Does a car speedometer measure speed, velocity)h1h,cavhr.1 s d krq6m8ljg-, or both?

Can an object have a varying speed if its velocity is constanh.k2u. j 4qdnmt? If yes, give exampd.kn.u2mhjq4 les.

When an object moves w zlyz8b h3bd31ith constant velocity, does its average velocity during any time interval differ from its instantaneous velocity at any instant?bzb1y 8lh 3d3z

In drag racing, is it possib e.41fcbaw-mtle for the car with the greatest speed crossing the finish line to lose the race? Explaiw-b4mf atc.1e n.

If one object has a greater speed than a second object, does the fi:2zwce2 ec3+xv +dcf3pjtydko 9:-w xrst necessarily have a grw :zy3w3+t+po -fxc2vc:c 2ej9xkde deater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accek /dc .3kzzjf:lerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 3 zkj./dc zkf:10km/h in the same time.

Can an object have a northward velocityw:// :jsd bfn3h 5nbup and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is y.w 49kw;drnlpositive? What about vice vers4.lw 9wn r;ykda?

Give an example where both the velocity and accele.i6/t sh9fem3hkikr( ration are negative.

Two cars emerge side by side from a tunnel. Chz+g dwhl(-djb)h 9 o-ar A is traveling with a speed of 60km/h and has an acceleg bhdlz 9( +-hdh-w)ojration 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 sgx.u+4q+c;y)y x-ny loakvqd u36to3peed as its acceleration decreases? If so, give an example. If not) 3c+xlqov6out a kgnyy -3;q+4dyxu., explain.

A baseball player hits a foul ball straight u- sqhd2h7h8zz7l1yvl p into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catlhlqh1 2z7dsv-h8 y7 zcher catches it?

As a freely falling object speeds up, what is happej ,:ej 5h.hlqgning to its acceleration due to gravity — does it increase, decrease, ohe .jjh:,5gq lr stay the same?

How would you estimate the maximum height you could throw a ball verticallpur dtj -.iv j1j.gh0)y upwa gt.. huj 1)ijvdjp-r0rd? How would you estimate the maximum speed you could give it?

You travel from point A to pxf7sx 0xji;r *oint B in a car moving at a constant speed of Then you travel the same distance from point B to anotheri 7xf; 0*xsxrj 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-long v)7dbuo b+qswnpcv kz6- bx 59+ertical 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? Wilpq6xsk bu 5 cvb7 -wdn+z+bo9)l the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rock 4 m07lvg-:( otf,ye6w x(t3l lnjdc safalling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way,e(mtc 4-sjt6vloan y l0 fdgw3:x,l7( a dish resting on a table?

An object that is thrown vertically upward will returf0 c)2-yw sn )klaa2zyer1z(ma we91xn to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motione (fka)a12y 0lzx ywmcz1r-wasn 29e).]

Can an object have zero velocity and nonzero acceleration at the same time? Giv /x;r q 4+lj 90tyiq0cinnme0te exae/y4;qciqn ljxr9nti0 0 0+ tmmples.

Can an object have zero acceleratio/zi-ynhja0(eivd1 , an and nonzero velocity at the same time? Give eni/,zeva(ayj10d hi -xamples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. hso2hof/w)q wsn32(s [Hint: First try to duplicate the motion p sw2oh)o/(s n32hwsqflotted by walking or moving your hand.]

Describe in words the motion +gds;grcdlt wz6:jt47)l 8vk of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order9.yk+ ma xs)n4(zoub sldkt2( to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it / ,i.;nr r5ppq0 dfedi d(m,sjtake to fly 15 km?    h

  If you are driving along a2-*boau.( ex*kr a1gm msp *rl straight road and you look to the side for 2.0 s, how far do you travel *a-up*m r.g*ae( kb2o1lxrmsduring this inattentive period?    m

