Does a car speedometer measure speed, 7 f9;x+ 98jazuz4-oixd gtcnuvelocity, or both?

Can an object have a varying speed if its velocity u(0*y q fiuc*qis constant? If yes, give exampy(q0i qucfu**les.

When an object moves with c a1mh +/iuc:fvc5ns x1rvvl16onstant velocity, does its average velocity during any t6 cls :uf1v+ 1/havc rm5vni1xime interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing zbeufk.q)* b 5the finish lin*uf. )bk qzb5ee to lose the race? Explain.

If one object has a greater speed than a second object, does uor s4nq.w.k w/ z7km7qnu/6wk)y6e ithe first necessari6ky/o q7k esw. 4uqi7u6zkmn/wn )r.wly have a greater acceleration? Explain, using examples.

Compare the acceleration of a mov1)+v k7zwfyp:n8f m+ypmuc-torcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that1n)wk+m p yf7u+yvfm-z: cp8v accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a south) zyzar xpjrfdl 6,,5*ward acceleration? Explain.

Can the velocity of an object be negat7*7hr/el);eeexz fy0 +rm 0cwy, mw suive when its acceleration is positive? What abo /c )eyfu ee0rxsm07mrwh7yl ;w,z+*e ut vice versa?

Give an example where both the velocity and a;t1k 9loqad *icceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling wi 0qeet4h4 ed/ .5aftsath 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 acceleratia0hee5/a 4 dfe.ttsq4 on 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 decreases? o /80otjhuht d;1wo g:If so, give an uj;odhot:0 t8h wg1/o example. If not, explain.

A baseball player hits a c 4 d57c xu)5apepcvurf74m l0foul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the x5f aemu47crdv 5pcl 0pu7c4) absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its accelerati ykag+7h7tnm) on due to gravity — does it increase, decr7tmhagynk7) + ease, or stay the same?

How would you estimate the maximum height you could throwjj093 iw9+irx96,ng5yyswvsx t/ yl t a ball vertically upward? How would you estimate the maximum speed you crgjt/j y,viwnw9yi9 xx 3y 6905 st+slould give it?

You travel from point A to point B in a car moving at a constanv -d-t gkdwjli-o2 2fjp-yfo3 d :c0(pt 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 trip from Af o 0p-3v- wjfddpc2 -2k-i jg(tydo:l to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long pj*;x5e4g wpl4qk,:ksle1-txro f s ( vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a ttrpeo-4g(q ;xje w,l4 fxslkp*:51 ks in 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 motio)cd8o*u f c;zxyb28d r.ut1tkns is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fi .co8tcd8)xduru fyt1*zk2; bfth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will 3t*fx zdg 0-mqm/l v 7v7u3j tv3joq6yreturn to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if sox /6-3fmlj7u3dm oq* qvt yvjt3v7g0z, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleul*i* :dze po ,ov4tk6worc1:j27apuration at the same time? Give examrz4 ijl*vw p,ot ooca k7e61p2::u* udples.

Can an object have zero acceleration and nonzero velocity uqrw31v frq/, at the same time? Give examples,1rqrq v 3uwf/.

Describe in words the motion plotted in Fig. 2–28 wst-jy 2,7gdqin terms of v, a, etc. [Hint: Fgwy-dj ,t2q s7irst try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object grap4++lw3vt r q+-m jq+ryhg q3cpl zr2v3hed in Fig. 2–29.

