Does a car speedomet-/ jygeoen. /53etf5t/ygg zi z0 .cpzer measure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant?oqjw,ng d 62m3 If yes, give examjoqmw g3n2,6 dples.

When an object moves with constant p,3v8rqxn k.i :mj6 2 dvuyiu6velocity, does its average velocity during any time interval differ from its instantaneous velocity at any instun k 8vm:v xuq2.6j,d6 iy3rpiant?

In drag racing, is it pu q2*o , f3ovz6izhpa1smg.,nossible for the car with the greatest speed crossing the finish li*3vsm, o,.pg2 1aifzh oq n6zune to lose the race? Explain.

If one object has a gn9n*:d :lwmqn reater speed than a second object, does the first necessarily have a greater acceleration? Explnld:mq9n* w:nain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/n wz,8t- p+p)yoi)q- nppo- xjh to 90km/h with the acceleration of a bicycle thao-,tp pqp)ypx oiz 8)-+-wnjnt accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward accelesyp, u;(hi; zxration? Explain.

Can the velocity of anvucl31py qh110 .61dqr 4yk 5re ohogh object be negative when its acceleration is positive? What about vice vuyh lgy 6r er o.1 d0hc11ph35qkv14oqersa?

Give an example where both the velocity and acceleration are nl jk/jak2mi/zf x4-osm*b2;xegative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed ozeka. k(+mc*af 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 passing the other as they come out of the tue.ca(+ma*zk knnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, y+eg7kkj;db - give aky- +k;g7ejdb n example. If not, explain.

A baseball player hits a foul ball straight up into the air. Ing(aln;2,pqi t leaves the bat with a speed of 120km/h . In the ab n(q lni,p;a2gsence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up,tf4n z-k+4sf bg80b0jbwh; km what is happening to its acceleration due to gravity — does it increase, decrease, or 0hz +k0-4fb4tgkm ;bf jsb8 wnstay the same?

How would you estimate the maximum height you could throw a ball voly3d2.ds d,pertically upward? How would you estimate the maximum speed you could giv3od,y dls. pd2e it?

You travel from point A to point B in a car moving at a constant speed 45 ud iw6bbxfl/zy,dsp6bk9 + zg0vx2of Theng xyw0 9bbzx,pu6bv2d k+ 5iz 6dl/sf4 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 why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied to:p1r orj9m m25la 6dqx 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 9olmxr:pdq261m 5jar bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constant acceleration:myen)xl/ u 37n a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along th xmy3n)7el/nu e way, a dish resting on a table?

An object that is thrown verticalbyhu;zu+ x yi9s5e a*r q8.cg/ly upward will return 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, ai yc/z+suh9q;yr 8xg a.*u5be nd if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at the sam ao; ,fjv n7ip7 cpxi;w4ja7w.e time? Givepj77ivnai,jp; 74fox .awc w ; examples.

Can an object have zero acceleration and nonzero velocity at the sameubp 2cd )7zal7 time? Give)72lcdua 7pzb examples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etmtg;h )0r fynha- r*g;,0bba dc. [Hint: First try to duplicate the motion plotted )bhra, h-ny dt;bgf0 0*grm a;by walking or moving your hand.]

Describe in words the motion of thnhwr s8/: :dtoe object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel plf4d .yqe)7w 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take 7i g ac6fvmv(h;:(dvfto fly 15 km?    h

  If you are driving along a straight road and you look to the sida0 q:*ptb. dyle for 2.0 s, how far do you travel during this iyb: l* p0dq.atnattentive period?    m

  Convert 35 mi/h to zxgvyy g:r 35m3h5yg 0
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fa0,mmuo cm1 s5rom $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for 130 km. It t+oidio : s;k/bx5zg 0 :osre*chen begins to rain and you slow to 65si e+oc;i b0zor: dk*:og5/sx km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconut*g/q 7ybw;*a,p0zviy*g n6(hdte c ds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuminde,y(g gtt *u;nb v7 h0*pz/ wa*6iqcyg 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-milgl dlh)s3lp4(e track in a total time of 12.5 min. Calculate d( 43pslgl)l h
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in act 1jp a)p-nq( 9vtd+h straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway b-vjh(t+ nc ppta)dq91 ack 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 haqy4v .cyhoo(8 jg3xy90 zfwn/s a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each o 04xwognqyf3o9vzhjy y .c(/8 ther? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long wit :c ( ardrlg-;3r9ifpll it take the car to reach the trupcl ;-rg tfrri9: da3(ck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounb2+rddt kxb dl( 8a;7wters a tailwind that boosts itswkb+2 b l(d7 xdar;d8t 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 spee9)d tlhb)4g ftd and average velocity of a complete round-trip in which the outgoing 250 km is coveredh t9 4ltb)f)gd at 95 km/h followed 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 constant speed hits the pinsja-6b0 j tda(bb z+x4hl6e3wo at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of b0j( +3-46 ztae 6dojbwbhxlathe ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to joxbp:j nsbg5pkq y7;n;:6 /w95 km/h in 6.2 s. What is its average accelerati;g5b jjwkn;::yxp b7q/ so6n pon in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is 78 5pfs cf:. ieskrm.8avela( her acceleration k fi(a5fm:cpssae ve..r78l 8
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, ay y.(sva92tkq :f2tlwbk+ 0l j particular automobile is capable of an acceleration of aboutwly2k:+ fa0b2j v9( qyltk.ts $1.6 m/s^2$ 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 sp*9ompv v1u0qdeed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleratiovdq p* 10uomv9n 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 i5dac33 y3m*jm6u5+2r8ei*)d aon l ywjvot qhn a straih3vyciyu jd2a*o8em q a5wn5 6 )rm 33*l+djotght line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 v)o ppc:knbq3by,, /ys. What was its acceleration? How far didn,3 yq,p )yo:bvpkcb/ 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. What was its gst(h:zc/ ytbqp/ (7yacceleratioyqb c t:(tph//7zygs(n, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s fo dq4fj*x nq 9r la))b dlh7u 5-ych3*rns22jjor takeoff. How long a runway is needed if the (constant) accelerationdnh 7q)22y9l3)**fa- jjs rcqh roj ulb45xdn is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially dobtlim q24vm-9c 8 97tsbh5mtop 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 859smh c 9t o24bdl7tq b-mimvit take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/sge)y12 eox9i f to rest in 6.00 s. How far did it 2ye9 xoe1igf) travel in that time?    m

