Does a car speedometer measure speed, velocity, or both?tj1/ g x8xcw98zge-dm

Can an object have a varying speed if its velocity is constant? If ye7v0i+gnu(mt ys, give exampl y+u7 gmiv(0tnes.

When an object moves with constant velocity, does its average velozqrl so5x1:/gcity during any time interval differ from its instantaneous velocity at any qz rogl5:/1sx instant?

In drag racing, is it possible for the car with the greatest speed wyq:j c*hf-,wcrossing the finw wq*y:f, jch-ish line to lose the race? Explain.

If one object has a greater sp :sn ,2gnx yq0fgast5-eed than a second object, does the first necessarily have a greater acceleration?,nf-5:0nt2y a ssxgqg Explain, using examples.

Compare the acceleration of a motorc,0 m6bn3+iiuu kw- wxeycle that accelerates from 80km/h to 90km/h with the acceleration of auw xw,b+0mnu6- ei 3ik bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward nalhzfe9))/ tp o3g 7hacceleration? Explain.

Can the velocity of an object be negative when its acceleration is positive? x*2rptuv7q.jsys: m4 d 71su sWhat about v7sussq7v4:r2d.* u sp1yxmj tice versa?

Give an example where by fo7eiehiay;0. (3 *br gqu0noth the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A isr4j4z69 pdi fs traveling with a speed of 60km/h and has an ac6i 9fz 44spdjrceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreas1v ej)k :z)t.w+ srocwujlt rkw (/6p5es? If so, give an e wkp+ l5wrotvu:k j .est)/)6wr (1jzcxample. If not, explain.

A baseball player hits a foul ball straight up into the alqz)-rg90v)a o rn1moir. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it-0alqmv or9r)o1)gzn ?

As a freely falling object speeds up, what is happening to hke2l1o/ 4 ktyits acceleration due to gravity — does it increase,t1y/k 24hke lo decrease, or stay the same?

How would you estimate the max3lhh- onbs *hlsxj,52js8j v. imum height you could throw a ball vertically upward? How would you estimate the maximum spee-oj85vl32j lx b js.h ns*h,shd you could give it?

You travel from pointz * .whsew9:v4xv ph3y A to point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a consta y9v: ph.xwzeh*wv 3s4nt 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 t a- vd+g)jm9hden bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin pl-a)vmjg9h+ ddate, 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 mut xd45oieyo0v;aa78c ql22 qotions is not at constant acceleration: a rock falling from a cliff, an elevator moving from thu25 vca id40q7q82oyeo axl t;e second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original position i9sn t 7w90xkrwith the same speed as it had initially if air resistance is negligkn i9970r swxtible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzgs/-es 830ad d8sun-n nw dzp2 2 -unw0wxwix(ero acceleration at the same time? Give examplegu wn8s0p-3s/nswn28did -nzaw(2 e-x dw0u xs.

Can an object have zepqzu1f, k5 (vyx)*dva-gvo8cro acceleration and nonzero velocity at the same time? Give exay(ogxv 5)cfvk8*zuv-p q1a ,dmples.

Describe in words the motio1+m2stb 9g,lgrq :xj qn plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or 9g1 lg:b, j2t+qsr mxqmoving your hand.]

Describe in words the motion of the object 49svd2ykx2 x4 su v+xsgraphed in Fig. 2–29.

  What must be your car’s average yncgetsgs5 - 76zu./f1mv g0d speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly vhsi cs (; 1kzx3gh26rx+98 dazg2vs d15 km?    h

  If you are driving along a straight roahu 5m*l17io tyd and you look to the side for 2.0 s, how far do you travel during this i u17*5 thiyomlnattentive period?    m

