Does a car speedometer measure speed, velocity,lmi kh6afi/; 2io(va3ffx 4h- or both?

Can an object have a varying speed if its velocity is we6w tq; 4tp x(1ocd-wconstant? If yes, give example-qttd4pwe6 ; c xow1(ws.

When an object moves with constant velocity, does its av(cax x):i2.sy w)jub8cp ,hgjerage velocity during any time interval dif)a.(x cubx2)sc,jpjgwy8h:ifer from its instantaneous velocity at any instant?

In drag racing, is it possi0/o,ap ffli(q4c-y 9ic i/vvable for the car with the greatest speed crossing the finish line to lose 90fipv viq iaoflcc/a ,(-/4ythe race? Explain.

If one object has a greater speed than a second object, does the first uv-7+ )7adtlnx*zky52 hbqdf5aa .ppnecessarily haf z vd2.7 a-q dtap7hxn*lbku5ya5)+pve a greater acceleration? Explain, using examples.

Compare the acceleratir4 866yvd7e soq gjor9on of a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the 68r eo46gyrq ds97jov same time.

Can an object have a northward velocity and a sl 3nv6udg0zi (outhward acceleration? Explain.

Can the velocity of an object be negative whd93 ixu 3z io2;/yikxken its acceleration is positive? What a 9k3dx3o k iiz;yx/u2ibout vice versa?

Give an example where both the velocity and atss- iwjhw z73z(c )f(cceleration are negative.

Two cars emerge side by side from a tunnel. Car A isikh**y.ryp8vpc )x 1d traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passinprvc ky**h1 8x.d i)ypg the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? Ifb ky.4l3;j4mg :nig,knz -mck so, give an example. If nokg knblj-k 4y gc,.:zm3mni 4;t, explain.

A baseball player hits a foul ball straight up into the air. It leaves ak** cf( 2k gesic:z. zds8n+qthe bat with a skns8*df:i .q+ e*cg z za(sk2cpeed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling obq(3+wkfm e v8uject speeds up, what is happening to its acceleration due to gravity — does it increase, 38mv+euwqf k(decrease, or stay the same?

How would you estimate the maxd9twpn,b1 rj2h2+y g uimum height you could throw a ball vertically upward? How would you estimate the maximum speuypbr 2thj1g+n,9dw 2ed you could give it?

You travel from point A to point B in 4:gro(gr7p ouuz-xe *(im+po a car moving at a constant speed of Then you 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 u 4e:ozgor x (ppomu i*(+r-g7trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstr1 dzk2,f9 7sshrks+yvation, 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, h1sf vz2yr9k7k s+ds 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 consta4 3h3d;5hg34luip sjx,c i hdknt acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?ul3 xd5ghk; h34phs i4cd,j3i

An object that is thrown vertically upward will return to i bk+gn b,,lqe7ypu 31uts 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 res1n qblbpueuk+y7, 3g,istance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleratio.r+ 9q8xnf4hzc :bkfh ,li0y un at the same time? Give example:q l8 f4zhui h.n,br+ykf9xc0s.

Can an object have zero accephrq t,n;ibci + odw5l.ayl* ;)0g-hzleration and nonzero velocity at the same time? Give w+-,;hi z0)bnyc illg* prht.;aqd5o examples.

Describe in words the motion houwj 6v7c *c qc836;lri2p qwplotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicocwq*h iwc3l76 urj6cq8v ;p 2ate the motion plotted by walking or moving your hand.]

Describe in words the motion of the oipv 0fd *)a;tjbject graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km k4g s *a5dcxwl1ye d,c3odd 30in 3.25 h?    km/h

  A bird can fly 25 km/h How lonmct: s:(b(2ou:9f xuq3gln1c c qs u/ug does it take to fly 15 km?    h

  If you are driving along a iqzd qaxwgk0+- -7l)mr 8zzt/straight road and you look to the side for 2.0 s, how far do you travel durx -drzatq k)z gilq w-/m78+z0ing this inattentive period?    m

  Convert 35 mi/h to x)mv2quk h-*;fu wvk 8
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves(8llxxtg hkv+*e feue5 qn:02 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 s7) 9n xztobia0:rxih.chool steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arri 7o xznx.i0hir 9:ba)tve 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 libc ;x dg. /7ce:ldesm5e3-eqoghtning flash and the following thunder 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 freqx eg 3md.c7 e;o5/bdesl:c -om this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a tota+tbt 2(mqbn2iox(kbsa9 :mh/ l time of 12.5 mint(b29:2+mk/anhi qb sb(x omt. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straap 6;z: l.kgk m*tfiznu ,2h.aight line, moving 116 m away in 14.0 s. hkazgt ,uap zi*l:.m 26 fk;n.It then turns 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. Each has a speed of umcwtk* 0:,;tfp e im7fgge ,095 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be bipgk:0,te;mw* 7c0,ftmgfeu efore they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will it t 6b k3- 6y(diqos6he9mcer lc1ake the car to ikqd61rys63ecmh le o 9c6(b-reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounteryqlodj.m ks;by: j t +-:41v hn1dlf/gs a tailwind that boosts its speed to 990 km/h for the ne l h/gs+:qdtn-;j lf14 yymk1:vjbod. xt 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 copovm9h :x*wc8;v ;gymmplete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch b :hg8 ;*mvmwvx;9cy opreak, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end of:p +t,jy-hv b0wkt.lsafng;8 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 h-t;jf:ysbl. ah8 n+k wg,0vtpands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from - z;xlmr+g *nbtwx0ccal-3x9/ n 1mkfrest to 95 km/h in 6.2 s. What is its average acceleration c0+m1-rnwzk m; xf9 axg/l-*cl3tx bnin $m/s^2$ ?    $m/s^2$

