Does a car speedometer measure speed, vcw9) 8*xq z,v1, tnc1nhmxbj celocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, q-y)otda/ o,a uv ))( zdrkk-jgive example)rdk y,)-(a t kvj/)oazd-oqus.

When an object moves with constant velocity, does its average velocity during /k:u)ry02qtr:j bij q d (orv,any time interval differ from its instantaneous velocity at any insta v,:/0 q ry (:jr2jotuk)bqdirnt?

In drag racing, is it possible for,ri23aqzz sq );t9tf v the car with the greatest speed crossing the finish line to los isv zqr)f9tqz, 3ta;2e the race? Explain.

If one object has a greater speed than a second object, does the first necevt:o/t srdax,tw2 sn-) ,wz1 issarily have a gz1-:/ s ,isdw wxt,nvor2)ttareater acceleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates frg2 t1lx;noo :som 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10kltg:xsn1o;o 2 m/h in the same time.

Can an object have a northward ve/em72w e(ubax*y rs /rlocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleratiodz;9zavu 2hauwy3+ 2gn is positive? Whatgud;w aay 2hzv3 +9z2u about vice versa?

Give an example where both thet(xfn3h7 r0 x 4kfd;tk velocity and acceleration are negative.

Two cars emerge side cfbo5:*w7h kez ( yu+yby side from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passin5zw* eky:fyu och+(7bg the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing ile-u mbp .yn5gr9s-x *n speed as its acceleration decreases? If so, give an exampl.gns -mupb- xe*59lyre. If not, explain.

A baseball player hits a foul ball straight up into the air.z bzrvk*vc,c ;66 5rxu It leaves the bat with a speed of 120km/h . In the absence of v*b vzz5cck6x ,6rr u;air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happeni*kds o+jj37nzbk / .dge. us*tng to its acceleration due to gravity — does it increase, decrease, or stay the samb.g j*es3+td7.nkj u/ kzds o*e?

How would you estimate the maximul1pch5 t6f;lpggu 89i m height you could throw a ball vertically upward? How would you estimate the maximum speed 6icu51t8flpg;l 9 hpg you could give it?

You travel from point A to point B in a car moving at a constant spes7 +ju )-nb)c*r;fin /0 u1ioxmugvized 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 trip from A to C 80km/h ? Expl v07o*bi;1c))ux f -mijnn z+ug iurs/ain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bitn pb06u32wllof f.3 x :fuaso( g45rolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equaln:fo5 s4.2l(lurtu33ib go 0wf6pafx 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 co7,vv o9 * 9gbiv+86cgrybso ccn5 5drqnstant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the9 rv,vocc+v7rs5 qgi96 8dbo c*5 nbyg way, a dish resting on a table?

An object that is thrown ver l12qpc976d1p,l4)tkygck yc1liag etically upward will return to its original position with the same speed as it had initially if air resistance is negligible. 2lkkc4l g9ad71,1 )p6lytq1pi cygec 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 vela4vm 0/ :yqke a (escz-/qc:olocity and nonzero acceleration at the same time? Give exampvlaqo a/mq4 (ke:-c:eyscz/ 0les.

Can an object have zero acceleration and nonzero velocity at the same time?7j m6 ( phuxp;fnhi1xvz:w8i +ggo2 p- Give exa;gifix76v 2 p8 p:n gh1pxj(+wmh-z uomples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, ettg8wp0 k3(mq: lhc,+c7jq s h53ep flqc. [Hint: First try to dupl30elj hk5(pmpg 3cqw qc7 q tf:l8h+s,icate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in Fig. 2–29*np yj u,:t1lx.

