Does a car speedometer measure speed, veloq(;bn 49eplwbcity, or both?

Can an object have a varying sp/q v .m qndzl:lk+a-o5eed if its velocity is constant? If yes, give exampln/+5o:dv.qlzqa mk- les.

When an object moves with conswqu.6pcl p4u lxlb-90tant velocity, does its average velocity during any time interval differ from its instantaneous velocity cll 4x0qp l9wbu-.6up at any instant?

In drag racing, is it possible for the car with the greatest speed crossing thyqwxhtx71:8 q e finish line to l8q: q7 wxtxh1yose the race? Explain.

If one object has a greater speed than a aapb (6hfef5j za+z8(7(-fzphupp + u second object, does the first necessarily haveu haz (7pepju6fbf (5z-ap(ah++f8pz a greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h a1i52. e zv)(vr,xh3 -)ezkvihbjisfto 90km/h with the acceleration hi3j,x.-2 eikhva ri) vf( vz5bzs)e 1of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward accelerar q:dh 2ujd--uxk9fz m+.-xmsu ;m xy1tion? Explain.

Can the velocity of an object be negative when its acceleration is positivf svj0,to7tb9xtz-b phfx1 -) e? What about vice versa? 7,sj bvpx -fohz f0xtb9t1t-)

Give an example where both the velocity and accelera* -l r8bbv -ccfs(l9rvtion are negative.

Two cars emerge side by si khl.8lbg0ruz*c v7i8de 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/hucl80 bgvkr il.z 8*7h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be incr9zxs2h 5(xtx ,dzf;jweasing in speed as its acceleration decreases? If so, give an example. I9df x,hjzwx52s x;tz( f not, explain.

A baseball player hits a foul ball straight up into the air.b( )+4);qz)uts w3z maqu.pfiquzn,u It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the balqqwa t n3 uus.)pm4) zz()i+bz; qfu,ul be traveling when the catcher catches it?

As a freely falling object speeds up, what -t5jjsj h ojuc/w)hs3d55z+slmi 8r9 is happening to its acceleration due to gravity — does it incre w9h/i)s3ztjo-jjcrs+uj85sd l5m h5ase, decrease, or stay the same?

How would you estimate the maximum height you could throw a42idqt r,rc3t ball vertically upward? How would you estrqit4t2cr 3d,imate the maximum speed you could give it?

You travel from point A to point B in a car moving at a consc:1mb rxae; jo x9kk8 ;2japbvy/83 kmtant speed of Then youjv1cake;ba8 9j : xmxpm/3o;ybkkr8 2 travel the same distance from point 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 demonstration, a 3.0-m-long vertical string with ten bolts tied t(swzjqx b;m6(z h:gkkau 6 ;q+o it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the z;q6 s ; jbzk:u+6w(mahqgx( kend 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 accelenid6uwjho9o2 1t+d-h w 6o 5hb-q ,qsdration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish re6howhq62on9o 1w t5jh-di, q+b ds-udsting on a table?

An object that is thrown vertically upward will returnz5ky1 j mqt68*pzp3*fvuxq-n to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction oppos y-tzk6nv8q3 q5fup x*m *z1jpite to the motion.]

Can an object have zero velocit.8-)evd6 o l3nsjyj)fv*b qh 9pz6olny and nonzero acceleration at the same time? Give examb9dq6h-*) n8yzsvjleol 6n)fo v pj3 .ples.

Can an object have zero acceleration and nonzero velocity at the same r)(.nv qccs,t time? Give exarq ,cs.v)c(n tmples.

Describe in words the motion plotted in Fig. 2–28 in terms of v5l,4ka9j sop okg9(mx , a, etc. [Hint: First try to duplicate the motion plotted by walking or moving yg k(9 , mko9xjpalos45our hand.]