  A sprinter acceleratevm71x ;x1.p n:zb ojbps from rest to 10.0 m/s in 1.35 s. What is her acceleration zp1:x.b p1;vjm7 onx b
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile j2cf f-2yb zh:wy-bi 0is capable of an acceleration of about yfj- b f2cybz-i0hw:2 $1.6 m/s^2$ 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 e sn 2pt6)hq: 2aje1vbtravels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what isa)2 e: sh26ne vjqp1tb 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 m2etr,1 gl,slvoves in a straight line, is given as a functioglt1 le2,r,v sn of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleration? vfzwq1hsw*jw 8 x9+p 7How far did it travel in this time? Assume constanxfwzs1w j* 9p7h +vwq8t acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its mclo 1l y0y/zb30om3raccelerati0o1b3m 3r/ mo0zll ycyon, assumed constant?    $m/s^2$

  A light plane must reach a sz/ ud(l/;se0tmsk6xa peed of 33 m/s for takeoff. How long a runway is needed if dal/s/u 6 szmt;0(ekx the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top speyqu6(e f*n7c cxge.z8 ed (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 lo6y (gnx7euq* 8fzc .ecng does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 (i,c8dlq:d1ki/ky s.zc zs7ms. How far did it trave7 cz1ikqlcdyds.m 8, :i/(zksl in that time?    m

  In coming to a stop, a car leavesy)ko -,i,w1fov ktng) skid marks 92 m long on the highway. Assuming a deceleration oovk,t wnf-k o )1)g,iyf $7.00 m/s^2$ 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 com3b kf 1 bd89bxdbo vycrk23r g0kr0*4tpresses and the driver comes to rest after traveling 0.80 m. What wa3kbrxfr b o 92t* 4vd0kyrg0cd8b b3k1s the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a cawvoygm / a53*sr with an initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleratg w3a5v yos*/mion
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping dismmz)k72a 4sgq tance 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 drivh key-8mw9 3c1owmw4kw*3fhwer looks for an opportunity to pass, guessing that his ckkw 8e 3ohw931wf*-w4hw m cmyar 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 33 8u,lemxj+ deu 8rzdin less than 30.0 min. After exactly 27.0 min, there are still 1100 meu 8rjmze +, d3l3dux8 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 ap.y6j,o5lycuf .ng7 yxproaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). 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.ygy,6o.y 5c nf7 xjlu $-5.8 m/s^2$ , 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 groung+qa-wa:(5m cmhy 9nwd below after 3.25 s. How hyh-aw(+gm59:m ac wq nigh is the cliff?    m

  If a car rolls gently c:wm6o.5subg(vu)q . s8wrvd)svy k* ($v_0\,=\,0$) 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 of 22 m2 pk)z dqm:w:op5 sv-f/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 tv10p3a0ei cjxrl30il /l;qvvhrowing it vertically upward. With what speed did he throw it, and what height did it reach?a1cp l 0q vil0j3;vi03xre/vl    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the i0fa wmisjd(/4+r/h dlu w f:*tnfluence of gravity. Draw graphs of (a) itsl4dt/f( j+af*dm :h uw 0irw/s 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 qja(7rid2 ap/ with a speed of 5.20 m/s. At a height of 125 m above q(2rpji /ad7athe Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, ( hbx p-ww18ur*/a3ml sa2nptshow that the distance traveled during each successive second increases in the ratio of successive odd integers (um-*1bht pn83 2x (lrw/waa sp1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a bajvx4nbdc1t c31zs :hm8+c a1c ll thrown vertically upward with a speedz+ 1n4ma1 bs cc hdvxct8c:31j $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed of irs ae d/rr/ntf *el d/c(e;5(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 photoflass;2kz kir*( x0chn) nnh of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple ( 0 *in;kzxnc)2k nhrsis about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a windcs9y/jzl1 7 6xacx k6lx9qkm 6ow 2.2 m tall (Fig. 2–32). From wham96sqx lk6l xzj9ccy7 x1/ 6kat height above the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it eo0 pk i:ck +/)f(s;ol,tljbpstriking the ocean is heard 3.2 s later. If the speed of soundse0,ki lp:k ) ;bp+of/o( ctjl is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream o9)mxe dmk)gj)f 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 spg xm9kjm )de))eed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s froyc xuk *yxo9-kl pzj 42 7p4osgbs86/sm the edge of a clif 4c ypj 8o6 by9ossk/*-gz24xusklx p7f 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 streec*gaawz1( f- ezu7ruo7 7ao3 lt with a vertical spe1f7uu(lca37 o7gra*ze a-zw oed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of timez7h:rfmani,/ . (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 the acceleratii ham,fnr7: /zon constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straightqx 26:uhm.+h5pk y bxurp.9nt tunnel as a function of time is plotted in Fig. 2–:u p.k.xh9+n p5q ym 6brxuh2t28. 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 kh4yl3uuj ve5re5qb8 -xnl:2the velocity–time graph of Fig. 2–35. (The k825l 5y3 ve 4ulxq:je -rhnbushort flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average asod*n9l* oz .ycceleration of the car in the previous Problem (Fig. 2–35) when it is z.dos9only** 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 rb uff8pue .r6ho8.d- traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t gbt)w w koc(3b/raph for the object whose displacement as a function of time is given b/cobw3 kwt(b )y Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an c74dzvdqe r3 pwo2;.tobject along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the t twozvp3rc27d d; .q4eime interval from C to D.

