Does a car speedometer measure speed, velocity, or both?*7po+ zi mx .kk9bj0eg ++fnno

Can an object have a varying spe8-geecz tz*f7msh s -9ed if its velocity is constant? If yes, give examh*9mes-8zetc - 7f sgzples.

When an object moves w vr42 ktd ra9/o:ab:mjith constant velocity, does its average velocity during any time interval differ t:o k9r/a2drja b4mv :from its instantaneous velocity at any instant?

In drag racing, is it possible fo y6bmk*2v aef6r the car with the greatest speed crossing the finish line to lose the race?6av6b * fmyek2 Explain.

If one object has a greater speed than a second object, does the first302fxz 7*4am co:5i ,f)fanyejwe9:mzq sw mo necessarily have a greater acceleration? Explain,mmzifz:) y fe0wo ejq,wcnxo3mf a9: 247a*s5 using examples.

Compare the acceleration of a motorcycle tc-+nn4 mco+n ehat accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h-om nen+nc4c + in the same time.

Can an object have a northward velocity and a southwarvj1 e0:jsq (kzqw97h* 4n y; ip)tufhfd acceleration? Explain.

Can the velocity of an jp8yh4(k39 xq)5 8dyddo ehkwobject be negative when its acceleration is positive? What about vice verdq4d( okx5wy8eyphj9 d)8hk 3sa?

Give an example where both the velocity and acceleration are negativniff8 .r 9vlx*xw )+vwu.wi6a-a a9m ce.

Two cars emerge side by side frm); zq f*6mcr,iprs(y om a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reaz 6m rsmc*,)pyifrq(;soning.

Can an object be increasing in speed as its acceleration degm +pa)-pw6u;c l))hr 0n cbntcreases? If so, give an0)mh)cr 6a-lp gu;tnbwcn)p+ example. If not, explain.

A baseball player hits a foul ball straight up into the air. Itze7+f) /czb yh leaves the bat with a speed of 120km/h . In the absence of air resistance,+c)ebyzz/f7 h how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to l 12v qhq)mo24 jsy.llits acceleration due to gravity — does it increase, decrease, or stay j hy.)q1qs 4l2om2llvthe same?

How would you estimate the maximum height yoz7c9,o9bbl h: +1 ecocqbkf-fu could throw a ball vertically upward? How would you estimate the maximum speed you could gi1l ckfbo9c:+,ze7 h-qcb9b f ove it?

You travel from point A to point B in a ca7ca f5tksrk,7e t+s) sr moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed oftc)kt5, 7e +ssk7asr f 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.:zj)r2 gayh h :ez6;p o+jhbv+0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin p)z pr6h hb:e2j;+ozay :jvgh+late, 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 motions is not at constant acceleration: a rock falling from t0f x z/-9c, l+pwklb1fzn)h ra cliff, an elevator moving from the second floor to the fclz,k/wx19 +r tffp )-z0nlhbifth floor making stops along the way, a dish resting on a table?

An object that is thrown verticallj4mxnl fb 8t:/y 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 altered, and if so, how? [Hint: The acceleration due to air resistance is alwayn: b 4fx8/jtlms in a direction opposite to the motion.]

Can an object have zero veixh)2/ 3qcmkxlocity and nonzero acceleration at the same time? Give examxqmh3x/ ki)c2ples.

Can an object have zero acceleration and nonzero velocity at the same time? Giveb0z-8;c8ib)a -m+uz xtxg eqh 8;azmq8b-+-tcxg z )ih ebu0x examples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. e2/pkzkts5(mh :1 csqaj 1tp .[Hint: First try to duplicate the motion plotted by walking or moving cjk1:tze1tm/s5k2 qh.p (as p your hand.]

Describe in words th1c9 u*effo)vj e motion of the object graphed in Fig. 2–29.

