Does a car speedometer measulde(;rdhu )3z7.v yilre speed, velocity, or both?

Can an object have a varying speed ifag) gxvgkw5i9q 2uj3 9 its velocity is constant? If yes, give examples.w)2u3q j9x5gai v9g gk

When an object moves with constant velocity, does itxmr:0v*+ pxem s average velocity during any time interval differ from its instantaneous velocity 0m*mper:x +vxat any instant?

In drag racing, is it possible for the car w )-cg +xx)0*te4 el o v ttvxvk4/we50ci8rtffith the greatest speed crossing the finish line to lose the race t8+0/)xrk vc)-tix 5e0tefcv tolew4x *f 4vg? Explain.

If one object has a greater speed than a second object, dokgg /ck cbyc:6d) lu+.zc o+huy.k:8tes the first necessarily have a greater acceleration? Explain, using examplesbhc :)ogyc ..8+ u6dzkk/ :tk ug+ylcc.

Compare the acceleration o :crq-lu f;x+qyjt 1c0f a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that acceler tl;r :qyx1uj0f +qcc-ates from rest to 10km/h in the same time.

Can an object have a northw,:zf v yym arifc;:57dqv 5t*zard velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is posith o*0/0m iensjive? What about v0 *ijoh0n/s emice versa?

Give an example where both the velocity and acceleration are 6 kbj,-g.pe3c28 y8fwz kh8ut dap ujk;9r(ue negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed of 60gk8tsy4ub ;yxe0kn ii q6)8h0km/h and sti8k0y8e ib0 nykqux)6hg4 ;has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increaseh o3o5nkc/ +b,mm-c ming in speed as its acceleration decreases? If so, give an example. If not, explaiomec35bk +o, -hc/nmmn.

A baseball player hits a foul ball straight up into the air. It lea t2g5avq)lcr 5c87yxaves the bat with a speed of 120km/h . In the a5a7 c gc)ty5x alqr8v2bsence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling o /8aoa: g4jncvbject speeds up, what is happening to its acceleration due to gravity — does it increase, decrease, or stay the aj a:8 c4og/vnsame?

How would you estimag2yhskqr0lyqe;0 d2ad/9 8vd te the maximum height you could throw a ball vertically upward? How wouldl2e8d ashr/qv2dy g0 90; dyqk you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant speed o3i;p t 2vuyry1e oeg5z0g0xbma-24 e wf Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speedogvz e egw-am5e00x;pt yi4232y 1bur for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstrx0(7jsupffq 3z+g (rl dz2n 5ration, 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 fz+z0frlsdgq7(ru 23n 5fx(jp alls 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 constant accelergxx8s1pm:es/ v*5i 5t zywwt)ation: a rock falling from a cliff, an elevator moving from the se i/xz5tm)5w 1 svy x*e8t:wpsgcond floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically up -32sz3ciezcp ward will return 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 azc c3e2p3 is-z direction opposite to the motion.]

Can an object have zcxa:7cj)cpb.oq 2g2 d ero velocity and nonzero acceleration at the same time? Give exam :cpdx7.a cj c)22ogbqples.

Can an object have zero acceleration and nonzero velocityq;(t 2*lmjz2qxpjj ( vt,wzs9 at the same time? Givex l* qqt2j 9vwzz j(m2,;jp(st examples.

Describe in words the motion plotos xo: (+qc e,mruuad;/sv1z3ted in Fig. 2–28 in terms of v, a, etc. [Hint: First mua ex o/r+3 (v:,q;uzsc1dostry to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object grav,9ir0;i mwsh ng ya 735;qqbophed in Fig. 2–29.

  What must be your car’s average speed in order to t -cv+ax4kee6px 1 wr.kravel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take tp wtrg4wfxn4 ;( jao))o fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.ts7:nb,mc h :i0 s, how far do you travel dur:sc i m,t:hn7bing this inattentive period?    m

