Does a car speedometern5m x,jfwo qnra9c0m; (. 1qvx measure speed, velocity, or both?

Can an object have a varyinga ,tc:eoo8 o3l4: ovyz speed if its velocity is constant? If yes, give examples.:czy a olo8e: 4tv,3oo

When an object moves ,,fj3yve2i lv6ab,ko with constant velocity, does its average velocity during any time interval afy b3 ,lvo2 ejki,6v,differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greates93glvse-:y.kqp / u:cki*blj t speed crossing the finish l/s.:piykjl -qeu v*:3gcb l k9ine to lose the race? Explain.

If one object has a greater speed1/ ; xulbivpq5 than a second object, does the first necessarily have a greater acceleration? Exp;bxqivp5l/1u lain, using examples.

Compare the acceleration of a motorcycle that acceleeqmpy2az 811g n-z 3yhrates from 80km/h to 90km/h with the acceleration of -3me npa8g2 zy1yzhq1a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceleratic w 9nwa(v)3pcon? Explain.

Can the velocity of an object n q1 p4;i5 uwwn8ild4ube negative when its acceleration is positive? What about vice vn54in4dw u8;1pui lqwersa?

Give an example where both the velocity and acceleration are nyy ud7 9av o8kz5 j2m2-m:dxzgegative.

Two cars emerge side by side from ay7) - jsk ybatxbn33lln 1e;/,zynx(e tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B hatejz1sxx3 n(3l7,bn/ln yaybe;y )k -s a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleratiocr+ r;6 )ri )p0:tv 0mvoldluqn decreases? If so, give an example. If not, explctp rvm;+l :i 0q) uor6lr0dv)ain.

A baseball player hits a foul ball straight up into the air. It leaves5;k3 9th v1qstwwh, mrj tqf-( the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling w-1 w, v9htkf(mtjw5q rt 3qh;shen the catcher catches it?

As a freely falling object speeds up, what is happening to its accele)z+0i vt6d dok msj 5;n1c,yldration due to gravity — does it increase, decrease, yv6);okz,+t1in 5dl jcsmd0 dor stay the same?

How would you estimate the maximum height you could t5n. -dur br r6o8,avsxo)g2eehrow a ball vertically upward? How we b2u6ngao5rro)r ,.- e8dxvsould you estimate the maximum speed you could give it?

You travel from point A to point B in6 g;;e;gn eeah 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 for the entire trip from A to C 80km/h ? Explain wh;gg;e6 ahne ;ey or why not.

In a lecture demonstration, a 3.0-m-long vertica:hcdag.a/v. ll string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The scaalhv d. g/.:tring 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 clinks occur at equal intervals?

Which one of these motm y+:djr52xb 9a-sm vnions is not at constant acceleration: a rock falling from a cliff, an elevator movxj:ydn rm-s92abv 5m +ing from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original posg .ost 7xhh rxom3g./;ition 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 opposis..txm ohgxg;7/3 rhote to the motion.]

Can an object have zero velocity and nonzer952.d;g7dvgx m hyxe t4jk5 dno acceleration at the same time? Give eg gyk7x.nmv5e2hxd; dtd4j5 9 xamples.

Can an object have zero acceleration and nonzero velocity 2uv-jycj0 h0ekj*, ,h)*xoybw n0nq oat the same time? Give examples.xu0 y*be00 ,hno2,- ykwvq )ocjjhj*n

Describe in words the motion plotted in Fig. 2–82qzvj y fz-79mhgsum+87w d x28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or moving youm8v77yxw9-uzdm2 j f+hz8gqsr hand.]

