Does a car speedometer measure speed, velocity, or bol67pof70-anro qcl : dth?

Can an object have a varying speed if ijk;.m 4 x2bj5;ryhkhrts velocity is constant? If yes, give examples.r2;j ky;h.j5rxb h4mk

When an object moves with constant ve 8m- (mn,uo dov (- hdusle .52o/(lbzsy(heojlocity, does its average velocity during any time interval differ from its instantaneous velocity atoeoh z.bs(j,s ln85- 2uvedyh(d(m o(u-m/ol any instant?

In drag racing, is it possible for the car with the greatest speed crossy mazo,)y 0)y/ j/jzpding the zdyj, om j/)0zay)y/pfinish line to lose the race? Explain.

If one object has a greater speepvwjex-)e)ue n +1a amtu 0l3.d than a second object, does the first necessarily have a greater te xm. +)3lu0aan) eu epv-wj1acceleration? Explain, using examples.

Compare the accelerationu , bhzr9cf qyd::0(a4la1olx of 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 tima0 1y,ulzlf hor(9xaqc 4::bde.

Can an object have a northward velocity and a southw0njz0hx m61 8fkm(nkyard acceleration? Explain.

Can the velocity of an object be negati dey tzr(6:m+hve when its acceleration is positive? What about viced t6m:r+y (ezh versa?

Give an example where both thez(et2byk /;fh8t 2ut.3wxilk velocity and acceleration are negative.

Two cars emerge side by xle 1c u6kun;nnj46;k side from a tunnel. Car A is traveling with a speed of 66e6ku 1nnx j; ckln4;u0km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, gi,q5b-gph+ /t1u sbot eve an example. Is-q+t 1oup, g/b htbe5f not, explain.

A baseball player hits a foul ball straight up into the air. *exdto bk)8zr-u-db2 It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be tru-x2 zok*be -t b)r8ddaveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acceleration due - )wve/b h;tgi0 7ii *rya7aglto gravity — does it increase, decrease, or stw0 -i; ia/7i) e7lybvr*gg htaay the same?

How would you estimate the maximum heighik,i0d; bwr3 u1, lrigjl/ 7bot you could throw a ball vertically upward? How would you esti17igwou;/r,d l3 0bb,lrj ikimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant speed of k tuu6y/a+xe:s0ag 5 q 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 faau skg6 xq:e5/uyt0 +or the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long verc(rqgn 0;q8eytical string with ten bolts tied to it at equal intervals is dropped from the ceiling of (q0;qyr egnc 8the 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 fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these moti ;4o ce -rsmvim307hmqons is not at constant acceleration: a rock falling from a cliff, an elevator moving from hqei 7mv c mrs;m0-3o4the 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 return to its orig6)x2xsq dwgl+fg3+l minal 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 df+mdq) l xwg x6lgs3+2ue to air resistance is always in a direction opposite to the motion.]

Can an object have zero veloc 8a3;tukdyd *aity and nonzero acceleration at the same time? Giveu yd8a*;dtk3a examples.

Can an object have zero acceleration and nonzero veloc78 esqo ,m hlbc bg;z(vro0)a:ity at the same time? Give exampl,hb c:7)s 8lo;(rozgmev0 baqes.

Describe in words thpsxtp,)q l83s e motion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moving your handt)lxqp, 8 sps3.]

Describe in words the motion of the object grapl -*s;wqj *7 jhfqdpt(hed in Fig. 2–29.

