Does a car speedometer measure sp-cpojcu a(z ;/g qpqfq5 g(1g2eed, velocity, or both?

Can an object have aco4j9 bif75 nv varying speed if its velocity is constant? If yes, give exam5j7 vn4 obfi9cples.

When an object moves with con+aghz *7d tkdyob u47e 56j4gnstant velocity, does its average velocity during any tiotz+ e*4g5d7djny6u hkagb74me interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for tm eb :om65 1re9/iguxshe car with the greatest speed crossing the finish line to lose the race? Explaisxe /: 1or u9bige5mm6n.

If one object has a greater speed than a so4yw*uiu p ++o,oo 2vaecond object, does the first necessarily have a greater acceleration? Explain, usiyo4a vi2o*u wo,++upong examples.

Compare the acceleration of jfk oay r,,l-53f: jxk6cod k +6wpme;a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same time.d m3k 65 oaplwx;ejj,+kf-cf6o,kr: y

Can an object have a nort. x5yqwyln8 l):hwz:ky 9eyx5hward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positive v -swl9)klsg6 p)tzd,? What about vicp-lkgz d,swv)l 9t6 s)e versa?

Give an example where both the vel15dw/6m 9 oktr zkk9qoocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed of xavr bs+ p97:x)dtk6 q60km/h and hpaxxvstdr69 qk:b7) + as an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increaskj (b iv9dm+h)k6u22 odcm ,vfing in speed as its acceleration decreases? If so, give an example. I(jv+h2cfdk26mm,k9 dub oi v)f not, explain.

A baseball player hits a foul ball straight up into 7u5 jhk ax:0xzu qv)f0the air. It leaves the bat with a speed of v5fux a xuq kz:)0jh70120km/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 ef3f pdl/iplybqnl6 85:e n 7+happening to its acceleration due to ef6nlpe :fp5 nyi/8 qd3l7+ lbgravity — does it increase, decrease, or stay the same?

How would you estimate jm-ai 0xag+3w the maximum height you could throw a ball vertically upward? How would you estimate the maximum spe30 ga+mijxaw- ed you could give it?

You travel from point A to point n q.qvqkk+t6j 3p4a-pB 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 the entire trip from A to C 80km/h ? Explain why or w knq63 kt4qpj-+qp.avhy not.

In a lecture demonstration, a 3.0-m-lonsczavkqu))) . 6fsp0c g vertical string with 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 between clinks increase or decrease near the end vafpuqs k6.cc)0))sz 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, y5ln-jjz:iv,fu3e0rvm x1n falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way5m0jun- l r,yexnv:, ijv1f3 z, a dish resting on a table?

An object that is thrown vertically upward will return to it+/ q3s*z2rzq 5 rdufihs original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altz/+qr *35i2fsu q dhzrered, 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 accelerationu k.3b.;asok.e1pi a q at the same time? Give p e k sou;3iq.aab1k..examples.

Can an object have ze2*2d j 2tjj,0tzdymd3k audp)ro acceleration and nonzero velocity at the same time? Give exampled2*d zy t3,jj 0tjk u)22dmpdas.

Describe in words the motion plotted in Fig. 2–28 in terms of qjj0el d6:xlx++8 jkxv, a, etc. [Hint: First try to duplicate the motion plotted b j+xkj8l+dq:l0x 6x ejy walking or moving your hand.]

Describe in words the motion of the omcf.7sqse3i l3x:l *ebject graphed in Fig. 2–29.