  What must be your car’s average speed in order)49p*:v6pxk* hiktd xm, gvxr to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How lonfj qkuesdbt)7) +//ibg does it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s, hlmq qv1,l-p1n ow far do yop1,lmq v-q1nlu travel during this inattentive period?    m

  Convert 35 mi/h to yq. p5o3vsn 0b
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves r:.xaus4(bn nqe4lw )wsh3v;from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for 130 km. It then begins6 inpa w+ wc1:rzskqpq7y)(+ r to rain and you slow to 65 km/h You arrive hz:c(6 q sqrwn1ipap)+7+ky rwome 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,.goznun:x j,--i p67dy :c iie every five seconds between a lightning flash and the following thundern:izo-yn.p ,igc76xi- :ujde gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps arouxh4qh0) vhw(o hfc7n1 nd a quarter-mile track in a total time of 12.5fhhc4wonq(0vh7 h)1 x min. 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 m awayh0t0wi5xj i6sjm-*ez -mf-gr in 14.0 s. It then turns abruptly and gallops hat6 * m fh--s05i0jm-gwjizxerlfway 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 approacfr 8bxbp; ;9wdh each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5;fd9bb;x p8r w km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/he/-sk f6tu-50mjd c:fn9 qxt r is 110 m behind a truck traveling How long will it take the car to reach the tr-/r-06n mj sc udktetf:5 x9qfuck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters a tailw8cd5/ rgp(m-ll81r f -8colq1 xk rsyyind that -llyry(f s8q5 pk x/- crcdl8r8go11mboosts 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-trip in x lq)7cz t/bi5which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 25qxc)b57/ zlit0 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end x r-(.q+hnkcf n *;wsfof a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pinsf-c*kx+hwr s (n. fqn; 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.u)iyz7hs(4*c+y hkrh 2 s. What is its average acceleh u)yhrzk*+ 4iych7 s(ration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1. ojg)h- qyu8z0pr0e*y35 s. What is her acceleration)oh0epz jy uyqgr 8-0*
(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 accelercjpi* x.l /7odation of abouxp7d. /c*lj iot $1.6 m/s^2$ 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 aqcwp62 l, n :wa m*njzc49up3dt constant speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its nw:d*plnzjcw2u9m4c6 a3p ,qacceleration 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 movef03sn eqfgm l1(ihf 7+fqd1q;s in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a dsf+f3;q (eq1lf 0 fiqmh n17gTable and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleratio*tgh sr;ee9(;jhzq. cn? How far did it travel in this time? Assusze9jh ;( e;.ctrq *hgme constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85q52y (htjl ek 0fs1t,j m. What was its acceleration, assumed cof jth s1t 0,e5jql2k(ynstant?    $m/s^2$

  A light plane must reach a speedqh4aca fj1i98z*i-d k of 33 m/s for takeoff. How long a runway is needed if the (constant) accelc 4fdhiki qaa91-j8*zeration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially t+c vry-*(rilj op speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprin -cji rly*r(+vter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.2/v cjn 0rwl(u00 s. How far did / u2 jc0(nvlrwit travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m zrm5;t sdc*:iiw aq2-ni mz-pzm, 6w0long on the highway. Assuming a ws m5z-rc*,qzmm6a ni :w-it2zdpi 0;deceleration 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 compressgt; jp* d)(lr:hvfzcds 0h6j8es 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 anr; (0chvhgd:pfj8 d*sz 6)tj lswer 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 iiy*uxc1i .td) nitial speed of 95 km/h and human reaction time of 1.0 sidyu1 it .c)x*, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stgalsrx:pb, / gy dz4d )2gl1(vopping 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 zh ov;x)48to mgn ),uqon the highway. The car’s driver looks for an opportunity to pass, guessing that his car can acuovq8xgn;zo t) h4m,)celerate 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. After exac e,jcnjcf:duzu 8 rz7,px m71*+wo0 pvtly 27.0 min, there are still 1p8p7xmzo+ ,vwu* 70urzcd fej: , 1cnj100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection jha* 3xc:0scsxo x4;wvust as the traffic light tuvxcxsxw*:h 30 scoa 4;rns 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 $-5.8 m/s^2$ , 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 frovk* jj2+hi4urlwpb1 tn4 ;y4xm the top of a cliff. It hits the ground below after 3.25 s. How high ibk 4li* 4wxr4n+v2ypjt uj;h1 s the cliff?    m

