Does a car speedomet5 d nd owta2j,xm*r+8ter measure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yem+*e2hrvi0.qz 6y l acs, give exampl v l6 2imcqyz0.ea+hr*es.

When an object moves with constant velocity, does its aj-j/qau wwy ae2 *5 hnpkp:v:8verage velocity during any time interval differ from its instantaneous velocity at any :*wq5p h -uewja2j/v 8pk ay:ninstant?

In drag racing, is it possible for the car with the greatest /bzwr( ujr2r )7 - +addbbo+qispeed crossing the firbj7)rudza r+ +dbq2/b(ow i- nish line to lose the race? Explain.

If one object has a greater speed than a sec;cg e*g(ghtrf(- dp rxcr99b0ond object, does the first necessarily have a greater acceleration? Explai (egbx fcp(gg h;0 9r-d9rr*ctn, using examples.

Compare the acceleration of a motorcyclpy(( e (ffty1wjyk*g: e that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that acce:gtykp 1 ye(w(fj*(fylerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleration? Expl 1cg)zhc5ui /(k 6r ob76vffsvain.

Can the velocity of t3,y4mc yn/h k rtfj*e5 ce5t*an object be negative when its acceleration is positive? What about*/ ,r4ch*n53tc5e me ytft jky vice versa?

Give an example where both the velm8ewc42 os x pd1hwlvuk/ oa8qq,9c88ocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed tdn( +scq h24v3gd 8od (;yxhrof 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 pass 4hqc 2xd (;dyn8t+gsov(drh3ing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so,i1dbt ee o,28 sjzmu7l))7 zej give an examps,1)8e ol7dz)7e2ejumz ib jtle. If not, explain.

A baseball player hits a foul ball str*r8 eh byhcswe6 5x89laight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fa 68ry5 *w8 9hlxhebsecst will the ball be traveling when the catcher catches it?

As a freely falling obj,)49*bd 07so fizzfams4 clu-ktd g4qect speeds up, what is happening to its acceleration due t sb k0-dt4 7zaig,)f9dzsq fm*luc4o4o gravity — does it increase, decrease, or stay the same?

How would you estimate the maximum height you couldfvmoi d +l* i1zpn-e7/ throw a ball vertically upward? How would you estime/n1v7l*ii fzpomd+-ate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant speed n38pgtrbkr tf(h*4.;oxpq3jof Then you travel the same distance frb t3p4;o gf3 rkrh8j (n.qpxt*om 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 ? Explain why or why not.

In a lecture demonstt2kl16l0xq2v9ju hum (7x/8w rt jf,z pmb8dgration, a 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the kvw18 mx0jub q7 mrl(f j8,9glx/u tpt62 h2dzclinks occur at equal intervals?

Which one of these motions is not at constant a y4awxlu8wz:155b sqa cceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish rw 5sau1wax5zb :8q4yl esting on a table?

An object that is thrown vertically upward will return tolp00sg ; n7t/kgvnz7v 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 op7np0n g7gv/zt;0s kvlposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the same timj fkxo 3lg:-fp. axyuoyg /8)9e? Give /9-: fpgyogxljfy8 x)ku.a o3examples.

Can an object have zero accelvo/:gf -sqs0oqj h3,zeration and nonzero velocity at the same time? Give examplejs ,-q3g:z/ hqf ovso0s.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [Hineo3 4v7 iptcv0t: First try to duplicate the motion plotted by walk e3pv07 ct4oiving or moving your hand.]

Describe in words the motion of the object gri(j ciav0fx, :aphed in Fig. 2–29.

