Does a car speedometer measurei ).h j7upy.se speed, velocity, or both?

Can an object have a varying speed if its velocityw k4sn ox+iq.knu :w.; is constant? If yes, give exampl.uo.w i;k4x kqw:n+snes.

When an object moves with constant velocity, does q)g;2pu za 8vl3 y0dsmits average velocity during any3s8 quzm20)agl;vp dy time interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible foo;3;m,r jiffg;2 z5afkfu :o / fzli(kr the car with the greatest speed crossing the finish line to lose the race? Explain5kl:z;(gi fuz,3 mof;rijaf;fo2k f/.

If one object has a greater speed than a second 2:lao2xbwgmd 4it+5 ii y:k:tobject, does the first necessarily have a greater acceleration? Explain,2+l5x m 2kgtioiw:aiy: tbd :4 using examples.

Compare the acceleration of vsro-stkr 3a/4t3 w:u a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 14 a-/t3: utksrsv3o rw0km/h in the same time.

Can an object have a northward velocity and a southward acceleration? Explain.iq-r0 2hfa)a qaqcfdl0ne3gvj )+ r8 9

Can the velocity of an object be nqstlv6 .0zu-/gtcv 1iegative when its acceleration is positive? What0 - vu/lstczq.v g16ti about vice versa?

Give an example where both the velocity mn1afx -, q5uuand acceleration are negative.

Two cars emerge sideio0p cs nx;v )bf1o21g7/a7y l2c gkxr by side from a tunnel. Car A is traveling with a speed of 60km/h any 1bl)/ x7vs0;rxg2ngpco of2ic7ka1d 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 reasoning.

Can an object be increasing in speed as its mp*q(dnsc2 4 +ikuj*k acceleration decreases? If so, give an exank4cj*+m *pd2i u (skqmple. If not, explain.

A baseball player hits a foul ball stra 3mg3sp o2el1pi74jhfight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will o1 4l3ps2j3eipg7mh fthe ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happenpnd5 +/yg(v9s sk a;iying to its acceleration due to gravity — does it increase, decrease, or stay thviy a ss9kd+gn;( p/5ye same?

How would you estimate the maximum height you could throw afdic +3(viee:t*sn* e ball vertically upward? How would you estimate the maxim*is* ( 3i ev:dnfctee+um speed you could give it?

You travel from point A to point B in a car moving atsq omkl1)n8 n9h745yg.sld2,u sjhir a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed ofhslqd o)m9gi7s4y.nusjhl 1 kn2 5 r8, 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstratp;708jq g c(+ury g5quqel (taion, a 3.0-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 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 ij;pl(8q+uau re57 (g0qgct qyncrease 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 a1x c) 94odnayucceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a tado1a9)nyucx4 ble?

An object that is thrown vertically upward will return tk2.wsiae4s 6qo its original position with the same speed as it had initially if air resistance is negligible. Ife2q.s6i s4wak 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 jw: v p2iap*8ynonzero acceleration at the same time? Give :y 8ijv*2pawp examples.

Can an object have zeroo: lna9v:p.es acceleration and nonzero velocity at the same time? Give eapn.9 :s eol:vxamples.

Describe in words the motion plozgwvpjr6 ln tqkl0y, 0z+y*(- tted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to( v*0 pw6z y0z-jrk+qly ,lgnt duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object grv j9 q, h;w5)fy1hpnwoc;5 atcaphed in Fig. 2–29.

  What must be your car’s average jo tm,y9iiz/ s ce7/;y7h:mfospeed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does i7bsax0ezdnv0bg7*;jg*p ap 9 t take to fly 15 km?    h

  If you are driving along a straight road and you look 7w0edl2-q mdw to the side for 2.0 s, how far -7ewm0d2 q dlwdo you travel during this inattentive period?    m