  Convert 35 mi/h to zeyiq;eq bf fz:f7( :*xkw,k6 lcm;md+u )m/k
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fr,n-b ujw3+pen7e,lqu he0 a0gom $x_1$ = 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 steadii.o v .yr,r51d cyq2yqly at 95 km/h for 130 km. It then begins to rain and you slqo r1.qd .25cyy r,yviow 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 between a lightning flash oqnj k .q(3-epand the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all,. pkn3(eq ojq- estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile tiw luq/4 (jt0krack in a total time of 12.5 mi qkiu/40j (wltn. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 m 72r20,m p z ex-1, xlpgvlorhw-1d uaxaway in 14.0 s. It then turns abrxp7, ,x2ug lp10azxrd2r -le-1omhvwuptly 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 t* sm1ye;9 uo55vmjoqc racks. Each has a speed of 95 km/h with respect to thvmoey o5;j*q9u 1m5c se ground. If they 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 travyg gbm75nai,x/z. gr,eling How long will it take the cr.ga 5xin gm7g,z/b,yar to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , ;1zrt j zbaxf1i:+ck6and then encounters a tailwind t1 f+xicz; r1:a6btjk zhat 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 average velocity of a complete round-tc/ 3be.1r+afnqjh 7a grip in which the outgj71r3 bqeaagcf+hn/.oing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits ty1yi lnhb 2(x+he 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 th1hyxln+ ib y2(e 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 to 95 km2ey 2(cac2*cu2k bzx c/h in 6.2 s. What is its average accelerat2c e22 2cca( zbxuk*ycion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to c t6i*-x s.khf10.0 m/s in 1.35 s. What is her acceleration-ixh*ct6s. kf
(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 accelegs:4rqwa7e, oh)0 x atration of about s oa40w rg :qxht,e7)a$1.6 m/s^2$ 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 q j 85pn bzva8e 1dc/guyy)l/+speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accelgzl/y+cd 8)8q /byj5 v1e aunperation 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, whicnmd hirh+:mz:zk90/ch starts from rest at t = 0 and moves in a straight line, is given as a function of time in thec0mmh nz 9: +:izhrdk/ 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 de3om b2d92r+xjq c-q acceleration? How far did it travel in this bqxe m3o- cqr+djd922 time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s txc/xa skr9 ;4ko rest in a distance of 85 m. What was its acceleraa9 krkxsc/ 4;xtion, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for tae*bu yaa75) xhkeoff. How long a runway is needed if the (c *x7yu)haeb5a onstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially ton/y9g(tl wyefvdu;lzd, )*)qw8q 1yap speed (of about9v)dfd,q)y nq*(y zagy;lw1etl/ uw8 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/(:cpraq ozkm/fy,bus/o 8h .me q/)y05 sn-lws to rest in 6.00 s. How far did it travel in tha(0z./5ry am-,os q/psh8enf qokw /u y)cl:mb t time?    m

  In coming to a stop, a car leaves skid marks 92 my(9h ak-v8qaw long on the highway. Assuming a dkva 9ya8hq( w-eceleration 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 compressosw;njut *s4 lgp(8: des and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the dos8ls4n(;w*: dj tpu griver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 km/h ) c):qkr z9lnt-9nr krand human:nz)lrk9-qrrtn)ck 9 reaction time of 1.0 s, 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 stoppini6 fil r6ce3l1.5erg li4yatj)m7s.ug distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver ,tbc7kj:t4u i looks for an opportunity to pass, guessing that hisi74,:kjtt b cu car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,0wu 3 /5h ufcwfe;spr+500-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must thewuu/p5w+c f;s3rh e5fn 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 azjrm)c+3fzoo 0c g 5v o,q(m*opproaches 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. om* 3rzjzo(+m go 0v5cqc) o,f2–31). 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 a cliff. It hits the ground below after 3c8udk w2yc 27f.25 s. How high i7c2 ywudf 82cks the cliff?    m

  If a car rolls gently (w lseh/;0xjy 4 wv-vm8$v_0\,=\,0$) 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 ,b)gn-ngc5czq+ rr(n *je8qh 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 vertically upward xjiz n2t67ik-dreg6xo.z 2n). With what speed did2tnzieg )6jk x-ord.27 xizn6 he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influencelxrwfn)0i,f *9cj pspo-13 wa of gravity. Draw graphs of (anrwxfl as31w9) of- *p,i0pjc) its speed 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 ascepyl,; tjz/1ux 2u(x,e4ov:w)dl jubqnding vertically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a windo (ue,q,xup;)4:j2lw1 uvob/ty jlzxdw. 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 distan:*ol-*/a jg(:;blf5 usrs vwh( cgfckce traveled during each successive second increases in the ratio of sucflfg kjb svlg(rc5u*oc;-( a: ws:/h*cessive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, shoaud+jlcbtfia5)/ .+w*nbhu;8 l scp8.zu 9zow (algebraically) that a ball thrown vertically upwa) + pfl/bz;uio958zc u.sn d.a+ctu8la bhwj*rd with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown verticalff 3utd2e)9 wlly upward 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 betwe3q1 vuoem*w gs)f r77ken each photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear or1*7gf7wkeum qv so 3)nes at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travelq bgk04 xjxy2yu,7.ub past a window 2.2 m tall (Fig. 2–32). From what height above the top of the winu7b20 yu4xb.x ky, jqgdow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it p: ;2hrvalzpk5)k/ jh,r xv5hi* x;awi o4r8qstriking the ocean is heard 3.2 s later. If the speed of sound 4lai 8arrvpo/5kj px qvk*i ) 2hwx:;5,h;hrz is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose ni+3,ncd /i:v mot 5hz v./tz1niymbc,ozzle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you chti/o:vinz/+53 1dm,b my .n,zitvc 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 verk po+ l:kor8 g yn;fu1t7b,b tw7k;6tktically upward with a speed of 12.0 m/s from the edge of a clib7tk ;ryk8tfk:7n6;bol w,uo p+t 1gkff 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 towab4 n;*gp*ux v0 zz4o pass upward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the street,*zug vnb *zap o44;0wx
(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 p5 7:uqutf2tot 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 coft75u 2t pqo:unstant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a functiorg4 :bnsry/n( n of time is plotted irb:nyrs ( /4ngn Fig. 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accelerate approximately as shown in the veh.ydcff; v 5l-eo,z1o2 :salcs 4uxs. locity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting ofouf ls,ycx 1a 2z v4cs5:.fe ;-sodh.l the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Problem (Fig. 2–*p . 6fkji)vand s(ix835) whenfvpdn( xasikj . *)86i 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 e40jcq ji*1fkdistance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for y2d +,q0mxg tnthe object whose displacement as a function of tim d0 t2mxgy,nq+e is given by Fig. 2–28.