  Convert 35 mi/h to z3cxeq26 g;fq
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fb(m; ezbtwo;4d.co mu drj-24rom $x_1$ = 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 the bv,*dabak vg(j(*bo 1n begins to rain and you slow to 65 km/h You arrive home after dri(k,bda1o*bavj( g* b vving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a l .m48k ;v jw3attzzel7 b zb.agz5j2d,ightning flash and the following thun.5 8 w.z de7z2jajb4;z3kat zl,mvtgbder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quartemd* xw( ds(.0rz y4akvr-mile track in a total time of 12a 0sw yx4d(mkzd. v*(r.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straigylk 2jirgjk wlz,4f8yka 8dhv ,7e s:6a.39ljht line, moving 116 m away in 14.0 s. 89zldwjk,h a2skv6j 7 ejy.l f,ri 4kl:ga3y8It 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 parall0c w57a1dvw uzpb7 g-zel tracks. Each has a speed of 95 km/h with respect to the ground. If t1a u0w5z-7bcvwp7 zdghey are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling Hhed h6ra9/fm 7ow long will it take the carrfea mh/76d 9h to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/.lw9x;s8e pnj +m,wdjm/07 jm;lrlknh , and then encounters a tailwind that boosts its speed tr.k 0,/ndj;sm9l+ wxjle lwm;7nj mp8o 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 averageh10*e8 i1 rw iklzhpn;8+tzp2rczx o/ velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followerh;wpki p*x8n21zol rc 1hzt+8/ i 0ezd 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 speed hits the pins at the end o2w,nuwrj(qcq2h82 u r+c3zd yf 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 speed of sound is 340 m/s. rqj2 hzu3w8y(2w rq u2,c+d cn   m/s

  A sports car accelerates from rest to 95 km/h in 6swcty8mb /v et-(8 ,sm bax6)8dr3p4d bce y;k.2 s. What is its average acceleraticybr ); /8yxbts- dt3,k(8v48amc ed6pe bmws on in $m/s^2$ ?    $m/s^2$

  A sprinter acceleratesrg 6-(wxa/bcol,ck. r+wf +ej from rest to 10.0 m/s in 1.35 s. What is her acceleration wbxkr(wf g +/o6a l-,c r+jc.e
(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 acxbu rro1m 1+)iceleration of about riorxm1) +1bu $1.6 m/s^2$ 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 it tmihv1d2up (9 khen brakes and comes to a stop i2 khu(1mvid9p n 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/r((yv kfm883w hxgek from rest at t = 0 and moves in a straight line, is given as a function(kfh3 v8 wm(g xy/8ekr 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 its acceleration? sq,v kfn y7d07How far did it travel in this time? Assume condk7f7n, 0vsq ystant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance b;lo r m;.2od3y a*ok0x;rvuwof 85 m. What was its accelerati;ko3y0ur v ;o2xbwd;mao*lr .on, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runway is n n0*efiw2094f lo8m: jjooeim eeded if the (constanmewnl8o9*foj0 4joe f2 :0m iit) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks h z jlnq30io* *(qj8gyto essentially top speed (of about 11.5 m/s) in the first 15.0 m oq *jlhoni zg(0*qy8j3 f 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 n0f+:qtsxqgm0*7 oxcp0 k ej*of 12.0 m/s to rest in 6.00 s. How far did it travel in thtopf s qen0 ck* 7+xq:g*xm00jat time?    m

  In coming to a stop, a car leavesg)v /tdwe .d bahd;7v.i k5zr* skid marks 92 m long on the highway. Assuming a deceler*5kdrgiev.h 7d.da)/ tzb;wv ation 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 e wi,zqwwk -)6rnd of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in termszkq) 6,wr wiw- 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 spee 4t x648hr b z-nbwll*ww-vv)zd of 95 km/h and human reaction time of 1.0 w8* l-x6l-4vnv trwbz hb4w )zs, for an 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 ca6hj g n7 :efgkgug-u p99riq /qg6n:9hr 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 f xct+ukk7d(xd 3f9ue3or an opportunity to pass, guessing that his car can acdx73 ue(k +ud9kfxt3ccelerate 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 0tac6rm. hpr3zj6sr d2tyf-, exactly 27.0 min, there are still 1100 m to go. tsyard-r6tc ,3jmzr. f2p h06 The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as the nrf/e jt-1ckw :9lh-q traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide.9l/k-wet -nj h:qcf 1r 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 .gi.opb vec+ b)eg3n8cliff. It hits the ground below after 3.25 s. How high ib ni8.gg.v +3pee b)cos the cliff?    m