  In coming to a stop, a car leaves skvm d/bfoz qbj76+-- ejid marks 92 m long on the highway. Assuming a d-do/-z7m+eqbjbjv 6feceleration 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 frou(5yiv 27ah oant end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average av(yaau25 hi7 occeleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an is,oyz 3q,f4*um eeq j+nitial speed of 95 km/h and human reaction ti,oz*em yu3 4qj,qfs+eme of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of mq g8u3zr s3. mar5tt/ c7aj2ia 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 tha9 s3f1f*3)4wgcq wpw3e re/;vd yakke highway. The car’s driver looks for an opportu/3ad)egsec f3 ; qkp* w1kywfw934vranity to pass, guessing 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 30.0 min. Aft) nzyl*i-y fbj;+p5tver exactly 27.0bz *5 -p;y tyj+inv)lf min, 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 ju9bh0zii r *af fe72+jfst 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 should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her ca+fijr2h ff7be0z9*i ar’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 hilw+mri,vg j3g6fq 1b: ts the ground below after 3.25 s. How high q1,j f3wlm6vg:b+gi r is the cliff?    m

  If a car rolls gently6g/)v igc 9 bn24eaa/7qskcvm75 lttt ($v_0\,=\,0$) 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 3uphl9cz a.92mt 6 2znhwqb9u speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwing it v 5 u98pcl0jgmpertically upward. With what speed did he pcp g80mjlu95 throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts fromz+n3iey( h/f 2uy nl+kur16rm rest and falls under the influence of gravity. Draw graphs of (a) its speed and (b) t3(+ l26yunk zrui fn r+1/myehhe distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. (g*m1kdvynktwz4/v48 *ni gxAt 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(vkxv4gm *zyt/ 1dgk*w4in 8n? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance traveledj qp nox2r((;-; wvuug during each successive secondrv (uuq( nj2 x;g-w;po increases 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 vemjp7tr e(-u3 qpcvy.57lan*ic,z r q 0rtically upward wma ilru-n*7(3c, jv7zp5p.0tqcq ryeith a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a speed of 18.0 2-5;shue vfk+f xjex 6m/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 bex*wt:g 76ii ca3fskziw p-(f8 tween each photoflash of the apple in Fig. 2–18 (or number of photoflashes per setfgw8i *3:sfpzw6iai-7 (c kx cond). 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 cisha:g+k7* on v ke44m tall (Fig. 2–32). From what height above the t :hk7 4svk *a+cne4oigop of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the oceana:h ywc0 ofk3uv8.;cjo)p0rr is hejy;hf:30rc8kp) wco . 0oaruvard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust ysck8ubrr ez7+ uu;9)f our 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. u czsf e78r9k uur+);b2–33). 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 water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with40 ikiai6t:rp9- tza7sd: ty/+pjsv m a speed of 12.0 m/s from the edge of a cliff:4yvpizjt- istdim06as/ k :7 +apt 9r 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 mmw3 c1dh54l7r5fepta7pj xa, above the street with a vertical speed of 13 m/s If the ba77cr aahl5pp ,4tj5xw31ed mfll was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function of time. (vze ;3 ((b3qi0v : ps k5qpcvix2guzj-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 magnitude of the acceleration;gzbvvvqixpe 0 p5j3c(32:(- uqzsik greatest?