  Convert 35 mi/h to sgzn )j9w-j-b
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves :b if/g/b onw-rgd3*/gr fig r 7dqu h5)f5i4gfrom $x_1$ = 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 steadvuw 1 q) naa(em3,jy5jub;1x dily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h Younjbum , e(av)w15jy;du1 qax3 arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds betwe vfvjk(4b9fpy e8i fuou+*5c:en a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in ee5:f+ 4ufyv vkju 8fic9pbo(*ssentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight cgk.rgmk1h ba52z*w dy7 gll51omplete laps around a quarter-mile track in a total time of 12.5 min. C5 1r lk zaggl5hg.*dw1mk 7by2alculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 1fsna:) n+o9hx16 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calculahf+xos a: nn9)te
(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 otp3ydzs40hc + wher on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are ins+dc0pz y34hwitially 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 traveling How long willsr1ct4j1 s 6h cpa5k6p+ brt1zbc 31ne it take the cbs16k4+ cs5jtztprc1 b13rce1phna 6 ar to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 kqs 6bhif/od)( m/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 28s q(f/biodh )600 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 spee hw ;w4dg0dio(jh+mry.ybqa:- 0:izad 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-hou.ymd-+ wbzhjo h( agqr::y;0 4wa0iidr lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant s ht y5 ut:vg-7vj r*p(ji:o;g 2g;xgklpeed 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 isxg ttggjr(p jv 5:l2 h* ;o-i;u:7gyvk the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its aver4 d8/ 8rdgocwp, mt3tyage accelerad3ty8cpwg/4d,r t 8 omtion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acceleratio ,hg;er3h6rv 58tzqlz ea*rs*nrrz g* 6ees,a3vhhz* ql8 5tr;
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particularmkzs7obr48:7fdl : nv automobile is capable of an acceleration of abou87kd:4m 7 z slfbv:ront $1.6 m/s^2$ 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. If+aynih s,-7z z it then brakes and comes to a stop - + iyz7a,zshnin 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 in a s3q wbrb3t nr9)traight line, is given as a function of time in the following Table. Estimate (a) its velocity an3 )3w9rrqbbtn d (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 mdgfz g l-q1l k3kmn3u ) tiaus88)v1(m/s in 6.0 s. What was its acceleration? How far did it trave 1uml1v3su8a g 3-k8i (km)zntg ldq)fl in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distxi8*y)m;lied.h :5x uzlra, jance of 85 m. What was its acceleration, assumed consta)uih8l.e,i z:dl*mr; y axjx 5nt?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long7lhgqha.yz *qf la5-ea- +z4h(bw2ph a runway is neededh qah54 ay q- ahz*e27( .h-gwzp+llbf if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can bursz 7;9yjx kb -*sc -2f8t9dpkahvgsjp;t out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleratpfvt -ybhpzc7;k 2*j gkjs d-89ax ;9sion 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. Hrgt uwfb2: 4ts 61c2fhow far did it thfbu:trwt6 fcg2 24s1 ravel in that time?    m

  In coming to a stop, a car leavd drn )l16g3a3k ejb3nf:v1qqtmko2 7es skid marks 92 m long on the highway. Assuming a k nlbv6oj3k1qadr 1)3 dgen23mq:7f t deceleration 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 fros9zde0-p7kin nt end of the car compresses and the d np-ez0ks9i7d river comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 ll9;h x:vs(pfd n,e:kkm/h and human reaction time of 1.0 s, for an acceleration(elfd vn;kp l ,x:sh:9
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation forzq7kbrj wo* (5ush3/;q pkg,:k- fw ne the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver looks for w8 s1a .g+cqclan opportunity to pass, guessing that his cwccsa 8gl 1q.+ar 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 thc ,-fz)fd. wxd64fuwtx 9pur+e 10,000-m run in less than 30.0 min. After exactly 27.0 min, thwuf xzx ddr6u-f+c,t wp4)f9.ere are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h apprg d. zt hlwxly31 yp*wh-c58s ;xc,9hqoaches 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 side of the intersection (Fig. 2–31). Should she st;hyc d1*cp,x . wgl lhy-5hx wz8q39try 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 grsg 0*nty 8f5jh dyg06 yjv f6hb6jsohg+7:6qy ound below after 3.25 s. How hqytgs yf6n *jyo0j b0djs+8g6 hh:f6 hy75 g6vigh is the cliff?    m

  If a car rolls gently n q;/ qzo6o ;,2rzjjizao)*y+(rhoww($v_0\,=\,0$) 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 k0 l4:dh;i)w6xz st caair 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 vertically upward. With 8ff7ua .q9snnmvkd;2 what speed did he throw it, and what n d;fma8ufsvq7. 9kn2 height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of grx 3uu3kf.qwp2avity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time fro .wufuk3x qp32m t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a heigmv6 wp.z p255usqp9ot48vzi 9rjxd-s ht 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? 4-5 . js8o25t9xqw9u dz pr6mizpvvps[Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the*owgc0l (qi76 y*avey distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown6*a 0oyl7( *vci wgqey by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglecud9am7)+p kellx l,g8s./u xited, show (algebraically) that a ball thrown vertically upward with a spia l eskud.x7u +98/lmxgp),leed $v_0$ 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 ofdkub7 stl,51o 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+g0)kw4gq s0+ m4nue nx unvy2 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 +nqnys0 0gn2x4vm kewu) 4g+uapple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travelr/ e)vkcz* l4j past a window 2.2 m tall (Fig. 2–32). From what hjc lzr4) e/vk*eight above the top of the window did the stone fall?    m

  A rock is dropped from a *,my f5 migx;th25lvnsea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the x ,2ni;vyfhtg l5m5*m cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water.h1 0 l/vlet*rs 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 striking the groul0/rsl*1v th end next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertii4f pqdym mt)la b)75/kpfa++cally upward with a speed of 12.0 m/s from the edge of a cliff 7mif4 ft) pap/)qa kl7+m+dby 50.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m abovo:yerx2rj;z ,qv1c v+e the street with a vertical speed of 13 m/s If the ball was thrown f1,vqr2o vjc;e :x+zyr rom 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 vel7-2kwmg(*la o,bveum(qk:y socity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration grea( -uesm2q :myk ,low*avkbg(7test?

