Does a car speedometer meas uz:ngu4v2r4is (tuocj1nl* ,ure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give eqs/b8 +it2*a nk5, 3.rxnn*pksmxlenxam xpi*nen8l2* kb 3rn5,q+xs.s/mt nkaples.

When an object moves witjv5 u+iy bb9 7bl8o-qnh constant velocity, does its average velocity during an+i b8u5v qj7-bonl by9y time interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crosst7s tr6zt.vg*-:a qi ying the finish line to lose the race? Explv *rqs tatg7: .y-i6ztain.

If one object has a greate b tk2s 4m*yk.jgyf xtt4o))y+r speed than a second object, does the first necessarily have a greater acceleration? Explain, umxgtf .*+s4ty4yob)ty k2j)k sing examples.

Compare the acceleration of a motorcycle that accelerates fro 2xm:+v:p )gj3yx smbym 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same timey: 2s)jmy:vb gp +xmx3.

Can an object have a northward velocity and a southward accel axws/.l8ir4hzf 87 jheration? Explain.

Can the velocity of an object be negative when its accelerat5wdbak/ .mw/9iyb c 3yqq1 rv7ion is positive? What about m qw 5ba1q7 /dwcv3k.ryiyb/9 vice versa?

Give an example where both gj.-t+v) n;r vdcl6hl the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel(9z t:7w oxcpdu(h7hn. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed7 7xcuh: zhd9pnw((o t 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 t8/* bxtflg) 8r ofe0)j:hzrn/f7p eyso, give an extb fjy)tfo8h)f0:e/*7pzrrngxe/8 lample. If not, explain.

A baseball player hits a foul ball straight uv6op 3 -hufsy.p into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catche.pso6-f uh3vyr catches it?

As a freely falling object speeds up, what is happening to its accele h*0hvoj 7(anpta*7vn0, zk txration due to gravity — does it increase, decrease, or stay thehz0pak7t*,o 07x t j*h(vnanv same?

How would you estimate the maximum height you could thrakzsy5b,c;rs1 dv* 4.3mamqhtji 1p ;ow a ball vertically upward? How would you estimate the mas; d;m.3az imj4 byp1 h51tqsk,* vacrximum speed you could give it?

You travel from point A to point B ind/ gm,rs la/z+ 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 am z,/drg s/l+why or why not.

In a lecture demonstration, a 3.0-m-long vertq jl c:juz 6bx 3oue*lxk7-e ag**(*vjical 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 occu: qzu*g bo lxj 3*6axkvcj-j7el(e* *ur 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 mojn.:9dlobk 1 otions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the secodb1n:9 olojk. nd floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is throxyeh 4zkm8ufkh40a8ot+f7 p, wn vertically upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be af4k0h8ea,8z +tfpu m hx47o kyltered, 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 accefnl/smank,te ;h 2) sep)/5rmleration at the same time? Give examples e,krnt he) /nmpamlf5) 2/s;s.

Can an object have zero acceleration and nonzero velocity at the same tix/*b6o-nj hbqme? Give exaonx/q-6b j*b hmples.

Describe in words the motion plotted in Fig. 2–28 in terms of vow,f tm 46fh);cuzosbq (9c/v, a, etc. [Hint: First try to duplic; qb(h9zcvf4s c6o)uf ,mo/wtate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in Fig r9hmnpy8*niq5,w9( sq c3vvg. 2–29.

  What must be your car’s average speed n.wvo1(km ,qwin order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it tacd5e5i jx:ho l jq;,1;c+nxqbke to fly 15 km?    h

  If you are driving alongi(z wurrx .ak6w*6/om a straight road and you look to the side for 2.0 s, how far do youk/x.i *za wom(ur6w 6r travel during this inattentive period?    m

  Convert 35 mi/h to zvy.c)a4d0w; ecx7zy /tix (h
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frovwgc) x)t)f2 um $x_1$ = 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/h for 130 km.ib 7 cnz3b ;k3b0csc5e It then begins to rain and you slow to 65 km/h You arrive home after d0kes5cbcb3i;37 cnb z riving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds bhmroc)73 n 2fwtg ,0ryetween a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives rcmfh)n,2 rgt ywo073 in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a qu :1mxw,n3w zfvarter-mile track in a total time of v3fm,1xwz: wn12.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its treql voo+h-m r1c5rx48 +jfem7ainer in a straight line, moving 116 m away in 14.0 s. It then tur+7lreh-je8crfov4q mxo5 1+m ns 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 9 :yaxglly,-+j 5 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be beforeg-xyl ,a:yj+ l they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind o- od ynk1r8ts3.:h uya truck traveling How long will it take the car to rea 3ut.ys:rk8no 1h-yo dch the truck?    s