  If a car rolls gently (0)-x i s 1g*rknn9drzkxy1dr +$v_0\,=\,0$) 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 straigh4 vla6)xi(np,0 x yc13qgg ymqt up into 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 upwardt 4tr 4qfmob/). With what speed did he throw it, and what heimbo4q 4t/f)trght did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity9os 6untt;7ne. Draw graphs of (a) its speosn unte76t9;ed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At aaya9-7vgvo5 qxxa+sjum m,c fgm 8) 11 height of 125 m above the Earth, a package is dropped fromg+s-v 871yf cjxqaamm )x m 9gva1ou,5 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, show that the distgi5cyq9qnp-c 3v/w st7o (vf9ance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–s3wfci 7vpo cq95y-/ (9gntqv21.

If air resistance is neglected, show (algnnx( ul *raf/m +(yx6uebraically) that a ball thrown vertically upward wi6l+u/(nxnxu (mra * fyth 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 m/hrdrho mjd/ :t)0hrg; c5ee*7 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 photoffmarsqil a8i+ 9i uis(001el2 lash of the apple in Fig. 2–18 (or number of photoflashes per sec9 f(a+8asuiq0i01 rselml2 iiond). Assume the apple is 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 y24crfj+*6g 9y0vy lq9bft cg travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the wind 06 t29yglffyj r qbcg9yc+4v*ow did the stone fall?    m

  A rock is dropped from a sea clifsdia* ..5jqou f, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m *.5uisd.qa oj/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard s5lrt q0vzjqpxd c9b;q+c06p0 tream 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 watc qb;5xv06pqc r 0j9q0+tplz der speed as it leaves the nozzle?    m/s

  A stone is thrown vertical0kibe 8il h:gw;+h9 x.ig-ze ily upward with a speed of 12.0 m/s from the edge of a cliff 70.-h+iw0i lzg .i8:behk9x;ige0 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 upy2x 2 nd,(cmyhbp1 ;ccward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the street, xc(yc12, n;cy2mbp hd
(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 tim+a 0 bsdj+ hohcy0+e-ne. (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 acceleration constant? hh j 0+s+ayobcd +en-0(d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a fuas qd3a c w6ln6mze( j9qmhpep a.4)22nction of time is plotted in Fig. 2–28. What is its instantanj )ez(4 s mecq.nmh w92qp2l3aap6ad6eous 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 show*n tfyshivsdx+ lwi15x4k1-7n in the velocity–time graph of Fig. 2–35. (The short flat spots in the 5n*vkys-wdh+ txli7 x1i 4s1fcurve 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 the previ5d*t ),hcz1mksmr ; nhous Problem (Fig. 2–35) when crkz)dhm n5; 1*,thsmit 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 dis* luu5u ):f 9wmbxiky/,qr 6u xh)t;dctance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the ny+of4 sdh 41ei9ma(t object whose displacement as a function of time is given by Fig. 2–28. +ntoe9dm 1yfh44s(ai