  Convert 35 mi/h to k z7js.9czvc (
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fro6ihv30n 2 8zsovnbo7 uub1/tpi+ we4tm $x_1$ = 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. It the; ;ex/ujvitfy.i5pd6c +k*jnn begins to rain and you slow to 65 km/h You n;tvyuj6 cjf k*d/pi.eix 5 +;arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds betwem /:/6qy/sc8n bbcfia en a lightning 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, ebysnb/6maf: c8q/ /cistimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarte;k1-jkv l mcoc.m rbc8g rzy1neh5 **.r-mile track in a total time of 12.5 min. n8h-k1y5c;1clk mz.verm cg bjo*r*.Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 tvnif6o1fzf n6-f8 b g.2a:ris5a 3paj6tho 7m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s.ffi pi8on2 navg tah b6 1 o6f7:jfzrt-a.5s36 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 hb pbiv90c0:b.o7 ia unas a speed of 95 km/h with respect ton9ivb7u:cp 0ibab0.o 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 traveliyn) y mgt ne,3k,ohbjr-;k cags.4 9(vng How long will it take the carv.gt4 s;ary(cmy,hkn je3,ng)9obk - to reach the truck?    s

  An airplane travels 3100 rl*y:cz9 zpwxy-hwp cu (.ck)gin 9-8 km at a speed of 790 km/h , and then encounters a tailwind tx:* uyzzkpgn8- c9 (wcyhl)ipwr.-c9 hat 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- 5+x eh,to*ullyj6u6htrip in which the outgoing 250 km is covered athlhut ,6x*le6yju o+5 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end ofgtu p2-zw*( uu h tv+1s0kxrr. a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed -ut u1krwx*0s+ p(z2rtvh gu .of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is it ltsi*)g0y77 xz exi+ks average acceleration ily+z7*xte kg7si )x0i n $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from r(traqfg )n u:,est to 10.0 m/s in 1.35 s. What is her acceleration,gfqt)(a: u rn
(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 accele1iw+ dg3drjnshd*a x8a) uq7 ej,r/d *ration of about unj /x 7dsgd*edi3,r*r 18adq+ w)h ja$1.6 m/s^2$ 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 jpi3pgg9gw )aaw6zc.( qh9s .u tws4 7constant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is it 6h(z7s)49gqjg gw ws.wcut9i.p3 pa as 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 t gtf-im/d.(9wa4fe w rest at t = 0 and moves in a straight line, is given as a function of time in the following Tablett a/ 4(wmf gwef-d9i.. 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 9 q wpwhks,bj(k8 4s2z13 m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant acc kkw8w (j2zhq,4 bpss9eleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distanceu fb6p3 e v88mupfguqi +e7/9njlh 43r of 85 m. What was its acceleration, assumed constant?+v6urqjl3i3hf 4uem8pg p9f bn 78ue/    $m/s^2$

  A light plane must reach a speed of 33 m/s for miho)ujfo /9,i.fxb-4rum5a mua:v 4 takeoff. How long a runway is needed if the (constant) accelerat,)mo uu fbiho:u9 ri -4m.x/jma4f a5vion is $3.0 m/s^2$ ?    m

  A world-class sprinter can burs; 3(0u rw*eri.mc vwxet out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach we rmxwi(c3v u;e*0r.that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformaz4 eoeb o6u2-ly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in6aeob o u-z24e that time?    m

  In coming to a stop, a cad26 ybsx:ffla 74+tp4r (pijcr leaves skid marks 92 m long on the highway. Assuming a deceleration o7piarx2b:sjf+4 dc 6(tp4 fl yf $7.00 m/s^2$ 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 compress8x5y bxft5x( r(puj5ges and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9p((5gyfx5t x x br5j8u.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an 5 qkng90.x+fey:j(;jdjj5o mj )t kqninitial speed of 95 km/h and human reaction time of 1.0 s, for an accelq5ym9jjjf5j. otk)ned+:xg (qk 0 n;j eration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for )/kzyg4l bc:ouzvoof, +kw j0*c,scz-r8ra;the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck goings(js/fb-.k -(2rann yzbpsyn(6w*hh -dr5 xr 25 m/s on the highway. The car’s driver looks for an opportunity to passyshd nr-2nxpbs( 5 /w-r(( rs*kz-af.yb6 njh, 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. Aft pis fhy;( kqd8dh3;g/er exactly 27(;phyfd;8g k3iqs dh/ .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 wey3dm:h, *c6 ub v5qis1 gvg1km/h approaches 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 shoulg v ebhygi65m1 :3qdscuv* 1w,d 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 f:g u *nsfe14usrom the top of a cliff. It hits the ground below after 3.25 s. Ho g1 *ussfeu4:nw high is the cliff?    m