  What must be your car’s averag ltmtnt ;2n1)re speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fl: c:ugypleooqgqca8o.k8gn*u 3775 ey 15 km?    h

  If you are driving along a straight road and you look to th7r6 9xawv. 5dszl8:s9sraxooe side for 2.0 s, how far do yo976x9 svl.rwxr8soao:as zd 5u travel during this inattentive period?    m

  Convert 35 mi/h to ) 1mf zrti(um6gxrqv+e3 26l6 2smaop)zc/me
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves feq5uu5tma- k02k8,p 3ij8/d t6- yutpbottqfrom $x_1$ = 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 fryd 1krgsmon)n .ic//ahq,*z3 om school steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3n./a1rsymhnz d ,3kg )c *oq/i 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-opy)z9)mht g:yw-q -mi /nv)nzf-thumb, every five seconds between a 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,igqzzyn m )9ny):m/phw )--vt estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a totaqat0n23(4:y7 btxpy oum0 hai l time of 12.5 min. Calculby3a(7 apyn4 o2hm xq0ittu:0ate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, movinwt)m g0o zii/atgs ;b38)5pmes+ hp(lg 116 m away in 14.0 s.w 0smth(og5ea 8)p/3 plim +b;tgsiz) It then turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has a speed of pe :/hbvr/epc1 .(eee 95 km/h with respect to the ground. If they are initially 8 1eb e(evc/h .rpepe/:.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 travelin3+lp nq1uhrdjh13 b s8;rm9w e8zou ps1:cg.xg How long will it take the car z 1;8ocmpru lhwjp 1.9n3d81qg ruse +h xs3:bto reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then en * 2oehz -p efrqq io-3y*oley*g,2,qjcounters a tailwind that boosts its speed to 990 km/h for the-lo3jzfq*y*2ge*qy,h, 2eo-q roipe 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 averagev0s,5(k gor:. gqm/zj dgdu 8h speed and average velocity of a complete round-trip in which the outgoinj. s,m/hug:z gk(og d5qrv0 d8g 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling withd9yguk w1a1l5 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 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of 15udlkg1a y9 wsound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 kmn tx:y/hi35 xm/h in 6.2 s. What is its average acceleration i/ixxht5n 3m :yn $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in;wr-gc8k( jg h 1.35 s. What is her acceleration- ;w8gkrcj (gh
(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 accel)ecgrfua9j8 :7,ggf* uldr7y3 9d(e xe s oa-leration of abou f cle8gu du,97ya rg3ee-oar9 (s xj7dl*g:f)t $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travsu y1skrg,g 0: lod*3vels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is itu0dl1okrg * g s3yvs,:s 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,c +la:94 pidwy which starts from rest at t = 0 and moves in a straight line, is given as a function of time in the f+ l4 ad9ciypw:ollowing 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 it1ser 3a3 y0dpdxtkf3+ s acceleration? How far did it travel in this time? Assume constant acceleration.er3 xf+ 3ds 01kt3pyda    $m/s^2$    m

  A car slows down from 23 m/sd25ep+ vohhe+ to rest in a distance of 85 m. What was its acceleration, assumed constant?v2e++ dpe hho5    $m/s^2$

  A light plane must reach a speed oyb8f3lek.bvd g6h /9o)( nfqof 33 m/s for takeoff. How long a runway is needed if the.g of3bk6oq(yd9lbe)hn /8f v (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to esff c-0-g hqk2bsentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach thacf-2hf q0 -gkbt speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest idpf qln 1v*e45n 6.00 s. How far did it travel in that t1f* qp5nd4l evime?    m

  In coming to a stop, a car leaves skic a4 kzb+a0ma :xmpn 9-/fvop;d marks 92 m long on the highway. Assuming a decemp/:0 cpzanf x av49+abk;m- oleration 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 compr2 7iv s3l+l6l y5ps) i2uzfolqesses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’+7fl) i 3soy lzqp6l2i vl5su2s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distanu tokyyw ,*e1h: fbb.5ces for a car with an initial speed of 95 km/h and human reaction time b*kyb,1 y5h.:wefuotof 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 thes+exq80g;a3w0mszhyw q. z e5z f4tq+ stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The ct4 etpd99be d3g7 uznutb1(z ;ar’s driver looks for an opportunity to pass, guubuze41e dz79t ndt9;gb (3ptessing 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 -sg3nim zgo6 - fw t:qv*w)fy9the 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 acceler-): nfg6gqt s3m-vi zwfoy*w 9ate 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 approvk+9 xwu)lfo 9aches 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 (x9u kv o)wfl9+Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below after 3.2 y;uxe3i+q htd 4gd)e:5 s. How high is :xydutg4 ie+q3)h;d ethe cliff?    m

