Does a car speedometer measure spk//xfmtww8ax :lr -;aeed, velocity, or both?

Can an object have a varying speed if itsw ,/t7mwf) ijr.fm pe4 velocity is constant? If yes, give exarff,.p )mj7 wei wm/4tmples.

When an object moves with constant vewrfkh h+ rbm.aa+ juns8a35a2 ra9+;clocity, does its average velocity during any time interval differ from its instantaneous velocity at aaf2hm.r hsa;r u++kcnb8+9 5 waaj ra3ny instant?

In drag racing, is it possible for the car with the greatest spe;a n(xl- c n7i,/htouged crossing the finish lin(lagu-h n/ ;x7cion,t e to lose the race? Explain.

If one object has a greater speed than a second object, does the first o4y.py7v7r+; firr lb necessarily have a greater ;+irr.7pry7by olv f4 acceleration? Explain, using examples.

Compare the acceleration of aha3.s9lt 9byg *akh( a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates fro 3ab9(lys aght9k. a*hm rest to 10km/h in the same time.

Can an object have a 7wpbf o5o ,5sonorthward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positb p fn37pcy/)5yj8o1l:uoe wj ive? What ap:1u nf3/c5)b 7wyy 8eojj lpobout vice versa?

Give an example where both the velocvt2z:uz8zjn9 3)iq gc ity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a speed i0x(3o agqlr4of 60km/h and has an acceleration of 40km/h/min . Car B has ag rx(l4a0qi 3o 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?8jjsbs j 7g/iq33;f:e ;gjdxz If so, give an example. 3fjd8/ xqejjzs g 7big:;3;jsIf not, explain.

A baseball player hits dw0idzz6 78fda foul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistanw8d6z fdd iz07ce, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its accelerc6wb*w(l w+wwk ge.h)ation due to gravity *kc w. 6(whbw+lgwwe) — does it increase, decrease, or stay the same?

How would you estimate the maximum hei; q4z :)jix7j y5yntkwlv u:6qght you could throw a ball vertically upward? How would you estimate the maximum speed you co7 xy;q)ytvz5jn :uij w:l6k q4uld give it?

You travel from point A to point B in a car71(odl8axv r :1e wwva5p3 ay.ck ;lqb moving at a constant speed of Then you travel the same dkaaw(v xw 1b dr;7a.eco p3v58ll:yq1istance 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 demonstrath2i88d shk u(mion, 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 timuih8ms k( 28dhe 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 motions is not at constant acceleration:dv1 :e zcaf6b s3:qjx z7+eoi1 a rock falling from a cliff, an e:3 b1sja zx q7d:cf6eoeviz +1levator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thtd/zb-c v.0l gc v0pm;rown vertically upward will return to its original position with the same speed as it had initially if air;vcgl/c.dm -tb pvz00 resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have z6 (rox/zx j *3osv8dx(knm wg:ero velocity and nonzero acceleration at the same time? Give exz3kxg mn6x *(r:soxo(jd8w/ vamples.

Can an object have zero acceleration and nonzero velocity at the samehtr8sl: lc1p7 time? Give exampl 8ht: cl71sprles.

Describe in words the motion plotted in Fig. 2–28 in tel54gu:rwu9bxu 5 ie4p xk c,b/rms of v, a, etc. [Hint: First try to duplicate tpwru xl k c:b5g44, ibx/u5u9ehe motion plotted by walking or moving your hand.]

Describe in words the motion of they*c p7 cjdoo),4c yp/a object graphed in Fig. 2–29.

  What must be your car’s averp b9hz:2otq5se7nwg 9age speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 km? 3kz/ ,2ikitmw etxr02   h

  If you are driving along acau,7iist: ,r0 0t wup straight road and you look to the side for 2.0 s, how far do you travel during this a,pui ,w t:ucsi7r00tinattentive period?    m

  Convert 35 mi/h to p0tct dx/.eec* l 1gn-
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves:.(vooj- fkhh ;v 4p*q1aart s from $x_1$ = 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 h zzj dz,4tox8r- rw-.130 km. It then begins to rain and you slow to 65x .o rzw8-z 4jh,rdz-t 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 szchoz6r)vazfffa0 v) 9;:qq 2econds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of szzvq6a 9 f)h rzavf)cf0qo ;:2ound in m/s from this rule.    m/s

