Does a car speedometer measure speed, zb9skz(*uhhrtv 0h:50pm h rc+q 4io 5velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes5 l,wxl uj4,nz, give examples.z,l 5x4,ljnwu

When an object moves with constant velocity, does its average velocity dfe g vwx.y6kdn18*t(juring any time interval differ from its instantaneous velocity at x8y *j(v.f k tg1e6ndwany instant?

In drag racing, is it possible for the car with the greatest speed cb6 u+j*45tbg ;mbq)3lapu qrxrossing the finish line to lrx+lt)q6 ;a*jbpu3ubg b4m 5qose the race? Explain.

If one object has a greater speed tc03zy1 e cspha,72 kblhan a second object, does the first necessarily have a greaterzy ecl2 310 ,chk7sapb acceleration? Explain, using examples.

Compare the acceleratio2 coa b)y :wi0p7b hj-cu/sge;th0 wr-n of a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of yh2gp-0tj bsr c h0)e-;uww:ai7 bo/ ca bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleration? Emv x9d-q+o o,fxplain.

Can the velocity of an object be neg2zoj jr+ (zrd:ative when its acceleration is positive? What aboutzr2o( +zj:j dr vice versa?

Give an example where p09g 1b-pqxe tphstl+,q.hf-j +mj3nboth the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is trav(yydo l+ce m,5uld kb.qn 97w1eling 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 . W dm7bel oyl91.dy,+nqw u (5ckhich 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? dxo j.*xpt osy 4/ pu*7k oxr2,xz/ot*If so, give xu2ot. pdx xy*/4x*j or,o o/pz*s7ktan example. If not, explain.

A baseball player hits a foul ball str3a3z,j 5i7p qjktlx* oaight up into the air. It leaves the bat with a speed of 120km/h . In the absk*jpai5 xq3 l37joz, tence 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 acceleratio 8j9 n fve8jak/3e+x,erzeq 4dn due to gravity — does it increasexqj9 8, 3vr ke/aefn j4zee+8d, decrease, or stay the same?

How would you estimate the maximum height yojg 1m+z tf9andk19+/rk(i js/f uf2rmu could throw a ball vertically upward? How wouldk2j kuf9a1g9dnr /j/1i(rz +smf f m+t you estimate the maximum speed you could give it?

You travel from point A to point +;wd7ukcsw0 a iaq31a 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 constant speed of 90km/h . Is your average speed 17w+s;awqick d a au30for 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 ten bolts tiedy 2e1n dcg/shz,akvz61ts9w7 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 b2zt6h/k sv7c w a,n1ze1gs 9dyolt 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 motiv)p dt8iii3prt 71lp+ 2thyzj7k ql3,kc4ub4 ons is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making 7+u t tbkzk2lp4vjrldpih 3p )17yci4, 3 i8qtstops along the way, a dish resting on a table?

An object that is thrown vertically upward will retul;mn7 g ey7x1krn to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the mot7mxy kn 71;eglion.]

Can an object have zero velocity and nonzero acceleration at the same time?qp;i*b /md*pc7 gexh2 Give examples./p* ; 2egbciqh*xdp 7m

Can an object have zero acceleration and nonzero velocity at the s5:bp8 jd dtf s8i (fjqe8jcs/hmh-e,3ame time? Give examplesbstfjh/qs m , ic3dej:h5 (dpe- jf888.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [mr;)rpl /av fr.mz6hgi b0 9: f1dxk0uHint: First try to duplicate the motion plotted.f9i ;/u dm6v1 f:gr px0rm0zlkr)bah by walking or moving your hand.]