  What must be your car’s average speed enih(0-t (u6skow b:hin order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How lonqfj;o2o+ wb:cg does it take to fly 15 km?    h

  If you are driving along a straight road and .3b;x aheo4ar you look to the side for 2.0 s, how far do you travel during thih4xr b.o3;ae as inattentive period?    m

  Convert 35 mi/h to ,l9zyv tv5wd4
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from x dd(eom: 5l4t$x_1$ = 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 13n/*,e +c:gvoyt4mm wo 0 km. It then begins to rain and you slow to 65 km/h You arrive home a,m*emyno:tcv4 / o+wgfter 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 betweene9 kvuva idu e 6016.rce4*xaw a lightning flash and the following thunder gives the distance to the flau ia.6vuk10 49*wdervaxce6e sh in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-,- k)npztwzgdr0 z441m;i kn 53xtprcmile track in a total time of 12.5 min. Calcuk)zd ix4;5kp nmnc03 rz4- trgt1w,zplate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainemuto( k-,dpulp-- +vhr in a straight line, moving 116 m away in 14.0 s. It then turns tmhl-- u kd+ ,puvp-o(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 para* f uo2vo/i6ruw/z4ybllel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 / v4rfiuyu6 /2*zwoob 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 trukudsh;+dtr*5:q9b sfck traveling How long will it take the car to reachhf r*qds9dutb5 + k:;s the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters12j. i.pn0vwjz hrc 43o4or rv a tailwind that boosts its speed to 990 km/h for the next 2c owp4vo31nhvrji.4j 2rrz .0 800 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 velok1m ldvvok -rg.i9 -jc(s1n5rcity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0o. v9ng 5-jrs ckki1(1lv-dmr-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling2g q2 8fpgnx6x with constant 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 f2pnxg 8gx62 qball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car acceleratestp0 aod tfq ((j-ja-3gpj l+; jqk -6gswsp7-c from rest to 95 km/h in 6.2 s. What is its average accelerat-ajf c+pw- j( ap0gpt3q6tjkl;s d qg--oj(7sion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates f2ry /yhy s/net/db6-drom rest to 10.0 m/s in 1.35 s. What is her acceleration d t/ey/y nh2d/s bry6-
(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 acceleratmi2fg9o6 /8hh4y etv qion of aboutm6i4hq9t2yg o 8/ef vh $1.6 m/s^2$ 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 e (6 swu;.yfovconstant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its accelev (s6e.; wyofuration 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 ty0md rb7(-gr 0dmn 4trest at 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 t0rdn g7r4y0td (bmt- mime. 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 acceleyx( th* w6syx)ration? How far did it travel in this timets h )y6xy(wx*? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s /atu5 cv5d,buto rest in a distance of 85 m. What was its acceleration, assumed,abt/ u5 5cuvd constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runway is ne +2 tu9lm:5pelu dnuw*eded if d9tu*l5lnme+:u w2 upthe (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprint5y /)*np umjfyer can burst out of the blocks to essentially top speed (of about 11.5 m/s) in the first y 5mpu/fny*) j15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down unifon, a l-o3 i+pd-/uszalrmly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in that time?/iao dl,anu-zp-s 3+l    m

  In coming to a stop, a car leaq:sui g3a:te8ves skid marks 92 m long on the highway. Assuming a d8:qasuge :t3ieceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the car compresses and 0t tizgp6x0p( 5g3bsithe driver comes to rest after traveling 0.80 m. What was tgi53zp t0s xt6 (ig0pbhe average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 km/x*8u;9mlloc3bw: p iqh and human reaction time of :xiwcl3 op*b8ql9mu ; 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 forv 534t4jjy- isga 6ans 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 going 25 m/s on theymz+0dv va*nubf37f cbo0 4-b highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate atb3nc mfz+0bdya7b0-v v*u 4fo 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 con)e b bm66shq5v8q :sgmplete the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m t v:en h s8mgq6bb6q5s)o 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 interdacao;bgze tt6o9*q yx3 c05: section just as the traffic light turns yellow. She knows th:;cxg aaq90c6oo t e53 ybz*tdat 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 $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below after 3.2 lf)x5ei2spfp/cvkqk/ z+ 2;h 5 s. How hkxpe vf) f+k/zil/;25qscph2igh is the cliff?    m

  If a car rolls gentls:aj)6y rfu gt9 2)ilfy ($v_0\,=\,0$) 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 ih 3q jspod44 3;otruzw9,jf/ znto the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it vertically upwakh1al/b./z sard. With what speed did he throw it, and what height/ls za./hb1 ak did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under pd*sc8al e2, ,:hacm0cb) zspthe influence 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 air resistanhb*:c paaezc)0p2 smc l,s8 d,ce.

