Does a car speedometer measure speed, velocity, or0 u7oeggs qr1 v 58/ynxgda)g- both?

Can an object have a varying speed if its velocity is constant? If yesusxq5ik/ xj 4 h0;n0kw1p/bt o, give exa w 5h/4xxoi;qs jtupbk/n1k00mples.

When an object moves with constai:qnei l j 7hwk7*. w+hyd9g*ant velocity, does its average velocity during any time interval differ from its instawak hyl 7i*j e9:.+7* dhqiwgnntaneous velocity at any instant?

In drag racing, is it possiblxy3a.kv5 0evf e for the car with the greatest speed crossing the finish line to vxv. k53 ea0yflose the race? Explain.

If one object has a greater speed than a second objec-38 fhncf 76 do,appmht, does the first necessarily have a greaterop-f 87c6,nphfmh ad3 acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80kmxd6a1/l edqo3 /h to 90km/h with the acceleration of a bicyclq6o l d1/adxe3e that accelerates from rest to 10km/h in the same time.

Can an object have a northward velk7y274ttq7uz7jkf 4i) nj tic ocity and a southward acceleration? Explain.

Can the velocity of eal5yv 8, 0onlan object be negative when its acceleration is positive? What about vic o,0lvyn 5a8ele versa?

Give an example where both the velocity and acceleratio* k;yxoub ll)fl: 9vfkd-1y e2n are negative.

Two cars emerge side by side from a tunnel. Car A is traveli+e j8n1 p)0hs m1ke.rona/atnng 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 cohe /no.tm0nrap11n8s )a jek +me out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decre,9+mj 6qngo mqsq7i0kz7u ( bt)zz+rqases? If so, give an example. If nis9,7zrjt 7z6 qk(0mzmn+gqqq+ou )b ot, explain.

A baseball player hits a foul ball straight up ierm4+ m v*y2gysk1iyb31h 0iwnto the air. It leaves the bat with a speed of1 vg1w4m0b32h*i y ieysym +rk 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acceleratiok 2y8)p3m8*ljjyjhar o pghb ;n31:oln due to gravity — does it increase, dbapyjlrkny2pj h gom*88jl1 oh;33: )ecrease, or stay the same?

How would you estimate the maximum height you cous px 6;pdhir/5 lz/a0xld throw a ball vertically upward? How would you estimate the maximum speed you could give ;/zd 5sap6l /i0xxprhit?

You travel from point A to point B in a car moving at a constant speed d3yy );zdmz6sof Then you travel the same distance from point B to another poin;yzy6d) mdzs3 t 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 demonstra3dy qvm1 0kym(tion, a 3.0-m-long vertical string with ten bolts tied to it at equam3k qymv(0y 1dl 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 end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration: a rocibt.v (mp1 z5mk falling from a cliff, an elevator moving from the second floor to the fifth floor making stops amm1v 5z(i .bptlong the way, a dish resting on a table?

An object that is thrown vertically upwardoc(bq)7 1oql x 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? [Hxl)bq c1 q(oo7int: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration b.f-vyg- n:qyat the same time? Give examplesv :.gybn-f-y q.

Can an object have zercq hgu*144ea lo acceleration and nonzero velocity at the same time? Give examp4l qc4ueg 1a*hles.

Describe in words the motion plotted in Fig. 2–28.*d)n ky u,x6yu jlni;seo9r9 in terms of v, a, etc. [Hint: First try to duplicate the rn.u9j*d, e l6uynyx 9o;)iskmotion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in yg 47hc*fi3ycj/pgti ;i b (s0Fig. 2–29.