Describe in words the motion of the object graphed in Fig. 2–29. wg0kb9ry7 pd/

  What must be your car’s average speed in order to tr1+: e0nm iy*tr7v5c2zlouw hn avel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does w29gfe0k2ykl l(c-o5mmfl +bi vk ,;dit take to fly 15 km?    h

  If you are driving along a straight road and you look to the side fo./rsh ow7ca /y( oqgxdq0(+tur 2.0 s, how far do you travel during this inatoswqrg. + /ay7uh/t0xqd(( cotentive period?    m

  Convert 35 mi/h to ;xh vff-k: t*b
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves f.qaq4gce4kh3c q v)2h rom $x_1$ = 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 forpu6fmby.c 36,rs :-gy9hp oj e 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 so,9h: jcyur-f6eppg3 m b6.y 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-+vsnbqn3rk r(x(5m9d vwg2v 5 of-thumb, every five seconds between a lightning flash and the following thunder gives the distance to the flashs( rqb+n 53rvxn952mgdkv(wv 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-mile track in a totallwkrb9e11kqj n: 5 d.sbcl7)yxer: :l time of 12.5 min. Calrdylk lq1b)xjk r 9c.l5ne::s7b w:e1culate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters awayk, eb5jxbk7;r from its trainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calculat kxk5,7;jrbebe
(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 to ariadmw9. ;k(+0nbhas a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be be0oimnw+ b9 kt(aa; .rdfore they reach each other? (See Fig. 2–30).    min

  A car traveling 88 kv s1vhs:1mcn o)z qig5r1 ib:,m/h is 110 m behind a truck traveling How long will it takv:bz,ir)15i on:1qsh gm1v cse the car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encdz ta+520mbu n7y 7zolounters a tailwind that boosts its speed to 990 km/h for the next 28+ymt0577bduzoan z2l 00 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 avcsp0 i5gn:l 1j46yl e5tb5lv werage velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed bylv551b5c6i ey plw :jlt 40gsn 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/d.b7nesw)ml b9f cyr )14jgg end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What isg)smwf9 .l ge1dbn bc /)y4jr7 the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates t9 s cgmv68qbnkz88a /from rest to 95 km/h in 6.2 s. What is its average accel8nv kqzg/689 ac s8tbmeration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Wqm6uhrii2 8-what is her acceleration 6m u82r-ihqiw
(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 acc9/ 6rabk4 7dycbygk o,eleration of about9kao6gb7 c r ,d/ykb4y $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110 m in 5.0 s. If it then brakes s7 a tkd+jze 2329zzwfand comes to a stop i f9as3zzwk jd7e2t z+2n 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which stax,hj f /1y3ymqrts from rest 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 timeh, 3m/q yy1fxj. Display each in a Table and on a graph.

  A car accelerates fromjzk(1bu w7. whpw*bsioc-e, + 13 m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume conshjkibw.o7cz bu+ es,- *p ww1(tant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to revf/ip fi 48t14y u2cocst in a distance of 85 m. What was its acceleration, assumed constant8yfut ci/ pfio14 c4v2?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a rdyxq:tv7ve *x,2 cf)z + zj0ununway is needed if the (constant) acceleration i*+xv0cet ju zqv,7fny)2 xdz:s $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially toc cyj7b5-/dj bw4u, ypp 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 that speed?4y 7jpb 5bcdc/u,ywj- $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a splx um8c:qc i;el-94t keed of 12.0 m/s to rest in 6.00 s. How far did it traveuxt :i-clc8q;l k9m 4el in that time?    m

  In coming to a stop,-u; t7 /wh(bn7schsdb a car leaves skid marks 92 m long on the highway. Assuming a decelera7h; w7- ssubh(dbcn t/tion of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h stwpmu83.c kic +n60knl zo5wul5 0ddi7rikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi on? Express the answe0l wwi3l u+ o0c6u5mz8k7.dn dnpi5 ckr 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 tk 4ycyxq fq ht-8d7tg.,+tf 9for a car with an initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleration ,yhf 8kgyt 4 tc .-dt7qfq+9tx
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a ct -(tw1lpcw (aar is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver l /-ff:ykp sjnh1h(f x;ooks for an opportunity to pass, fnp/1j-fh k;hy( x:s fguessing 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 30.01azua53 up7 xr min. After exactly 27.0 min, there are still 1100 m to go. The runner must thz7 x 51au3rpauen 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 intersecte 2fgc lxb*,d:q)j mf4ion 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 shoulxmel :2jfb f4q),cg *dd 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: un4s /v6:jts2 gqsbyql t/m;v bt.e1.25 sbn g2y1bm sqv::stv/ ;tt6/4su.eql j. How high is the cliff?    m