Describe in words the motion of the object graphed in Fig. 2–29. )q/ro)5lm)xn7 zo fyp

  What must be your car’s average speed in order to travel 235 km in 3.25 )9kxr .h,heqch?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 km? d.c)tprevt +b5hc9 usq3ngmqzzx 8 9-4o6ri6    h

  If you are driving along a straight road and you lo pchc z/jqh;bewhlf)q3 w; 51;ok to the side for 2.0 s, how far do/hzcw;5 ew;h 1 qblp;qhjc3)f you travel during this inattentive period?    m

  Convert 35 mi/h to u* x:46 vwxjnltc6b (*vwd5ad
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fro g y++q(.ga pwj 6ruba,y1etb2m $x_1$ = 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 skyj2ye 6;ypl -qg7.ykm/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive y2q6lkgy. ; 7y -sjpyehome 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 flas e az/7, 0-/9a;jrkoawvrnls fh and the following t;f9je,r zos ra k/-w/ al70vanhunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total tim hw, . gz+/:-qby2kudwqbk;zze of 12.5.zzyk,h dgw u-w:q bz2b/ ;kq+ min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from i fr/y;x4- :xnq0vlpod ts trainer in a straight line, moving 116 m away in 14.0 s. It then tud-yx 4p;o/xlf v q0nr:rns abruptly and gallops halfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. E n xvsz6i(9xc3ach has a speed of 95 km/h with resxisn(z c9 v6x3pect to the 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 traveling Ho8qmmskhy :dz3 3w)uj; w long will it take th3:zk3 d; )8qh mswujyme car to reach the truck?    s

  An airplane travels 3100 km at aqb3cj l;72 8qd3uvifa speed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 2800bclvqi23 d;qj7 3u 8fa 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 cg)vwpq) +r-ruomplete 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 kgr) u +q-vprw)m is covered at 55 km/h.    km/h

  A bowling ball traveling with constant *wtch0p 9+ sq/s8bmve ij:xl-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 sl/jc bi pwv0+s*-mte98hx:q s after 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 to 95 km/h in 6.2 s. Whaskc 14uv-bkgz)(u: 3k9mab2 ij : jxizt is its average accelcikk ibxvuz:bu mkj-214 ():gjzs a93 eration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates fr1bl(srkyx p 6* nen3-rom rest to 10.0 m/s in 1.35 s. What is her acceleration-(rb1e r 3npx6 knl*ys
(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 acceleration ofb;vm 5s/*: y 9y2cvql/zqhog3ayu )sa1dye u; about vsl yqcu/yuah:;yg oq3e*25sd9 ) b ;1y/zmav$1.6 m/s^2$ 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 11n(ozn9 acx kk2mo 8s(w74j+l.li0pz k0 m in 5.0 s. If it then brakes and comes z7sjk9+p(aonlx 4ko2 kcnwz0(8mli . to a stop 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 982b2 ma ivmulin a straight line, is given as a function of time in the followi2a92ml8 umv ibng 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 (fdh)l d qj-i/m/s in 6.0 s. What was its acceleration? How far did it travel in this tii /hdl(j qf)-dme? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its acccd unqga:j4acx 3h)j8 6ye5qn+ uba-:eleration, assumed conq6ej gu jn3a: yh-cu qx8c4 )abn5:+adstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runw578ec(nsx omu xw/u w6ay is needed if thm7uxw/ 8s(o w6eun x5ce (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the b h9ws 5tys//fjlocks 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, s9hy j/tsw5 f/and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in sugkzs275*a g 6.00 s. How far did it travel in thatg*5z g2sas7u k time?    m

  In coming to a stop, a car leaves svz 27: qewtl4wkid marks 92 m long on the highway. Assuming a delw7 evzwq2t4:celeration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h striked6s(y dm8(b1v-ct,hsl 4hle:k y,mz zs a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was t,mzhs6de(ht48mlyv: ,(bk zc s 1ydl -he average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 9e , lti rf,t1tl)23c.o em*vy .y*vtob5 km/h and human reaction time of 1.0 s, for an acceleration ft),*voecyl.y oev*t1l3r2mt b.t,i
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stoppi9uu 9-m5hkq3rvdpt1 zng 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 looksf;essgo o lws0, n0:+n for an opportunsn wn;f0 :eoo0gsl,+s ity to pass, guessing 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 the 10,000-m run in less than 30.0 min. Afkj*lkqfq6 3oab/ybq fbed5+506c8 lster exactly 27.0 min, there are still 1100 m to goa5sdqbbelky5 o c+b f8 q0k3f*6q6 l/j. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection just as tc ihukjdojv (u+k8q, m7 qc3d( 9rpp);he traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28d (;pkok8cj+qp,c(u ju )dih 73vqm r9 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 n) iea.75bcb ctop of a cliff. It hits the ground below after 3.25 s. Hoi .7c5ab) nbecw high is the cliff?    m