  What must be your car’s average speed in order to e)zw.f f n5m5 w-ag0qusi+7ly travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15sb )(jcids+)k)vhy x f)jmm8sg.2s ;o km?    h

  If you are driving alongx mu(1cvihh58 a straight road and you look to the side for 2.0 s, how far do you traveihcv h5m(x8 u1l during this inattentive period?    m

  Convert 35 mi/h to *cs b vv((;vgx
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves pnkn+/smjx)br+c f(h) 7 s:2q(szd2p0wn gpifrom $x_1$ = 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 atm ru ev 6u-j6ne*gu*r1 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes. * rn1 *euuvmr-g6u6ej
(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 n620fmga ( brp))lx c)m8xbexa lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from thf)a6 r08lpc2b m )g(x x)mbenxis rule.    m/s

  A person jogs eight complete laps around a quarter-mile tra ce-vfrkx8fz)x44n t )ck in a total time of 12.5 min. Calcula)xx)c-f 4ztrv8e4f nk te
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its tra-2 /bvws z 9yt),jvjseiner in a straight line, moving 116 m away in 14.0 s. It then turns abt9 )s b2vwezysjv,j/- ruptly 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. Each has a spe*2i,+ f gvlev4qw2hud ed of 95 km/h with respect to the hdlqe4g fvv2i,u *+2wground. 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 truck traveling How l20nt gsio0lv:-ywbu /ong will it take the car :y nvg0-ob2iusl0 w/t to reach the truck?    s

  An airplane travels 3100 km at a speed of 79.7dbh4ft / jo rv*u7guk; l1zs0 km/h , and then encounters a tailwind that boosts its speed *duk lh7s4b u ;vogt. fjr1/z7to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete roun cjayx)i50g,m d-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is cov acj5 g0xy)im,ered at 55 km/h.    km/h

  A bowling ball traveling withlpn w6uj zp (xkf5,0k2 constant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50zp6jlp fxn5k20,w (ku 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 6.2w4cigwuv +/)wv 7d*g p s. What is its average acceleration iwu/v) 74*dpc+ wgiwvgn $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. 1 u -c3(3 e3ehl.anyudaici7o What is her acceleration e37.eau3 ccud a lny3(1i-iho
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an accelir*)*m 0g3qoe+1fqbta bef5 oeration of aboutgqe*1a*3 qf 0mto)+ ireo5fbb $1.6 m/s^2$ 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 then brake;pq) : hppi71lc6i3ox/nie tjs and comes to a stop in 4.0 s, what is its acceleratj :p/ipc)hqo ;e7i1 n6x3lpit ion 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 in y7 .)kjpre+tj3z( flk a straight line, is given as a function of tj r73k zf ly(.+j)epktime in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. jegc 0;6xu+ u0rnd z+yWhat was its acceleration? How far did it travel i;6yc+ud0guje n+xz0 rn this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/ss 0jlk(u:hvd6 to rest in a distance of 85 m. What was its acceleration, assumed cons (s6 kuhvjd:l0tant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for ax x/7lrx: f:ntakeoff. How long a runway is needed iff7:lxxx a :n/r the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of t dmsfa 9/z8x-*da)92xl s ggqphe blocks to essentially top speed (of about 11.5 m/s) in the firs8 dpq 2ags9)xs mdlg9*x- azf/t 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 from adlz:y94gj/ p8 hm n ep/.dew2k0gprmhs(9z 1 h speed of 12.0 m/s to rest in 6.00 s. How far did it travel in t g//8ds: l0 jhm (neypd9 rhwp9e.4mh12zgk zphat time?    m

  In coming to a stop, a car leaves skid marks 92 m long on theso/q99 --wrpm *:o dljzkdn +f highway. Assuming a dds:+k -pr9ono*wmd-f l /j9qz eceleration 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 txpv+n7cz t +(iree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of th+x7p n zcit(v+e 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 aa6ri fp: 6yr2distances for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for anrap i6fr2a6y : acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping de8cdgp2,co e 1/ )jvwxistance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver looks *m 658bd- gab8dd vndbfor an opportunity to passd8bvmg anbd-5 b*dd 68, guessing 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 complete the oq wk0uvt9s;b8cwkh. 3q z59dvg./ eh--zsqv10,000-m run in less than 30.0 min. After exactly 27.0 min,s z9h. ;tc9v8g-s3q/d- k0ho v5e wuqq.wbzvk there are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car a twvyl gp/ 3,cgf0iue c)/d*h rs7.7pst 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration ispc vh*ls7/u cfirdg/es 3,gw t07.yp) $-5.8 m/s^2$ , 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 -( rxf qlr /(ll.ard69g s)kmwcliff. It hits the ground below after 3.25 s. How high is -(/wkrll a6rs(mfxl )d.r qg9the cliff?    m