Describe in words the motion of)+sn 4 . hjcd/,mh)lkqfoq m.z the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 kmq zne;*8m t*zn in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to ,;lrsvfjjr2+i :qh4l fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s,a f61zhxn-4 jj how far do you travel durxfh jz -164ajning this inattentive period?    m

  Convert 35 mi/h to jaq): uq+ylo1
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves froz6etqx(od*yui9nj*hw z5d 0f by6/n 9m $x_1$ = 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 steadi(gwb wi:2v,ln ly at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home afterb:gil,vwnw(2 driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lighsof.(yh7hyf-w+y (bj tning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in f-(yy (w.h+7ofyh sjbessentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete l-k;t) rha h-qzxoqb18aps around a quarter-mile track in a total time of 12.5 min-8 q;x1ba tzh)-hkrq o. 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 a55uqua6 688xonsja5 zoq-n cgway in 14.0 s. It then turns abruptly and gallops h8sac8-qg xuq6onu5a5o6 jn 5zalfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has aqxg51cld,:5 vjqu -1v qm-kcs speed of 95 km/h with resg, xcduv1v-q:ckm-1 js5lq5 q pect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck travelijr h,5d k3to j(e53vhfng How long will it take the car to reach thetkr5 (hvd3j3 o5,ejhf truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounter+2wulko5a;,z zx sya3/h9oya0 h/aw ws a tailwind that boosts it2 ,5 lwha/3 ok; 09ohzuws x+zaaywy/as 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; vanx6vw .jx. a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covvv ;xxja .n.w6ered at 55 km/h.    km/h

  A bowling ball traveling with constant gqr3 9n*jt8sv64tmn xy*(tyiws ()awspeed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound ofm)it*w(jt9v3q6*a r(ny nsx 4s tgyw 8 the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its averag)t3l qhijb1 8yucuiqq3p2 *c /e acceleration*j iucq 1)pi utyq cq3/3b2hl8 in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1., /kh z kr(zg 1i8qioc1kiyk+*mw)nn; 35 s. What is her acceleration(+)rihm;8 ng/*c1 ,1k kwzkkoi nzq yi
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile ivjif;.q eaq k(;ois, .s capable of an acceleration of about .o qq vkj,fi. (;;siae$1.6 m/s^2$ 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 spee2-e,;pv2imhcqfm 6iug r 9jm8d travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleratimv;g-9,h22ic riqu mepj68mfon 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 moves ie- j6 mf )jgvgj : jg;k,c1wtn1i+k(v;i zws:an a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its ajw-zk:c em1g+k(sji;1g t, j: f6 ;nj v)waigvcceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m.-8n ge gvant-/s in 6.0 s. What was its acceleration? How far-8 -tvn g.ange did it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m 0zeoqd,a* qe)cv .av:faz;d4. What was its acceleratio)vz0 av*:codfqzqe a, ea4.;dn, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long:esiw vy4i,/i a runway is needed if the (constanteii: w4vs,y/i ) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially t8u)upv(r-b. ru luz( bop 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 speedb uuupr.-vul(rb) z(8? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m ijdps r3z(8c;/s to rest in 6.00 s. How far did it tj 8rzc s3(di;pravel in that time?    m

  In coming to a stop, a cg c 9e5iv fcj9mhi4,7yar leaves skid marks 92 m long on the highway. Assuming a deceleratio5,i9j4vyeimgf7cch 9 n 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 compresfoni *i3,9x v:xniso/ses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi s ni,9/3xn vf*ooi: ixon? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 95 km/h a w ltpqzzlt5d*lr:sp63 g4:vxjpc3 0-nd human reaction time of 1.0 s, for 4*jll t dwp3vzz3-0 rc: qgls5p tp:6xan acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance hwr8 kh; 180k/6lci)qvuxkb nof 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 the hiuoz,8+9seld o+-sje pghway. The car’s driver looks for an opportunity to pass, guessing that his car caleo++ed -sps89,u jzo n 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 10,000c lib-zs) dv 8,x d+y;/k3onvy-m run in less than 30.0 min. After exactly 27.0 yzyk8dsn-3c /+, odv vl; xb)imin, there are still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an intersection gfth cnzv)kc/ia09 /8just 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 0vzc c )ftgha/9/kin8, 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 th2sz: x pb0r*ppe top of a cliff. It hits the ground below after 3.25 s. How high pp:bsxz*20r p is the cliff?    m