  If a car rolls gentlf39 fnn,8u7f80t qk kad-vapvy ($v_0\,=\,0$) 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 w;+u1 v j;;lbvnxvqr4 7ss;u wiith a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upward. With wha6 94zgx ch1m:6xhpa tifop; ;zt speed did he throw it, and whax zt6 1fxz oa;6cp9h;gm4pih :t height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest ai+oogvp*hq 7j wu 9cp8y)n )/pnd falls under the influence of gravity. Draw graphs of (a) iun/y9hpwq) j7o p*v8og+)cp 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 ascending vertically with a speed of 5.20 m/s. d8bhyzk7nx4qg 9k8r-At a height of 125 m above the Earth, a package is dropped from a window. How muc 4dx8k-n7b 9qk8hyrz gh 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 dix+h tj1g fglonsb7-):stance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galig-blj:+1ghn f7xs o)t leo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a baw2m m92wm1uutzi u-y f pa..w:ll thrown verticalu9uzf tu2:p2 wwyw. 1mai mm.-ly upward 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 vertica t(y4;b ;i 0m (xczfoq9 das7kgj)pmiow1 :ap0lly 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 between each photoflash of the apple in Fig. 2–1::o77a0ek x:l4t ,pfy pinmzp 8 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter.xept :okzi07l p:ma7f ,:4n yp [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m talgkytrd 2mj * t2j4yzdw qae-hlu.+893l (Fig. 2–32). From what height above the top of the windogy3 2ke9tywrdm+ -j .zthqa d4l*j 28uw did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the ocex rusbj/dz i-vh* ,zzbe0 )0p7an is he0 hzjbuzsdx7b0/e v z -i,)r*pard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your gardyc;il;n zn spclr 0 42kvpadw56igd*h6/9p+ xen hose nozzle 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 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 nozp*60s/6ip l h;nz vdp kcl+yrw;gdac5i9 x42n zle?    m/s

  A stone is thrown vertically upward wiyif4 c+s1v 3vu1p r1jnth a speed of 12.0 m/s from the edge of a cli+ unjis y1 p14f3vvr1cff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the streew2- pkx xzwwho)nfxiz2.c 64 8t with a vertical speed of 13 m/s If the ball was thrown from the strcx)nz.pz8-whi wf x64 w 2ko2xeet,
(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 k2o sx(plt cdy/,28o wvelocity of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was thelpdx( ,o8wkot2c/ y2s acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel 8 g o*jv7cfvjbj;w:u2as a function of time is plotted in Fig. 2–28. What is its instantaneous velo: gucfjoj7;*2bw8vv j city
(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 approxta 6idne-0eay*, v0 esimately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represenyv6-n, 0e eeid* tasa0t 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 acc ( xy),b wx,*ykal7eoezco.c:0 hp ;jyeleration of the car in the previous Problem (Fig. 2–35) when it isz ;y,a)b.07ojce,xw lx(cp*y :oek yh in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object travelhcqh*z*w8pzx- mg8;f ed during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t g.innvp2qy3p7q:yc;z raph for the object whose displacement as a function of time is given by Fig. 2–283iyn: p7p qn. ycz2;qv.