  If a car rolls gently wl.vk:gk9 zq2o9nn c+ ($v_0\,=\,0$) 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 22629vwf**ms 6bmyo rjrq 69ure m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a balv3+4z n2vich(wimi, dz1vq *p l 3.0 s after throwing it vertically upward. With what speed did he thp 2idvz (wh4q1ncizv*i ,v 3+mrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence ojx q: 9w9 1h3:5bxmm+ x8qzl*audlw xvf gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s 9uwmq9lx j3b*qx8:xh:dm v1 5l+waz x. Ignore air resistance.

A helicopter is ascendingqa**3k y hm:fa;rab l9 vertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a wi fmlar*aqka3y9 ;b: *hndow. 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 travelevye(f+ 4) dakqx cuiu()e6jz/d during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18u)/e(eiv d(c4jqzx yf6ka +) u and 2–21.

If air resistance is neglected, shs9 2rbi/8 tgcfow (algebraically) that a ball thrown vertically upward with a s9/ cb28 iftgrspeed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed of 18.0 m/sl ,jkr x5qmwet6e6+e(
(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 ina ,0ft/ ndzu(f Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 c/(0 dtna f,zufm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. ylxq/ ahrn ;zga;83-l2–32). From what height above the top of 8y3l;;axarg nh/l-z qthe window did the stone fall?    m

  A rock is dropped from a sea 1t1o,/w rlbfgfg8;c 1qbuwinyn;*p5cliff, and the sound of it striking the ocean is heard 3.2 s later. If tht yc;wl ug11,r ;o bw/18 fbn*ipgnqf5e speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. c6r9ttz 8i5 cwYou point the nozzle vertically upward at a height of 1.5 m above t98wczrc i5 6tthe 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 edge of tp.z 4v7nqzk0a cliqvz4 7.n p0kztff 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 upward by a wi-4ikwsr 5fnwy3f ud 67ndow 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the strffs7nuik6 rw54d3-wy eet,
(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. (wgn7o9ixu6q3cp z5r rk2(c8b 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 greates bz 327rrpu 9k(wnxc qco8gi65t?

  The position of a rabbit along a straight tunnel as a function of time is p11k5l3vxylns *x7d d,yqd6+ac zpg/q lotted in Fig. 2–28. What is its instantaneousasq xx dq61 5nz,1ylc3vykd/pgl +d* 7 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 acceleuba*3 fyan(z836x dpae4 4 eqwrate approximately as shown in the velocity–time graph of Fig. 2–35. (The sh3ufa* d 6(w zy83eapxqn4eba4ort 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 b962k5n*ejpbxowf h:ir o l4+car in the previous Problem (Fig. 2–35) when2x ke:o9jrwb4+ o5pb h6ln if* 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 8-p6ynsv he6dwo x1u, object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a functn-hp7h2.rogxi nzle7b0lt.i 8n5 8 ubion of time is gi bbho7g2xrn p.-ntlin h0ez8ul. 7 i85ven by Fig. 2–28.

Figure 2–36 is a position versus timemb1 b )6u xyd-bppdrti5(53p k graph for the motion of an object along the x axis. Consider themxrd)p5u 6ppkytbi-5( bb 13d 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 15.0 m above a firefighter75y v jbs9fe3bqdya q;a42c g4’s safety net. The survivor stretchesbyq ef;d 4ca32j954s yg vaqb7 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 4koy vg -)vvjzy(-e3p about one-sixth what it is on Earth. Ifzgv-( vpy )43k-oeyjv 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 belt rl6 62wly8wzf has a good chance of surviving a car collision lz2w 8 r6f6lywif 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 belowszj9r sl:0smev8d39fa *nd .ix ;s/ ni, and his pursuers are getting too close for comfort. He spots a flatbe sva0x r: nsdij.i l9f89snm*z;es3d/d 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 it?    poles

