Does a car speedometer measure speed, velocity:5 3up mg1qzi(,wu nlb, or both?

Can an object have a varying speed if its velocity is consbt3b9hmn h0xv 0qs) v0tant? If yes, give examplestv0q9n bh)3h0 m xbs0v.

When an object moves with constant velocity, donx8 sr7 s*5.wx6 9wd8lsqu rg(by l(skes its average velocity during any time interval differ from its instantaneous ssb*drq(7w(9w588s.xrly snlg 6kux velocity at any instant?

In drag racing, is it possible for the car with the greatestnzm g)lwcy-i)*snl2, speed crossing the finish line to losen w lszng2li*)y),m-c the race? Explain.

If one object has a greater speed than a second object,up/n.knyfx ; aa, a/w7 does the first necessarily have a greater accelerationx/7a fkp,/ ;awun .nya? Explain, using examples.

Compare the acceleration of a motorcycle thati;b6p7cdd+ l4is 5gay accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the a6bcl7gisd + 5iyd ;p4same time.

Can an object have a northward velocity and a southward acceleration? Expla7 2/31pv j dmmtbd2dolin.

Can the velocity of an object be negative when its j-8z3 ;tbo 3 jc+x h.fia9*vtjr/tadlr9s; aq acceleration is positive? What about vice versa?;-lrt;z bija tv *ofa8h/ t c93xq3dsja.j 9r+

Give an example where both the velocity and acceleh7qvohkdr5s(-hkw-4 xd lz.a k 3 82etration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling wit apr(l4l 1 rk:kp ckdsia);:s9h 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 tunne4 ;cpklrsasr p k:9)k :ai(d1ll? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, puxdl:/;,d27,g p9 jusqzpmv give an example. If not, vd du,/jp p:l,mqz2xu9;ps g7explain.

A baseball player hits a foul ballpl.nd0rk5- ua nieo3hi:ge* 1 straight up into the air. It leaves the bat with a speepe rna0 l 1u-*dn3h oigk.5i:ed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, w.gto;qpn+ md; hat is happening to its acceleration due to gravity — does it increq m.d;to;+p ngase, decrease, or stay the same?

How would you estimap(8j81bw tovpr )huu3te the maximum height you could throw a ball vertically upward? How would you estimate the 3vjup8 p1t8burh ) (womaximum speed you could give it?

You travel from point A to point B in a car moving at a constant spe jdmiu(dc,g/m fr4oj j.:/2 sged of Then you travel the same distance from point B to anotherf,gj/dsimc 2dmj 4 ur(jo:g./ 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 not.

In a lecture demonstration, a 3.0-m-longex cky w*y68,y vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that wyy8yk*x c,6e the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock falling from py-my iybindsm11i545e.t ys6 1e2sca cliff, an elevator moving from the second floor to the fifth floor making stops along ssnd151 ct ys2m4 iyp6ye-bmi.yei51the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original position, joyjff -8k- -zkx6rm 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 always in a direction oppo-6fkrkj--,y mjx 8zfosite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same ti;c ramr y7q-q8,k ,+q6fce t s5x2bzhpme? Give ex, be2p rsfq tqycx ar 8qhcm-,67+z;5kamples.

Can an object have zero acceleration and nonzero veloc (vj ,n-ol1ynwigd7w 6ity at the same time? Give examplesl7 wn( 6n wg,viy-od1j.

Describe in words the motion plotted inq*p-d9lvmx x 3ez6e9 h Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plo vh3z9 dmxelx*qp-9 6etted by walking or moving your hand.]

Describe in words the motion of the object grvwdho. 2lo*qs d jf.pci.,f + i 17mnilw+9pf/aphed in Fig. 2–29.

  What must be your car’s /dfp5. n:v2n ngg sf0kaverage 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 flyt3,ura nl +z fbrk-i*x +4j dd5ivp8,u 15 km?    h

  If you are driving along a straight road and 1f/ uaec(fix:jwc ;4eyou look to the side for 2.0 s, how far do you travel during this inattentive period? afxc fewe:jiu ;c4/1(    m

  Convert 35 mi/h to 9ef/+xkpr7 5 gjc6pag
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fia0yi(f1 /v:* 0r4fwzs qirpgrom $x_1$ = 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 o*6txs)aulvq; 1 e.jn/ vesk6 then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and e*6et6lsx).uoqvka;1v jsn/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 lightnir /hln cq9pn136o6 ,opw(vz dgng flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimav6hw9/rgqlp 3opd( 1z6o n,nc te 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 1w0lkdg-ft 8 dof 12.5 kt0dl1d 8wf-g min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a stra-l 7wd fdqk84e. bf7aqight line, moving 116 m away in 14.0 s. I8w7ffl-daq7qk.b 4e d t then turns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has a mn,fm;gr **+ dx+xopo j/nx( ,wl4 rlespeed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other e+ jnm;/pl+*lg(wx dxor*,mrxf4on ,? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will it;ub0w hc qw(*s take th0(w huwb *;cqse car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , ano(8/3x n(gb lbbqixgsbk* ozrr0x/ c6m.;(xud then encounters a tailwind that boosts its speed to 990 km/h for the nex * lbg/gck m.; oxbxsx6u r3bb/8rnixo((zq0( t 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 spe9.gh3lg l,dj-chod (fed and average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at fdh gc l.g,9(-djhlo 355 km/h.    km/h