Figure 2–36 is a position versus time graph for the motion o4an ; lrwknkj7dn- ; wy0f98wwf an object along the x axis. Consider the time interval from A to B. (a) Is t8w-f4a 9k r;n0ykww dnwn7;lj he 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 time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safety i )mkkp,flc5 7uz2 *hjnet. The survivor jh2kczl*mif5)pk 7u,stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due9t7 z0n)fdlkt to gravity on the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go 90l7k)tfztndthan it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-s97l t) w 9ykecrw7 p0l p*p7tgvan*f7ghoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed0*l7gnypcpwa) 9 w*9tf v7l7gprt 7ek 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 bridh3nl:dwendpc;oo. d*3b)ib np1 v 4t ;ge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poleto.;iwdnn1d3po;p43ebn v b*cd l : h)s 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 98izntt4)erkrqwc-( cars for front-end collisions by hauling them up on a crane and dropping them from a certain height er9tizq48n(w- r c)kt.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth t jy*rnh.b5f8me/,wk travels 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 frvf9 bb 4rue4orx)kd v91hl -6qom rest. The front of the train has a speed of 25 mbk f )d49l uve-hxobr496rv 1q/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 worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a cd/f3p4 ii-*mmbmf s( deep pool. The person’s cfmm sm*i34dp-/(bfi 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 rapalsdz s8xc u*:2jf1j( id transit system, it is necessary to balance the average speed of a train against the distancec(jlxs :21u* zfjda s8 between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wi 3.u4dh5 p w) ybnk*u:kysy9mpngs and 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 perform evasive action, at what minimum height must it spot the pelican to escape? Assumu5*kpy: bum syd hy p3n).kw49e the fish is at the surface of the water.    m

  In putting, the force with which a golfer str t4a0z n 0 4nsoyq8lo.kcr)cw6-p ,jwrikes 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 whjcy0lo qst n,z 6rw-4an.cw)rok80p4y, 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 constan:o l:y*b 4jtnet speed of 6.0 m/s Just as an empty box car passes him, the fugiti t o:nj4b:*eylve 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 dropp-.gg ( bpa92n/nxhfnvx8syw8 4 uodw5ed 1.50 s later. How far apart are the stones when the second one has reached a speed of 12.0 m/s ahbvnngs 45x doww2gyp8fu9(/n8 x-.?    m

  A race car driver must average 200k auo;s,(xz/l f:7iwr.0 km/h over the course of a time trial lasting ten laps. If liwo7 a fkr:z(u,;x/s the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain passrm*h 1 xipoo2/z7q9:m3eg)o hfv.b h u as he moves at 18 km/h . At the bottom, 4.0 km farther, 7mgxho1rp obq)v 23/.zo*:hh i9f meuhis 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 trampolinesf,ms s dy.rj6v5f x0f(. The first child can bounce up one-and-a-half tiv0 ,ysxfjf (6ms.5rfd mes 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-nzqzyl g54;b 4long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train ary;b z l54gzn4qe 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 jlzd :bx0svj();t9elbaseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement sdb;j 9tz(xljl0: )ve 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 vertibwxice b-lasf*h5 w7c srgx208 h (5b7cally, from rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42.u xwm*/k3tt x0 Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the weu0 x/mw* xk3ttst 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 :e yads/cm+w+tg 3l5g at a constant 120 km/h takes off wm/e+: gsg yadc53 +tlin hot pursuit. 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 the roof of a building; 2.00 s after tha)hq-am7m n 0e0 c3;2b ig-uafqp.z i:sr4cizqt, a second stone is thrown straight downzcuep--r43imna 7 cga is0m:qb) 0i2f;zq .qh with an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically upc*yqg lsis3c13-h snt878x l.5nl 6jupgiti 1 at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hitsx 1sygh8ti 3c5l p ncg-*it1nsluj.6i37 l8qs 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 i+wte;vbeo6j ,.+ sd-nkf y+rresistance, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, thtd.ifv+ 6syn+rj;w -obke ,+e e air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses aauge b+t:yin.+j2b: a conveyor belt to send the burgers through a grilling maayt n:.gba2 +b+iu:j echine. 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 burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a spe2 w8h/e,zvrck ed 1.5 times faster than Joe can. How many times higher will Billv8kc h 2z/ew,r’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cli-5wswq-i8 tp4l k7uesen- b/qff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the bkqt85l-n4pe ibw-seuw q7 -s /all to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to findw9o4.* 73d qle* lje.:qgglas zbnua8 the height of a particular building using a barometer. Instead of using l9* en:gdg q3u7l.j.8e lzaos* 4b wqathe 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 of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B. (a) Iswh, cs9qt(b;d there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the h9d; ,wbc q(shtigher average velocity?