Does a car speedometer x2 *, xvm8a0*dmn)ki pyg: etameasure speed, velocity, or both?

Can an object have a varying speed if its velocity lau,j v.8ma+z is constant? If yes, give examples.ml jav8,a+uz.

When an object moves with constant velocity, does its average velocity duriq:n lju )u j)vdwsmm/s;5a r48ng any time interval differ from 5j)ml/qw:vjrsd u ) ;um a8sn4its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest spees 7j103lcu p(lv5pbkq10 qinwd crossing the finish line to lose the race? np0k lq1q1j l(scw0 5i3bv7pu Explain.

If one object has a greater fx,vn57quji lb8 yea0m ( *vp/speed than a second object, does the first necessarily have a greater acceleration? Explain, using e/8p*qivbnvm 7l (0fajy5ux , examples.

Compare the acceleration of a motorcycle that acceleratez/4svm4un-si y6+q.n.s w lx gs from 80km/h to 90km/h with the accele .4+-6s is4nz./ nlmwgvus yxqration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a s7lc0-x d 9a tuf-d*plwouthward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positi3o8mao 0o-l uhi;h1 i5hpge*bve? What abouhhi3oug0o* oi8lmpb1 -; aeh5t vice versa?

Give an example where both the velocity and acceler.zp3z ,oq/a /l.wiqs/ skdh)sation are negative.

Two cars emerge side by side from a tunnel. Car A i om+ jl(wqk,e id+c/z)s traveling with a speed of 60km/h and has an acceleration of 40ke+o,(k)dmlc+zj w q/i m/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 tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? Ifbt:e lp r0wmqs yp5k2 3(6le0x so, give a6t:wp p el 05bylr(emsx 302kqn example. If not, explain.

A baseball player hits a foul ball straight up into the air. It/q4b1dia1rby 1 ka: azxyzd8) leaves the bat with a speez za8 1qd:a b4b)yx/k1a1riy dd of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its acceleration +4 h ,of(dxjym +db;k (jy5uvtdue to gravity — does it increase, decrease, or stay the som+(j+uyhj(bkftvx d;dy4 ,5ame?

How would you estimate fk p zqt80t:ado(i:.3-ts7ctbt qe 0mthe maximum height you could throw a ball vertically upward? How would you estimate the maximum speed pt8tbt: doq3z7 0 fck -iam(qttes:.0 you could give it?

You travel from point A to point B in a car movingqu:usuj0-oz * uzjr3 4 at a constant speed of Then you travel the same distance fru43:souu-uq j0rzzj * 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 demonstr4hdr4 p0 2rdddr- l:s tlyi/x3ation, 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. W4d lrx/ d2:di-lr ts3yr d4hp0hy? 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 motions is not at constant accelerationov9ck wnb7(5.wg )is r: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stopsoi c. wwk vr()59gbns7 along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its original position coi( */ 0qdydhwith the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite ch dd/o(0*iy qto the motion.]

Can an object have zero velocity and nonzero acceleration at th) xtr3ulp)o3pgeos.goy5* 9 1ef9v kve same time? Give. so9veuo5)tg o3 9p*1l)r xgev3ykp f examples.

Can an object have zero acceleration and nonzero vehr7 zy4.1j5hrw1 dc xylocity at the same time? Giveyxzjcrw dhy51 r.h 741 examples.

Describe in words the motion plph*t (1d:xko/ kpeiw+ otted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by d:(*kk ph/e pwto+ xi1walking or moving your hand.]