  What must be your car’s average speed in ordeqxfr4 ppd hri-w2 (o+fn0);sir to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does m 3o nn /6h/wzyxgim7.it take to fly 15 km?    h

  If you are driving along a straight road and y7a ztlf 24bdw/ln*1giou look to the side for 2.0 s, how b27td / il zwagfn4*l1far do you travel during this inattentive period?    m

  Convert 35 mi/h to fb9ppkz:gvot g(j,)3
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moveszlum //sx 76br from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily at 95 km/h for 130 km. in x; iyyxnvh1 /6w21wIt then begins to rain and you slow to 65 km/h You arrive home ayi16xni h1xwyv2;w n /fter 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 fln 7v jx3p+ma:gash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all3xjm+ p gvan7:, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track i3 .xoq +2zx54n bnf:frv ;nokvn a total time of 12.5 min. Calcul;n f2n+oxk3. fzvbr vx:onq54ate
(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 z7)5ac6z d 4a cfvrqf*away in 14.0 s. It then turns abruptly and gallops halfa5 qdfcc)*z r4a7 6vfzway 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 ot.rqx:f,o xr5 (/f p y(nlgetzuc-7h*uher on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each o7nqe *:u- x o c/xrfugpf,yrlh.((t5zther? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m beh3sxcn ri3c5-t /74 x :jtl9vc zn(ifdmind a truck traveling How long will it take the car to reach the t tc (dj -ltrcz43mfxns7vin9:c3 ix/5ruck?    s

  An airplane travels 3100 km 0q ia.p17lx bej,/ kfnoi04p a7*lzyf at a speed of 790 km/h , and then encounters a tailwind tlqb .iazlpn, i0ko7x *4ef7f/yaj01phat 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-tra5wq 2/l*kr oymvn90rip 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 r rkn/w* 05vyam q9ol2covered at 55 km/h.    km/h

  A bowling ball traveling with yeqq-1iy2n. yconstant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is ey-.1yiq2yn qthe speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates fja s*,1uthl6 srom rest to 95 km/h in 6.2 s. What is its average accelht1js6alu* s ,eration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accelerati0(sj g3cj.z2lhkw b0 )svk /jron h)0j.0(wks2j gs kc3brvl j/z
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a p)dr)c(0q*hw-z a jdcparticular automobile is capable of an acceleration of aboutrca0whp))z -d(jc *qd $1.6 m/s^2$ 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 5.05e(yw pc9 3rya/t(wsz3;uvxw s. If it then brakes and comes to a stop in 4.0 s, what is its acceleration in xcwyaz59p(;u rv t3 s(e3/ wwy$m/s^2$ ? 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 pa: ;0uix+y-s* vpglnat t = 0 and moves in a 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 - xulay* npp+0gsv:i; Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its accelerat2v iv8+u:*z 78bguglae q1wwfion? How far didww1 b: g8v+ lzgq28uauv7*eif it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What wa,7bq ez7sx cn8s its acceleration, assumed consta ne87bx c7sqz,nt?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff:pqigf-z:ejbe8o : 8u. How long a runway is needed if the (constant) accel:ji: euog q ef8:-z8bperation is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speed )s7 4ipe)j47 )vyaqrb t+sjmw(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 long does it s4 4mpr7)t+)qve a)7 jji sybwtake 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 s. Hoj9mjl ua/-z o6;mmi .5shc*r (oses0o w far did it travel in that time?.z hma-m5 9o6*c ljuosj;em/i ( ss0ro    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assuminv cokxzf 8++q;asa2op)4yc 7sg a def+psxk284vo z7;oacsac y+) qceleration 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* otz2b:*pqb b9z :i* 5iyhcba tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the dzqbpz: iay:5 29i*hb *bb tco*river 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 initif k2)1+ s.joyiqx4sbj al speed of 95 km/h and h.y 1kjfs q4i2)jsxb+ouman 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 stopping distance blf.ve02,vx kxi pj-;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 vtn./11 t ffjugoing 25 m/s on the highway. The car’s driver looks for an opportunity to /.unfvtt1f1jpass, 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 complet ;y;r0:x edhqx s ffah;0i)rh*e the 10,000-m run in less than 30.0 min. After exactly 2 ;i;e* ;hfrasd )0hxfhyx0qr:7.0 min, 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 car at 45 km/h approaches an intersectiol)hbw,bgyh 8 )n just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before th,b )ybh8w glh)e 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 hitcp lbbgj;8y mc4 b)m42s the ground below after 3.25 s. How c; 2c8jmm p4bbb 4y)glhigh is the cliff?    m