  What must be your car’s averj *b fp9l 24ty b;dv2ile3uqpjcth:0ef-g 69xage 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 1y*v u/u ,y fo;yfzm5hfly 15 km?    h

  If you are driving along a straight road and you look to the0ivf ku xc+,us8wscgz) , w*4k side for 2.0 s, how far do you travel duriu f*g)ikwk4,8s wc,cs+v0 zxung this inattentive period?    m

  Convert 35 mi/h to pdg-47r tti+(hci n,h10 yn ie
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves6ry,7rmk3 sp b u-vms7n fe,5b from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily at 95 km/h for 130 km. It then+qv;3z poza, s begins to rain and you slow to 65 km/h You arrive home +3;aovzs qz,p 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, every five seconds between a lightnin :e+sgb((xkg:foc l3yg flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in esceg +obfy(xg::3ls(k sentially 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 quarter-mile track in a total time ofnfl5. pq; hxvitbm:d xu/ 38x5 12.5 mi:v5ixntl/;8q5fubpdxx h.3mn. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a sty ,egspp ud1+m0rzq 2+raight line, moving 116 m away in 14.0 s. It thene,msqr + py2z10d ugp+ 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 p xrraxfjj2o o);r:k*5arallel tracks. Each has a speed of 95 km/h with jrf2ar5 oj;:o*kr x )xrespect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck b. : 4/ a:bqqwm6pc(pu)jrrtktraveling How long will it take the car to reacrmpj b( r6 /:wtc)ku :ap.qqb4h the truck?    s

  An airplane travels 3100 km6t .+xuidz/kdlv7:nl at a speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 2t nil7dl /dz6 xk.uv:+800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete round-trip in whiv *cq3ar fq2(cm)3/mx4au c.l h 1htywch the outgoing 250 km is covered at 95 km/h followed by a 4lxt 1ccqavcuwmrf *y.2 /3hh ma3q)(1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constantrz. v 20nh fe.dm9yv*w 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 af.*vned2m09.hw z r yfvter the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. Wha2ff (:z+7aqrsi/rj bqt is its average acceleratio:r2z iqjr/7ffs+ (a bqn in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates gp e2n*2ij /soijy)y7 from rest to 10.0 m/s in 1.35 s. What is her acceleration i)s j2*j /gynepiy7 2o
(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 ow6k 1x- hr,e n-g/hrxaf about ,rrg-/1xxah nk 6h -ew$1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110 m in 5.0 s. 69y3ykn4bhiq If it then brakes and comes to a stophq3b4n y6ky 9i 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 starts from rest at t = 0 and muu/0z gmzi(9toves in a straight line, is given as a function of time in the following Ta zuz t/g9m(u0ible. 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 13ph0yg +:nh :ga m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant acceleratiagp:g h:0 hn+yon.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its accelfv; fbl4f .;d-+nlwp eeration, assumed constant- bf+nf4w f; vdle;p.l?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeofruxokq946n o q wosz53j:r9 l:f. How long a runway is needed if the (constant) acceleration iss ku9ojwxo9: o qz3 ql64r:nr5 $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essenti2 fp (cpa *q/n9vy jjy5t6,wczally top speed (of about 11.5 m/s) injpf,tpwn (avqjz 5y c6*y2c/ 9 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 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 lk jv57o mgjl xk+x :n,o/7cz7s. How far did it travel in tvkglcx lk/ z:oxj,7n oj 75m7+hat time?    m

  In coming to a stop, a car leaves skiqzyk . /lh lgh7+s7a*t9i otr-d marks 92 m long on the highway. Assuming a de/h.7lt oqrg9 tsi+7*l -ya zkhceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h str;sjqea oj5st; c5 )b+xikes 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 tqjx5 ;b ast;j5ec)s+o he 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 cargs h+y :z5n(io with an initial speed of 95 km/h and human reaction time of 1.0 s, for aiz(yh5:+gs o nn acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for theu3gwh7)r..7 o lbh ykj 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 goinh1l8 t-4s7)lbknqw q og 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerah4q ol- ts7bwnk8ql 1)te 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 r-y0nn,1 4x km2ug/rl xnq2czxun in less than 30.0 min. After exactly 27.0 min, there are stillqxgxz l4ny- 2x1un0m2k r/,cn 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 inte3p5z(,boig il rsection 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 ma5i,3li(zpg bo ximum 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 3.25 qz )agg ghp /h5u(v1voy l.+qjg9a c,)s. How high is the clif golp .a9()qzug g1g),+5cqyhv/ajv hf?    m