Describe in words the motion of 3h8(iejyia xou)ilvxm1e.+1 the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km zdn j qw3hy5b9/;p1 typja5pqnfp;:, in 3.25 h?    km/h

  A bird can fly 25 km/h How long doesl -4*kc 48nnc5:olrzfquhz1 t xm)f+p it take to fly 15 km?    h

  If you are driving alonr:/1go ,8lwh,ut.3;nip* s+br qdmwqmr 7vtc g a straight road and you look to the side for 2.0 s, how far do you travel during this inatte/ t3;biorr ,wqs .v1l p r7*dugqh,: nmc8mw+tntive period?    m

  Convert 35 mi/h to /bj0 /h,o ec 11nsqmu3ur4ixy
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fn8j9 + inqopprp 26:brrom $x_1$ = 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/ g3jdaz5 s3r;ah for 130 km. It then begins 5zjrg d3;as3 ato rain and you slow to 65 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 seconds between a lightning fla fx fyjr4o+r1.g g5br(sh and the following thunder gives the distance to1frb yxg( rfr4+.j g5o 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 mm9w99re7vis q bbj r,:)o1.sj:wwtt total time of rtibb 7.wts1)j o w:9mvrj99,q: swem12.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer 4e d2id6w .qwa r9vu-5.ihb ede5h+cgin a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway bi6wr d.e 2ebd.h9vuwge4 hqai+5 5c-dack 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 a speed oa2;1qr,u1 t kz pw8 mgasb9 c1mj1;eojf 95 km/h with respect to the ground. I1 ok;mrmbus w;jzea,a91 q1t1j p2 8cgf 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 l yx,.n fik18fis 110 m behind a truck traveling How long will it take the car to reach the trucf8, 1fy.xn lkik?    s

  An airplane travels 3100 km at a spsf:g.o ikzwqm, y14 ( n;lylxl,+t/dpeed of 790 km/h , and then encounters a tailwindzdx4yyl1 s, . poq,+tfwnkl/l:gi m;( that boosts its speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed auva085i emy k*nd average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.8*kiv5 au0y em0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins at the end of a/+iscgt x ( 7m8vv3e ita3bag) bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 vmc/+v ( x83bit)g7 aa3st eigs 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 average acce azj+y2bv46cwzc .wd4leration i+wa.4jy46z cwdb 2czvn $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in+plb)4d3 j/8 nenntfpg+i h7 t 1.35 s. What is her acceleration4n8en+d tjh) +fplp 7gn/ ti3b
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular autfmt;.rmhc7vx f *1 cr7omobile is capable of an acceleration of about tf.1;m*7f xhr v m7rcc$1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110 m ino/wf5jwy6cx 0 5.0 s. If it then brakes ac6y /foxjw5w 0nd comes to a stop 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, which startju wk7c i63sj/s from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph i6swuj37ckj/.

  A car accelerates from 13 m/s to z5o/9 m kncrwx+3fwn(25 m/s in 6.0 s. What was its acceleration? How far did it t/kr9(w m nzo3w fnc5x+ravel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to eo3*w )cg+f cy3y5vtirest in a distance of 85 m. What was its acceleration, assumed constant? wctgoc3 y5)eivf+* 3y   $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff.t)c92wgwryaz3a 7 9ac How long a runway is needed if the (c7atg2y9c9awrw3cza )onstant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top sp7 ,5w/vu bdrjaeed (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 doesu5bj/avd ,w7 r it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. 1oe pe : r8qyzvytxw2v mtk7mw1f xsh.,i4**,How far did it travel itovehipkf1qzytw* 1m2yrx.8ews7,xv ,m 4 :* n that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Assuminl1h md6i5 ;vo orfkqhb 2n1y6 4f 3pxo)ml8g*eg a deceleration of dml;ie 5yhrv*m hq3fo1gfk2 ol bo8xn6p)146 $7.00 m/s^2$ 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 cau*o s lwzfj2,:r 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 1.: zjwufs,*o2l 00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a caqz7ui38: oiig d6denbuj-. ; kr with an initial speed of 95 km/h and human reaction 6beui d i.j;qz-n3 :dk8 7giuotime 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 equatib 1o-app ic/*0w7b lnj :x(-eis tx1qpon for the stopping 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 goingeslvz-*0td3q/et 4sk . yfp 7g 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate ae7pyedq lk4 v0s-*tt./ f zsg3t 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 leasdv,4,l /da qq 4rb/qss than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must then aaqqav/lsd qb4r,/ 4,dccelerate 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 just as ny l1,jmbn/)j()j8q tsfmh,e 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. 2–8nj, s ())m,htbl/ jqemn y1jf31). 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 fr (b)vjwh3x1 f6mejn v+u7f v)b(/xxm bom the top of a cliff. It hits the ground below after 3.25 s. How high is the cliff?bvnwu3v1)e(6/v)7fxxxjh mj( +fb m b    m