  A bowling ball traveling with constant speed:;(h;x c k7dh)v)kp 9bxhiwn 3v9teyw hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is thh 9;vncw3vkk h:)xy i);7 dxpetw(b 9he speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h ix ida,-: npi5rn 6.2 s. What is its average acceleration in np-5di a,:xir$m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What ilwyj-lqhu5 ,z- ht5xjx.i xm2i* 0i/o s her acceleration .uwxhj lyoq h- z -imx2 l5*,/i5tjx0i
(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 accelera s,a p0d:uqzu5tion of abou5uzp0us, qd: at $1.6 m/s^2$ 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 i qqpnuakse(996km4.e2j69fn q( m ts constant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop m(e9q2k ep at6.6ik9nusjfmq9s(4 nq 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 r 8kil t9 ailv1*q/;vx*vc.hjstarts from rest at t = 0 and moves in a straight line, i.ii rx* 8vjh9qvcla* ;l1vk t/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/s to 25 m/s in 6.0 s. What was itsic+8o;heliw pee4 f b3f;m7 h9 acceleration? How far did it travel im;8;b off eceh3 whip+9l e74in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What wx2v 2mdx3)plgas its acceleration, assumed glvp 2dx )3m2xconstant?    $m/s^2$

  A light plane must re3v), yvy u*ecace*vp 9ach a speed of 33 m/s for takeoff. How long a runway is needed if the (coae*ve3v * c,yp9c) uvynstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed (of q ) l.y;:ukso6os pk3iabout 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of thil u6:ip;.o s)3qkso kys 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 t3ixpu7yuaa+no lumc u8./6 k;o rest in 6.00 s. How far did it travel in that t 38kx u;/ u7a.o+pi6ymlacun uime?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assumin ; be-iv/m:pcy 1bufk2g a decelerat1u-bm 2ibe /yk;cvf:pion of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a .f5 . vsadbixeeh5*;o tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acfbh de.voe;xi s.* 55aceleration 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 eh+ n3wvcu7cds6 v4. lspeed of 95 km/h and human reaction time of 1.0 s, for an d ec6l.uvh7 wvs3+c4n acceleration
(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 a 4sc 0wn9j iau8car 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. 2 dju1w/d6b8fj anjwr9wfo 0 .The car’s driver looks for an opportunity to pass, gueswwn8jo bd a91r06 2jdw/ujff .sing 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 ewrmx2(v3;vz ogow8p3 3 2ag bhxactly 27.0 min, there are still 1100 m to go. T 3mo(zxp g2w;w33vh 2av8gborhe 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 if 3:j6jj4ylyi+jd7z 2vb4sh k rj/t2zntersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning yrj24hf:sl vt /jjzdb637ziy+24 kj jred, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration 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 belo7-a amr* 7juh3(6qhrr ugoj)cmbb16 *abdlo 9 w after 3.25 sqblhg 1rrb)j7ub*-ja6u3oc o dmr7(h9 6* ama. How high is the cliff?    m

  If a car rolls gentlyj* uyon*20x jj ($v_0\,=\,0$) 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 thhf zyaxg7 /3eayr o,,-myv58 re 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 vertica9kt 6;wvh cgk9lly upward. With what 6k9twg h9k;vcspeed did he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls unr /i)uuecx* :eder the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function u*)x/ie : ercuof time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending verticallywpd b4sf55nf;i kuv65 with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a windo 4sb fndv;5f ku6p5wi5w. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance trave,r:: jhuxr bdf 2z)*sgfriy9 9led during each successive second increasesrh r9:z)u yfb if9x,d *:gjrs2 in the 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 (algebraically) that a ball throvou,;h0 n; nghwn vertically upward with a spu ;;vg0 n,honheed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertics4c.pvwxy 4g;f/ w5o rx zkd-(ally upward with 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 begviw2i ;7/ljy tween each photoflash of 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 positions, bu2g/7ijy; wl ivt not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel pak56ehlb: d kwj)uf18/urex*d st a window 2.2 m tall (Fig. 2–32). From what heigh)u/ 65fer1dk d bkjelh: x8u*wt above the top of the window did the stone fall?    m