  If a car rolls gentlyzxhp;qoe w9b51e2 *ji ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up into the air with a speed of 22 m/ tq85)4. frhamfvp p8xs
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward. Wi5 akdx,5b8 r,bmi5lgeth what speed did he throw it, and what height did it reach?e rb, d,8b5lai55xgmk    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influenc2(hb 4 yz2sqvc;0wwa -ju ;mroe 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 . Ignore air resistanu4womc v-(aqhbz js w2 ;2;y0rce.

A helicopter is ascendinev10 8eaetlls8- 2pjw)s ol3sg vertically with a speed of 5.20 m/s. At a height of 125 m above the Earle828asetvwe )0l -jspos 13lth, 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, showe-x joj 7yiwmb 96at:mo; du3/ that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shedyj3ammj;- woit97bu: ox 6/own by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically-i60 ,ezjf,yjpa hb1 t) that a ball thrown vertically upward w,fye1,ajz-6b phjit 0ith 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 speed of 18.0 m/s- ;bj usxfj9u87o wy,p rr:v8o
(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 f 69zup0.l-p3osu tsc in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, z0p 9sp.s tcfu63u-ol but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takesb2v+mpg 1eok a+q92.hex y )o,zcojw9lwhk 6: 0.28 s to travel past a window 2.2 m tall (Fig. 2–32). From what height aboveyw , l1ow+2. h29b qho9gejxkoaev:m kpz)+6c the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it strik q5u9u6y +vrlb.qz 8yhing the ocean is heard 3.2 s later. If the speed of sound is 340 r z.v+q9qu 58 yyhbul6m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream o7 ba 3lr1up o4x*i(domf water. You point the nozzle vertically upward at a heig7dl* 3ioou rm(a x4bp1ht of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the7blb( l kw*4peh70re4nmipr + edge of a c7lb4imkwr7eb(*p nh +r4 e0plliff 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 m above the street witq6 8e4t+ jl 8of4ko1*tlzu6dylr zf,n h a vertical spee8qjkroetdf6 4 ly+*ofl6 nu,1tzl48 zd of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocitr7vq0)z pfg hpsrws +-1chett7 z4).py 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 zgeh4 hvt 71sp +z s.-)rtrcpwfp7q)0what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a sx21qrr+1 p- fo pnay1yhh*fo/ traight tunnel as a function of time is plottedhofpofx1/har2 r *p-yq+ny 11 in 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 can accelerate approximately as shown in the ve3l-q kg jz0au(locity–time graph of Fig. 2–35. (The short flat spo kqa3( 0zg-jults 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 o-enac e*c 41nnj/yek lhc2 93yf the car in the previous Problem (Fig. 2–35) wh49n2 cye1c lne-3y/k* eachnj en 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 tr+zi: h9itz yu (akj6,p- x8mq(cfq+t daveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose d wvz+s,/4o yolisplacement as a function of time is given by Fig. 2–2z4/+osv ,wloy8.

