Does a car speedometer measure speed, ve1yix6 xu5ct*e/*hvcf locity, or both?

Can an object have a varying speed if its velocity is constant? If yes, g br(s0n9a+edw ive examplbs( ae9+0drn wes.

When an object moves wi*i9 yg 4 sadwi(cmj-ive(i-e(:isb:rth constant velocity, does its average velocity during any time interval differ from its instane cdyij((- s ais b i4ii:gw(:9m-rve*taneous velocity at any instant?

In drag racing, is it possible for the ca)i;kn im q)k5br with the greatest speed crossing the finish line to lose the r)5ik bnm)kq; iace? Explain.

If one object has a greateuwo-y3ja t71a r speed than a second object, does the first necessarily have a greater acceleration? Expltoa-7w1ju3y aain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to-er;s pm a3)tz 90km/h with the accm s 3)rtzepa;-eleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and ljkvtdmib ,dm 7v* dp47n6f;5 a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration ih*s.clujla c5 ) hza,*s positive? What cj,lhluzch a5)s* *.aabout vice versa?

Give an example where both en/ey6 dlwlfkzoo+7,;3-wg ii9 i1 gwthe velocity and acceleration are negative.

Two cars emerge side by side fr0jp8w9f q noq+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 tunne qq o8fwpj+n09l? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases)8omw*lj7gc e7x x8(5eee uxe? If so, give an exampleg)lxxceemw 8uj8 *( ee7xoe57. If not, explain.

A baseball player hits a foul ball straight up into the air. It leaves(mn z40kurdya/so4 x9 the bat with a speed of 120km/h . In the nm4(4k xzrs 0u/doya9absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds uplnh*l zj2: el3 ,wml7o, what is happening to its acceleration due to gravity — does it inc,3zl l*wemno: l27jl hrease, decrease, or stay the same?

How would you estimate the maximum height you cnkm*o), u+ pub+2lhf0 q m.qqkould throw a ball vertically upward? How would you estimate the maximum speed you could qo *+,p0 u )lk+ mun2qmkq.bhfgive it?

You travel from point A to point B in a car moving at a constant-s*aa +/rb,wri3ofd z speed of Then you travel the same distance from point B to another point C, moving at a constant speed ofrf+,ob/d aw3isa r- z* 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-mdybb85 gd5b-axi(9xxb0g k- x -long vertical string with ten bolts tied to it at equk8 xx 5xb-b5g0ixa9 -dbbdyg( al 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 the clinks occur at equal intervals?

Which one of these motions is )w8j jge+wp8z not at constant acceleration: a rock falling from a z)8wg wejj +8pcliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward wiln9v .poc 4da(ll return to its original position with the same speed as it had initially if air resistance is negli p9d. avocn4l(gible. 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 velocity and,0gli+kg3 o 9cxqq)lbv,: xvq(is p8l nonzero acceleration at the same time? Give examplespv(+q9 g x 3o) 8xc:0qlbgli,qlski,v.

Can an object have zero acceleration andf02s-vou37lklo w8w9 vgrg6f nonzero velocity at the same time? Give exampvw7k 2 wo6gosf803lul-v rg9fles.

Describe in words the motion plotted in Fig. 2–28 in gin8va ud0mc4 ,qo/ y3terms of v, a, etc. [Hint: First try to dupli3 dic80an/qymv4ou g ,cate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in Fig. ym,potl3jj*67 q *sy b2–29.

