Does a car speedometer measure speed, velocit+u ow+ejb)lj6hc f6 x.)bb3mqzy: - sby, or both?

Can an object have a varying speed if its velocity is constant? If yes, gg;4ry ;paubs9wuup ; h ;se+w:ive exampleswa ;ursegusph+bw 4 ;;u p:9y;.

When an object moves with constant velocity, does its average velocit5b osiu .cp9v 3smdyg+(l d gp-fk3k/3y during any time interd39sc( spgum3/bdop+i.k 3vkl5-y gfval differ from its instantaneous velocity at any instant?

In drag racing, is its5 t y5c4recq vcts5;db2ro07 possible for the car with the greatest speed crossing the finish line to lose the rc qst brc4e5d57; 5cvts y02orace? Explain.

If one object has a greater speed than a second object, does the first necessju cr9p+hc .xj1 ,t enjd 56h.1rmkp0garily have a greater acceleration? Explain, using examplejtk d1uh0n, 5phcjr+19cempr .jg 6x .s.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90km/0sb j0ttep;z 3ln.ks26 wml x6h with the acceleration of a bicycle that acc02bslnpt m zls6j6t;k3xwe 0 .elerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward ac-yeiks u6l1 j8q//lf hceleration? Explain.

Can the velocity of an object be negative when its acceleration is positi o o)xc6);rwwive? What about vice 6ir))xc;ww ooversa?

Give an example where both the velocity and acceleration are negwx,.+t+qesr s ative.

Two cars emerge side by side from a t;-gnq8n:pg gsxw f2w5(aqatbo-r) , runnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . qg;2 g(5aw : obq)ratw8n- psfrxn-g,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 3sh:dk8 b6a rl po4l fp9bb/s+decreases? If so, give an 3 bf6kr ao+d4plb8/9spshbl : example. If not, explain.

A baseball player hits a foul ball straight up intoz9 h5kk ukkl4d8o/k-x the air. It leaves the bat with a speed of 120km/h . In the zxk kho/l-5k94k dku8absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds oju+: flt39)dlf hq7r up, what is happening to its acceleration due to gravity —qjfol+hd u)7l93:rf t does it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw .nsu qj/6u;6u e9) fy dnjqdlan*fawgf-q2+, a ball vertically upward? How would you estimate the maximum speed yo 6uf)wanu qf ./,ulnn* ye+jd;qd2 s- q9j6gfau could give it?

You travel from point A to point Bz 6-y5/bv kvvt 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 why not6bkv 5/yvzv-t.

In a lecture demonstration, a 3.0-m-long vertical string with ten bo9:q:ocqw u ew 3p6;tvxlts 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.tpex:uwcwv o :36q;q9 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 motionxnl+o*3 q;xrbk ;)dcts is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor maxdq)cl;kxn3t*+r ; obking stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its ori 3 d vgm;su33h.p ;lcs ,r(xvr2lu/cetginal position with the same speed as it had initially if air resiv h;p3e3s rlc.g,s c;3mu( drlu/2vxtstance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocit vl2rdp: x2 y /f8k(tueqx, 9vthww:d6y and nonzero acceleration at the same time? Give exaqv62:wefw9(/ xpvdrxyh2tu: d, k8lt mples.

Can an object have zero acceleration and z3,i yqd-e q8rnonzero velocity at the same time? Giveq ,8rq3z-edyi examples.

Describe in words the motion plotted in Fig. 2–28 in tern1n 8/dj:jn knms of v, a, etc. [Hint: First try to duplicate the motion plotted by walkink8/j: nnj n1dng or moving your hand.]

Describe in words the motior,nq i ,2nu)jd ktbqik4g ((:qn of the object graphed in Fig. 2–29.

