Does a car speedometer measure s 0q ,rzmtcf 22o;krdwhx615wupeed, velocity, or both?

Can an object have a varying speed if its velocity is constfu 0x/7v3ydj n2gaxn 0ant? If yes, give exaf 2xd0jy3g/nxu 7n0avmples.

When an object moves with constant velocity, doew n86rbn,z.+r 26sgkn z3rkszs its average velocity during any time interval differ frk6,w3 sk8r s +rnnb62zrzgn z.om its instantaneous velocity at any instant?

In drag racing, is it posirv,z5y;(/ mzqk r gw:sible for the car with the greatest speed crossing the finish line tz/y;w:(zi5 mr,vrkgq o lose the race? Explain.

If one object has a greater speed than a second object, does the first nr/e./7zqkrzm vx5u (thhkk ,+t)k9vnecessarily have a greater acceleration? Explain, using examplesn79zkv hv 5q +.k,retkuh)z /t( /rkxm.

Compare the acceleration of a motorcycle thaz,z2i3 d j)yqat accelerates from 80km/h to 90km/h with the2,jzqd) ayi 3z acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velov5lhuk uv:k /3city and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positive?p:ut n 7wm60og What abo6n7 :pw tugm0out vice versa?

Give an example where both the velocity and accelera 2+d0*.+,a oa) epd /kynho jpsipott(tion are negative.

Two cars emerge side by3puc) bn86xj+x c: uxlwd,f9n side from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your re:ldu9j x )fx+wncx6uc,3bp n8asoning.

Can an object be increasing in speed as its acceleration decreaseyagdb 0xx1204ipm tj) :ru3; khrvf7 es? If so, give an example. If not, ex b7 t 02ru4dg)e0: 3k xarvxmhy;fi1jpplain.

A baseball player hits a foul ball straight up into the air. It leaves thndx :fxxk, 6ke cw.)r3e bat with a speed of 120km/h . In the abw :d)3fxerk 6nx,.kcx sence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object sr1er) 1mb h pz;:iz/zcp0wp56qlk qx*peeds up, what is happening to its acceleration due to gravity — do* pme/ i: 5wc ;q61rp0x1b)hrpkzzqlzes it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ballker r t:qpi6ah(.g: 9x vertically upward? How would yo kr:pa(hi tx9.: 6qegru estimate the maximum speed you could give it?

You travel from point A to point B in a car moving atkaqm4( s;qk1h a constant speed of Then you travel the same distance from k(1qs haqm4;kpoint B to another 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 demonstrati)srzx)ve/ y9 dl k 73ptevde5g86v2p von, 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 tr3t752v68 evp/zxegdye )v k 9ls dvp)he 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 me rw 3y* 92:yhavd9sizki0ll/otions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making s9di3 ryel:vh0yazl 2/*wkis 9 tops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its origib*fpjxfm1 -+ jnal position with the same speed as it had initially if air resistance jfjmbf*x-+p 1 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 motion.]

Can an object have zero vlwrl842:n7 ydc ld)9tgf 7qsvelocity and nonzero acceleration at the same time? Give ex2tq7wrflyc7n)dl4:8lv g 9dsamples.

Can an object have zero acceleration and nonzero rytt sw8/6+kk velocity at the same time? Give exampl +tytsr/8k6wk es.

Describe in words the motion plotted uhw/s9sxma 9v yy. x.t 6m8z:rin Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walkinz .mxmtyhrs6uwy a9s/:. xv98g or moving your hand.]

Describe in words the motion of thed*t38s 3ihtdq object graphed in Fig. 2–29.

  What must be your car’s average speed in order to traq 3k6-q,d -lowuw8gt rv ;gs1ov6*tqavel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long doe) qr ,uwj d4mcneicln-l.p48 9s it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 sf; lh* w;d92zku3 wlch, how far do you travel during this inattentivekl ch3 dhu2*lw;;w fz9 period?    m

  Convert 35 mi/h to 91 wuwqm( r gb8g9euu,-d0x2sd+och z
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from -aw gdk9n 05;oein1nb $x_1$ = 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 kmln-*rkwhl ht1w / fq/k8g;zy4/h for 130 km. It then begins to rain and you8l-tgwy l*khn1/wrh ;kf4zq/ slow to 65 km/h You 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 be8wy*l e/ ky9 d:wki2uvtween a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash 8:l /wk 2kuvyiewd *y9of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track ir+rqvb/fej19 u nwg3-ss d*o/n a total time of 12.5be/oq/dvuwrn 9g3 j-fsrs* 1+ min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight v5uhg)( el :nm7/rnso line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Ca lvn:)eg5unrsm ( /ho7lculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has a spe.h vh .+)qwn4q.sfzi 1fnf+k ved 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 othef vnwhfi+.)qzs khvnf + 1.q.4r? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will iy wjijb;h2iv4dj*,ohd ;5ir dqy j (;)t take(wvh y j;2;d4ob,;d*ijji hdijq 5r)y the car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters.su 9yus, du+ahnb /6l a tailwb+ nudh,ys s.u/l9ua 6ind that boosts its speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and a/./twmdm x*0,iykjn8tz (o 7fassv/uverage velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered mo/vk 7t*.,ujyms 8dix //zf(at0sn wat 55 km/h.    km/h