A helicopter is ascending vertically with a speed of 5.20 wz+nf +xnjh)8sv4b9 ):0dntr5y xyu wm/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 the ground? [Hint: The package’s f wtdyzb 5yn 8xr)4) hws+jun:x+vn90initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, shwrq9(mp()v mny aahrt p p;or(+0w5 ,zow that the distance traveled during each successive second increases in the ratio of suyp(+wa0r9p(onmwv( r)h5;rmaqz , t pccessive 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) +w z h9v2v2 lex*q(cof/tkij0that a ball thrown verticall h *2fv+0wtjoi/l e(q ckxz29vy 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 vertically upward with a speed of 18.0 v l:l co(dsu)aqvb)8+ 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 photoflas;asq 8f d*mo3kowgpyb0 1e (0zh of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Us ;wq zg o*08 efaomdb3(0psyk1e 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 ai39jjghqht,wm) w-f.li ,0 cq window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the j03wjt,ifml q-) i.hwh gc9q,stone fall?    m

  A rock is dropped from a sea cliff, and the so ;9 ptvu qy7ns+yyp;r)und of it striking the ocean is heard 3.2 s later. If the speed of ;;sv+yq p )7py 9rtynusound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzl rmph-c p-+qr8d pi8vf(o2k4/h e0yjle 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).(c rh epr2p/- m4d-8+hlvkif pj q08yo When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upwardlc- bvy6b6k6 y w)x3z3h 9tfhr with a speed of 12.0 m/s from the edge of a cliff klb9hvc3 3h y -66 yfz)rbwt6x70.0 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 byd) hfz;n+(z guskwpmfqqm (7;5(mi( t a window 28 m above the street with a vertical speed of 13 m/s If the ball was thr tp fqmhzwd((fgi( qzu5m k;n+7()sm; own 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 :cqul, (zepd *train as a function of time. (a) At what time was its velocity greatest?z(cde*lqu, :p (b) During what periods, if any, was the velocity constant? (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 tunn+p34eo)btque5ftn ym f1 y0.eel as a function of time is plotted in Fig. 2–28. What is its efpeeou3f.y)tt1bm05n 4 y+ q 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 ae:ql,5me vy+ ih 9 7nrz9igk)can accelerate approximately as shown in the velocity–time grapk zh7ea qen9l i):ym,rig5+v9h 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 thy5zgw11pjz 42u t 5m p6by4vice previous Problem (Fig. 2–35) when i w5 1m 54pg6t42jzcuy1yzvpbi 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 distj /- s1:ostd ;yb6ruvoance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a :, z+(kaz66jrtmt(e *f p/ep yg.jsslfunction of time is givzrf l6e.ajegj(*m,ttp(/+6ks ysp:zen by Fig. 2–28.