  A rock is dropped from a6z/ 1wp nf-ckl7h0pb n sea cliff, and the sound of it striking the ocean is heard 3 wk z 7l0b1phfpn-c/n6.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for ae2 m-.i72o6 wfhg gnfh hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water strikew67 fg2hifn2gmh-o .ing 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 speerxyf(/56 v :ojf+/odxg7hvj pd of 12.0 m/s from the edge of a clix+g o f:y/v5vdjf 6( j7hp/rxoff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upjdo q/9)ry2tz iv.0c pward by a window 28 m above the street with a verticovd/ . p )y0i2t9rjzqcal speed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a functi-r+g (f6ye3q: cpih8tznf r )uon of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constcni:hru3g (t zrff+y )6 8e-pqant? (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 straight tunnel as a/ xgys l7jp f qy8z+to.g7hp/yd7s 7f7 function of time is plotted in Fig. 2–28. What is 7 f p 7.+od8htf qgjl7/x s/77syypgyzits 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 acced* :3vabojf)elerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the ge b*:)3od jveafars.)
(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 Probl r c/jx*ad5/mxdfvzp +*i0lg,em (Fig. 2–35) whexp* imd50jlv*g+ca zdrx/f,/ n it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object2u5 y5n: jkjfa traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph forrz 9ly 9h+rd0k the object whose displacement as a function of t9kz0r+ yl9dr hime is given by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of ift )wcr/mr0x1 pt6 g7y- nqbi9hs6 w5an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions fo6xh 7wiptry 0c r6i-)t9gn1 sb/wq5mfr the time interval from C to D.

  A person jumps from a fourth-story windk x:f50jwa p7.pbc j4dow 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before c7 pdfkjja wb4c:. p5x0oming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth k fkh r-9z4lg/what it is on Eart- /kfk4ghrz l9h. 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-shoulder seat blfqy8 i+ztt83elt has a good chance of fy8 +tlz38qti surviving 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 w9+ 7zoawjmh. on a bridge, 12 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 the truck is 1.5 m wm haw+jo97z. 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 front-end collisions by haulinmw5t2 fex/l1uo5 r kk;g them up on a crane and droppkowfu2/l51 k m;e r5xting them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels ,t.7gr4zofpw; t p (0kumob k6about $10^9\,km$ 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 accel+e. 4lh k-dkqgeration 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 speed of the last car as it passes the worker? (See Fig. 2–38.) h4dk le qg-k.+   m/s

  A person jumps off a diving board 4.0 m above the s 9qq:8yqq8ie8dx 63 lqu3uhjwater’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estd6 q88x u8:3ilusqhqj9qq 3eyimate 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 neceszq m)2dm51- 2esgxdc w*)gu zvxrv6+tsary to balance the average speed of a train against the gtu *x5ve62s+zc mr v1q2mxdd-z)w )gdistance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall v5dg4 d*iut c -six*l2straight 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 2 iv-sxd*lc*iu4dgt 5takes 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 strikes a ball is planx.k, iwfb7;sd2mhz n2cef9v ;ned 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 w.2;cn9e ;v 7iffzd,xbk h2msfrom 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 speed of 6.g;0x+;w5q-rplgp f qi0 m/s Just as an empty box calpr-xq5 gf +gp0i;wq;r 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 stone is d,t.1up:h a4u vuwpb0qropped 1.50 s later. How far apart are the stones :,.ubt0qa p w up4h1uvwhen the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average snys*+b5r b b a,q9lv(200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be mbnsy9q v,bl*ra sb(5+aintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves ati 4o5ufvvrf * 1rm2cf5 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average accelerv54r*vfc5ou ffrmi 21ation (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are plays( 9lgsdsv dni18ev8 8ing on two trampolines. The first child can bounce up one-and-a-half vne 8gv8(si89ds s1dltimes 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/w/km2(fjoa wa+g vo)j2 a ht+ overtakes a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the trai2a fkw (a /o+jw /)a+mjg2othvn’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 a baseball with a speed of 44 m/s In throwing the bas * )kdc w/ttw+q.ex xowh2m *ceavc73.eball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it t7*wxhmv+tde/ cc)q3c2 kae *w..ow xis released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an aldsp- aa *k2e:cceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each inters2p z we1.pjz gz 848bb,ym+eofection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed lizpwb m41o8g ,z2feypj8.z b e+mit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a cn:hxhk; q or c( 5m,q9tf99sljxx/ow/onstant 120 km/h takes off in hot pursuit. The police officer catches up to the spee/ 5x9frh onm9wsl; cqk(x : oth/qj9x,der 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 ro 0 bdp10dk+klqof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the tlk k1qd 00+pdbwo 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 vertically up at the h3 uphtgu9l m.q)gd-5same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12t- pg3guhm)u dlq.9h5 th-floor balcony 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 free vg wj;):yhm4r-falling parachutist to fall from a plane at 3200 m to an altitude of 350 mjh rv)gw :my4;, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers throcl 97agad: m1kugh 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 apa:17c9gamd ka lrt, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertic;t2:vy:eke i 6 hocjt4cz5k*dally at a speed 1.5 times faster than Joe can. How many times highe*jec6 etc4dkkhi:25 ;zto: vyr will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top ofahye07tu5 in ( a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below.uet 7y0 h(ia5n 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 askce n3wjb 8wv;:ed to find the height of a particular building using a barometer. Instead of using the barometer as an altitude-measurijc8b ;nwvew: 3ng device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the3)ouj* cpqc 3e position vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has c*cj3e )opq3uthe 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?