  If a car rolls gently(k4r9wfhby .v erxsn0 2 ll2:c ($v_0\,=\,0$) 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 wal d): im27jyfith 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 throwingrt s:r2flkyxnvfyr t;lsmg/ 2) 9w2/* it vertically upward. With what speed did he throw it, andg:mt slrv)fr* k2ns r/2 9w/tlxfyy;2 what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls /nvm,0eqgtr/w mq - 0gl jlf73under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function ej q,0l lm/tq3- wr/g7mnfg0vof time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertical; 2nox dqf;1aply 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’s initial s x2dn1pq; ;faopeed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distancwsr/h: : psoqycg6;2j e traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 anq6w p/h:;y:g srsjo2c d 2–21.

If air resistance is neglected, show (algebraically) that ekxng,.m7 pixd 9.k 4,4vb.yjighz/j a ball thrown vertically upg/ mi..j4n7 bhygxv4.dix9j ,,pkzkeward 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 speed of 18l2 1ypyl4dz :7 tif:lu.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 in Fig. 2–18 (or num; wuz5 do)f7xhber ofu7 5d x;z)owfh 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.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past dl6:f rjbx1*j0qwh kj0nv/( qw w9nc+a window 2.2 m tall (Fig. 2–32). From what height above the top of the window dqbv/rfxn0c6jwl0(d9*1hq +j:njk w w id the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocean is h)p t irynxp)*qlzo v*6m*7g*beard 3.2 s later. If the speed of sound is 340 m/s , how high ii6poy7 l*g zx)p* vntm *)*rbqs the cliff? H =    m

  Suppose you adjust your garden hose nozzle fo4xi zmq/.ja35 jxak;afrl;4 c9h(vsm r a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear theax.lxa4k4 93qv/i hrs z;am( ;jfjmc5 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 o,yem37-h9u9a1)+u lo dfcna gyq w 7vm/s from the edge of a cliff 70.0 m high (Fig. 2–3n7+9luaayv3f qmh 9w d cu,1-)gy7oeo4).
(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 24 ,d;op,5el )u o gnb k.pw1:4xuukbh4jvh6ku8 m above the street with a vertical speed of 13 m/s If th1up6bgpouh wh4 :5 j4n;ved.)loxbk ,k4u uk,e ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a) At p+ 8ddkofs/r;4 ) cufswhat time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration gre fu4odck)+s fs pdr;8/atest?

  The position of a rabbit along a straighf*d0omav( 580l s,goa h fd+fft tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneous vf*fa s+8 d5flodvog (0am,0fhelocity
(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 askkf eeu*;nhw: t 0b4 6f*k3sar shown in the velocity;f fh6s**4eu:br0e nk3twakk –time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of,kq yr6k ii1*5vwms4g the car in the previous Problem (Fig. 2–35) when51i46 ms kkgq*i,y rwv 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 d,/+;tfy g0x zc ae:/g:6swqisg;kbva uring
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose p;x1a /peg(tmc -4uyzdisplacement as a function of time is gi- gp1mt4yxe/cup z;a (ven by Fig. 2–28.