  If a car rolls gently jbxiv7vdqe(wf+a 2 ).s 9jg-e($v_0\,=\,0$) 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 str h- qi3dtrcv/3aight 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 throwk6*4 dl5v0q9v r4csu lwbb9p ming it vertically upward. With what speed did he throw it, and what height didls4lm04rvc6v5 d 9kbu9p qw*b it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. nv. n8pem7tp ku5( o(ohg 9v77urh6nwDraw graphs of (a) its speed and (b(uvm7o ek9t gnvhpu7h8rp75n (o n.w6) 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 verticall915xezlvafrte8 v(wnmi, 8( oy with a speed of 5.20 m/s. At a height of 125 m above the Earth, a packe5 ((rzlvf9wm8tn x81vi oe ,aage is dropped from 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-rou+f .2hpz n3 2jkxfke 4a0u freely from rest, show that the distance traveled during each successive second fu02rp24 nk j3- .a+koezh xfuincreases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown vertical7lan6wdb*/* wlzqqinv ,y l (8ly upward with z (lywqi *wndlb*,/786nqavl a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertiw2sf3 sk, fjn9cally upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each (p/l)dk*gx p)/kw rd7e w(ik r0c-rjophotoflash of the apple in Fig. 2–18 (or number of photoflashes per seco-/wd) (legrk ko) p r7w cpj*r/xkd(i0nd). 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 travel past a window 2.2 53.4 jh1cg zoothbi9im tall (Fig. 2–32). From what height above the top of the window did 4i h3bhiooj. ct915gzthe stone fall?    m

  A rock is dropped from a sea clisi 4xh,dyql w /w frw:4owj7-88cl 89n oou.yhff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how hiwd/r h.4 -q 7ly,cw oso : 8ojwwi8l4fxu8yn9hgh is the cliff? H =    m

  Suppose you adjust your garden hose nozz yf8kgr5ra 9m.le for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water859a.mkgf ry r speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.1r5s9vg 1fp w- eywf8g0 m/s from the edge of a cliff 70.0 m high s gr591pwe 8f-v1gfy w(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 2ty0rdn-zcte /nuqg++du, -j 38 m above the street with a vertical speed of 13 m/s If the ball was thrown from the str+rny dtugc- ,t3enz+-udq j0/eet,
(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 veloclunmd11v,n zi c6nze-0 j,2roity of a train as a function of time. (a) At what time was its nr m- old2nz1vie 0j1n,zuc6,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 magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function of time is pl6b8q;:i:1c thjji42 xjf (hxtqi6 xuzg 7zek: otted in Fig. j:jgh4 7ik1xz2:x zitu ( ij;6qcbe8htq6:fx 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 automo;nd:.nr4;j s,hp j 2h 8d;wpc ejsh4nubile can accelerate approximately as shown in the velocity–time graph o.shnj;hw 2 hnn,pd4rj;c; 8su:j pde4f Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average accelerati7 9rje70imx;d pyw2 qlon of the car in the previous Problem (Fig. 2–35) when it is in7idwpy 079 ljme 2rxq;
(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 xb s/ze3gmmhn )nuk8 9/vi2e1object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the objec ;5i3gle( qcbrt whose displacement as a function of timerc;l(ge53bi q is given by Fig. 2–28.

