Does a car speedometer measure 2 ys*vlogo0k tf5uchg0-:z2z speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give 7wc6lo ) s;0go,cb2mr br3;tc2 cdo eu(at,uzexamples(b c,ge0t d u7,ab 62cuws )2oclc;o;mr3ozrt.

When an object moves gnvifz0u 2;0mrua .,b3xg)hn hs co,-with constant velocity, does its average velocity during any time interval differ from its insta-guru,fnv;bc 3)20oh a is h ,0gm.nxzntaneous velocity at any instant?

In drag racing, is it possible for theuxgmh61 b) 6f +oibsh6 car with the greatest speed crossing the bhb)fgm6 oxh +s1i6 6ufinish line to lose the race? Explain.

If one object has a greater speed than a second objev(c-1. onwzst( n*c sgct, does the first necessarily have a greater accelgcwn -vcso( .*(n1 zsteration? Explain, using examples.

Compare the acceleration of a)sqh(sht*ayu*v2 /r6 z /botl motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accel/q oay2t(*z) l*/ tbhur6vhs serates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acchf2i;j p 6wng4b v-ou,eleration? Explain.

Can the velocity of an object be negatrf 5 9+efkb;euqdoh--ive when its acceleration is positive? What about v+e k u5-frqhfo;b9e-dice versa?

Give an example where both the velocity an mv:1kd :eiu+v0*sqy td acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling wit9 h:ka61wb j6s3lap csh a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed ofwka 6ls h93: 1sjc6pab 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 acceleraaz+6- jcs jci3 m1i)potion decreases? If so, give an example. If not, 3i16- c imp)jjasz+co explain.

A baseball player hits a foul ball straight up into the air. It leavefs /a.l,y;hhq s the bat with ;qhal/fy, .h sa speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acq5h) ctf l/a6uceleration due to gravity — does it5uah/6 lqtf) c increase, decrease, or stay the same?

How would you estimate the m p*px0sgm c)(e rnn*c:aczz 29bt13craximum height you could throw a ball vertically upward? How would you estimate the maximu3: bnr(2m ng*s1pc0czrpct )z*xae c9m speed you could give it?

You travel from point A to point B in a4osn -p:y8)2dfwe1dw (6m5sh yt somm car moving at a constant speed of Then you travel the same distance from point B to anothe5dmh-62ts wy e4 f8wd1:ms(y)ompo snr 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 vertical string with3vq9piq,f-/. cno cqn ten bolts tied to it at equal intervals is dropqivq c9,3oq . n/cfn-pped 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 not at constandeash; q 442ko1;a9/ phivqs pt acceleration: a rock falling from a cliff, an elevator moving fro ;4is2 d9q o41k/qp; aphhsavem 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 will return to its originalm4ngo -:d yj:d 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 accedoym:dn4 -j :gleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleratike3fni82 lug4 on at the same time? Give e3i8luk 42genfxamples.

Can an object have zero acceleration and nonzei1 (nicezbsm.5wx2u:k fl.f :9ofxirslv 3 22 ro velocity at the same time? Give exxlf u:ssi2.1inizb2(o2l. 3 w c fk9 mvfre:5xamples.

Describe in words thgk qr+4+iw xx zt/)7oje motion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted btk+wx xg)+ji7q4ro /zy walking or moving your hand.]

Describe in words the motionguei yx4 v,y+q9z77pl of the object graphed in Fig. 2–29.

  What must be your car’sab 4k7tlnf5x6 average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How longy9sd)u 4.hlgf does it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 lw;g8o0/ gmbcs, how far do you travel during thgm wl; co/80gbis inattentive period?    m

  Convert 35 mi/h to k,b1 ovb 9h:pa
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from l/dt .mc(l hwb2x*3;nnvl1i c$x_1$ = 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.g;az(g(u (x ul It then begins to rain and you slow to 65 km/h You arrizx;u gug((la (ve 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, e 5bl4z, zca dg9y(dt8ddbb,:fvery five seconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives izbd9ta ,5gbyc4d( d :8,fzb dln 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-mile sukp)54z*q li /y+k tktrack in a total time of uq*z kkisky)p4t/5 +l12.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away fropi9w* 7* v5ci5gced ehwc:e4 nm its trainer in a straight line, moving 116 m away in 14.0 s. It then turns c7w9dg :5iece w 4ievcn *5*hpabruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel trackskq5 mru c8wbd67)gn5c. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each ot5g w7 r5bk)8 m6dcunqcher? (See Fig. 2–30).    min

  A car traveling 88 k7awc2.q,st ted+/qzn 4jkw3 fm/h is 110 m behind a truck traveling How long will it take t7 ket.f+ wdjn34s2wazq ,qtc /he car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790zx,zzu2 uf c8m n iadz833x-7h km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the nzxu inm 3fcdx8zu 8h,-z7 3za2ext 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 average velocity of a complete round-trip in wnio w4ylro8) 8hich the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 8lw4oo8 ynr)ikm/h.    km/h