  The position of a rabbit along a straight tunneq4 1 *dxv82pae cxtlz5l as a function of time is plotted in Fig. 2–28. What is its instantaneou xcl avzt2px81d5* q4es 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 automo w59khae;)ryj 5i yfn:bile can accelerate approximately as shown in the velocity–time graph of fhnya :kw e5jry;9i5) Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Problem8+w 3cqqcde6 wfy d)p+ (Fig. 2–35) cpdc+ q8)ewy3+qfdw 6 when 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 object traveled duringst) g0kf g.,c6ygiew+
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph 9yv0keteud42o p7wxfp-22 gnj-ge6hfor the object whose displacement as a function of tfk26 eg -4oxng7 tpph2vue9djy2- 0 ewime is given by Fig. 2–28.

Figure 2–36 is a position versus time graphm0c2c u .i 66vpoydid3 for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (2u0i o6d .3ydcivm c6pf) 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-ss-qyaw wfe)3 2iz;b.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming yswsq2i ezb ;)a-f-3wto 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 eo ,pnplb377yd w 3,irwhat it is on Earth. If an object is thrown vertically upwa7blri,p 3nwyoe,p 7 d3rd 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-shoulc,wz3s ij,ij c/xn+ e4*) 7lvuqy,c/ vdy ac5nder seat belt has a good chance of surviving a car collisq,/yylw s 7 i/)c ajvvci+e*nn4u,c,dj5cz3 xion if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road beprby 3n47ax) elow, 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 bp)r 4xy3e7nahe 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 front39tw*rrapy7 via p1c( -end collisions by hauling them up on a crane and dr( rrvc* 1tpwpi a93ay7opping 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 hbzraq-3l: f5 travels 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 from res d rh6(bih+n tl+l:c8pt. The front of the train has a speed of 25 m/s when it passes a railway8:rnbh+6l(l h+p tdc i 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 the water’s surface into a deep pohznduj4 r.z 5d ib +d5n hl1j8ue5e6o.ol. The person’s downward motion stops 2.0 m below the surfad 5ln1h.du.oed i rzb eu8j+hnjz5654 ce of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is783mct2 3xtsz6 ec ice necessary to balance the average speed of a train against the distance betweei 6st c278mex3zcce3 tn 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 str2c/ ogvs9rib- -x,wp94chn lwaight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish ipn /-r xslohw -w99v,c2i4bgc s at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball i-y v70vvm a91sc -hejas planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhillv y9aea70v--jmcv s h1, 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 fre j nsolxha51v+,x7*tiight train traveling at a constant speed of 6.0 mnva1 *j xhoxl5i st+7,/s 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 frav bri*2g)6 fd.*n jgyhi;iv9 om the roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a spe2ybng g .6fhrvd;*j9*i iv)iaed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time tri+v eby1m,y2pg(1mgc m al lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last ge12gmpv my( b,m y+c1lap?    km/h

  A bicyclist in the Tour de France crests a mountain paspt- qf.7ugl.4 )sjr2 qu4mitos as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 k.ioft4-mrs p. t gq7uj2u4)lq m/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bous-l5)u1+jo0b p8zlvfo;dj5z2 as n lunce up one-and-a-half times higher than the second ch+5 1loj-sl; f0l u5z)un bjp2oza sdv8ild. 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 1.10pqb;a58ym4 hhvn5db-4 v)q2 jy gcr0;6 ekwox-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 x5;r;4v d-8y avehgjnc2 pymwqkb06b oh)q5 4does 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 thro.lguc y- hnp wm417o3awing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from bg-wp.1l 3cmay4o n 7uhehind 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, frmv j13 *idu/et,10 dm*cvpwk wom rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–z+ox*qy-o gl: 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 fiy-* :qg+zloxorst 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 cons3q*8)cv.ro x7ynt f vstant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, mar)q.8n3f txv yvsc7*o intaining 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.m j yd5(b0 frt-bqu37q00 s after that, a second stone is thrown straight down 5j0b r7 qqtdu(m3f -ybwith 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 verticasd-k 36fep ma/lly up at the same time. The first stone is thrown with an initial velsmdap- 3/6kf eocity 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 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 fre0gjj 8z(u0p)8nk mpefe-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull 8j0 fejk(8 g) 0npmpzuher 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 bus8 n88dgxj.8hzg2f y)3qjw gfrgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, fj8nwx2.qg j) z 88sghfy3gd8 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 vertically at a speed 1.5p5;a2t( kbcq x times faster than Joe can. How many times higher will 2ta kx5pbcq(;Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the z-n/ci., t(yk/ xep fqa*tq/v 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 in your hand. What is the spefeq ,/( t/cv ./n-q*zkaipx yted with which your friend threw the ball?    m/s

  Two students are asked to find the height of a pa1y1nc78 tzas,bq rzsw;e- 4rarticular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its f47 -rzcn;qb eyst,8zra 11aswall. 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 bicyd,9u*oasn6 zm:xtg j//d q.micles, 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 omn d: ,.q6gstjz* /adiu9x/m(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?