northward velocity and a southward ar s s n(w*c2+nje(j3ognwk:w6ba6u 3ycceleration? Explain.

Can the velocity of an object be negative whm eao;wmzzvu5q 1.a10 i /v7xgen its acceleration is positive? What about vice versa?v zqmimwoz 710gv5eu;/ x1a.a

Give an example where both the velocity and accelerav myv8a2bu)okb2q1e. tion are negative.

Two cars emerge side by sid+qj0fmcufm 6e-ck7 .pe from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the ot7mp ce. cfu0+j-fmqk 6her as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decr fox p:5l-p(pseases? If so, give an -:s5xf( plppoexample. If not, explain.

A baseball player hits a foul ball straight up into the ai 07qrpvu 6chk/r. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the bckqprh7/6 0v uall be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acceleration :0:f*pxra g+jxa xjbydt7 / w;due ba:; xy*d7jx +x0/p jtwar: fgto gravity — does it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw aiei;x)qqm);fc+ cb9p ball vertically upward? How would you esfmc)9+qcx ip be )i;;qtimate the maximum speed you could give it?

You travel from point A to dlc,vq3ve y)b39 *eod9z-ob rpoint 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 constant speed of 90km/h . Is your average speed for th b ,l3r3dzeqo- 9*do)y9c bevve 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 * ic;5qhqs/jcd to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fal/ *cc5 hqqijs;l? 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 fallinng2p rjb g3m;7g from a cliff, an elevator moving from the second floor to the fifth floor making stopngbr3gp7m 2j; s along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original positioepba+o69u6o *0mk 8iga qkad-n with the same speed as it had initially if air resi9- bo eoiakdg +qa* kpm6u8a06stance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same time? Give-j ns4s +,eg+btbbi0/2nmic e examplesii+/m,e2 s b 40t-bc+nnjegbs.

Can an object have zero acceleration and nonzero velocity at the same time?gqvl4 tcwv 1)* Give ex*wlv1q g v)t4camples.

Describe in words the motion plotted in Fig. 2–28 in tek )8smt5b) -z8rv gmzq6d*lwb rms of v, a, etc. [Hint: First try to duptqbw)klzd *mz6v-b5 8 grms )8licate the motion plotted by walking or moving your hand.]

Describe in words the motion of tqqlw:yyx( zh9; ii2v4 rxgd* :he object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.x z.ptqgoqicm0e :5 j244f( cw4yy*oi25 h?    km/h

  A bird can fly 25 km/h How long does it takvky7o7ehu 4hr67 pg + jf:5hjh9sk/kh e to fly 15 km?    h

  If you are driving along a straight road and you look to the sidu*w09cy- jl pzbcbb(9e for 2.0 s, how fwb90 (l9cb*p z- cybujar do you travel during this inattentive period?    m

  Convert 35 mi/h to xj75q0i/79i wvjd+8cln fehw
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves u+3qm7zxdx*u 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 km/hc 9:9 t*ouxklg for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours k t*x99ulcg:oand 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 lightning flash anh7f;n,x., q / ex +ahppccaau,d 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 speed of sound in m/s from txxneppa;cc,a /, . +h,a7hfuqhis rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a tota q.w- zsvasb+6l time of 12.5 min. Calvb+a. wz-s6 sqculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight 5*pk0dqi0uyn- kbth 2l0.s njline, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8k- yt0 *udb 200qnp5 lj.hinks 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 p4x 7y u19nlta(hy-g.zcs8h dw;gf1ay 3:c cnqarallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5:g83-a4nf;xwst qcl u1yyy1dccg. (ah9 7nhz 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 betbo61))xn/c6*;eur ad .qs qxt krm/ vhind a truck traveling How long will it take the snbr/x uta eqrt.;qo1d)xkv /*6 c)6mcar to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then enco rz9xu(5cy:r iunters a tailwind that boosts its speed to 990 km/h for the nextr9:(c u5xyi rz 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 complete :rinw -bjq-2nround-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lur:2n- bjni q-wnch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed e p kmw6aq17m)hits the pins at the end of a bowling lane 16.5 m long. The bom7k ewmq61ap)wler 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 sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 n 5bzfm (jg6(vs. What is its average accelerationn (jb(fg6vz 5m in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m.p+3d gg1xtgu/s in 1.35 s. What is her acceleration u+.3dpgg tx g1
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable 0p cj+b6l mj k/efza owasego/,2gr89k9d7 5zof an acceleration of about wj f a8k b9kco/ rzpjm67s0goa9 gd2e+/e5, lz$1.6 m/s^2$ 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 68 am9hjwcao*then brakes and comes to a stop in 4.0 s, what is its acceleratio*jwa 8c6h 9oamn 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 itn-5firz ) /xyfa1o82k11l/exxko vzn a straight line, is given as a function of time in the followi1zfkx1y/ o)l1n trk5fia8 ez v/-2oxxng 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 acceleration?rhc8 qjvak)55l -xdis+ xxa,) How far did it travel in this time? Assume constant acceh5+j-)v)s,58ak rlax ixqc xdleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 j8fdi l;9im:pf -ro :hm. What was its acceleration, assumed constant? dmp i8r;i hj:olf:-9f   $m/s^2$