  Suppose a car manufacturer tested its cars for fron zlf) y6hwks80t-end collisions by hauling them up onk)sh6f zl 80yw a crane and dropping 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 aboutz55yn3i1(g 1n 4puc9n hs:o;u nxfcbw $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begindl09du8y cny +s uniform acceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 0d8u n9ycd l+y180 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 pgpooh 9 zyq3e4qwt2+ ,)gb )upool. Th 3, t)y2ewpp)gu9b q 4ogo+qhze person’s downward motion stops 2.0 m below the surface 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 systems:pp-dz,vu(l g 1nq g), it is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speedu-g(1,spqgd : zp n)lv. 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 straight dow+89r+rel;tb 6va o6 bmjk0omfn 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 performmf;0a6r+j6k e+ o9b8tob r vml 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 s1(qb zzutd0t:d/b2utj 95u .5obvmv,vcb 7tl o 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 downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the c5:2( uzo9 b b1d5utzqtbv7mt0l. vu,vtj/db 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 travelinuttzbu7j6 gy8 850lic g at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest t7 856u8ybig jutc0zland 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 xwb-vu/08jfyq 0 6..cunxja l36uqbv 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 rej -0.xw ub/j6 uycl03 xa.qnuvfqbv68ached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trial lastifxcj2u49h2i(,zjodr u 9lbv2a8 9h hdng ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the lasvxzi2u899c4 ah, 2(uo hj dljb drfh92t lap?    km/h

  A bicyclist in the Tour de France crests a mou lf7ttds b0rg32 rl)cwl4;5jfntain pass as he moves at 18 km/h . At the bottom, 4.0 kmtj4d5;bw3f2rlt7 s )lc0fgrl farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounce up on3oxgitl1 n,x7s +7 lsw m.qz9ie-and-a-half times higher than the second child. The initial speed up oflstz 1+3xxl77ii ng wq9o,m s. the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long traq7 rmp 2( w 6f lid:v8b9ascv*df2o+mcin traveling in the same direction on a track parallel to the road. If the tr8o cs+acfpr v 9lfw i(:2m6v2*7 bqddmain’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 baseyjbhxe: 5w xom/p1-h-ivng,2(hqj :bball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball thrwby(-x b,1gpqj:5xiem jo: v2 hhn-h /ough a displacement of about 3.5 m, from 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 acceleration of)/z f)lafq - rnd/i(uu $3.2 m/s^2$ 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 intersqo(4 ftzk0x4wohj. b62w; as qection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first inters4zho kbf;(s.4x 0 qtwq6j2oawection, 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 -cd4epm(ees1d d.cgj 3w4t/u at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 7e-jd.eegcs/ d u1d4tp3w m4 (c50 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 ofmt 140j9 / ,0plfe fkhxm(rplf a building; 2.00 s after that, a second stone ip mte9j 1,0/fmp0 kl4r xflf(hs thrown straight 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 u9(k:ene3ijv ) eb m;w :yllpl0p at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second ston v9:w3pbleeymei n:k 0l)lj(;e 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.zao; b8-tb -t2f ;cj3 vhpayn free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, t jyton-tf hb .3b;paavc;-z82he air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to s 7ti3ik1*e8s w fb-6ui(r7yg zhgoeg/end the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? wbi1e*sgi yht7ei8f6( zuk7g3/gro-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 speepdmh.+:f / xipd 1.5 times faster than Joe can. How many times higher w.p pi dm+x/hf:ill Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friendg,ek jc bs)9bhw 5w9zr dmc1+, 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. Your friend then picks up the ball and throws it up to you5 ,wrs+jdeb9ghc1 b,w 9 )kcmz, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find th o3wc*pl,p0g: +r gwahe height of a particular 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 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 bui30 w*wop,grp +c:a hgllding’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. silgai;2ycm:,d rb3 5 (a) Is there anys, di3 aml2:bigy ;r5c instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?