Figure 2–36 is a position versus time graph for th-25j edl2ihad: n5usne 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 negatdai525 u:lsh-dnjne 2ive 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 firefighq djf5 v)s;e4eter’s safety net. The survivor stretches the ne vee 4)qdsj;5ft 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 dl)xk pkm,;z* :j1a lxis on Earth. If an objx xm:; )lz,akjlpk*1 dect is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder s/ x /2nwp:uy1 yd xcw(, klne)(ggfz)feat belt has a good chance of surviving a car collision if the deceleration does no:c) g,(fl)dp1gne /2y uzwwx/yk nf(xt exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his pursuerd 7f,qq6 au7kvr 6feg3f6w3ijs are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , whic6, jd6k73fwi67rq fq3auv efgh 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 for front-end collim5nl v2ph;hjua (x5 v;sions by hauling them up on a crane and dropping them;l uv2pjn 5x( hav5hm; from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels about yvu.ox8;wj/kx+6; k)d ivpvmg7( vva $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begiwzxu1u1 urs6-lt./5jgm- xj.w g.nbqns uniform acceleration from rest. 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 w-jn t/b.lxr g1ju5s-..mx 6w wuz 1uqgorker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s s- 6g7axonn7mi urface into a deep pool. The person’s down-6n7m nox7ia gward 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 rapid transit sy h x/)i:q;n)i b0wliszstem, it is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the slh ns )i; i0:bqxwzli/)ower 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 straight down when diving fou:.0 vpoqm,0 / lqvwydr fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committ.,v: o qul00q dwmv/yped. 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 of the water.    m

  In putting, the force with which a -u.ih4wfsu1z5 fth- igolfer strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing tfh-whs-t.f4 z5u1iiu his 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 h8;tlb wh.tdy) op on a freight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from resb)yl t.;td8 wht 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 yu2xp39:go rfnm l 6i6roof of a high building. A second stone is dropped 1.50 s later. How far apart are the stonel 6ygronx6pf:2u93ims when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver musl.pb i6n.)br1igd- mbt average 200.0 km/h over the course of a time trial lasting ten lapsnd bg .-6.ib lp)1rbim. If 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 ax)gqbzq z(7c- mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his avq)xq z-zg7c( berage acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can706hc)a 8cwht skijq jk 7y5y) bounce up one-and-a-half times higher than the secoyc)) h5 8tjw0cakqkj s6ihy77nd 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 osgnr57 aw ) vfly2v5+jdzj: f(vertakes a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pa wray5vjzg75 jf+:n )l2ds( fvss 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 bas9r. ;uxj*t9 p w (0soy4qs5f9wnthes geball 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 (w( fheo49gs95wyrtt .jp0 qsxn* 9s;uFig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertiqxu7l u+jch/(+xia.k1 ksi l3l:b 1kkcally, 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. Each intersection has kcp 1f-wnnmj+- ro 1yw:0hqy,a traffic signal, and the speed limit p0r ymhyjnoc +n1,-qwk-1 :wfis 50 km/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 kmco ;p79opf9ic0 lskb9 /h takes off in hot puc 0il99 b7k;9osfp pcorsuit. 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 that, a second sto(*dc3lxq tl1ld4k*bpnri,l fbo5 s42ne is thrown straight cbn* qflld*r214il,s(4 btxd35polk down 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 verticallytw3 k63zlco w; up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcon6c3z lotwwk; 3y of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it ta0 7zbht yjmg,f4xu24 zke 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 wilyzf,7jt xm2 44gbzuh0l restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers m ck fsm3x:q -o/ddr9c8hm29nthrough a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers m9f on2qkcmd:m8scxr d9/- 3hare spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball verticalbe+0.jv w3lbj:b/ 75bt dfcvkly at a speed 1.5 times faster than Joe can. How mavvjd+bt7.k:e05bb wl c3 fj/ bny times 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 , 4qqq3q3ji ndumiu3. ground below you. You drop a baldiiq33qq.4u, q j m3unl from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball 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 heightbjyy3q2top6t px( 2+ui-l0m n of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and dr3ou+ bt(ty 2npm6pq2xl0i-y jop 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 an:3io egqtzznp6m 9psri1u7 + 2d B. (a) Is there any instant at which thert6g qo:32 npizep 9u+7 1zsmi 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 higher average velocity?