  A bowling ball trave l,t 6(*(n. u2j7t,fp+jpabhrnz*p q9bb bau bling with constant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s at*(rbubb b7pplnf . +qajbnu 2 j (,,tz9h6*pafter the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest t 8;h6ur(ausr go 95 km/h in 6.2 s. What is its average accelera; r ugrus8(ha6tion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 1wzqs/;je9),c as50aag qxm(x0.0 m/s in 1.35 s. What is her acceleration j zm(q;/gewxc),s90 asa5qax
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a p8t* *aaov; 9 jbx0mefn- 1qhcwarticular automobile is capable of an acceleration of abou-a1wvto* fm89; eqbha j 0*nxct $1.6 m/s^2$ 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. ltcp.8 39nbdj5z2 1t gzuod0k If it then brakes and comes to a 5o 2j.dc1tb89u n gdz z3pkl0tstop 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 in a i:srdhnp .81hz)ffu,p2yb * ystraight 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 gru)zy.dhpp 8* nh2 :fi fby,1rsaph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleration? Howy0s5jgsh-cbjqfq5 () far did it travel in this time? Assume constant accel)j(j 0 q5shyc5qbs -fgeration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. W 4jjctyxm5bx0f zt 2o1(h8z;ehat was its accelerbj t0;m12xt jz xf5yc4z( heo8ation, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takntnahz1 x:w2dfu(p ( 1eoff. How long a runway is needed ipwan( txn2:1 h (1zduff the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out *(imn45asv oq of the blocks to essentially top speed (of about 11.5 m/s) in the firs5o iv*4(qnm ast 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 resyp5p ac7 - itsm4hvx./t in 6.00 s. How far did it travel i.4tcsy /m pav5-x7 hipn that time?    m

  In coming to a stop, a car leaves skid marks 92 m long onl(z81ijq pr3i(q u( of the highway. Assuming a decif((3rul(p1o q8ji qz eleration 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 of the car comprsq ,x/(3i o-omwaov wwf5in.d z6 p,/jesses and the driver comes to rest after tdfoj/wo po-3 iw,.5sa,zv /m wxin6q (raveling 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 initialqhu2tc )mxo 0woxy; qm,ac a77p66 n4f speed of 95 km/h and human reaction time of 1.0 s, for an acceleration 2xq ap,7mncyo;660x tcoq)h m4au7 wf
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the 4liffj +/qxjejza 3*0ls40p zstopping 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. Thex j4;i2g ytd.0zcpz6,sof :ydk6 +ljd car’s driver looks for an opportunity to pass, guekfd,0s;y+d24ol6zjj: d cz itxyg.p6ssing 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 -c t1vhph0 0j:ke xfc29)e mm0b .ekzlthe 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1k jm01 h009f) z-chelvexcep.bt:2mk 100 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 v.;nc mpsuo pcx + 0/n8p.l3hbcar at 45 km/h approaches 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). Sl0p; ouv p cxh3c.b.n+ msp8/nhould she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below after 3;1smjfingy 23m/l(x i.25 s. How highn1ms(xyjf /3g ; lmii2 is the cliff?    m

  If a car rolls gentlgf0lx1 *fnq+-9ru pi j+e:xxxy ($v_0\,=\,0$) 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 near6b ,x5-gl xahtly straight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it ve iytvyd*fnv,1 2gi4 i;rtically upward. With what speed did he tyinft ;vv 2ygdi ,4i1*hrow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under thqtyrevc /qjn2 ;s83 dw:h+7togxwl 53 e influence of gravity. Draw graphs of (a) its s8jd lx7v3c:etg wh+ryq5s n;o 2wtq3/peed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically wivgmw)yx3 ; rnd+tji+2th 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? [Hint: The package’s initial speed equals the heli+iw)vx; gy2+t3jmrn dcopter’s.] t =__ s

For an object fallinuvkp5 j2,/wxk,t.)8 uvvxzsrg freely from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers k/pu,jr wxs )8v 5uvtx2.zk,v (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is n/bwljc4x3tx2x r/zf. 6o4sp(tw an8l eglected, show (algebraically) that a ball thrown vertically upward with a spalnws /xj b4w( 8/ot. rl24xt3fcxz6peed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upwrsemzcm v/d338 8 ;p lgvefd58ard with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in Fig. 2–18 (b9vx-,tyf d j)or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the tojtb9-x,d vfy) p.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to txp3ht(..ta hcravel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the w.t( c.xhaht 3pindow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound xu,rd qh1(8c y 2irbe)of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high(c)h u1xde,yibr q8r2 is the cliff? H =    m

  Suppose you adjust youriob qe q4s0u23 garden hose nozzle for a hard stream of water. You point 3is402ebq u qothe nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a s(oaucni m 624ipeed of 12.0 m/s from the edge of a cliff 70.0 m high mo(aun 2c64ii (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 f:5jnt oo 3gd-q8-wtjpass upward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was throwj-q owf-gd3 to8n5:tj n from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a vhm.w 1qcziyfw5/-/ e) 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 z/vewhq1 y.mi-/ 5fw cmagnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of t)z bj (+tefo1oime is plotted in Fig. 2–28+ jt1e)obzfo( . 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 accelerate approximatelc7 i fii*rcv/5t)ipmi eas;,,y as shown in the velocity–time graph of Fig.s7/ ,i ieiv c;,t*m irf5cpia) 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-l( zw:x 9wrr vuonftg 3+h;0r acceleration of the car in the previous Problem (Fig. 2–35) ztx wr-9n+ ;:row0vgh ( u3flrwhen 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 thekv tiz-o+;eo8 0w +unh object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose ;ef3(. vtanucsg r6q8 displacement as a function of time is given by Figcur f;n q6avgts 83(.e. 2–28.