  What must be your car’s average speed in order to travel 235 km in 3.25 h? 0v,suqg2-2wv w9ep ff   km/h

  A bird can fly 25 km/h How long do1l.tn vlib p9)3x pnp s4 (ff8fm6eoy7es it take to fly 15 km?    h

  If you are driving along a straight qo,nik8s6t,cc. ayuu ser1: /road and you look to the side for 2.0 s, how far do you travel during this inattentive periodak ec8,qct1:youis rsnu ,6/ .?    m

  Convert 35 mi/h to ef4 sl0r sopn*o74wh ec94cz*
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fr3 w/te.ildro8y f2:v rom $x_1$ = 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 f 9wq vt: vqusht,4b+o5or 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours a ,9oqvvqu4tt5: hsbw+nd 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 lightning flash andopel +3q tr-v*d20b8fhshu c* the following thunder ge3dv oub-hp0q *crsl8+*fht2ives 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 laps around a quarter-o zuuu+we; 33omile track in a total time of 12.5 min. Calculaou u e;3+o3wuzte
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a 9ebwll8z 35 ;da9:xfvb rfz3e straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway backlxw fee8 bzlf5vzb 3ra 9d:39; 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 approachybiv y5kkt)y6kvi:y l+ hz30* each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, hbz3yt *0ki6v)yk k vy:5y +lihow 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 tru/xv0)d7 rrk gv 676s.jf8qkarhpd/swck traveling How long will it take the car to hr.)xfk 7 gk/80pq6sdsra/vdj 6 rw7 vreach the truck?    s

  An airplane travels 3i.n m(1v oalb nv579ho100 km at a speed of 790 km/h , and then encounters a tailwnmaloho ( vb.n1i 7v59ind that boosts its speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and a mpxc+5rhsh2 1nx596vn yz5wqverage velocity of a complete round-trip in which the outgoinz hr+ 2xyw9qnh65smv5pxnc51 g 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant sped 6. zf4ml;xseed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The spee.z;fml4x d s6ed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 3zar-u- v5c64 feophxs. What is its average acceo -uc 36f-veazp5h4r xleration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s wjidq5* * uq+rcp,a j2in 1.35 s. What is her acceleration *,5jda j qq2r*piwc+ u
(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 acceleratiov/e kmz fgjd2 x q 0at5d-yyy,;2ys63kxcd f9;n of abou0ded sgfx6 ,y;-z2 y t52 ydq/ cv3xk9j;mfyakt $1.6 m/s^2$ 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 5m y(5 ul dli4kf*v1 voj pwil4cv30p;4.0 s. If it then brakes andpc vdl5jvyo4 l*i;k uwf (i1v3l4pm40 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 starts from rest at t = 0 and moves xpbt .twb8i/8ca(/cx 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 and on a graphtitxpa c c.w8/bbx8( /.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was iyx97hb;y z;p (e4mdshk q8k s;ts acceleration? How far did it trav;9;dhsq yh7spkek(b;z 4 xy8mel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance ow1ds d a17z,msf 85 m. What was its acceleration, asss 7zd1m ws1a,dumed constant?    $m/s^2$

  A light plane must reach a speed of 3398fehbazy u23c 3u rl) m/s for takeoff. How long a runway is needed if t2 a38lhbc urey3z)f9uhe (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocksh7hm h+bb yw/c 9c*u6q to essentially top speed (of about 11.uwbhb9+c * h7q/ c6yhm5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach 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. Houxi h:g+:q0mvo3y1yexj/ 1rl mmq -3qw far did it travel in that time?r-m3q xe0+/igyu qo1 :3lvy1qmjm: xh    m

  In coming to a stop, a car leaves skid marks 9hgi( . )ly3,z44m5ow sdlvtyo-(eq up2 m long on the highway. Assuming a deceolgdy)( wvt35p 4.4qyz s,hlem-iuo(leration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end ofqnk o334k,h kr the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisik343 qokr, khn 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 car6t7e1b e 5gg,)ukghd k with an initial speed of 95 km/h and human reaction time of 1.0 s, for an accele5u t hk) k76,1ggedbgeration
(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 car is r:9,x0 uwytzi$d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The c-n :z bmhn::oexsi 2twb3x7(sar’s driver looks for an opportunity to pass, g-nmt3:sbh:o7i zs2x w(e:bxnuessing 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 d6p :g6l/ mcs9wgvsf5a /ega;min. After exactly 27.0 min, there are still 1100 m to go. The runner must then a6/ls wdve96/a:gc 5pa g;sgm fccelerate 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 appr bc u,ah08gf1z9uvb7yoaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near suc fz1yav,08h9bug7b ide 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 had 6egzv9o 24jpx6lb2j i79 4qst,pd of a cliff. It hits the ground below after 3.25 s. How high is the cliel6 v49zjx b6sqpiha2j ,op9d724 gtdff?    m