  If a car rolls gentl 6w)oyycy6.tzy ($v_0\,=\,0$) 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 u2qtignsh/; go(2b8w2zgo4 l m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a lkcvot hjhq6(p n3 /in,m9w(9ball 3.0 s after throwing it vertically upward. With what speed did he thr9(j k9vnhi(otnwp l 63c mh/,qow it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rese);3t4lrjhy )o.e ogwt and falls under the influence of gravity. Draw graphs of (a) its speed and (b) tj)wg 3;e. )rey ohtlo4he 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 ltynwy1;a wy0uj/ c255.20 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 5/at 1wc2n0 ywlyju;y the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from 1iz nq,. +y/hjpuiec3jo( , oprest, show that the distance traveled during each successive second increases in the ratio of successivjyuzn oi/(,,q.eppo+1h3 icj e 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 (algebraically) that a ball thro/: *vuz yth5awwn verticall5 vuw*:y/htazy 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 vewit1w9cm6zkzqhcfk+ cxt/1ei70d 8 3rtically 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. 2–18 (or number sf8l n4ehcy.0vq9 (swof photoflashes per second). Assume the apple is about 10 cm in diametern evfhwcsy49l s(.q0 8. [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 /u -ghdz cnxb9 2k:xd3ko v6adi1p8x- travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the sdd -pcx/gkx nh:-oaizv96 2bk3 u xd18tone fall?    m

  A rock is dropped from a sea cliff g0.kcr4z jzrorgx 930, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how higjz0. 9rzk 4rgg0 oc3xrh is the cliff? H =    m

  Suppose you adjust your garden i 7wzvc3/.p f5ujdjut27p 0 ybhose 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 thejijpbc 7 3uvyw7t5f2u.pz/0 d nozzle?    m/s

  A stone is thrown vertically upward with a speed of 1mz; jgggbz1/,5ib.k6 bl v5u:o fyto62.0 m/s from the edge of a komb.,l6g/obgiz;155j z6gu tfvy:b cliff 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 the91kvl7iij/ d r street with a vertical speed of 13 m/s If the ball9lk/ 7ivd jr1i 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 aw8v3(nl s2uj7kc (oco function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity conson(o u3 (lk7 8cjvwsc2tant? (c) During what periods, if any, 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 o3oitdfz n;:l25j*i l,1fb sn of time is plotted in Fig. :3i n1;nbl5z,lofdfi2tjs*o 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can accelerate approximately as shown in theot7n */h 7kbre velocity–time gt eo/rkb7*7 hnraph of Fig. 2–35. (The short 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 acceleration of the car in thfx+wwv*a e0 .l-8**jwipykcee previous Problem (Fig. 2–35) when it is in 8 w*y. k0wxcvf* pa-*ei jl+we
(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 travel 1/aa; kwcnsi/obw6v) ed during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for th /ts-jp+h*nu1jownna ,v d7q 4e object whose displacement as a function of time is given by Fn n n-vu how7a, pjq+j1*t4sd/ig. 2–28.

Figure 2–36 is a posie7j fug27 q+5ybjr;. r9w qbmxtion versus 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 qjfbr e7j+rgm ;.bwy957qu2x 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 time interval from C to D.