  An airplane travels 3100 km at a speed of 790 km/3v r*sk-.brgya;m/dy) xqi t0h , and then encounters a tailwind that*b/q t)mdr0xy- .igky rv;as3 boosts its speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocu:l)h:a)u yb bhc9gb4 ity of a complete round-trip in which the outgoing 250 km is coverb bgcby)u4 l )uhh9a::ed at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end of a s )uccn,0j+nd 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 )cnu,j+ csdn 0from 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 s. What is its average accrg+in,wkf7..6; ym5jk i iqmyeleratio7y, ny .rkimw+;kq5.jmi fg i6n in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accsqzj 7o6 9sga;eleration g6 9jss7q;oa z
(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 acceleration o0e 9ultnjxf-nu 6r8z .f abouf0 uex8 l tz-jru.n69nt $1.6 m/s^2$ 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 sf-dz,pbkvi,qd-dz 22. If it then brakes and comes to a stop in 4.0 s, what is its acceleration v- k2-pfdzi 2,qz, bddin $m/s^2$ ? 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 rac k ca*any:)vr-ing car, which starts from rest at t = 0 and moves in a straight line, ira-)y:a*kcnv s given as a function of time 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/l +v dd4+z4rmv5zcs1un (nl4e s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this tim nuedvnrc4 4zm4sdzl+(vl5 1+ e? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What w/f2j v.a (ea-ewut lv:e:j-z gas its acceleration, assumeduvgj:/wtfa -v.2(z:eeej al- constant?    $m/s^2$

  A light plane must reach a speed of1x.hk6d r2z)rgq,hgb i0r/mbh7wf( o 33 m/s for takeoff. How long a runway is needed if the (constant) accel2/1gifhh )z6kr7 b(rgrxw.b ,mohd q0eration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blockso u-u.yfsi*5s to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race ysfs5i-ou u*.. 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 a speed of 12.0 m/s to rest in 6.00 i 0o0 twp5wyf2s. How far did it5i0ywwtf2o0 p travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. As;;s kxjpofr+4 s+t t:64 fblprsuming a dece stb;ro+k 4tx:pf6j;f+sl 4rpleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/4vva)7ujm: xv: yk bq+h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver d)mvbyq: 7kx+av v j4u:uring 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 dipv7c 3v 5ut lczbh+w506pc,oystances for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleratiu0p w yo 35zlvh vcc+5p,b76tcon
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation f0ye5ex ah+za 4or the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. Thcgn/6 0 iuhy2je car’s driver looks for an opportunity to panuj /g6h2c0yiss, 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 10,000-m run in less thai4gfztioz 1y s9g+lfsv1m) *,n 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The run)ym1vg+t9slf1o *, zigi s4z fner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an i)hmwas i.,xj.ybv3g 6 ntersection 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 dece3mgjhws. ab)yiv, x.6 leration 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 fi)lcw: 3*+uex8ce u0mn30l wmf/ :3dw mpdxqf rom the top of a cliff. It hits the ground below after 3.25 s. How high is theecx 3dwm p0fwm /qexc w: +dli38l0*fn):muu3 cliff?    m

  If a car rolls gently fmyf2s 5ctovm(g,n-yijw;7xx t( c7, ($v_0\,=\,0$) 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 wit7n3 8b* )msf6vdp zwjzzj+g;ih 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 iik( eh2xo8ht xxc1yu -a--*xat vertically upward. With what speed did he throw it, and what heigh(kx c21x-8xhatyeh *-x io-a ut did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls un* tef1v yxb05loo z:bz26;ii mder the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as m;526lyzvif b ix t*bze1 oo0:a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height tf:ubnca )f 53go+2 ,4muoualcgws gm9p6l -2of 125 m above the Earth, a package is dropped from a window. How much time does it tag,a ogm:mu6+9up4b 2) un f w2llf53cga-tocske 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, show that the distance traveled+k r x4s/i,br oti.j,nfqrjrb 786)uq 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 andf+4ir)8.,j b/ri,7qu s6tro njk xq br 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown ver c4 +p) 8bssze8xc pjdpn)r+m4ccv1e *tically upward with a speed pr*))mnpx4 epb4e+scvc8scjc+z8 1d $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward withne7: k bop67ht 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 oj sv*s b6h) toqc+,8hmf the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple p+6)chs*qvbjo8hs,t m ositions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. mjk w nrm283stp 2e3)jk-hz2 d2–32). From what height above the tod-kkm w3jn)2e 83jzr2psmht2 p of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the wld::x5dh; lvsound of it striking the ocean is hearx;:wll dh5 v:dd 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose notl2 c*so .+kfozzle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–3 fo2l+kstco .*3). 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 zz8c(o 1t xp30g *tmi;) fsoqlof 12.0 m/s from the edge of a cliff 70.0 m high (Fig8*fc3qzmtx1;0)spz( goio t l . 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 28ozv5 dc5fjf5u/ c u2c6o7b tci y9yu2; m above the street with a vertical speed of 13 m/s If td 7c2o5otu y5 cuz/f52 ;ubif96jv ccyhe 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.qx/ hk-52rq ldk5yq6 d y9x(li h2xp-f1qi.fo (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 thry.x l5pk( 5xo1il62ffq-/q q- x 9 h2didqhyke acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straighzqrcn 9l nhzz8s7 r -,bop):sy s*h9+tt tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneous 9hr :yssbqo98z p )+stn-*c zzl, rh7nvelocity
(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 t:x)3tujk z f1ahe velocity–time graph u1 kj)3x:f aztof 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 ther mq6 ex-h/;ty9ubihcqx3 53f car in the previous Problem (Fig. 2–35) when it isy96; mcqxebtru3 -/hi fhq5x 3 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 trav0 fi kna/i1i rxi.pm6)eled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose 4 c6zd9hw(v npnvd4( xdisplacement as a function of time is given by Fvpd9wd6 4(zx(hnc4vn ig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object along mjdq( ) 2hja3 e/ mk3rq1 rwba*qs (;3llmvmj5the 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 positive or negati;q3rl(q k(m/3 )mrjd*m shj5a jl b1em3wqva2ve? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourthr,uu1qfdg8 pae6i-bhq)0 s , u-story window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–37p)uu,rh ,ag8q-6qus db fie0 1.
(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 osj n8:5xxwj- Eart8ws -x5xnj:jo h. 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?