  The position of a rabbit along a straight tunnel as a fun2jp* pc(vgl*; h 2ffqhction of time is plotted in Figfq2hvc2gl*f ;phj* (p . 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 automobile can accelerate approximately as shown in tcqw7;7 *wcvl she velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of thewq7 cw7v*;sc l gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Problem (Fig.9lwsot(96y lu a+p b5f 2–35) when it 9 st9lpflwab +6(ouy5is 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 th 3-vzl,yvu2ukuw n(g*e distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement asj fdcyma3w +4r5w 3: h(9aqydr a function of time is gcw4 aa :(rdfh3ym y +39q5jrwdiven by Fig. 2–28.

Figure 2–36 is a position verlxsc./68ssjaw tv f b.e(f-z*sus time 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 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 negetzb f8wj *fl/xs-css(6 .v a.ative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safety n8) heu 7ni;zpr w;8x xt:5ejsmet. The survivor szp8h7we 5 sijxt ;nm;) :eurx8tretches 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 Mt9izcmwq+wzu 0q i9zf0u b( s31j 3rs9cd8z b3oon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the samq+d9 ucrsz w9 mzw3i3 cs8 tfj3biuqz90(bz10e initial velocity?

  A person who is properly constrained by an over-the-shoulder j(sias wkv (w2c8o:w3seat belt has a good chance of surviving a car collision if the deceleration does not exceed about 3i:s3( wa( ck2 oswwv8j0 “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( 4pq qsqv0 s6tfm33)d dtg1sf pk:f+d above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his gmf +q3ks f 1dt6pgv ):3pd ts4qdsq0(fetaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisio (t8 q9ykv 4o-xcvvoz658pu bvns by hauling them up on a crane and droppinp9x5ykqv oc6v 8vob4t(v-uz8g them 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 iuny :s)ed: *ktravels 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 res7nm:k5)n uzv w hymj2/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 thewj2nh z )7ymnu 5k:v/m train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a dekug* 1e-hlj a)ep pool. The person’s downward motion stops 2.0 m bel1)e-*gk aujlh ow the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessaryl1qas6 f 33t nfjq :,aplu(y8s to balance the average speed of a train against the distance between stop3ufqa38a,p ly6 :l1s q n(fjsts. 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 2 dx3ohq rjfj6o ro ajsl2;c.b.98ok9fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a lho.o2co ;.f j6sj2bd 89kq9r3jrxaofish 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 yb. 0rje* zr5iplanned so that the bjze5ri.r *0byall will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a 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 )9pj cite .jd(;hyimixq2 43yfreight train traveling at a constant speed of 6.0 m/s Just as an empdt)i4x yye2hq3(9ij jcm; i .pty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building hj)plis2 ajr 1z -)7 c0is/;pza*gyah. A second stone is dropped 1.50 s later. How far apart are the stones when the s0z 7zp-2i1ahshycg;a/ aji jr )ls) *pecond one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a titqm hi0b uf7vq: hk-;3me trial lasting teqvb:khu;q-m th0 37 fin laps. 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 d3 3huvl zq8;ecnt +bm4:ix)x ie France crests a mountain pass as he moves at 18 km/h . At the i8qx4:inth l xm3)b v;cez+u3bottom, 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 cdi) qj :idp; 3t(rhyyr* /p.kghild can bounce up one-and-a-half times higher than *p(hq yr.jg dp ki yd3;it)/:rthe 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 ktnc vs,,om- n;m/h overtakes 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 pass it, and how far will the car have traveled icomt sv,; n-n,n 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 tg9+,83dpm2 did -vj ayouaey,fi) w 1speed 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 gya j2p),3w9eda+of,1i8u-vtd mid ypoint where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises verticallmjb226dja o m6y, 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 pyzv81gm3a e6 shown in Fig. 2–42. Each intersection has a traffic signal, 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 first intersection, all the lights turn green. The light za eg813mpyv6s 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 -t-jsj8qcicha k hfsa.q 943.. es0jaat a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, mainhjk.s -4iacsf 0-h9j 3 sc q.jaqate.8taining 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 izl2yi qq nyo v0vk.l7y;, 56nstone is thrown straight down with an initial s72liz yon.ql ;v yyi6n,vq0k5 peed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. u)re q:jzf7r,g v5 3gt 7m)wq0kae)dd 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 s w37tef u7zq gmqda)5j,r)e dkr:)v 0ghould 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 resz bq+g1ci+ m6n+xia9 zg h5t:sistance, 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 59hncmia+gxb+1 gs ti zq: z6+her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers through,6m z /mh5e pcn:8 /mqshfw-rd a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, hoz/cqmp 5hm,:e nfs-h68/d wr mw 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 faster9y qyxir 46 jutl-j(o3vn j10e than Joe can. How many timeslqy9631 (xjj t-ouyejniv 0r4 higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff wr c-9t 46o-ol 5-3jnxe: d oubrtac+ivhile 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 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 ballt c - o4oat+o6nxd-uir39r 5-c: vjleb?    m/s

  Two students are asked to find the height;pq,z4;opoi/ k k9 9tjn;u qhs 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 drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of 9k ui;n t,p/o4 zkpo;q9;hsqjthe building’s height?    m

Figure 2–43 shows the position pc gr/ 12z+xgmvs. time graph for 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 accelerationmr+ cz1g/xp2g? (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?