  If a car rolls gentl)q 04rhan .szjy ($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up into the air with a speed onq axb xust9n91 4c au/o1eh0(f 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 u 4i4on axvhdb+hc8 b+uo +n)o:pward. With what speed did he throw it, anc d+oh8)+nxb hai:obvon4 +u 4d what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influ8 .msnnng t*p7ence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore a*ns7g.8pm t nnir resistance.

A helicopter is ascending vertically with a speed of 5. l+ueq0h /1p+naynxzzst) 8+n 20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach th zaxz+qe8yh1pnl0+nu+ t)/nse ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance traveled during e8x gktm q(*sc.5:(si i;zhw ojach successive second increases in the ratio of succesk5mi(szh;s*gx:i8 t qoc (w .jsive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (alg- vzml8, o,syxebraically) that a ball thrown vertically upward with a speed vs,- zoy, mxl8$v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a spee 1o jzz6+9hstmd of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in Fig. 2–18 (or n xu7m 6ya4qw i ntv.q5l63uot(umber of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positionst4votq6 7a.mi l3nx(uwyq u56, 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.f oz:.ysv8/mnqgo 6i.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fa ymsg/8z.o6:qvni.ofll?    m

  A rock is dropped from a sea cliff, and the sound of it strik5 d 4eojmqdsy/:h 6y2ro *6lpwing the ocean is heard 3.2 s later. If the speed of sound is rwye6d4:o/l o2h jspmd6yq *5340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. You poi)*-bora 3tro tat;5p knt 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 th 3bt-okt);pr a5t*oar e vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the,h d aw8mwv2u8-x0 kk7vn ij*n edge of a cliff 70.0 m high (Figm2djvww8k70i 8 vu, -hnkx*na . 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 street with a 1pfvlkgkxu(;b sz, 7 9joda1yfl84.gvertical speed of 13 m/1g 7 bk8jfpkv1luygd,o 4(sz f x9;al.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 n 6dw52j (;xk 8koq+zl-qckpb 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 a-zjbldo5p82c qn kk+kxq (;w6ny, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time is wbe+7 .gxq9pxew85 ugplotted in Fig. 2–28. What is its instantaneous velocit.xe+g7exu wwp5gb 98q y
(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 dqq zt)g,3e* :df )y::arhif happroximately as shown in the velocity–time graph of Fig. 2–35. (The short flat s z r:da)f*qti ::dh3f),heygq pots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the )xm8ho:3ca n /mlyi( hs0+l 5:qwfjh xcar in the previous Problem (Fig. 2–35) when i:yc/m nq:x(h5fsh)8woija0l xhl3m + t is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the 5 ,cik6 8oo40 i (pbx+qmmbzmyobject traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph-qhru b2jx 1v1+5(sjlx2n lj g for the object whose displacement as a function of time is given by Fig. 2(snj25ubq xg lv-lx1j1r j2+ h–28.