  If a car rolls gently 4d6 q es7:qumh($v_0\,=\,0$) 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 speed ofc uc1 ,h+v*pdx2 hejl. 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 8fvduz(ayn+ kv l87 8kafter throwing it vertically upward. With what speed did he throw it, and what height did k ud88klfv8an( + vz7yit reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under th+igq 2zov30g datsc: ,e influence of gravity. Draw graphs of (a) itt0cig a3zqv+2,gso:d s speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5k5yyy;vz( s .u.20 m/s. At a height of 125 m y.vu y;zy5sk(above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show thazvgw3lhk7ypns;bzo d q*012id3oo07t the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc31 2q0zypg vsbld 7odoo wk307h*in z;.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically)fd( / /dt wu1)3q jaf2yqh:p50counaq that a ball thrown vertically upwa/ 2a qya f nqdj p5u0/)o(qhtdcw3u:1frd with 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 upwardmx74hsc9kx b/pdvx/ek 0f* e: 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 photoflash of the apple in Fig. 2–18 (or number obch), pfcxh 8( jb.6nrh,gdy :f photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at tx6c. g j :h,( bhrybn,d)h8cpfhe top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a wing7mkw za t1v o109u*u4.fl0ylpon t*edow 2.2 m tall (Fig. 2–32). From what hvp 01le of*m .u7oz*1ylw4k 9nut0agteight above the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking1q8)gxjyh.z 0 vhdh v4 ai1:sm the ocean is hearvg8y1vqihhjd hzx10)ma4s.: d 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust y z:(t6ylryfpkiarnd95p i6+ 2cp 7 6ehour 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 p (7h6a ieztyy5nl6f 6rpp+i2 :rdck 9for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with ml95w hv5fe4 nk;mqyxh2b9i, a speed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2–34).lky q4 mi nevb xw29;5f59hh,m
(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 m above the st6tdib2lw1 jbqp9ypa4.g rzp (c ax9(2reet with a vertical speg9z9pq wpxb6a.j (drya 214c itpl(b2ed of 13 m/s If the ball 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. )8a6f5 ttclh tsuk9f5 (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constanthfu9 lfs5k5ttc8t)6 a? (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 plot0xfmfche s 91ue.xm5 p jk945sted in Fig. 2–28. What is its instantaneous velocitymss4xf5cujfx1 9p.mhe9 e0 k5
(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;w(kcr7j -rgw approximately as shown in the velocity–time graph of Fig. 2–35. (Thjg-(7kcwr r; we 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 thjpua9x* k49v+ru3igz l;oh*i e car in the previous Problem (Fig. 2–35) whei p xl+3ujg* 9zvi;h roa9*k4un 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 object traveled duriu;)biyzzlu 2 /ng
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function oml; n,j 0tflkg 81dy*r4l.vyhf time is give,v8knljhyld4l;r 1 gf.t m 0*yn by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object alonx/g vbrfe00j swgg82 4g 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 objeb2sjwgx84 e r/gfg00vct 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 fi a;dztss/yb6 0q5ez;urefighter’s safety net. The survivor szs ;bt y0s ;zeu6aq/5dtretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what itfawg*n ejz c43+,:o5hpl*x ie is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on: eg pi*e*4f l,3ajczw+5h onx Earth, assuming the same initial velocity?