  If a car rolls gentlfg9rmwaymu-+7 ,2i qwy ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

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

  A baseball is hit nearly straight up into the air with a spednd k v-zj.yu (+2lto4ed 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 bt4gh*hejckrm nr08pg rs ,af,+0t,7 it vertically upward. With what speed did he throw it, anjht0rs, g f8mtkh7nca,g0 pr,4e* rb+d what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls undeti9dg v,e356geh(dk uhxs/ h4r the influence of gravity. Draw graphs of (ax(ig s6 5h9hvhkdee /udgt4,3) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a spewa vucjqc1o )q8 y*2f4ed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How muc)4 coj1 *8cyu2avqfwqh time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance tr1a h ,m)((sziwlquapq1 8al )maveled during each successive second increases in tha aaqmz1s(l (, iwmlu 8ph))q1e 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 neglorty (q8pj + aq6is72chq xly c 0pbd21wq/z18ected, show (algebraically) that a ball thrown vertically upwari2szqq bytlw+qr /oc2 1a ( 6ypq70ph1c88xjdd 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 wit.4jues:nwuhu j:zr, +h a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in Fig. 2–18 (or nw31 ou o5l7n/(oti rrmumber of photorwl15t 3 oo7r(unom i/flashes 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 0.2*(i vpg;*yh cn8 s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fall? n (gv*;p*hcyi   m

  A rock is dropped from a s-bxw g02*4 xw vy+-*seynuv9ct :ibdf ea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound iui+-bd4*sfv29nb txv g0yxyw*:w- ec s 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You po6d/ct dx.nf o/jr u8+(1wfjqiv t8 w4vint the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water si unwjw4foft 6.t/vc xr+1dv/8dj (8qpeed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.mfkrfnwjkp6 1cj nc:97e (j9j3f z6h.0 m/s from the edge of a cliff 70.0 m 9kj39fzhne(mpc7 rw k j6n.1jff: j6 chigh (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the street cnx(t( 3:-vrqfdz xl q.yn0 .kwith a vertical speed of 13 m/s If the ball was thrown from the street, 3q.d(qx-txnl nrz0y( . :kcvf
(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 8r k(nl5q2eei velocity of a train as a function of time. (a) At what time was its velocity greatest? (b) During whaknei82 e r5l(qt 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 rabbyd99/7sazdu6vp hm1u it along a straight tunnel as a function of time is plotted in Fig. 2–28. What is its instantaneous 179zm/pdvyh96 dsuua 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 approximaas.(v 4n x8ywt*vzl d(tely as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve repredyzt*(. 8 v4v(x anwlssent 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- sxku3 i(r (8rdg1;oz/mrsr e previous Problem (Fig. 2–35) when idz8r/ur-m( rxrsk1i ( o;g3 set 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, estimateo 5pbsh(bvhn di-,/2 f the distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement:c /+dp xhj,ndmjy,2 m as a function of time is given by Fig , hny :+cmxjj/mdd2p,. 2–28.

Figure 2–36 is a position versus time graph for the cx v ee43n(ee*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 sxec3en 4 *e(evlowing 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 15.0 f wf ah- +5r-ah.idub7m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, 7 -h-uraf.id wa5hfb +Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth wxv41l ( amldqrt0f5 )ghat it is on Earth. If an object is thrown vertically upward on the Moon, how many times high)m 51x vr4 llgatdqf(0er will it go than it would on Earth, assuming the same initial velocity?