Figure 2–36 is a position verkzzr/k fq, g56;dc-zfv gkc-xn,w78nsus time graph 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 slk; zf-gcv,wzx5 qf-r/k d, gnzn8c6k7owing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safety nyg+3n09 5y owgsvob.niur11 net. T0o3nngv9.15 wys+n ir1 byu gohe survivor 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 Moon is ab4rb).aeo+ hrlout one-sixth what it is on Earth. If an object is thrown vertically upward on t+r)oa.e4hb lrhe Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly const*fr r139kh+o rds 1w+v8ht f-ep(xj qyrained by an over-the-shoulder seat belt has a good chance of surviving a car collision if the dw1(+fr8 h3jqf91re ty *s+or dhx-vkpeceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridgeg 1 zwq:1 bo9yzmb5soqcu6 y99, 12 m above 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. 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 th1zqywmbzou9 g195 :o y9q bsc6e truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its carsuil3s:o is;68p4obbtd 3.g zi for front-end collisions by hauling them up on a crane3;4.pgisbi38itl bos zo6 du: 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 travjuqvp 0j md2p;83h l 9p;vxx.iels 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 xpp9(opmqe ,- hr8-d,f qvg9nfront of the train has a speed of 25 m/s 9 - , (gndf-rmpvhp9xp,8qoeqwhen it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surfmlrqx :lfa;t8:mljc9b dg758ace into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average dece9cqmm8llra87jb;5 fx:g td:lleration 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 necessary to balance the nm)qx raj 6g9+ng*:zx,w3mon average speed of a train against the distance between stops. The more stops there are, the slower the train’s aaqn6,z9o+g: )*mr3n nw gjmxxverage 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 f:ufh8 3mn:j+lltzh ,wree fall straight 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 spof hltz:l w,3jmn8:+ hut the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes ac vte-. a4hh.fg- 4:zn os,jnb ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short- sh, 4on-fahn ge jz..bvc:4t, 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 dc 0xltv2m11(gi nt ,oat a constant speed of 6.0 m/s Just as aniv(t,goc21 dx1 tml0n 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 pny)h jthl :);building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a spy; tn:)hp)l hjeed of 12.0 m/s ?    m

  A race car driver must averagr wv 0775p rl9stv0qhie 200.0 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 average speed must be maintaineds p0tvqi 95hwv7rl70r for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass s zark ,tfkgjy*4z/) uv:6d;b as he moves at 18 km/h . At the bottot):fv4sy bka *j6 r;d,u/gzzkm, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child canj*-s n-(z rq6gkcki73pp5 sfor/o) vc bounce up one-and-a-half times higher than the second child. The initial speed up of the f-o 6)o(pi*ss3pjz g7r-q5c r/ck vnksecond 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 overtakeywxu6i2 bfp/x- t n z0,)aqzb1s a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig2qbzwax60x)i yt, zf-un/p 1b . 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 throwv5x ny(zw y7j ,4th1ylkdf,/ss a baseball with 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 to the point 1y dl,j45nhvs/,y y( k xwzf7twhere 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, a+ay7rw 2 ms1d e2+gh:kdg9 ywwith 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 hep.,vio4zfao j c-d31z1x zavj2o3g ;as a traffic signal, and the sz x -.v;z,za1io f1a4je3c vpo3o gj2dpeed 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 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/uwx bkpl74 2s, passed by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police offb s7/x uwk42lpicer 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 after that, a second sweie t l,dt6wf;:c/g4tone is thrown straight doef:tg ec;i4d /w6 w,tlwn with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown verticalqv0w626ucq3fin z dqa k tj676ly 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 and hits the ground after 4.5 s. With what initial velocwqac6fq6it70ujq6 k62 dv nz3ity 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, hot8;.jdowp53 iwee r d0w long 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 be at 350 m? (In reality, the air resistand8w.tp rie;5o 0dj3ew ce will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a con .: zq5*9jwlkdgpe;q5sazfj (veyor belt to send the burgers through a grilling machine. If 5 kz*qw9jq(;eas f:gz5pl.dj 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 production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed (y;glvush n -81.5 times faster than Joe can. How m8yh(ul vg;-nsany times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend standssx.67r mzf5g k on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and thrkx5smrz76f. gows 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 particuk4 e i aq3 mg0o9;/k7hjzi+isflar 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 mui9k 4hkszimeqaog 7 i+f3;/j 0ch 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 bicyclbb:g,8*yoom3 jjaf7pm/c(/ 4 ti swcles, A and B. (a) Is there any instant at which t7as/m y:8 biojjcl f3g(/ b p4*cmtwo,he 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?