  A person jumps from a fourth-story window /9ofcvg w,-r r15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–37.r/cgrw 9f-o,v
(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 .s( 5bpvs,e4d.sy rp vis about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moo 5(yp 4,vv.bs r.sdpesn, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shou4lu9 qoi tci9x9ny;di;xyil a 6v31(tlder seat belt has a good chance of surviving a car collision if the deceleration doesx o u 9ia ;tlixn(1vdyy;9i3q4l96i ct 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 bridge, 12 m above the road below, am*k)pamgxjz*.;: t 1cok3lpc nd 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 ;jmmx:p*k gl.a 1p3 z* otkcc)the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for frty orh7ff 9oq+e:t*j-xri , .lont-end collisions by hauling them up on a crane and dropping them from a certaif+q,t othx- yre9.o:r j*f7lin 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 trav60jhfklt25k q efv(0bels 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 accele,m ieb4na7) g-h ndodj .s50;gzbs8eu ration 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 from where the front of the train started. What will be the spedeb g-5dmzi8).;eou sh,07j bnag4 nsed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 lsq s7/eo ov(9oay *9hm above the water’s surface into a deep pooloslayq oh*o9 v9 7/(se. 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 rap -tha1g94; qbzcs+9bcx bs6ua id transit system, it is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of th z4sc a99;gctb6 ux b1+sqabh-is 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 strao ;n:ueknt8 e1 (iugr8ight 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 n :en8k t;8(iru oe1gumust 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 a5j45dlno xo 1g 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 xndl1goo5j 5 4the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a coi (sqt* 60p6)pa+x s 1rrjzpvinstant speed of 6.0 mxrpp* t6az s( )6v0r+ qi1sjip/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 hiz 6 w gc-z6h7r ,,nv/dngbnj-lgh building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one hadcz j,v 7b-,nr6nhn-g gw/lz 6s reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of zz x r2u na//rj5qxv:4a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap/r5 4 2:zjrvquznxx/a?    km/h

  A bicyclist in the Tour dep3 wzkq3;r 48e dlqsi3 France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, hisp i ds4w;rzqk3l3q3 e8 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 can 2:z 8y43b2r0zv) ybkstv lckobounce up one-and-a-v8s22:kzl0 b3bk)4tz yvro cyhalf 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 t*x+mxodb6oa ax y,k;2raveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train arxoa*ko;,x+ ab6m yd2xe 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 ba9qs syz );mw 8+qnwmj:seball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about my w+j snq9 8;z)qwsm:3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerqrz 5g5sh: g:)uz-n4ct/fgqqation 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 trafficu5 6jk y1+delw signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 l 15 jd6uywke+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 speeder traveling at a conrhz ;xk *a5ub4stant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constanth ur;k z5*4bxa 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 r/ z(/ 0+s ya c(tide-fiz)2xiluekj (goof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25(i0 yx(gjd2-ciilte (u/zeszk +)a/f .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 vertical 7ol( yna*6:9afxsnxaly 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 aol6n97nayxsaf( :*xa 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-falling parae a-cp 4n.5 zb/ivkwt)e:-hndp4sl +gchutist to fgaz:w4 ci- es+ dl.n- ev5/n)hpkptb 4all from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyoo,fo5 0hp mr9xr belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers rexo5 p9r mh0of,quire 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 times faster than Joehaq9p(4fvhspl /ik b1q)*/vy can. How many times higher1fiy q*)hpa9b/ p 4(qv/vhl ks will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff whk34ts79jrs b4bd,i k. kid -mfile your friend 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 4d7kdjki , t4rsk9 m3f.s-bibfriend 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 th k:zs,rxx1f,an e02x ce height of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.,nfsc, ak x2:ex zr01x0 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 0-ou8+p qsfw.p aa ndl/3d(qggraph for two bicycles, A and B. (a) Is there any instant at which thpw8a lsqf/a-dg 3u0o dqn(+p .e 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?