Figure 2–36 is a position versus time gra rpt5cst+d,w *em xz0 secn0f 55*9ehtph 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? (f) Is the acceleration of the object positive or negative? (g) Finally, answe00 m rf,59pehtcenw +5dz ctst*xe5 *sr these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 1c* wg t.d) ue6n*mxh+r5.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig.dtg+r.hue6 n* )w*mxc 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 abo n) q9c6h5pmtwut one-sixth what it is 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 velocq6wh)n 5tc9m pity?

  A person who is properly constrained by an over-the-shoulder seat b 7vq6bpt j2l*celt has a good chance of surviving a car collision if the deceleration does not exceed about 30 “gtcv*q27l6pj b ’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 r2n ; 7dkvzzajb7/ n6nwoad 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 wvanjz7nk 2 n;/dzb76the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by h1f s d8hkz7u k711g2(gzjyt s9tmu )gmauling them u98g)1 jk7g7(1d hts u2ugf stkmy 1zmzp on 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,r-wb y u;j*ls 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 rest. The front of the y+2:3jzq a zhlztq:q:train has a speed of 25 m/s when it passes a railway worker who is sy3z z :lqq2ht::azqj+tanding 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(q99ebsz0z3 rgs2t6adx v2 vj deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while undej2xv sz03b a(gsq 96zrd v9t2er the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid trabsnnmkjp)s r-n.l1)tn6m+ *q nsit system, it is necessary to balance the average speed of a train against the distance between stops. The mn bnn)l1 n.smr6t +js)k-*qpmore 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 straig*u )c,q 9gkofqv n7:xzht 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 pelicq ozgkf*,quv): 9xc7n an to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball s1/jcsv7ir2h y7ku9re,1h aois planned so that the ball will stop within some small distance of the cup, say, 1.0 m longr2vaujes7/ hi1c o 71sh,yrk9 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 ajhi;9bk 6 s2 k,)juklh constant speed of 6.0 m/s Just as an empty box car passes hi)kkshj jb9l 6h ki,;2um, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second sta03b8 b(plg; j q4zv0rdpx3fqone is dropped 1.50 s later. How far apart are the stones when the second one has reached jp 3q00alpg(b; 3bx4f8drzqv a speed of 12.0 m/s ?    m

  A race car driver must average 200.04 4+ cu l3bhhe;zbl a2/0c+a yzghnv6q 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 avebah/ch4 uahlncq +2+46gyvzeb z ;l30rage speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour dew29zcs 1puijl1u5 xsq7cbei,(hb* a- France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his aqpbc w1,-cjhe5ib7ass* z(1 uxui29l verage acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bouncwwll d*j +40lde up one-and-a-half timesd04 ll+dw*ljw higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-lo:skfb.ode)uemutih .p cdck6 -*;c79ng 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 far will the car have traveled in this time? See Fig. fd-ce 9c;)ibkuc*76dhk o setp:.um.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 af2 yxn 06 .xnhfhn7bk2 baseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of h0bxx2fh.f6 n7y 2knnabout 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 ao1:5v j2t6b6 kjdastn n 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 shrhzehu* -i. 7kown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for.i-zhur h*ek7 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)hp sbvy818d+-zhsjnxub . o4 /h takes of s bs84y+db)-hnhx.juo1v 8 pzf in hot pursuit. The police officer 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 afte pwv*eq 34pse*r that, a second stone is thrown straight down with an init4*qseew*p3vp ial 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 sto yr 9lh jd7mss8l 783;dds6aczne is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground 8ss76cs;dhd3yz 97d8r ma llj after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-falgqa0 9/e+b wt zfymr:w06ra7u ling 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, the air resistance will restrictrm6+:0e7 /qrat uf zwbygw9a 0 her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a con+kf.oz cv b8j)grt3p+veyor belt to send 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? If the burgers are spaced 15 cm apart, what is the rate of burger productiog r zvf3)++. jpkcbto8n (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times fastejevi3kr su g01 5q,a d:v;qd0k1e dm*gr than Joe can. How many times higher will Bill’s gq* m :r1vk3skuvi005eq;ja ed1g,dd ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the groue n gfh tek;58vu5o-2 ca)ld99l d4isnnd below you. You dr eoi2-shcg9e u;d8n5)l lavtfnk5 94dop 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 speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a partichxhh1*omw 1+oqo7z,mv1 mq ;aular 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 difference1ho z1hh,o+a 7mqmw *1movx q; does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the azpsm2rxi ku8x+-ak w i 0c44mw6x)o4position vs. time graph for two bicycles, A and B. (a) Is there any instant at whichukzx04p sawcwam k-r4+ )824ixo x6im 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?