  A person who is properly constrained by an over-the-shoulderb29q;n*7 k zckd cbcg7 seat belt has a good chance of surviving a c ckbck;q d2gnc 7z*7b9ar collision if the deceleration 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, and his puhpt 3qct j1f/9rsuers are getting too close fth/3 jc9 qtp1for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be 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 h b lux-*m5ci7ol . 6;n)bpsccfor front-end collisions by hauling them up on a crane and dropping them from a certain he .nb)xl b* cl-7u c;m6c5ihpsoight.
(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 aboutr y, u.t)hcf8qbi/wc * $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins und;p wla i 2gk 3ila,bt)v3w+-ziform acceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the s2vbl3-z+iw3a tg lwdp kia) ;,peed 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 watex u l+2delt-+lr’s surface into a deep pool. The person’s downward motion stops 2.0 m belotld+e2+ux l -lw the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessarym;33 h wyyx0tto:ibl kip/cj n;n f;72 to balance the average speed of a train against the distance between stops. The more stops therennow yp; ;mj0 h :yi7xb3/c;it32flkt 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 djb r5w8 1agktu4zp+f, 8v)unrown 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 ac8tnzawu j4u5 b,pgk8 )vf r+r1tion, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is asn9q)icms 5opn;t 0z gf1)u(planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball di9 0c sg)qp() u15atsnz;monfecelerates 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 constan0mu)he); ew +e cer7/zba wylh(t*adu7nq6c1t speed of 6.0 m/s Just as an empty box car passes him, the fugi lu(ru*7q 7e+ t/dec))hawwma y nb6 0ez;e1hctive 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 froq 8ahn o5o yc90 b*.btcst7fy4m the roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a speed of 12 s 9qfbhc5y4t c*nbao7oy80t. .0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time x-pd6 lnw;z9j trial lasting ten laps. If the first nine laps were dod6plj x-;9w znne at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de Ffv8(o+ fiw/4)8p q; wellygs/9e gps orance crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his g84vp)( o s +; flwpi9//e qg8sfolwyespeed 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 r*dk, ,r1m s0kbigs(d bounce up one-and-a-half(0s1,gr ddsb km,rki* times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10(pdgna*fr+ *f cpau *--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 tha*d *gppcrf( -faun *+e car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/s In thf(38val hp( mhrowing 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). Estimate the average accelf (m3hphl8av (eration of the ball during the throwing motion.    $m/s^2$

  A rocket rises verticall:wm 2;k,vt yirodjr /u .r2fi9y, 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 in Fig. 2–ptaexg+.9;(v;h iyb *he lgt,42. Each intersection has a traffic signal, and the speed ptb e gthgy;h*e.;, il 9xva+(limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, 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 trdb w ; c*my-to1(silp7aveling at a constant 120 km/h takes off in hot pursuit. The po-c m t*7spbo1d il;(ywlice 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 tha u6z-vtlhgzg 5u)589gf q3lr9 kmmrl0t, a second stone is thrown straight down with an initialqul6-u0 9k59g zfmzg)v t8mhlrgr5l3 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 vertica,ik)lo5(duyy/c.;* 7 q 93 r nhf azs.cgtokqjlly 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 4.5 s. With what init;3slga.*occnz95 fj7(kqo uh d/),rky.qy itial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a freeg tb 0,.v:wt8fb*cky la*pb1v -falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would herb0* l*g:1 cvtt vw.,8yabpfb k 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 to send the burgers through a grill,f)-t7 xd2a6 yyar zgling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, ft yd26yl gx,ar- 7)zawhat is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball verticzq +) dcme ovzn25sc7.ally at a speed 1.5 times faster than Joe can. How many times higher will z5+eccv2s.dz) om q7nBill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff whixe8 :lov rm,t879;au+n1gm:1vq 6cs t yydanrle your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks lcv1xm rae+:,gra 1 t7on 8;s9ynd yvq8tu:m6up 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 particularz2 xj2m5g,rkj 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 fall time of 2.0 s, and the otherz 2g5xmjk ,2jr, 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 and B. (a) ftsr yg;rd-(1 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 o rsd( ;y1tg-frther? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?