  A light plane must reach a speed of 33 m/s for takep.mc;o(,t /(t*e: sz aask/lti;r zwsoff. How long a runway is needed if the (constant) acceleratio z;io,wtc ats:szs/*/t.ea; (k(l mprn is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top spq5y vbn:7tv.ceed (of about 11.5 m/s) in q5yn:.t 7vcbvthe first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly 6zub/ n-3od (ce)abc jfrom a speed of 12.0 m/s to rest in 6.00 s. How far did it travel da-/beu(j c )6znb3o cin that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway.m7yi 3f 6ym.9 3lynwub Assuming a de 6nli yw ym.m339f7buyceleration 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 anhr ,jt tv0t94nd the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi h0t4 9,rtvjtn 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 iniap2 d;;mp, b-l esl:mctial speed of 95 km/h and human reaction timapmm dep;bcl2:l ,s- ;e of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for t1uul u5xjx 6*z )8cpwrhe 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 goi2d baj312+dxw s7rrx jng 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accerx 2jr3 sb1aj+ d2x7dwlerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less t6ag;fgjn x71mzcn 1ke- v3yt0han 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at 7- f;c10zmk6vn ge1y naxjt3g 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 inter 3n ot y. fnz:z0)oky7;q6t (oacnqxn.section just as the traffic light turns yellow. She knownnqtk(o.0)fy o3y 6n anqo :z.x;7ctzs 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 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: asx62ce 9gpc cliff. It hits the ground below after 3.25 s. How high is 6gapcc2 exs:9the cliff?    m

  If a car rolls gentl69iekzs1ud0 k(jn+i 2gzhr/;,j t m vny ($v_0\,=\,0$) 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 nefl9szs;7 s4j5l f(k ww95jjo early straight 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 plh:x5eokjz tk-bs vej-31; iyt; (r1 gmt 4x4vertically upward. With what speed did he throw it, and what height did it reach? rx- ol;t:3(vbksetx1gm 4z4pj5ke -; 1yti jh    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravno97 a;qos9qvs,mvni ,w).b,xy v )ozity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistsvyvqo9ox7qvn;a i 9w),nz. o b, s,m)ance.

A helicopter is ascending vertoo u1z)e h27re.6nx7j(.v cs9eeqnd rically with a speed of 5.20 m/s. At a height 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: The package nee7nce)sror j1z9q (. 2u.7 od6xevh’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the dist n)m0:j)5w 8tq)crye 4sazsh )x4bvoyance traveled during each successive second increases in the n))85eom:ytycsq4 0 )b x4rjs)wazvhratio of successive odd 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) tpj, qjv.o)cc1btsrlr6 bz3 9; hat a ball thrown vertically upward spt3z;b9jb.r)lcjvqc,ro1 6 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 vertica6bj 82a)mb3 vr qobgkfyc: :nzcig2);lly 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 photoflash of the apple, qv,d (s;z)xe9nnh ok in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.] 9d(vhz;nksqx , ),noe
T =    s
   flashes per second

  A falling stone takes 0.28 s to t2p (ck,ua bn;bravel past a window 2.2 m tall (Fig. 2–32). From what height above the top of tbua,kb; 2c(pnhe window did the stone fall?    m

  A rock is dropped from a se.youw9 s ki6r1a cliff, and the sound of it striking the ocean is heard 3.2 s later. If the s9oku.6 riy1w 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 vf8bz)zmn) 5o3o.k0em sf)xwwater. 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 anom ) zs08bxk 3f)ow.z)5oevmn fther 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically u)5uq9;+jp yxgquvw d ffssgwow h9nw7;1*t 9 (pward with a speed of 12.0 m/s from the edge of a cliffq; )ywwf(wxv5 o1 ust7w*qgjuh99 pfd;+gns 9 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 mkg rkx06fe7*;,qxkrx above the street with a vertical speed of 13 m/s If the ball was thrown from the streeq gfk7,6xr x0x;ke *krt,
(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 g3fzsdi6+kqv4n ix4k0:9v qf 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 periods, if any, was the acceleration covkqi:f0i49nvgz xsq+ k63d f4 nstant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbi5jzmsyd n,qf (je36;st along a straight tunnel as a function of time is plotted in Fig. 2–djem5 yq;sz nsf3 6,(j28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can accelerate approximately a j19qoj +tims4f;mx /v-pju7hs shown in the velocity–time graph of Fig. 2–35. (T/9m;t7ju q ixo-1ph4m fvs+jjhe 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 accelerationgzq: ygf7g s39m,stb 8s8wrf) of the car in the previous Problem (Fig. 2–35) w symfg:z3sq8)fg rbtw798,sghen 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 travelem:t47a; yhl y+veqe* pd during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph s, +kjnc1m :gjfor the object whose displacement as a function of time is givenjgsj1c nmk, +: by Fig. 2–28.