Figure 2–36 is a position versuudhq (qn-w;x3 ma43t v gn3/uus time graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or 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 positivhd ;3wm3gut -n(uxvq /qau4n3e 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 aboveco70b f2poi5su91-ul p dp3jx a firefighter’s safety net. The survivor stretches the2uop-jp s7 cxd03 9fl uipbo51 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 cobqpr)i+t 1-rd9d6t nf,7oi Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go thabf,61cor-d9tritd7 n ) +qpio n it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over6 8rk)d08av vfush)vk-the-shoulder seat belt has a good chance of surviving a car collision if the 8dh )vs uvfa0r68)kk vdeceleration 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 above the road below, an lf .ut4e65mhpd 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 truu. 4ft mh6pel5ck 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 3c( zam t4yg8k7br6vftested its cars for front-end collisions by hauling trt3gm4vb7a kc 8(y6f zhem up on 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 a,sgcd*m pbye h2:3gb +bout $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of the.t,j +ted6rtl 3 suu*o5sh0n o train has a speed of 25 m/s when it passes a railway workertlje50 +,htoo n ds.u6rs3u *t 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 boardzwb;xa on07**) rh /xbs)vtgz 4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the perso oanb g)rv xzxzh;/)wb70**st n while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, itk 8*nis a/dj/ u/ (i8-grcw/rlc+7cvmxioah4 is necessary to balance the average speed of a train against the distance between stops. The more stop 8-u4lxi (rmcsg//airnjih d v ko/cw8*7c+a/s 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-a2ghhd6o pyf my d7o*z*nj 33 down when diving for fish. Suppose a pelican starts its dive from a pm-jydf*o y33h h*d n6o7azg2height 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 water.    m

  In putting, the force with which a golfer st/l/9udr e 5afpwlsy9 .rikes 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 i9 le5u/p da9rs.lfw/ys 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 b8h)hek wpw /;train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest abwweh/ p) 8;khnd 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 sty25* lnf fhmx n/y 0,)tsfk7esone is dropped 1.50 s later. How far apart are the sto,2xt*/esh7s )fknml0 5n yfy fnes when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 nf- unmkdf -4; 8zk9tikm/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last8dumzk -n4kt9fni f-; lap?    km/h

  A bicyclist in the Tour de France crests xfey 2khe5cy8xxi t4:b1v2 3h a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his averagx45i2v 18kt eyh:exyx3fbc2he acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. Th1nt4;h sz3nvz e first child can bounce up one-and-a-half times higher than the second child. The initial speed up of the second ch zn;nv4z1 h3tsild 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 travelins;l:cdy nw* w8g 95 km/h overtakes a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite dir: wwc*d 8y;lsnections? 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/s In throwing the basen xz6**fh ml 3cq4;jk 0-zimdrball, the pitcher accelerates the ball through a displacement of am r c6;3qmind h0fzz-4xjl **kbout 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 vertically, from rest, with an acct*izqnb46g nm7; ,r+-tkhsr eeleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection hasfp +bcom/wke e1lph)2m 1)cja98wxw) a traffic signal, and the speed limit is 50 km/s . Suppose you are drivle2afech) bk/1j)8 p wwwpcxm1+ mo)9ing 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 speeder traveling a (kzb*3xvxbj* t a constant 120 km/h takes off in hot pursuit. The (*jvz3bxkb * xpolice 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 roof of a building; 2.00 s after that, a sgq ufru:mq3b-m5 c3en(yi 5;oecond stone is thrown straight down with an initial s3yq;gce(qi5 3onf :uru5b m-mpeed 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 verw5vzxq.f5n 9f tically up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after f5xfw9 q 5zn.v4.5 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 lozn a4(6u vvgy(/ftv+a ng 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 perhaps 150 gan46va/fz+ tv v( (uykm/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the buoh k06rqa f:bl0 gwf2qh d5t4+rgers through a grilling machine. If the grilling machine is 1.1 m long and t tqo0bdlwg20q5h akr6 :f+4hf he 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 speed 1.5 times faster than Joe can. Hf 4nccxn6zq 59 c4)fvgow many times higher will B) f4c qcnxgcf6n5 94vzill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a clg4*xum9:8*wg*q e fg3qo v bsfiff while 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 frienwqvo*:mgbse3 f 8* 4fqg9gu*xd then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to 2,z (2rmexixnfind 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. One student reports arn,2zxmx(2 ei 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, Aw o6 0aobs11sp:pii 1zdv(; cl 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 bicypoa1c sizo lbi16; pv0w(1ds:cle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?