  If a car rolls gentl st-lkio ip ercqup+)7.i;x (/y ($v_0\,=\,0$) 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 speed of 22 m/s *7u--sn3ghu7 w wzjxy
(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 vertically upww+7w8k mlvcmq;; j 9edr,(7 l;n uprk 5gpch/zard. With what speed did he throw it, and what height did ;nmhl p; gk uq kjmcrw(9r p+75/cl zd,;ew8v7it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gra wjf7v m7yg1 )pwmn.c)qi)eu*vity. Draw graphs of (a) its speed and (b) the di))7q.fcmvng uye i p7*1m )jwwstance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertic.0 cug grmn8tlg69;dfally with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [g.0fr6 ;gtlg c8d n9muHint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object fallin4du+-a4sn:hz)x:zv . +tthhn x;eu wzg freely from rest, show that the distance traveled during each successive second in+vtth :z+seh44.dzn;uxnxh :z -uw)acreases 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 isg nyfqk89+u p.4,)2w 7yc pdo iikj2pv neglected, show (algebraically) that a ball thrown vertically upward with a si2p jykpdifn9 p4y+2 o7w,vk ).gu8 cqpeed $v_0$ 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 klmql-.yq7 k; 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*4zft y8/ auhb (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear outzabhyf8 / 4*nes at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–32mt v4 )z4yty(v). From what height above the top of the window did the st(t ymvty 4v4z)one fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocyl2 nzzo;3 m-iean is heard 3.2 s later. If the speed of souniz3y-; zmnl o2d is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You psa 6.cq40bu zyoint the nozzle vertically upward at a height of 1.5 m above thb y.0a6z sc4uqe 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 speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edg- v+ m2n0qt-mvznz +nte of a cliff 70.0 m high 0mn2nv - n+z+z-tqmtv (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 windocxsf (kpwz69p+ z1c.iw 28 m above the street with a vertical speed of 13 m/s If the ball was thrown fr sp6k1(pzz +wc9 .fcixom the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a) At o b51vm 2hq)eowhat time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acce5)mqb1oeh vo2 leration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as ig7xi1d;tx 8mcub; z4 a function of time is plotted 7;dizxu mcix8 ;4 bt1gin Fig. 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 ax fgrc/ tn;0;*hj.hxiccelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in0h*h i;/fxn.g; crxjt 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 acceleratme 1we4mmvu8qi0,ak d; x/dbf3)5t mt ion of the car in the previous Problem (Fig. 2–35) when im wq5,vd1ef0me ;bkmt/ um x3)t8a4dit is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object traveled dugbcc*4 va kaeuzkmjb-l ;x:+6 r12kc,ring
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displal1ev9m,prx3 h y ufc-4jlo ;b;flp89+ x3 jvmocement as a function of time is given by Fig.m4blo x8l1;rjjxf-m3,h9 p3 vy v;e +9clup of 2–28.

Figure 2–36 is a position versus time graph for the motion of an object alowspyou h ) 0 v4p-u5xxucxy5mcgq ,+a,.a94 ueng the x axivq4 acx,e.5-us )uy u0oaw5pp mx4cy+h9 gx ,us. 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 for the time interval from C to D.

  A person jumps from a fourth-story window 12 am 6dp)cc1ku7w2xku 5.0 m above a firefighter’s safety net. The suxdk2mc 61uwk au2c7 p)rvivor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it e:;w+lb tnnq 3smax,2is on Earth. 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 ste,x mn bq+;3w n:a2lvelocity?