Figure 2–36 is a position versus time g . xl3m2wokd apb(v:d(raph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negativlx.mk dw3v (bd :p2oa(e? 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 firefighterolw yzir 7e7p 0fs)1a5’s safety net. The)ywef 0z717ilo sa5rp survivor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on E cj* 8-g(f)/qjz m9ctzxk3 2rqfy5gkrarth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?y 8(- jt 5jzfq*qkgx/rm3 )9rzgkf2cc

  A person who is properly constrained/w/ n9t ke8mvl by an over-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does entmv9/wk /l 8not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his pursuaxp,fzf73(2ndchvo-st ) +mqers 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 qui)ops7xqt h,fdc-m a 3 (2fzn+vckly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end /2ce+ iywb 2meb5x0mqetm0bt7afm:+ collisions by hauling them up eb27f0 e5m e x0tqi bmmy/a+2:tm bc+won a crane and dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels ab ;xawutt2btk:c4 zg 6t3fsd-8out $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from remv9*d quflj/; st. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 l9 m ;u/vfj*qdm 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 ;7(b g1j.f 62p;r dj g;dg va4jrvc pyu)z9vizm above the water’s surface into a deep pool. The person’s downward motion stops 2(. ;4vdzuj fd6a;vp7i g p r;rgy2zj)vjbg19c.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 isb.tia 4tugg 1) necessary to balance the average speed of a train against the 14gubg). it atdistance 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 fally4 dgt6r*j r3wb xmyir( 9* -gfqp1e,a straight 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 esxrj3qa brfg6d*9tr,i4*mwe (y y-1pg cape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planned so thaee (1f ydnczh:jozam 1t75*dm 19uvn :t the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decele:1:une(oznh 1 zm19avfym7jc td *5 derates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a constant speed s :s+g wyr.7ex0-7idezh1zmo of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest :0sd1yh.+oi7wzgxzr7- e es mand 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 dropped:mjld.ieml y e81: do2 1.50 s later. How far aparmdm:l.d 2i e81y:j leot 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 /qdidg9 cyce( wlk53, nt tp)1trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average s/ qedwcp(t tgd1 kc5n9,ly3 )ipeed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crez4 d(u2wccnms-;- duuq m*m 8dsts a mountain pass as he moves at 18 km/h . At the bottom, 4.-w42qumu cdu -n csmd*zm(d8;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 firoyx*;53ol p zsb1pj5 xst child can bounce up one-and-a-half times higher than the second xyb5z5 ox1pp;lj*o s3child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long train(-fay+zp xu. uzbfoi;/87gsz 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 try-fzgfs pui+oz u;7z8(. a/bxain 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/ emc0ex41sgx) 4n-nd v;n oy-hs In throwing the baseball, the pitcher accelerates the ball through -c4neov0 -)hxds;m1gn eyx n4 a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertical 0co lc)yk:;y 4eby9udly, from rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown lwo93pin:iw)mm *vq (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 (w: m9 )pqwiov*3mnil intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km/h takes 4f sn 4 qbpx8*u 05ddhdvdbf/zgt:6e9 off in hot pursuit. The policd5 s:bt zd8hp64/*gxuf4dvq 0efbd9ne 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+ca5q bn n:p4i5, mouiz5u v/xof of a building; 2.00 s after that, a second stone is thrown straight down with un/:n5p b,vacqxiu5z4m+5o i an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The first sg.d.tdapd*)ql8xf.f: h( yqctone is thrown with axf.d.*dqgflc ):yhd8q .a( p tn 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, h *ly l tr*a64h2wpt3xnow 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 her speed to perh6rn *alwy3p hxl *t24taps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers e0vhs d9q yo y+5wlmg(x9a,2 jiljs9 0through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the coaxsi299 (mwv0j9+l qh0djs oy5 l, geynveyor 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 speed 1.5 times faster than Joe can. How m qviaj0zz9knua2us(e 3ll 4;5any times higher will Bill’s ball go than Joe’s? ukl( ;n9 4l5a2vsz ujiez3 0qa$\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground6jr3hggr i+i)e6 eu :r 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 pihijr 66rri)e eg+:g3 ucks 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 of a particularrq3fed f8s.4 f 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 fal3ffqfs .r8ed4 l 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;a3yh:ic( x g v/jq9ol8 rfiy1 two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycleyvi r9gc;qoafx3 /i81jlh :(y has the higher average velocity?