  A person jogs eight complete laps around a qub z 8sqix8+lk0arter-mile track in a total time of 12.5z s+kqi8lbx80 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from3)*n qmzz -uslf1 f85xihyxx+ its trainer in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfw51h u)fz3m* zxlsn 8x yiq+xf-ay 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 has49yagn n4p7tn a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be ban4794 gnpyntefore they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long wil skl39sf3ew6x ; pbvy2l it take the car to reach the tru2w;e3b 6vf9x spl 3ksyck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters a taiojv buz+yy7; 3lwindzvy;b y7+u o3j 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 andpl fb75prg.o 5 average velocity of 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 .p55b7p of grlreturn 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constu;q:r mrm919u u q 8e:vrsq.yamt9;a l +zwma4ant speed hits the pins at the end of a bowling lane 16.5 m lov yumm;wr.9:1queaa; qt8 l:9+ mrmrz 9squ4ang. 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 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 avera/i sttt*eookv;0xq, w7mv f6c08 b )ajge acceleratio*jkbx0o87v) aswt/it0v mec , 6;toq fn in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is herve, hf.ge5qb- acceleration 5qgeeb.,f- hv
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capazo scng/l /95ywchmob 8 )et;)ble of an acceleration of about 8b;h /)o 9ncoys)c5tlmg/zew $1.6 m/s^2$ 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 tracqe i9ag/dp4*v0a1vhvels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, wg iq901eav*d4h/p avc hat 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 starts fgwd*(.zivk2t5 x2 iuv rom rest at t = 0 and moves in a straight line, is given at 2v z5w*vk ui.i2xg(ds a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its accelelc: g w:* b+q1al:/bssqsahs *ration? How far did it travel in this time? Assume constant accelerac*hsbl:q/ w:1lq*ga +sbss a: tion.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distanl( v/*bemzlf2nc73wk vk;wbw+ p(,es j+fg+y ce of 85 m. What was its accelerationvc3wlyw7jl (znb gw+/+;s m*kf(f + p,kv2ebe, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a ryi e lvs7qs)50unway is needed if the (constant) accelerationy7el)sqvs 5i0 is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out kmerte,4gy 2,5towm6 of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is tteg265k, ,meryo wmt4he average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How far busr*rqu7u +6did it travel in that *+r67urub q sutime?    m

  In coming to a stop, a car leavestv-6u 4zdrbp5vf1 ia6 skid marks 92 m long on the highway. Assuming a deceleration of6iu4abpv1z t d6r5- vf $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end ox9uhb c:x ma m+7x-avuu*i k60f the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the imcux +-uxkxua:6*ma9vb h70collisi 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 initial speed o 0ge0wrt qfsp:ou.k0 a*6 u69im(nypqf 95 km/h and human re09:ikpg mqw6frt*uneoq y( 0 s.0 u6paaction time 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 dis va)0oxt2 el8itance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver lq dcbs/0)oy+otjd.d20 wdj :tooks for an opportunity to pass, guessing b0:/od.) j0+odcdjqwtds2yt 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 r/-w (7lyrrpmuun in less than 30.0 min. After exactly 27.0 min, there 7 ( wr-m/lupryare 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 just as the trl4n8dyo(d *xffn) 5q eaffic 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 th( * 4ofed8n)fxld5qnye 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 e6awwtu6 atdtq9ed 5 3(u4do)the top of a cliff. It hits the ground below after 3.25 6 wt95eae ud 6aot(4udt)3dwqs. How high is the cliff?    m

  If a car rolls gently (afrmwe)l g2,-.p j sq8$v_0\,=\,0$) 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 intirn0 z7c/ryl-z kr 1)sr/+ysto 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 throwing it vertically upwaia (r* to;whe, ql8,agrd. With what speed digal,hti (w aq;r,eo8*d he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Dqf*72bdp v bw.u/.hrdraw graphs of (a) its speed and (b) the dis2dbur../ 7q*pfwhb dvtance 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. At a height1 z+je*d i*ytg of 125 mie g1*d+ tz*jy 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 that the distanc2l/w, 069; 0vd z4fxlqhvql+cyy0 hwb yv gqw*e traveled during each s w9xq024b+6cw qq0g,zhyyv 0l f; dlhy/w* vvluccessive second 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 negl)h zqau;2 c+ pj(qerzgs(r0+bected, show (algebraically) that a ball thrown vertically up pe+ch brj(;z2zrq a0+qgu)s( ward 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 upward with bz fb.p363ce9m,x +v23jyfmtujxgzl k1j (y5 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 in7bzc*y80ixe 96csr w vz g-9md Fig. 2–18 (or number of photoflashes per s9ei9gmbcz vw -8xz r0sd c7y6*econd). 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 0.2kj6n e;+ 3z3lgaydg*l8 s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the winnj*z a3y+6elk 3gdlg;dow did the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking9(w0rfqgo.g7mchf2ld61c, n 7a zywx the ocean is heard 3.2 s la,q9ndgygw .7olrxf76 (f cchm0 a1 zw2ter. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of water. Y0.f(hshm *h.eoqj0to ou 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 o0h0(* se h.tm fj.oqhstriking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of a ejn xphh m87rr1n/c a2qd1 a+o8,amb9cliff 70.0 m hic + ae/na,q8j9nrmhbxramd 171oh8 2 pgh (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 bqa(0tgi xchk5i 79s6vnx z03by a window 28 m above the street with a vertical speed of 13 m/s If the ballc qbgnsi9 7av6xz30 ihkx05t( 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 velopd h y-qh7qossns*1ir 7e 4g1+city of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During w7h 1-4 oqysgq nr*pd +is7s1ehhat periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a stsp +b5s ydz).u+ 1t dpa8ii+ikraight tunnel as a function of time is plotted in Fig. 2yb . dskua+id+p+s)i18tpi5z –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 azg hj*,2unvabo1 a,i ;s shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gears.) uj,bao;1,vhgan2* zi
(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 acceleratiot3y7t z5l oe*hn of the car in the previous Problem (Fig. 2–35) when ittt5 3zy *7eolh 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 traveledetj1:/sv1fq*2 d hjf*ofr p8.z-if dc during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a func a0t8gc04 7evgdexuu(tion of time is given by Fig. 2–2agtv e0ecug84ux0 d(78.