  What must be your car4o 17*sm6iap *vv;nsglzzaul9.u/f9 u l th q7’s average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How y6haj2yxp lf70m8(y l long does it take to fly 15 km?    h

  If you are driving along a straigerzv0m.0sd:qv ;/i aoc 8.itrht road and you look to the side for 2.0 s, how far do yv ;irmc8ze.qs0t .irdv/ 0oa:ou travel during this inattentive period?    m

  Convert 35 mi/h to v5t pdum/,, nlwp j(1/u*+ btumqq:a lji (6xw
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves froc++w ; pdas(+ofl fzq,m $x_1$ = 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/ t )im8.agavf2ln2,f hh for 130 km. It then begins to rain and yof82n,f t. i2aa gv)mlhu slow to 65 km/h You arrive home after driving 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, ev;t afusofn:f;8vl),v80 ayr q ery five seconds between a lightning flash and tfr8vt, q;s:y f ;a)fvou8nla0 he 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 this rule.    m/s

  A person jogs eight complete lz9o6kg qo 33ktaps around a quarter-mile track in a total time of 12.5 min. Calculate oktqg9zk 336o
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer ts*ni+v0;i lkwd2d3zin a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halflk0dt+i i*w 3 ;2vdsznway 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 8kt 098ygeaeaof 95 km/h with respect to the ground. If they are initially 8.5 k8tee9 yk8aa0 gm 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 / fu b xbdadl,-g .)s).dk*urbtraveling How long will it take the car to reach tb- /s.x)lr duf. ,gu*da bb)dkhe truck?    s

  An airplane travels 3100 km at a speed of j6g;noduc,x3 790 km/h , and then encounters a tailwind that boosts its speed to 990 kmxc6j;un3d,g o /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 averaggj /mzj ug*g2q-2b 2wdmp-3qye speed and average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1mg*-q-mb32 pg /y j qu2zdj2wg.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball travelingn.w ,r52:ilau(y dk en with 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 balenyud2aw , ilk5.:r(nl 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. wm kq0,,x)9t*b qcab-fdg( jg2 s. What is its average accelerabcx bmg* wqf0jq9)-k tg (d,a,tion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest s+ wxg ;j;14twpa:oc xto 10.0 m/s in 1.35 s. What is her acceleration4ac+x: gwx tjo p;;1sw
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a part *zevzl.jjh565 dr ij p/2ffg:qqbz(3icular automobile is capable of an acceleration of abour36z 5(f2j dgq.iq:ph 5vjf / *jzzlbet $1.6 m/s^2$ 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 co.z 6bh8mvhl 27xvnv*t fm/k 9 i.gvod, s7w,unnstant speed travels 110 m in 5.0 s. If it then brakes f,7lthn.6/7mg8 zb in9s*vmx,v 2douk. hvvw and comes to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which stanbda7 ci.hy3- rts from rest at t = 0 and moves in a straight line, is 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 hyc-.a7bd 3 inand on a graph.

  A car accelerates from 13 m/s to x q3+a)g hip*k*obi n325 m/s in 6.0 s. What was its acceleration? How far did it travel in this ti 3h*pgx3)akq+n*iob ime? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its accelew+w(/i ktwau )f/ i+nli r5t*tpbe ,-dration, assumei 5nkfa)p+lb-*+/tdr,u w/wtie tiw (d constant?    $m/s^2$