Figure 2–36 is a position versus time graph for the ,m ceo2vns;q13qa 2jlmotion 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 objee2 n2s3v,mqcoa;ql 1jct 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 window 15.0 m above a fhehte,ddke, 5 3e4pt*irefighter’s safety net. The survivor stretches the net 1.0,5pe3dte e 4khhd t*,e 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 gravit*dx.1 uk2y lwhy on the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward o.hud1x y* l2wkn 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-shoulder seat belt has a ;06 a ,hxtr; qccrug,mgood chance of surviving a car collision if the decelerationx,harcuqtg ;,60cm ;r 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 onsup3h/iz52fh2 p( h) j;hefzi a bridge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by )s( u/3hef5;pz 22zjfp ihhihknowing 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 the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisiez2 r1 rvgva*kz 3d2d;ons by hauling them up on a crane and dropping them from a cerdvzd 2*1 ;3arv2zg ekrtain 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 traveleje897cdt g0/mmu p m7t(5upws 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 k3,y lcc-rtp9mo3 )qkfront 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 scy)kr mpl3k3 ,o tcq-9tarted. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface f,27 2p7mvlxv* bk+5 stpcep ninto a deep pool. The person’s downward motiofs 7nb2pmvk el5p p,2 xv*ct+7n stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary toipw **3.pwmpe 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 this problem, calculate the time it takes a train to make a 9.0-km trip pp*wimpw3*e. 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 divig s(q oaflhlx- 04o81ec on6w0ng for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is s( xlloeh8 qw 4aog-016foc0nat the surface of the water.    m

  In putting, the forcyqwm /oca+aj+a.a26jxo+(t ce with which a golfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a p 6mc2oc.aywao + (+/tjxq jaa+articular 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 tr3thm gcafyrm 28b;pvpv2o1-:v+exp 6aveling at a constant speed of 6.0 mpmt2 m :+b2yera8vf6x3pocv vg1p ;h-/s Just as an empty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is droj)5o1k)f:qjo vg b p mav7:p.spped 1.50 s later. How far apart are the stones when the second one has) po5qf):gbovs ajkmv7:. 1p j reached a speed of 12.0 m/s ?    m

  A race car driver must average 2.f3u:fd e7 +l d,*qbg9d yauwi00.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must 7 i ul9wf:3bg.dqdfe,au *dy+be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he t r b5zd:4l5r ol18ovgmoves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average a 1d oglvrbroz:tl845 5cceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child heyqfck5codc,4 z -i:mq t,kf:6 i5hysuj** ;can bounce up one-and-a-half times higher than the second child. The initial speed up of the second child ocde:q c,k s,tff5hy:uyh 5j q6;*z4k mci*i-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 t2 xk;troft.mdru 5:h:u7lz7 wrain traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and h lurkt5x27.ftz o7 whd:m;ru:ow 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 withm4-kdtu f :zktde (6+h a speed of 44 m/s In throwing the baseball, the pi6ktdk df:( mu-e z4+httcher 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 an0 3 em0hxrdou7 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 a1i/ mym(2y ez j it7ea5vj,9kq21 obft traffic signal, and the speed limit is 50 km/s . Suppose you are drivi ao2ey1, e fkimi9m5vj j(qzbt t712/yng from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant wph m3ot :f4i/120 km/h takes off in hot purs3ih4mfo/p: wt uit. The 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 thv62yc)a4ml 4q paux4wo1x/x e e roof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 2qv/w 4)4 auope6m2x41x lyacx5.0 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 vertically up at the same time. The f1)1;1m(bt olhvva tlbirst stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocitvtha; m otl1bb(lv11)y 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 ro rlj3c )7k,paesistance, how long would it take a free-falling parachutist to fall from a plane at 3200 m tok l, a7p)3croj 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 conveyor belt to send the burgers tkc7*kzm1(gl;-cn7 a u -j 7zso19hlrntfh j9ghrough 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 cm apart, what is the rate of burger production (in burgersf1rgk1 7 uchl9zlgo ;nh-j7k *j9t7asnz-mc(/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically ajzx;x -go;6i:y,4c k,jjmfu c t a speed 1.5 times faster than Joe can. How many times higher will Bill’s x; ,g6 c cym4o:jjjz;uixk-f,ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground below y8/z 8dhlfr(ub ou. 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 uuz/lhrb (f88d p the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the heg tue,t/7uold 9t(l7qight of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof tl7(te7/uqout9gld ,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 of the building’s height?    m

Figure 2–43 shows the positdh67gg3k 2w xej a+*qbion vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have te 63hj gqw2k+d*bxa g7he 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?