  What must be your car’s 25w0end -f ,rczus /upaverage speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/huh aux*vz3s6ottpv0)f8r q .- How long does it take to fly 15 km?    h

  If you are driving along a strai/3gbelw qe0a )m7*dey ght road and you look to the side for 2.0 s, how far do you travel during thiwqbeadl/ye* g em 73)0s inattentive period?    m

  Convert 35 mi/h to dmy+b2ulb y15z gtp*t5s )lpxmwex (/9c., om
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fcaaurczf8-xg1zx7bv9 h (5 w3rom $x_1$ = 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 frore0 y9:gs r5npm school steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.:5n0yeps r9rg
(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 secoz k, hpbij(e3l1emv70nds between a lightning flash and the following tj0ezbm(hp, 1k7elv i3 hunder 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 around a quarter-mile track in a tork)3i z t-s0a q6ap2zital time of 1irat )pq 6zi-a32zks02.5 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 g-, 9lqr lztl)z1wp-g 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.8 s. Calculate zl 9qwgtrz gl l)p,-1-
(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. Eatw(z z6efb5so7r 9 q0ao4 ao/ich has a speed of 95 km/h with respect to the ground. If they are initirzaqwo0ei/(7oz9 sbft o5 46 aally 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110ta/; :y aa4dmdm nb),a m behind a truck traveling How long will it take the car to rebta ,ay) dda;nmm/a 4:ach the truck?    s

  An airplane travels 3100 km at a spe2)wlx-kn i t:jy3hhsaw1 u ;2bed of 790 km/h , and then encounters a tailwind that boosts its speed to 990 km/h for the next 2800 kh1:h2l)a;y2s jww - utikxb3n m.
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 rounf; hf mqy9n36ld-trip in which the outgoing 250 km is covered at 95 km/h f6 3q9hmfynf l;ollowed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with cqwb-m eah.88 u( tnv6ew5p8: r trqz7uonstant 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 pin.tqw avt ehpu:mb -(e6n88q 8r wz7u5rs 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 inr-bqj1 0 .iecfv43 rzu 6.2 s. What is its average acceleration in e1 r0ij3c z-v4b.rufq$m/s^2$ ?    $m/s^2$

  A sprinter accelerates7+tm(v70de el osz b;0pe 6bjd from rest to 10.0 m/s in 1.35 s. What is her acceleration ov;(dt6+ 7dse m7lezj00 pebb
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a paapq*c) g -bn42w*jklv2jxc t5 rticular automobile is capable of an acceleration of abou2 tc45nwl2cxj) * gq avkjp-b*t $1.6 m/s^2$ 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 const 1pn7 op sb3ud2tq*j3mant speed travels 110 m in 5.0 s. If it then brakes and comes to a s q33ntpu *p1d2smb7 jotop in 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, k qp0p 0c-xungzp::qkw1a76m which starts from rest at t = 0 and moves in a straight line, qa qzpk6wkg:-7c x100p npum: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 Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What wasvw6jonksc9/d+ ;;a njk xyz0( its acceleration? How far did it travel in thi+ d;/(j6azkv9 yjnno;scxw 0 ks time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was its accelhsgsz t :uh;nc:-2e6a5b *qd xeration, assumed constant6hcst5q;-:*x snb:2adu he z g?    $m/s^2$

  A light plane must reach a speed dq d v2wg+j7z /0n 5(c.predbr6u6 nuzof 33 m/s for takeoff. How long a runway is needed if the (const ubqp dnu+jz(d6d 0gc/5.e2 rwr67nzv ant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprintewc035m t7.uh9lb kt;wdpptq3r can burst out of the blocks to essentially top speed (of about 11.5 m/s) in th30p.u7bhtd3tw kp5 wlmc ;qt9 e 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? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed m oe2ie.x eo6p36xdf .of 12.0 m/s to rest in 6.00 s. How far dideif d o.x6m2xo3e.pe6 it travel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m l .5abfyx;;g/a5* vasd(f bq jdong on the highway. Assuming a decelerag.sdyx*bdfa 5 ;/ q;fa(5bvjation 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 frontof;bt zkc6: d: 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 answer in terms of “g’s,” where ;ob :dck6:fzt1.00 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/h p)cn 2y4 gm5akq65-y (ag ziloand human reaction time of 1.0 s, for an acan4 2( 5gqc-ylag5km6)io pzy celeration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopp 5 1vf+jjv-hlbing 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 oz,vr:bs 7td. the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate at 1:bv7d.zr to, s.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 10,01v d7p*xh5mrn 00-m run in less than 30.0 min. After exactly 27.0 min, there arp 5nhdm7vx 1*re still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approacwy5kz pvfj5*,hes an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and shep v5jy*f 5,zkw 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 aftb7q:.jd txsx; b,ii7g er 3.25 s. How high is the cli , sqj :7x;.7idxtigbbff?    m