  A light plane must rea/wc kzgk+f7 .cch a speed of 33 m/s for takeoff. How long a runway is needed if the (conc+kkc zwf 7.g/stant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks2wb):f kvb6j e to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is v2 b:6be fjkw)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 s. How y c*;+cmu nmrmaypqd2 42k5 l/y6xa3gfar did it;maa pyl 2q/+2cg m u 6dcy43r5xymkn* travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Asuj 0m,4 o7h5(qtrw gvjsuming a decelerajr4(q5 t g0j,vohwmu7tion of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h stm5. ddrhm x/6irikes a tree. The front end of the car compresses and the drdd 5x6m/mih. river 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’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial sp (dmr73xzuk ;feed of 95 km/h and human reaction time of 1.0 s, for an accerf3xd;7z mu (kleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of q)-6i zo9jc7cr1 ecaj4 bdno;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 goin qomx ghi n0*a)6n)x-gg 25 m/s on the highway. The car’s driver looks for an opportunityo )m0nggxa h-)6q*nix to pass, 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 than 30.0 min. After exa+y( 6*9s1b ll/r h )onaktwfdzctly 27.0 min, thero /nbhrk+l91f*)6(sw yt zdal e 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 at 45 km/h approaches an intersection just b;sf5e *+f4hzjes4q zas 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 ts5*jezfe4+bh;4 zs qfhe 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-lnz a7e:bmio*m5 +sf the ground below after 3.25 s. How high is ea lzmn +5s:foi-7bm*the cliff?    m

  If a car rolls gently i lj 4m b-*i)kdp )-u*jqt6i)hy sr.euio0y 8a($v_0\,=\,0$) 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 straif: x*s;7cc vkad+uyd 8ght up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it verqe*vr ;bhnrw 6z-y) z9tically upward. With what speed did he throw it, anez6 n )q-whb9;zry*vrd what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls undgy4/i taniu):er the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . a:i/4 int) yugIgnore air resistance.

A helicopter is ascending vet.i q(j(at 4brrtically 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 ta(r.t(bqjt 4ai ke 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 that25fn x4ewn6: xnumv)w the distance traveled during each successive second increases in then4 w 2wu:xn6v5fnemx) ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraicm 3irqkie.bjq 82rke18n c:, um5j.u eally) that a ball thrown vertically upward with icmbkem2u rik8,5ej 1jqr8n. q .eu3: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 mj73g nluomv gi,-akl-og zz mo:y:--1)bc+wx /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 betwe40dy2n63 f4yc v*xpsayof1 g/k6bxo t en each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm inox4v3sgbt4fyy/ax o6 nyf2 kp*0dc16 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 a window 2.2 m u6u:z no xb+6u(+m ukctall (Fig. 2–32). From wha+mx(k6cnb+u zuo u6u: t height above the top of the window did the stone fall?    m

  A rock is dropped froemstpf)h 8+m 4m a sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed e)+sh4 mmpf8tof sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle. n1yfwiw q3;d).rrvg for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–3wv.rfi;3 n.) 1yqrgwd3). 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 vertical2waj.47 ihko -but + gmyrm,ox 3ks5j2ly upward with a speed of 12.0 m/s from the edge of a cliff 70. rumaiw2b7kmy4.-hk5oj3 xgs 2 t+oj,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 u1f 09chwcb. w(oftb-28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the street, whbfb - ufoc9tc1(.0w
(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 a/tux( h+k g5h anj-o hid5q:xie0m*p:s a function of time. (a) At what time was its velocity goa0/5x* jgikhq5x- ihmu ep(t+h:n:d reatest? (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 greatest?

  The position of a rabbit along a straigzvy:nz uqm 03,ht tunnel as a function of time is plotted in Figu z 0,m3yzv:nq. 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 veloc:w x;ay5hi b z1enta/5ity–time graph of Fig. 2–35 tzay5b :ne awi5h;/1x. (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 the car in the previous Problem (Fig,m2lqcxy1-j 6i b6 peqg5 mo1g. 2–35) when it is in jp5bq mg x2olimgcq 1-1ey6 ,6
(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 travele) hqvkg j rjcwh-* e1e3mbi,:mnqd245d during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph fordb lgy* ;y;y;zm4b. zd the object whose displacement as a function of time is given by Fig. 2–2; y;.zb;d*4 ylzmgydb8.