  A person jumps from a fourth-story win,3ifb j2ppd+uu; b ff5dow 15.0 m above a firefighter’s safety net. The survivor stretches the +bj,3fpi;u2bup f d 5fnet 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 about one-sixth what iomwf4f2: n3 i0raz xr0t is on Ear2n4 rf0amzo3rx0fi :wth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-0ke jv4o*-uxm shoulder seat belt has a good chance of surviving a car collision if the dec0k-j eou*x4vmeleration 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 bridge, 12 m 1w j3q5wjtjg+j vs 7e9above 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 hesjqj3 v 59 tw1w+7jgje jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for fby bq a3 q*elk8vnu830ront-end collisions by hauling them up on a crane 3 bkq*vu8a3b8lyn0 eq 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 travels aboutj mts*9t cr0/x*wgx81;emb4ua d 0bd n $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest. The front of the c10 eu kc4;k squtzpq (j98n6jtrain 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 speed of the last car as it passes the work;c(s z 018ncu6kj4 tjqkup9 eqer? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a d0vwp yib(4d6jv:b:b heep pool. The person’s downward m yvd46vhwi::pb(b0bj otion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system,goqsg 3w9u2d4 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’q o3sw9gu2 g4ds 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 anjs)gxfnm5w1rkc- id2b3 *6 t 0ovgk*9lw v/fxd free 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 l16 ow)j t*3nm 9-xxkgf 5fk* 2 wdr0sgvi/bvcperform 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 ball is planned so that the ; taymeg)1jd1ball 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, assume that on a particular green the ball deceleragd a 1ey;j)m1ttes 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 toh3 ;g+nf1 s0ria8aih rain traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest ah8gi+ o3s0ainr fa;h1nd 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 r; 8ex,tpgwxs7iv 9xs d z(b3q*oof of a high building. A second stone is dropped 1.50 s later. How fx x ,g3*s;p twe79qz(vbsix8d ar apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must averagmel5sy6wz; j9 0x.xj he 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 . l.jy m;zeh5j09ws xx6 what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Toury 2(o)y-3;n o shwinjh de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed isn( nyj o;s-ohyhiw32) 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 fi at;:f vhrb+p:rst child can bounce up one-and-a-half times higher than the seco+pav t :fh;r:bnd 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 9 dt9bscirhhkz1 3;q (:a7j4hp5 km/h overtakes 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 ta s1qdh3t4 jrah( c;bikhpz7:9ke 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 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 withw,nn,rm335wk g/y ;lkbvrq+ wgob ;.n a speed of 44 m/s In throwing the baseball, the pitcrb n;qn ,yk,5w/n+r gbko.;v3lm wgw3her accelerates the ball through a displacement of about 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 acceleration o 76cpl:rue k6jf $3.2 m/s^2$ 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 traffic7)5s7j:zl,m m r swzfj signal, and the speed limit is 50 km/s . Suppose you are driving from tsl:7j )s7,z m jwrmf5zhe 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, passed by a speeder travelini dt8lgz/me gw 2g9+i,g at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acceleration. ,i82del/9i+wgt mg g z
(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 seco )ad4wy7o0y 6fg hz+frnd stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at th hfdywg y)46+rfaz7 o0e 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 sameoel, d/se )4ct lt*ap: time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcoep t l,:soe tad4c*/l)ny 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 i.l fg8xg xye98t 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 resistance 8fxg.xy 9 gle8will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to sen;;p i n,k gpnz8;ip3qtd the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15,z;; 3 t 8;nnpgipikpq 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 thazk )njeck ;su p8c4g+v0o;4qzn Joe can. How many times higher will Bijkn )co; cpsegz +40vq uz;8k4ll’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the grzwo0v1qhc9 +f ound 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 anf c01 hovzw9q+d throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building usvd8 s07tpgpk.)u3eiwo wx 78 ding a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates oetww d7kx3sdp8vu 7g)0i8. p of the building’s height?    m

Figure 2–43 shows the posiymats)uwkpme lv.-jva53m3(hrp3. 6 tion vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b)p63t)jupav3ye m- k5( w3vmhs.ral.m 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?