Figure 2–36 is a position versus tc h08x/:t8a6ck+ofpf 4j sy)pvek1t pime 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 +xk6k h ef 8s0 j:8/p)ac14ypovptctfobject speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fob:k (:yj: hvc*t j7:ppf-k caqurth-story window 15.0 m above a firefighter’s safety net. The survivor stretchet:(7qj-c hc ::pabfj vpyk k*:s 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 thp;w491ky-f6n h mb /ml;kkumhe Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how manyk ;lbmkw49nykmf;m1p hh-/ 6 u times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat belt has a gw de(asn ):jy1ood chance of surviving a car collision if the deceleration does nojwnas: )1y (edt exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the r,h/aw x2oxf f6n4tc. 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 th,w2 nc ftorahx.6 f/4xe 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 cqfu/g-p ,37qylzzup1ars for front-end collisions by hauling them up on a crane and dropping them from a certain height. zyf,u l7qzupq-p 13/ g
(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 t cc*ge f238vioravels 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 ofd:4g00z2mnh80j1whf/zs pm; uxn p uo the train has a speed of 25 m/s when it passes a railway worker who is h 0/ swp pg0nm;no 2mfd :z1j0uz8uh4xstanding 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./p-qokq,z2 k , wo2u3jor an;ru8s0u t0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleratio3k u0 j/,2qtrwoaz82qpuo k ;rnuos,-n 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 a 5zfk.+d6;y 6mat 9xxgem +acdupi 8gbz2jp41verage speed of a t66 k aa49g+ 8yp zcj1.igtub5epx2 mdmx+df; zrain 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 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 diving for fi,tkra:,mco xlt4 u5a 0sh. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takesx:o,c5uk mlt4a t0ar, 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 golfer strikes a ba dfj 96su.3v gzi(t pjch/e5d,ll 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 difficult than from a downhill lie. To see why, assumid9se.6jd(v cp ,z gtj f5u3h/e 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 fm/ libq1d+ (-lmw zr4 wgtio;9reight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and l+-iomm b1;d9ig/ twwq zr4 l(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 bufv-9c5k9o+ ypf nqtpnbor- :;si25quilding. A second stone is dropped 1.50 s later. How fa5cuoof2nnq9rt p-f:s-v5yp+9kb ; qi r apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the c(- 0ha tc)gd9p u)/wodx.alixourse of a time trial lasting ten laps. If the first w9o(dluxh agx0- c)t./ ipd)anine laps 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 Frkk)/ q b gv ,k+:tqfha1l8cjx9ance crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed ihqa) cqlb: k8+kg, t1fjxkv /9s 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 cvdfc- .)bmxk c 3:h,gxhild can bounce up one-and-a-half times higher than the se:fm c).,vk-b hx3gcx dcond 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-kcfh7.cdhloi/bjex ,40lnft *wh 6x,) 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 ,wxcfhd xcho nib4 0)t7 .l,e*h /fl6jto pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/syw1iy17eqjz:sp c4z 9 In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from bezwj1pszc741 i9yye :qhind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, 8rv u2 1cwxu db)x60id e3vxdpow6(4dfrom 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 trafficgg/xx5p d0 *hx tzz12luv cc38 signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The g1lg z*c/ 5uh tx3d0zxpx 2v8clights 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, passedkgvn)- y91kbm by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The-)knbkygvm 19 police officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.4 e3xz-2jehky 00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones landx eyz3e-k24hj at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The fig( l2*kbwcdlcirpe t:78 -ke 4rst stone is thrown with a (dwl e7e4 2:cbp-crk lkgi*8tn initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second 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-fallcbca.x,9l)z9x 4a qvaing parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pul4zal xacav,)b 99cx.ql her ripcord? What would her speed 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 fp,4ef 4yq 90l5e;zedvixv .qepej.1uses a conveyor belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgeqzifq1ee vpj e4y;e950,xlde4 .f. p vrs 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 1.5 t i9fxx,m *w/ lru.;zxvimes faster than Joe can. How many times higher will Bill’s ball r;uxm.9i ,/vwlf* zx xgo than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your frienotw t4 2.v(ehmtz933 ck2zve qd stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with whichqm49vte 233 tw(tc z2ke .vzho your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using,3 ww-5 1y zmf8qicjrhw82ejz a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop itj z8ycmw,whe81i2z-fr 5wqj3 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 building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycleb1xb5xkcd v9xt7p 4 q/s, A and B. (a) Is there any insta5 xtxx47/ckd bqbp9v 1nt at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?