  A person who is properly constrained by an over-the-should8mu7xad6p4 nb83, d vry;pgdtfr *f 8ver seat belt has a good chance of surviving a car collision if the deceleration do8r3 br7vux pv8,dd6my8f f*4na d tpg;es 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 a4 nug2l3cq za7 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 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 iau4 zcq723lgnt?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by igxt7qv iyz7zig *q(4vvf8k *sv(3r. hauling them up on a crane and dropping them from a certav.t7sfkq rzzi* (x84 y*i(3iv7gvqvgin 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 travelsyoly3/t7o: s f about $10^9\,km$ 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 ji8oulvec-v* z.r.4efrom rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m*uvc84 zle e.o jr.iv- 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 thew7.jnw waw:m; kp.q6c 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 deceleqw.j:. wnwkw 6 mp7a;cration 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 necessary to balance the a9. 4vfi08tgh3r uidmj verage speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an g .drft4vui 9j38hi0m idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight dow83ekxk xv8 n gt4yj/(kn when diving for fish. Suppkj83v8g/k4 tk xen yx(ose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planned sa )v lrox;npo*ltze3+ yb/ +2lo that the ball will stop within some small distance of the cup, say, 1.0 m longx*abeolr+o t2yl 3l/zv+p n; ) or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a constant speed of 6.00vi0req97 ftm2;vzp. o :xps1utw 9mq m/s Just as an empty box car passes him, the fugitive starts fro07p19q9. s m2m rvu;ifp0wvtt o ezqx:m 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 )q5x o7ali sm1of a high building. A second stone is dropped 1.50 s later. How aqil7)mx5 s1ofar apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must avh.7ets7 3x qm 0tg8bq g+m9k ;lu.icnuerage 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 maintained for g70 tbm;cl h .q+nmug3xu7 8s 9qtek.ithe last lap?    km/h

  A bicyclist in the Tour de France 7lo0a xu6/w+x upn+s9*m 2qq i cexfh/crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 xe7pq/ i9/n*2 uxuo wqh+ 6 0mfxclsa+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 chil6)b3os lm2 jzxd can bounce up one-and-a-half times higher2 os)xbjl3 mz6 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 travelin 09p2fli6 j ss+egm24v48l k*coocuylg 95 km/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 fucjglml408o4 cvpsk9+2 l6s*yoif e2 ar 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 spee ubhwol1+w.3kd of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, fu lw bh3wko1+.rom behind the body to the point where it is 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 acceler8jr/kx(fp ;nrj2c,zes 8 x1 hiation of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has ,5jb4 uia6 w hb+et id/x6vy.ya traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west aedaw,y4y v t/ 6ui5i6+ jbbh.xt the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 120 km)0e 4 +o4sr pqmjbt1sh/h takes off in hot pursuit. The police officer j+ pohq4)41b m0ersts catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s after that, a sec8gfv4 i7punj- ond stone is thrown straight j ifgn 87vu4p-down with 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 thrown vertically up at the same time. The first stone is thrh;j4m8ss ncw ;f*zs 6fown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone cm *ws8 ff;;sj ns46zhbe 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 sr rctg (j:c8h d,lm+l77(g nftake a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? Whatrmg7( g 8crsfjtln hd:,7lc(+ 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 burger e,fu3;3ciq1x kfp1 8 f/gnbces through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to coo/f kgc,c p fibq1ue 31f8;xe3nk, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball verz*js4bk mg*)kavxx 8+tically at a speed 1.5 times faster than Joe can. How many times higher will Bill’s 4kxk8 gm) v+*xsj a*zbball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on y1jv.4iun0) ,x e h92kkjkgfhthe ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in2vjhgjkh,y xk .f1)0 n iku49e 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 bulh -30xlu v85 qt.m1ryz: sd: hf4yccqilding using a barometer. Instead of using the barometer as an altitude-measuring device, they takr.f-ym0 zc3 dlvt81xhs l: :q5yu4cqh e it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (ampt42a v; *ezp) 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 bicy;2 app4evztm* cle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?