Figure 2–36 is a position versus tlmbwv 3n su1 o4o)5d0eime 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 v uwmnolb1s5o04e)d3 slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safetyu-4c(vd6xz v.kcix9 b net. The survivor stretches the net 1.0 m before cominku .94v-zxb(cc6xv i dg 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 th+uq 5z6sfp y5ge Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times qg 5+6 pf5yuszhigher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder sew b09dpzles;f//c nn8*xns k 7at belt has a good chance of surv sbc/70nlz9ns*e8df p wx/k; niving a car 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 k e9hros3ivjl;d1h0 - pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , whish3e ljdho1r -09vi; kch he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for f(qt/5e5m r piop :zo)j4g dve8ront-end collisions by hauling them up on a crane and dropping them from a certr:pp vjt(o/e8edg4imo) 55q z ain 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 abcze *rrsdi ;o:, ge,whil*mhya112. /tvw 4nzout $10^9\,km$ 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 frontcvfi q1u 3wm,okzz;8) of the train has a speed of 25 m/s when it passes a railway worker wh,8ou)wm f;vzq1c z3ik o 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 s zd c0iu:l)06d0dgnfsurface 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 psg dc6fniu :)0z00dd lerson while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is neg.h n:ws6el 3: snoj5dcessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate th.jdwn3ls ho6:5s: egn e 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;8d zol n)3q-cdxa9ri and free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to e-iq9 d8a;xldnr3 czo)scape? Assume the fish is at the surface of the water.    m

  In putting, the force with which (ul2 c ny5ic7na golfer strikes 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 is misnu(yi 5c7lc 2nsed. 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 trainx.bxmig8in0qb-*sj 3 traveling at a constant speed of 6.0 m/s Just as an empty box car passes b038s i jxxgimb-nq*.him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A seco 8wz (fyqeb(q3nd stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a speed o3wf (( qbqyze8f 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial las0-w69im-zm/fnzx o8ij)lc j pting ten laps. If the first nin0znjmoxmif)l wc8i-p 96/jz- e laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France ox*8db8p)het crests a mountain pass as he moves at 18 km/h . At the bottom, 4.e)88 dpx*htob0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child/(-rfw8vc9loml 9sx i can bounce up one-alvow 8-c( rixf l9m9/snd-a-half 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 qfgas) y 6/(,nqgv 0/zfamq4b/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 trai4vygm/q , a )/z(6fbf0gsqaqnn 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 thr8 44qr qcxuyca9qc ijpg78 -u2owing 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 ur4 c7ipxc9u4jyg8 -2cqa qq8released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an acceleration of ,col 8auq pz65$3.2 m/s^2$ 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: h hajy.2 j;yarg6np7ic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 mj2nyh6 7j ;p.:rahg ay 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 spe q lpbqdotf6-tt163w 3eder traveling at a constant 120 km/h takes wttflpoq3 61b d3-qt6 off in hot pursuit. The police 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 fr q:gf pw9wy:4 ehxlbi39a/1 mhom the roof of a building; 2.00 s after that, a second stone is thrown straight down with a h fi:mbg1x9ph lw9e4yw3/q:an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are throw1ifw ty5sgfxl 969lhde i,u/tu5x (;0snnam 9n vertically 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 ground69fe59mn w9ttlis;(dgna x f01xuuils5y,/ h after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it 8l2dg0hz h p0+kjh)qttake 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 speedg) dhhk0qt0j8plh+ 2 z to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a grillgub(d :wo *ls*ku dc77ing 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, what is the rate of burger production (in burgers7 duoldsu *wk*( cb7:g/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a su7sm bm(v1i9 w* p7.k:dabs+wdu 9jurpeed 1.5 times faster than Joe can. How many times higher vw.ua1 997r(* sdbb+ i:7pmwdkujums will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while yourd3 cebk4 qn5a0 friend stands on the ground below you. You drop a ball from rest and s kncdeb5q04a3 ee that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to 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 ayqt+,,dk4 g,vwn yiq6 particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roofynk,,6q,t qy4widv+g 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 vss o.0di jgd+fp*kmjpx 2wu/(gl*h.)s. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicy*j o+ . *xpj wi gdm)dflghpks20/u.(scle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?