  If a car rolls gentltnep eu,57 sjsm +dkn96e93v1 /pq arhy ($v_0\,=\,0$) 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 spd2+ b r :vovjt0ps;,iieed 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 u kq ug.r,vap)- rkxr2/pward. With what speed did he throw it, and whag)krvrk ,xua2.-/r pqt height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Draw gxz7znn+z-suez:9c m /raphs 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 resistan n-/c: 7+z sxmznzuz9ece.

A helicopter is ascending .p +e1sn)j xmczm11pd vertically with a speed of 5.20 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 the ground? [Hint: The packe +spc11x1mmzdn )p .jage’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely f-80rhcdvz +sj rom rest, show that the distance traveled during each successive second increases in the ratio of successive o-d jrh+80cvs zdd 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 thrown ven9xwro +7 6*tziqvht)h,*2ul t k j2ap(h(pxirtically upward with a speedlhv j xtk 9hnuzwq6((a*)2t+*p opit2 7ihr,x $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upwardkx.d * z-cid,j 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 eag ,i eisx;-fyp5.f 2ufch photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.2sifpxfe ; - yf5,iug.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tayth3pkc6,0t/et vku ;0oa a0 pll (Fig. 2–32). From what hei;h0pta0yt 0tkopa/vkce , u3 6ght above the top of the window did the stone fall?    m

  A rock is dropped from a sea clmue +*,wvw* 5vm y apu6royx+0iff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how highu+xvwv urwmye m0,5+op *6a*y is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of w liaxi99h ,b 4wwx)pqhh04 lw-ca(z1p ater. 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 striki9 aqix lwh(-p,1 z9hchw) wix4b0 apl4ng the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of a 7r)l1.g ejsl w6c3dsycliff 70.0 ms.1 we r) ldjgs6c3yl7 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 sh.,i;7 ikbil28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the stb.l,kh;si7ii reet,
(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 as3 bxb imlb:4 u31pa :bw)yf-7fbz0vn ,/zh fyf a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, wab40:xzw) ybm byfiblh7nva3/uf1f,- z3b: pfs 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 alo4r fr;5gmgti*cp 6v( eng a straight tunnel as a function of time is plotted iei f4r6vpg5gm c(t r;*n Fig. 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 automobiltdk e m-4a(+xke can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting (x-edkk mt+a4of 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 carv xmn0 -c-+jfzt+,rmw in the previous Problem (Fig. 2–35)x -- cvfw+mr,jmz+ t0n when it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the objs td jr*e75j/ th2ls.sect traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the objec(bv*l mo bnq+5j kd22wt whose displacement as a function of time is given by Fig. 2–28.2b( 2 jvdbqk*wln+5o m

Figure 2–36 is a position versus timf k0poq22g).eh ltqi,e graph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the )2,top2i 0.hqqgle kf 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-stoh. 2 ax:9ot/( bh*jx5(,+ aywvwrysil izuo ;nry window 15.0 m above a firefighter’s safety net. The s 2yxj rvh w(*:i 9toais hblz oau/n+x,w.(5;yurvivor 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 due to gravity on the Moon is about one-sixth what it v,xh6y55tr/ioqe un1 j7/z rjis on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earr 5xe //o5r7u,ntz 6vjqi1hjyth, assuming the same initial velocity?