  If a car rolls gentlqh2 guz+.3 -dk*uidfa gm8bv+ y ($v_0\,=\,0$) 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 2, 2lnx(v,:plox yd g)lw*r ekspeed 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 upward. With wha /tcys(gz 6mbd d3tz2,u: gozr+h t56tt speed did he throw it, and what height dgt:hzr6bt6zszd,c+u oy 5t g2 /dtm(3id it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influeno j2e+sl3:5i)kj xchkce of gravity. Draw graphs of (a) its speed and (b) the disej:ol25 h k+x ck)is3jtance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically wif: sqfp 539ffeth 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 thfs9e ff:3q5f pe ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling fr9p63 zj3,5vse r u:uxm1pf rjfeely from rest, show that the distance traveled during each successive second increases in the ratio of successive odd is3 fpuv1jz p,rruxm6:9jf 3e 5ntegers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neca , cjn5go6+ok su1xouc y,69glected, show (algebraically) that a ball thrown vertically upward with a spe ujoxaun,c+o91cgs6 y5,c ko6ed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically x8. s:i;aejq:c t+iyrupward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photofv+3fa6b xs:0yi3cu lvlash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use tw3 yc:3sa0i lf+6vvuxb o apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2. iiuy4bz)ui; 22 m tall (Fig. 2–32). From what height above the top of the window did the stone b4iiu2 i;)yzu fall?    m

  A rock is dropped from a sea cliff, an(npel:g1x* n a,:ztmnd the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how higgaetp, (* ln1znn:m:xh is the cliff? H =    m

  Suppose you adjust yourrotmmg3dvag/ 3n43.2ywi n1b garden hose nozzle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you fog3vat3g i/3bdr1 4y.owmn 2n mr another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a udcze t8u 1+n,(ig;pdspeed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2–34+n(d e 18zuip,d tg;cu).
(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 vdkl0 63 4w/zj+ .r(hsbi q,drwxgac7upward by a window 28 m above the street with a vertical speed of 13 m/s If the ball was thrown from the street, .sq6vbz3 cg+/ ,wkr(l0ixj dwh ad47r
(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 *ssa9u krp 43oof a train as a function of time. (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? (d) When was the muk ro9sa p*s43agnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as d-cx9d+ zg,. qnl5g9me gvu1 va function of time is plotted in Fig. 2–28. Whax+m1czug9 nvl. gq9 5d-egv,dt is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

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

  A certain type of automobile can stk 8g0 6-k-l o2drmv; ztpfv4accelerate approximately as shown in the velocity–time graph of Fig. t-l0vs z6tr o2p-4vdkkmg; 8f 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 b)e3pr;1v jp kwhz0:h the car in the previous Problem (Fig. 2–35)vbzp w;hph1j3:)0k re 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 objwkgfm cdxca2 0ip*ku p64p.j;.2hd 4 aect traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph fyhftt-7xoa 5c,j gk97or the object whose displacement as a function of timyg7ak9,t 5-xch tf j7oe is given by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an 4 bn p2g/k/,xbnt, cnd3p:v ctobject along the x axis. Consider the time interval from A to B. (a) Is the object movingncpb ,4k/t png,bdt /v:3nc x2 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’s3f5m)f wx: twcc nc(l. safety net. The succ53t wln.)c x(f:m wfrvivor 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 .5c n/y9tblarabout one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher wi/r.ayt nc5 lb9ll 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 goob3srxd7/ c+p mt8 gt)ud chance of surviving a car colxpdm/) gs8+t 7 b3truclision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 mj/1t eojiwu*of;24ye5 osy v( above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approachu/f(* jo 4vj;si2e woeo5ty1ying at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars f oxz 7ob1/d7sly*6 -ax ohspv:or front-end collisions by hauling them up on a crane and dropping them from a certain heigh7b6o shs:oxozap- lx1 v y7/*dt.
(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 t8+ sd i9tphp4pravels 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 res2h crfy4y)0(wdaj wv2 t. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. j4 w0yavdyf2ch)2 rw (2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface int8 yv*3g 7ral13s,yqlcijii f b5t,i9fo a deep pool. The person’s downward motion stops 2.0 m below the surface of the3yit 1 il5v,qr*i7fc3 a8b,fiygls j9 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 rapicxeog ;m33vv qi 6:18iwrgi l*d transit system, it is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:i;8x36c g: gve lrmo31ii*wvq
(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 3zdsyu+b: f0zyo 20oj 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. I0 oo:us zyy 2+zjfd0b3f 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 of the water.    m