  A bowling ball traveling with constant speed hits t5/zq f/,rde-fl mgb )ahe pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the 5/,/e) zg-darfbmfql 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 avera:8c(9w fp hy fnx6w7hyge accelerationyy:9 (chwfxw8f 7n6ph in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accg5upz:sr:-r e rnzja +j i-,5veleration srje i5,zzr-a5r-:j :unv + pg
(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 ac8 v20q k/soindceleration of abou/qksnd o 2vi08t $1.6 m/s^2$ 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 then brakes-j+pf8.0q 8ojtfg69upkws w h and comes to a stop in 4.0 s, what is its accegp8khjj0w6u st 9+qf o-8pw.f leration 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 awzoj;i5 ru)z.kuj 75n straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table a.io ;u k5z)jwn57jurznd on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 j3/ik59 p* q rdfypeqpi*;xh- s. What was its acceleration? How far did it 5*q*-hqx d3p9; jr/ekpfp iiytravel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance; p4w eh3138pli lfyy6he az 7+fs7rxh of 85 m. What was its acceleration, as z;3+ h wxeyl13sh 7i8l7efpray h4p6fsumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/sxz9c2oi h oijqgs 6m/w( 13ji-wz;;ab for takeoff. How long a runway is needed i/6 zoajbx mww9oh; ; sigqi(2ijz31 c-f the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter canl p .tha5o):.b g;.admxntz s 468ipgb burst 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 acceleration of this sprinter, and how )x;6osizbm.b.lph a:. g84tnagtp 5d 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 ab /ytvq5+l9 xs. How far did it travel in thtb x5a/vql+9y at time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. yg 0n qi+6 l9o) dq1uj qwwkmwslghdy0w+2 1;5Assuming a decelerat+gly9g l 1s)q5 j dunk;ow6q w0 diwm1w+qy20hion 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.5lh4imk bu;oo k lb: e(oc2*s of the car compresses and the driver comes to rest after tr(u*5 lo:ml;oc os e hkb24kib.aveling 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 5m 63k ph)+hp6je1ys qkmr(3b qyq j5ospeed of 95 km/h and human reaction time of 1.0yj+ h kpy5 oebj5)6p3(q qhrmksm3q61 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equatijcrno41g0nj1c q) 2nton for 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. Thx d/;.jh4iejo e car’s driver looks for an opportunity to pass, g 4j;oie.x/jd huessing 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 coldodf zgu*4z00d z0/ emplete the 10,000-m run in less than 30.0 min. After exactly 27.0 minl4 z d*0gz0ed0/fuodz , there 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 c/csxbfm. .y/v/tz5: xu/ qub aar at 45 km/h approaches an intersection just as the traffic /xsy .auufz. //:cv bm5xqt/blight 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. 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 on fyzm+ 9o9q7a cliff. It hits the ground below after 3.25 s. How high i +7y 9oqmz9nfos the cliff?    m

  If a car rolls gentlt3:8 rhhl7w0y (ntnicy ($v_0\,=\,0$) 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 speeah 7 xh+5wk6gfd 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. Witdip(rkr. -uk+(x- o o wd,j6ech what speed did he throw it, and what height did it -p(,iwd(doje .k orukrc +6x-reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Dra1e1 1ipmf9x kjw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t =1j p fik11mxe9 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height of 123ttpf j 2 7hpuf5hd6r:5 m above the Earth, a package isdj r h75tptup:f 326fh 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 helicopter’s.] t =__ s

For an object falling freey/ 1 1f; sj,jn-kyfyfhly from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). k ,-/ fyyysnjf 1;fh1jThis was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglecte:-ytc 8+ z kn5.ktnovid, show (algebraically) that a ball thrown vertically upward witt z8-c5.k o+k ynnv:ith a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward wiwib.pzy6e 2e )0+ 3 sozih,pyith 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 photoflash8j:17o*xxig sll)feif, up 6m of the apple in Fig. 2–18 (or number of photoflashes peg uil, f76p8*i: 1j ofsxxl)mer second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 05nv)f6kvljlrg7,z 6 t .28 s to travel past a window 2.2 m tall (Fig. 2–32). From what height above ,j5vktl 6g7 zrv6lf )nthe top of the window did the stone fall?    m

  A rock is dropped from a sea cli4p2bpn rxc *k jv:kfi 8bo,9,jff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of s2ojncp4*pf8kb,b9kx v ,: irjound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream o.fc pys ncre 11us(9+if water. You point the nozzle vertically upward at a height of 1.5 m above the ground (F( i.p1ycs e9 cnf+s1urig. 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 spex,ra+an wcp2f+d o3p yduc*72ed of 12.0 m/s from the edge of a cliff 70.0 m higupd dwyx 3c*a+f,ar7 c2o+2nph (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 ponj6b5 zpltxe3w.l t,4 i 1nbh0b(2 xsass upward by a window 28 m above the street with a verticalxx063 ( lioh bsj 2lp5t1.tne,nwzb4b speed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (a) A zx3iy+ ,sfs(:+r trult what time was its velocity greirt,:yu3x (+sf +zs lratest? (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 greatest?