Figure 2–36 is a position versus time graph fom e:k *r3yfg ti+.yoy.r 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 accelerat3m*iygykre + f.:.ot yion 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 four-ub0)rmi/j qm th-story window 15.0 m above a firefighter’s safety net. The survivor stretches q-jum mr)/ib0 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 m fv; 6p5f.:agfh egg84a i*igon the Moon is about 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, :f 58gvgaeihai.;* ggpf46f massuming the same initial velocity?

  A person who is properly constrained by an over-the-shoul;*-u0.xj hpx g.fjhg wder seat belt has a good chance of surviving a car collision if the deceleration does not exceed ajxjgh;.h-*.ux0p fw g bout 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 ab;)dk,ywf.y8tamm5qt rzaesw gg d)5kk:)8a(ove the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country( ea ktgtymd)m, dkw:s)r8. yaqwf)zka 5 g;85. 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 front-0*g so eruwt q;x0s:d/end collisions by hauling them up on a cra ;q0ourws*x t :eg0sd/ne 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 i96,a w f)em+ anvjez7travels 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 unifo7ojjs/fzm0zok7 ; w* rrm acceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m froow* ;70sokrzj jz/7fm m 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 divin.0 /xadrmkt qs20nf9gh,i 4z7yay rw1 g board 4.0 m above the water’s surface into a deep poolm,zt. x92rsqg0kwy01iah yndr 4/fa7 . The 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 system, it is necessaso*8y-4hq6psacvhg 7ry to balance the average speed of a train against the distance between stops. The more stops there are, the slower the trais4y8ch 6sgp h*q7-ovan’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 straight down when divye3e5 k /baygc+qw5oy7/j pho.w3 a4 ming for fish. Suppoa57gok/eqy 34.jc/m53 awy woehp+b yse a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfeoeimm9h9 047u xpvq,xo61 pqkr 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, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more d xumqe9ix7qo,m1 p4kv0op6h9ifficult 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 on8lzll5s :,mxm a freight train traveling at a constant speed of 6.0 m8l5lm, zsx:lm /s Just as an empty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high build y3gew-(ktrfxe2d wb is jq,l78uc5 .,ing. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a l,u8y27g5x iejs( fqw. c ktrd, b-e3wspeed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the cours3m/3(6p2ps6yicr 0 b v9: h urhuglfrpe of a time trial lasting ten laps. If the first nine laps were done at 198.:gu(3frlr i y06 bpp/u2 cs693hvrhmp0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mounta);hp/6aohcx d kqoe(: in pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his spxd eo6h:;(kh) /aco pqeed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are play-w ea x;q3e-) 7fctajoing on two trampolines. The first child can bounce up one-and-eatcjq;e)37- -fxw aoa-half times 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-long train traveli 5+ hobo2dwz;4cb;a ncng 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 o;bz;coacn 25+hwdb 4pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball z+e 54dwv39dz)yhredwith a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body t3yze5dd)v9dz+h4 w re o 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,cjb/ik ( a,6mz from rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a traffrx r uqj7kt7//i8o6-*j hs/ hjtjupw*ic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you arejqj7tj/*/h*u 7ohwjs/ prx-uktri8 6 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speed6y3p4m h0 s4 zjsprq2der traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaiq4 yr0sj4mz2d pph63 sning 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; 2ib50w bm sluj ;769tjl.00 s after that, a second stone is thrown straight down with an initial speed of 257 6 si ujjlm;5bwtbl09.0 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 thrownc /jfn 3yu*yw300uucn vertically up 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 y*0wun0u/y cu3c fj3n and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how l.xam:;ucql*x.edj a : ong would it take a 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 beq .a; ml*ca:ed:xjxu. at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through a grilli.a 0ve5:qp-m imd9mn rng 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,q ae5-mrm9 :.dvnmi0p 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 c v48qbskq6rjw ri alo0b0ee4op0c4, * an. How many times higher will Bill’s ball go tbs6pc0 a40l4r4 qq ,v*ere8o b jwkoi0han Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground bx )c)dliqpi3-b s3-:byt jx;d v fr(2celow you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground byrb))vqtf-cls cidb (2jxp;i3x-3d :elow. 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 particular building using aa(av(9u9e(ntk pj nw4 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 wpa u(4jen(n9k(a9vtthe other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) vn )p(mw1+0c v n7rkckIs there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger accelerarv)mwnckk 1cv n p(07+tion? (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?