  In putting, the force with which a golfer strikes a ball is planne8lpgj/b cl/ 90v.pxydb4 it/vd so that the ball will stop within some small distance of the cup, say, 1.0 m long or short,x vtli9b p//yb4d.8/ 0cpgvj l 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 at a c 8g,zda6 hl. 3zpr9ghmonstant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts fro 39,hg6zm8 pzalrd.hgm 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 stone703zx) ugnk uwy .b0heuk(0v l is dropped 1.50 s later. How far apart are the stones when the second one has reac ex30)klbh.u0(nz uvuwyk 70 ghed a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course om 4*1lleisrhc9mkbu0ju;ze , g 0k+v /f a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must b r0m smclkeiv9 euz jg;+k04/h1,ubl*e maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mounta09vu p*:mu:dfasel-cin pass as he moves at 18 km/h . At the up vue:-lf0d *m:ac9s bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bounce up 6jg,fd (f)en(mwx /nv9nin2l one-av 69/n (n(f2d wnln)fmejgi, xnd-a-half times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long traini sle01 tj18,1jd wclinn:5h b 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 lej 5i w:i0bj,dnnsth1 1l1c8time? 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 b 8vvm3ypy ;dz,aseball with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. y8m3;vzpdy,v 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, w ::) n 3nl/:npd*goyipcaho5 4asgu:(a5a xppith 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 xr6 9xprt 0tbihf o 7vtt8n t)rr.*2h1Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 kmftt*6h rprt0rix9 vnht1bx)82.r 7t o/s . Suppose you are driving 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 120 ,/t2bz,r ivud9 t*x*z dk brw2km/h takes off in hot pursuit. The police officer catches up to thed*d,r2 x/ kw 2,tzi*t uvb9bzr 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 that, a secy)r n9yd(+tef)d4cr aond stone is thrown straight down with an initial speed of 29) rea 4f y+c(ydtdrn)5.0 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 tj/iuzfszh;95r/4i1 tt j3n d5bw p p/yime. The first 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 velocity should the second stone be thrown from;r1ns/ bw/zitjhj f54 tid3pu5z yp 9/ a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-falling parachutfy(/b:ru rmq1w 6hwz5 v0 zu(dist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What wow:dzumh wf((6u 1ry0/ bvzq5r uld 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 awke67oc1 +rqe5l :szt conveyor belt to send the burgers through a grilling machine. If the grilling ma keq:zr6t+ 5ec1 osl7wchine 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 speed 1.5 times faster thant9c7zz r v1w,e,fy8ew Joe can. How many tze e,9rvcz8 t,7w wfy1imes higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the gro/:w y1xdjp me kl,zg:hb./l,v und below you. You drop a ball from rest and see that it takes 1.2 s fo .gelm 1zdlp khbx: w,:j/v,y/r the ball 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 find the height of a particular building usiniwez4 w lo+ 8b*rxii)1g a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much diffx4ioi+8zew )*wlr i1b erence 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. mm2o ylr( f(1vv+l,+g;k:cvndep q +s(a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At whic(;m lemvs +v( v:qk cp+n+,dr1ol2yfgh 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?