  A person who is properly constrained by an over-y- ;n ;sefyz+dthe-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 30 “g’s”fndyz;e-ys; + $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above+/gxs 7+g :grvgpg4wv /qv jc1 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 wg g+1/vq7r vp/:gc4s gg+jwx vhen he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested i 0+z*05 nbeupd:m6p 0m i xu;kyi0kvtets cars for front-end collisions by hauling them up on a crane and dropping them from a ceryp 60e 0 m0mvp*inbkk u0ix;:ed5tuz+ tain 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 travelsz gv-ug,u*mzr1 i 3 1rpof1c2j 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. Thepu75o3aey v n3+8 -( nqculsrw front of the train has a speed of 25 m/s when it passes a railway worker who is stand-ru5cnpnuqe3 a o+3(ys lv 7w8ing 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 4.7(zm35h0xqy1i4f irr,g*zat f ic/us0 m above the water’s surface into a deep pool. The person’s downward motion stops 1raf5mzfsi,3 *0z7 u t(xyq /h i4rcig2.0 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 tra26pm 5orwdhf)tem p p.y,/zf3 nsit system, it is necessary to balance the average speed of a train against the distance between s6 pt3mmhy woz2f)d f.p/r5,eptops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straighn g:s,. 3;hnyqw(mm2v/ tpc o;*ulzuht 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? Assume the fish is at the surface oumgwvh*ts;:y u2(mz n/op 3n;. lhc q,f the water.    m

  In putting, the force with whi wiqai+e3 8o)ych a golfer strikes a ball is planned so that the ball wiawqyo 3+8 ii)ell 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 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 aq7a4a8dmbak/ t a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and q78b k4/aamdaaccelerates 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. /4wxq;m8 wvas A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a xmvqs w;8/aw4speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a timet rc-ketc;l 4( trial lasting ten laps. If therte;l4ckt -c( 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 Tobmeqed;n2csm0 ,e7:i6iud5.wx 4a ty ur de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/hinm6am w;cebetd50.,24squyx7e:id . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounce u5 jo, l4l khr0hc)cz3qp one-and-a-half times higher than the second child. Thel453j khclczo0rh),q 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-lolv e4ght ,tjg9qu:7 z:ng train traveling in the same direction on a track parallel ,qhttl:4 vjz7:9uge gto 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 are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speede y ixtl/5l*i1 of 44 m/s In throwing the baseball, the pitchy*li1lxe 5it /er 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 ac05p;t 4rqh btty 5ze3ab8z +gn acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a traffic gk b) lud;4;f7ra bb*psignal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the fu;7f alrk;*)bb4dpg b irst 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 consts .0-rvd,9 rammzre+o:zx vu8ant 120 km/h takes off i8+0vez ,or au:z- .md9rvsrxmn 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 yi 9yhxxhlz+*toxf 03dn1ni79 dgr0g)gp2k7 building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the two sto9+h0)rokd l7 gng1xi0xf hzp9 g7dnyi3*2y x tnes 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 v)lyo 30riv1im ertically up at the same time. The first stone is thrown with an initial velocity of 11.0 mr)3ilm vi1y 0o/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no airw-x./m a;(t0l 7*s jevukmwhcq xj18y resistance, 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, the air resistance will restrict her speewaumqcexv7y ;m-10j t/hl xwj ( .sk8*d to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyorym- 9ngfpms)* h ndwxm-6yj17 belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long andw mmjn-)9*d7 y-h6 x1mfpg ysn 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 speed 32a irjsu 6eg gt+9m vti*1d9b1.5 times faster than Joe can. How many times higheri s1bi +9ttv mggrjue36a92 d* will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a* 6iw0o.v aokn cliff 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 ball to hit the ground below. Your friend then picks up the ba*ov o6k awn0i.ll 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 height of a particular building using a bar(h4vw4t9 znj tometer. 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 vh t(wz9tn44j the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph f:dts+(rez aizzh)fc/q . pl6:or two bicycles, A and B. (a) Is 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 highriq6 +p:e lfsd )zh t.c/za:(zest instantaneous velocity? (e) Which bicycle has the higher average velocity?