  A person who is properlbjr-/9mc/ (kk ouax.6m pub g/y constrained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the decelkj rc/o/apgm-ub6x b9u k.m/(eration 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, 1y.2i,bmqz;hmde3el;50m z p t2 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of t;epmq,bh0 d emlty.i5z3 2zm;he 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 fa2qfxj g7 )vr2/dmr8sor front-end collisions by hauling them up on a crane and dropping them from a ce) 7 xgfmd vj/2qrs2ar8rtain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels a ev2tpsh 7qqstm0b9n.nf +g*gdnyiy,m *7 0 :cbout $10^9\,km$ 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. 3ows/y u,pp5r1 t2gzu The front of the train hau1rp3uoy g/t,ps52 zws 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 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 therzoe.*bb 4b j.1xfv 9cdq)z2 xrj g2z0 water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while qob92z.zf1 b ej0v4.jd) xz2rxg *c brunder the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary *f:wbl6 xex7h 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 id7 fewlxh *6:xbea 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 falk)jspua 9kc7 lz a,,p5l straight down when diving for fish. Suppose a pelican starts its dive from p a)j5zklp 9cuks7,a, 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? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer gk dxkh476njhj-/iez8hv x. 8 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 gxhikj v.8en 7h -8h/kjz46dx 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 on a freight train traveling at a constant spe:cx1;kyey9(rlu awl3 ed of 6.0 m/s1ule l;rxya3c k9:wy( Just as an empty 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 high building. A second st9t vo+oi;d qh2one is dropped 1.50 s later. How far apart are the stones when the secon2 9oqvdt+oi ;hd one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial last8h kkqm x6m/kqf/n;t2ing ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the lasmf/xkqm/hn t8k q;6k2t lap?    km/h

  A bicyclist in the Tour de France crests a c: qi0)ddyh*z. . psqnmountain pass as he moves at 18 km/h . At the bottom, 4.0 .ziy .0:qh*dps nc)dqkm 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 chil szpcv 6):p9er,f oww*d can bounce up one-and-a-half times higher tha wepzc9*) 6p frv,:wosn 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-km-long train traveling in t qj+ mxkrgi0m6 ht92c4han65zhe same direction on a track parallel6kz j9hca 4tx5hq gm+2 0nr6mi to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite 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 al e*+sc f5uvy; baseball with a speed of 44 m/s In throwing 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–eu5;fsv l*c+y41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an acceledc bi*gpsy.1( ration 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 pattegxx ixgzioy+r4. ;-w+rn shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green+4wrz.g;xy io x-+gx i 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,.5h dou4kq4wj passed by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder uw q5dj4o 4kh.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; 2s12g , s73sl)vzhvmry .00 s after that, a second stone is thrown straight down with an inz2svy hg1 )rms7,3vs litial 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 verti a2 z0*j.nda(k :cuthocally up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balu2knchzao* 0t(ja. d: cony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a fr+b w*flk6 m2ilrrjaw;pq74 2 8:syhrp8w1 i jzee-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her2y sl6lp 478qr;jrmbkw:wai8z1r hf+i j 2p*w 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 to send the;hk1d hxo9p j, mt4ck3 burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate ofjpkxt4h1c;oh 39, mdk burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe cavi:5edbz( 9wu. fxv 4nn. How many9v wuf(ez4x5.i b d:vn times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff:in8 mf jgs kcettie0;y.73w 2 while your friend stands on the ground below you. You drop a ball t0 m: sw23tcgekni 8;yf .i7ejfrom rest and see 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 a particular building using a barowotrp-ru 1ta 0 k2-4aameter. 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 other, 2k--1aworp24 aaur0t t.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 tw4j;cf tt fz0s6+ 1 ijkhw(,l6t3 zwniwo bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest t nw+tzwcfw;ht i s4l z3j,kf6i(61 0jinstantaneous velocity? (e) Which bicycle has the higher average velocity?