  A person who is properly constrained by an 2 i5.02wdomllgphr h1 over-the-shoulder seat belt has a good chance of surviving a car co5g2lh2mw.01ih drp lo llision 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 m above the road belowcm9q*kvg( r*we yfob,ala+. 1, 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*aab wro.1c,(e yg q m9*lfv+k 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 manufaa5jjy7bs mii; bj xv/2jdw;- 3cturer tested its cars for front-end collisions by hauling them up on a crane and dropping them from a certain heigd bwjm ;iv75;bx3ja s-jyi j2/ht.
(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 agxg2i.1q wxjt5 z0cb +bout $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins un8e:4v o-tl b k*w9fk6 bfh5xzniform 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 work4ev89o *-6bnzbkw 5: tfhl fkxer? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the w dhl6 v/87ovfkater’s surface into a deep pool. The person’s downward motion stop8o7lv/k dfvh6 s 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 system, it is necessbx,(s,v k mfs*eea7mo v2hb.9ary 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 sita2*m vk 9v7, ohbs.fbxme,se(uations:
(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 for fish. Su, *usy( kc+mtgppose a pelican start (m +*gcyt,suks its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is plannedf 0l01(fhe)2, v d8gt/f +hgcehfb ,.ycn fxek so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates con e0yfveb2el+hg(t c,h/ gfn8ffh)d k ,fc0x.1stantly 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 constgg/u,+ rdwxd0c /vg -tant speed of 6.0 m/s Just as an empty box cax rt dd-/wg0 u/,cv+ggr 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. A second stone is dropped 1 u;(w 3 v)nbj yd)ky8,1jgtvft.50 s later. How far apart are the stones when the second one has reached a speed of 12.0 m/syfntktdgvwjb 18v ) 3;),(u yj ?    m

  A race car driver must average 200.0 km/h over the course of a time tk.81*6plsbomfe:rz u rial lasting ten laps. If the first nine laps were done at 198.0 km/ eu:* f.bkslr61mpz8 oh . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 km/h dn7n r)alhgfkn.i0x9k4e ); v. At the bottomv n0gx7e) .kfdain lh)94k ;rn, 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 fi2 :u :b2u u.-gs 8+akwnxmydijrst child can bounce up one-and-a-half times higher than the second child. The initial speed up of the second child isj8ibau+ux- sd2.:k2 w unymg: $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 train traveling in /oq4 ludjmornt:- 28llf7fy4the 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 will4lf2jd u lo- 7on: qrt/yf4m8l 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 bases9;sq0l /p ijrball with a speed of 44 m/s In throwing the baseball, the pitcher accel j; irqs/9spl0erates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, frsv4b . hv 7-ivqqv3jc6om 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. j*9atq,fzmy . 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west aty.q*f,taj 9z m 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, p9 ln+9 vadic7nassed by a speeder traveling at a constant 120 km/h takes off in hot pursuitn 7 9vln9ad+ic. 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 or (ve5joxkyy /l r;r,o3pi ey6kx5 :-that, a second stone is thrown straight down with an initial speed of 25.0 m/s and the twoo; rv oeo5 e/ijxk5kyx ,6(: -3plryry 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 ve.hq n.zvvx2p y8-h fjch4yj.;p t,5wwrtically up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocyj4, t. p8n5vc hp.yhhx.qw2 z-j wfv;ity 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 take a free-falling ;tzzr- u oh p.moe(v,oouzm*- (sz-h;parachutist to fall from a plane at 3200 m to an altitude of 350 m, zoe -(vt;o z z( m,muhr-us*oz;op-h. where she will pull her ripcord? What would 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 a convecvw i cap5g*e*ic:.5 ryor belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to co5a i5e.:c* pccvw *girok, 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 than Joo zod:)xr4s 1y o;6kwce can. How many times higher will Bio )o: ;o kw1yrzdxsc46ll’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 grofg5xeqmh j 9m; ;uicgpm6/ 6i5und below you. You drop a ball 5/mc xm ug ighqm;56pif;j96 efrom 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 fp2xpp9x/1,v s svq 0kifa) .fgind the height of a particular building using a baromet29. igx ps)k vvaf,xp/pqs 0f1er. 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 the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A g,cv+u8 )l pn.yafca 2and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has t pca f2),ulvg+yca 8.nhe higher average velocity?