  The position of a rabu oycn4 zt9m26g /r1k;r:z.hygxng;sxe s81rbit along a straight tunnel as a function of time is plotted in Fig. 2–28.y2 g1zk:;zu gts/rohn;ex1c xr.4myr nsg89 6 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 approximately as shown i 1,cxc 3cjb*pbn the velocity–time graph of Fig. 2–35. (The short flat spots in thc ,3bc *bc1pjxe 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 acceler 8d( z8hshgsxryw94 .3pr 8epzation of the car in the previous Problem (Fig. 2–35) when it is i(8srpw. dyh rezz388pgx 9s4hn
(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 ob2qmdkdvg 2 *3 9tqty6eject traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t(:af2n yl, c-ssjl5m h,uh +cf graph for the object whose displacement as a function of time is given by Fig. 2–28,ff(-amh:5sc2ln lh yu+ s, jc.

Figure 2–36 is a position versus time graph for the motion0zx 10euwnw:w 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 pos0euw1zw x0 n:witive 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 d3:sb :x19xread.mi h8wn2 lpa fourth-story window 15.0 m above a firefighter’s safety net. The survi2esmni:pxwbhar3 . x d9 :dl18vor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moo0ntaj a; s/(odn is about one-sixth what it is on Earth. If an object is thrown verticajtnado /( s;0ally 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 b tq:qt 9jyw9k- s4.stcelt has a good chance of surviving a car collision if the deceleration does not exceed about :tt9 sqcyw -jk.4 tsq930 “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 * o:-twlvnnt2road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approa:wtn*2on -tv lching 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 manufacturef-c;i qf2vtv5r tested its cars for front-end collisions by hauling them up on a crane and dropping them from a certainvi2f5tq;f-c v 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 travel4fecax-qdt wk4s. *qc2)4 kwfs 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 p mxve :,5)leitrain has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front oem:ex,)plvi 5 f 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 wauhk0xklv9.nmnz t d.j (6l i:)ter’s surface into a deep pool. The person’s 9.:. nkljlkvu) xi(zn0h6tm ddownward 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 system, it is nece9; k(c3kq kmmessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train t 9k 3(c;qekkmmo 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 down when diving fodcfi*dmi*(:v 9 c3k btr fish. Suppose a pelican starts its dive from a height of 16.0*d9f :* v mkct(ibid3c m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with whi o /xds.dv9qq.ch a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, iqsv/ do.d.qx9n 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 tra4;mt*a n u3,cji4 t(,we21 lejr dfwpcveling at a constant speed of 6.0 m/s Just as an emt*ew jl( 34d2ujr,w1 cnta,c mi ;pe4fpty 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 from the roof of a hw yi.+skn;n4kigh building. A second stone is dropped 1.50 s later. How far apart are the stones when the sk .wi 4;kny+nsecond one has reached a speed of 12.0 m/s ?    m

  A race car driver must a f (tcwemy3w1g- oi2-xverage 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps 3fywg c(w-e oix-1tm2 were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain jsm:81)v xuw npass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his a 1)njswmx v8u: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 bz02zt ql)z nkr-p5g u8 hv+s7founce up one-and-a-half times higher than the shl2 vz-0zsz u7 kqf+58gnr)pt econd 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-kvvw8no sj7o:x 1v9256 lqrb ujgftg,7 m-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have travel8l:ot,v6s7j5w 9 xgr7gf 21jvq nuvobed 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 oaup 8r+:d(5 q,ta/s wubgw)hof 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is reastr,(u/ ah8w u 5g)b+:dowpqleased (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, 1m /cbswq6l3x 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. 2–42. Each intersection has a+ fze*ke xo+;2zzwr5h 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. *z f+wz52h;exo kez +rThe 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 atf)1:ghdv jv/m a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acceleration. )d f/hgv:mjv1
(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,wm0 0iipef : zjulu9c-5zygyu)z 7v.r that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time. -z .pu)jlfu0z ,iwm7 v0z9:iuecy5y g
(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 sau 3l asmmt1 czd79)/oi0-xi* pzwhe m,me 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 wh7*m l d9/zi- iuexc w,tsp 01omm)az3hat 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-falling plirr+kk;+m7 n,o l:4 -mrkkxui24fv carachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her ;4 crio lk 27rmr4v:+f-+xkk,mnki luspeed 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 s(;sccyr1uf 5uend 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 conveyofcc;5s ur(yu 1r 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 1.5 times faster than Joe can. ; j.obg b.lsbj: 4*ikiHow many times higher will Bill’s.j*.bb 4 koi:lgisbj; ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cli62u as3e* qey sf,8zcbff while your friend stands on the ground below you. You drop a ball from rest andb f8q 2e,c 3s*u6syzea 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 r/ l9-d z2zdnwvvj x3.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 buildinxz3 jv 9vz/ wd.2dl-rng’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) Iwu;gb 27d, jir3rnneu8+ apdt yw;)5hs there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are thp 7 u5 d;,ej)br;ya8 +rh3w2itdn wugne 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?