Figure 2–36 is a position versus time graph for 3d6fzlp8qo c: the motion of an object along the x axis. Consider the time interval from A to B. (a)86qpdof l z:c3 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 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 .mvk5qr ; : 57zlngc77jcrsxeabove a firefighter’s safety net. The survivor 7;lqce7vs7 5rgm :5.j ckxnzrstretches 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 Mo 4 /dvei g9u1paax) v,q6sv n)ua:lgz-on is about one-sixth what it is on Earth. If an objec1-gpqvv e/: ins),x dz 469lvu) uaaagt 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 seatz8 fxx ;26;cm. vu5y:wikqvsi belt has a good chance oz6x s.ik; i;: fxc5u8m vv2wqyf surviving a car collision 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;(ikzo*ih. s,d 5cf r+ elnu(8ycws5x bridge, 12 m above the road below, and his pursuers ar s dzcofe( 5ir;yx+5nw l8h,i sc(*.uke 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 getaway. How many poles is it?    poles

  Suppose a car manufacttb*t(b k+kq/q0k*sj mr+f so9urer tested its cars for front-end collisions by hauling them up on a+qk0k q(stts k9fjb+r* /b *mo crane and dropping 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 travels about rtz6+s 9,aghvyf 5 e0i$10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration from rest.c )z,z kds/5tz**gsel The front of the train has a speed of 25 m/s when it passes a railway worker who is /,zselt s*zczgkd)* 5standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the wi* rv3p :fftq8ater’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estpri:f 8*qvt3fimate 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 tran ;z 364risxj/+*utd3fqsar h msit system, it is necessary to balance the average speed of a train agais m+au ti63s4jxh3*rzr; fd/qnst the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(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 fre ( i;wp2xg9yhqe fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change 9wx2pqhgi( ;yits 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 planned so that the 9x t3xv: v1birczd.- xball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed z.vx1di93 xcrtv:x -b. 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 onppao-s5 nsb1j/ 70 emy a freight train traveling at a constant speed of 6.0 m/ 5asj0mo/snb-p p1ey7s Just as an empty 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+ 2zrwhwc;*0hpf12p+g)jp2xi zca tu high building. A second stone is dropped 1.50 s later. How far apart are the stones when the second one has reached a su2f; rw ) ah z*+ x0zc1jic+hp2gwtpp2peed of 12.0 m/s ?    m

  A race car driver must average 200.0 4)d k ubix1859d9kdja9+z b kbhm5uk wkm/h over the course of a time trial lasting ten laps. If the first nine laps were done a jd u+b9k)z14kbkwb85 5h k 9uxadi9mdt 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountadow2id3 0 y5xmin pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his avxydw025i3 mdo erage acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child ca :8sdw2uii 0psn bounce up one-and-a-half times h8 : pdi2sui0wsigher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10ztf-ic-f:y8 v-7ne k n-km-long train traveling in the same directio-nyv n-i7f t:k 8zfec-n on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this 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 speed of 44 m/s In throwitjf2h-,f;s45gd8 q) u fphoidng the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average accelerfh su8hf)gij 2;f po5d4,dt-qation of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertica. ckjiaf-fp 8(+/zqkc lly, 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 h 5tz-u6*m dyhhas 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 inte5z*6hd- mtyhu rsection, 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 constanjtr/le) onasz(a6nlsax. + )* t 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constaa/e+*l anlx)n()rs6 zt.sa ojnt 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 ayw *np6evnih tew 7* jg6-1) dz/gyod4 building; 2.00 s after that, a second stone is thrown straight peg*- w/z61yt)hw gv6dne*j n idoy47down 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 vertically up at the same time. The first stone is throw n3ljx +i oqk3 /9ausj/3rvw;tn with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be throns3 a/ij9v ;+t3l wk/3xo rjuqwn 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 leydq 4qm2p :t*ong 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 speedd: mpqeyqt*24 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 conveyor bek2sbegq/t( 4u9q ucv, m2v(yhlt 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 cook, how fast must the 4/2t(q2gvh( es m,uuy k qbcv9conveyor 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 taui (f hih.,ed)5mk) wimes faster than Joe can. How many times higher will Bill’s ba wku5fhd m),e .i)aih(ll go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top 3(g w/h,fehg mof a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your frienhw3e (h/,gfm gd then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using a baed *ifim(c.)6t6ygtec k(h+jrometer. Instead of using the ba).mt+idc6 ect(hijef(6 y k *grometer 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 bicyclqqy3l ;)rylnrpds;d +1d5p tm :wau(-es, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle :ry ;qya)p ( w;lln+u-dqr3 dp1s t5mdhas the higher average velocity?