Figure 2–36 is a position vexdye 6t77b.j2x1 ey qorsus time graph for the motion of an object along the x axis. Consider the time interval from A to B. 7jte12o dbqy7exx.6 y(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 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 154cd9y3rdxvowj 7hei3 b 1uw.( .0 m above a firefighter’s safety net. The surv d9(r jow4whbyv13e.c3 xd7i uivor 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-six6(iw, 7ru lnzmth what it is on Earth. If an object is thw7zuimlnr6 ( ,rown 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 constrained by an over(9v( of *r2o;vcfrz4k sic,w;py) lwu -the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 30 icvk ;yo ffp w(l94;r*,o)uzcw 2v (sr“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/wg.a4rf0 fud the road below, and his pursuers are getting too close for comfort. He spots a fwa4 r f.gd0/uflatbed 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 te5urx2p9r 61u9lkzcatsted its cars for front-end collisions by hauling them up on a crane and dropping them from a 9 r159ltrupzu2ck xa 6certain 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 abou1dbf nr9.e7w it $10^9\,km$ 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 ofa6a9pyfbri:00 d c5 ezc/ ;( ozvz5juu the train has a speed of 25 m/s when it passes a railwv5eaz y9zu; ojf/c6d:pra u50(i z bc0ay worker 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 into a d ol -16vk2doemeep pool. The person’s doooev 12dml6k-wnward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transim5mzpdrq 6u). ;/:0j bbydqobt system, it is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the :mbd)r0 bbyu5q6pd j;m /qo.ztrain’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 for fishvl 8:luptr*uq5+ jbl1. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Aslb5vtlp l*1 :+8 urjqusume the fish is at the surface of the water.    m

  In putting, the force with f/wjba 4-zci* which a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long ij-wcz/ fba4*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 0ryg a)spw/la h-xfh3)d+.imon a freight train traveling at a constant speed of 6.0 m/s Just as an em+gr a- sh3/ym.i awh)ld )0xpfpty 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 3ud - ) +)notlmzx.tjjje3o cu 80wah7high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reache3n 3j e .jlau7m8jzh0ud tw+oto-)c)xd a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a s sop(koi.8+ vtime trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintainskop +.vis 8(oed for the last lap?    km/h

  A bicyclist in the Tour de France crests a mou; ki; -amzk/8w.dxy m k;ge: eivqs*g3ntain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his spee imq .xi wa/gd vs*zymegkk38-: e;;;kd is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can boun;jfjaefsrc3 ka1ect-/ 94h 2cce up one-and-a-half times higher than the second child. The initial speed up of the second child2afc 4-ja3kj;cht9 ees/crf 1 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 travelg , l,e3- 9zk9asmsqaeing 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 smkq,e 9l-e3, sga9zain 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/s In thr:.2dw/w;z+m(y8 :vezwn ,cyldr iwum owing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41).m y(y8 dw:,di:uw zvc.nw;/l2ew +mzr Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an ak csvm(z+em x36x+ y1qcceleration 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 has a traff.2tck;2d . , cwqitgr sqbs1r,ic signal, and the speed limit is 50 km/s . Suppose you are driving from thec, . r.k,gt q1dstbswqc2 2r;i 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 at a constant 120 km/h taka 7uk/,ta/ l( avgc7abes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant a/ u,(7cava a/tlabg7k cceleration.
(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 n mw/ynt6h5 fa cjvzx8+rh35)building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the r h5m5nj8hc6 a/w) x+yvzf3tnsame 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 v7q8fx, 3rt z d7ufm*kstone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground aft x7t*zr8m3f ,ukvdfq 7er 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long d3mz m)nq;-tdug jk:1would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where sh-j:) m ndzt1ku; gdmq3e will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt tirpfx:85 l*;lhyyz(q4p3zd*uat8w b o send the burgers through a grilling machine. If the grilling machine is 1.1 m long and th3:hl ya *dw5 irpp8q4 (;f8txzy ub*zle 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 tnseipid o pw71/.x.zq+z+ j-f imes faster than Joe can. How many times hig /1niq-ezd.+xoi pwj7pzs . +fher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stan,rg9mp )aasu1a-l n, rds 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 b) ,arp aln,rsg 9uma1-all 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 parttc sv;hw/ g4 7dl)c.zricular building using a barometer. Insteadw.d s ; /cr)7hvltc4gz of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 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 an7qew 4r fzpkt7jn9k d.*g,t0bd 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) Wpz*qtd ektf7,b0wg 7kr .9n4 jhich bicycle has the higher average velocity?