Does a car speedometerjm5r4+bimw4tr.zvr ) measure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant1v yw/ ja*v32t 1bgwwe? If yes, give examplesvw2 ewg bt1*/3wav1yj.

When an object moves with constant velocity, does its averaglvp:to0e0b 3*(wwhfg muz.a9 e velocity during any timehwu bv(9 0g .f*: p3tzo0alwme interval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed crossing tu:xhl qu9 v s06+mfrc5he finish line t5+fq0s6c mhu v:u 9rlxo lose the race? Explain.

If one object has a greater speed than a second object, does the )e/ ee ix7vo;ofirst necessarily have a greater acceoe; 7/i )xeoveleration? Explain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h tb eey7j2e1aw- o 90km/h with the acceleration of a bicycle that j-1ba ee2wye 7accelerates from rest to 10km/h in the same time.

Can an object have a nv.uq b8 0t0nxgqyy-udp -) r5forthward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is po()qamdh0fn w .sitive? What about vice vwd nq.f( h0m)aersa?

Give an example where both the velocity and acceleratio 8p8d: s2 k,yfo9vkve* nrd* obgz0*svn are negative.

Two cars emerge side by side from a tunnel. Car A is trave,;hlqjm.p*h aling with a speed of 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 p*hj ;h maql.,the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speedkl*67c cl)gdfb; r8c)x0e mem as its acceleration decreases? If so, give an example. If nomrcgd8ce7le fm0 k *)6bxcl);t, explain.

A baseball player hitsfdr* 8fie9v op s ,kkpy8+.gv3 a foul ball straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fastdf,.9*8 k +vrko3gsp ypfi8ev will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is happening to its accer*.snu fpm 7r6leration due to gravity — does it increase, decrease, nf 7r*rmp 6s.uor stay the same?

How would you estimate the maximum m hn,7hoei 6*pbn*2ja height you could throw a ball vertically upward? How would you estimate the maximum speed you co7n*2 e*o6a h,im bphjnuld give it?

You travel from point A to point B im bm8vtrie k,n/824 jnn a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/imntvjnm2ek ,8r84 b/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied :t(9vmj2kmukg (a k 9bto 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 neajk v(bgtka:u9m9 k2m(r 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 2 (/)j d nhbf/igbjr-/ tw.)mm qiutn:bg8qv2 acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the wau m:)/j vjq)t-i2m8b2tnq( iwnrgbfb /hgd/. y, a dish resting on a table?

An object that is thrown vertically upward will return to its ou hk*gvo8a4kny 2*-d*qfczwij :4hoy0wn 8 a 7riginal position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the mo:vfn4hi a8y*oq*awjow z- u4hnd87 *2yg0kck tion.]

Can an object have zero velocity and nonzfs-q(ojwb7; mero acceleration at the same time? Give ;fbom( -swj7qexamples.

Can an object have zero nfhxutn 4/ (p59w;egx acceleration and nonzero velocity at the same time? Give u nw(fphn/xet5;9g4xexamples.

Describe in words the motion plotted in Fig. 2–28 in terms of jm aqzkz)962b v, a, etc. [Hint: First try to duplicate the motion plotted by walking or jz6b 2qmka )9zmoving your hand.]

Describe in words the motion of the object grapz5mqon : gak3w3v,; sghed in Fig. 2–29.

  What must be your car’s averagtx*3 +a ssrr-ye 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 fo/ szue6z5w7ezs62b;3wc fx b ly 15 km?    h

  If you are driving along a straight road and yi;tasf4:+tvih c6a kj,6qhw4 ou look to the side for 2.0 s, how far do you travel during this inattentive periodf6+4hi ik qt;a6j4 cvwahst:,?    m

  Convert 35 mi/h to 8* f wh9l hpwh:h8d lfq/7oxtoy;o(.l
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from 68*etwm q8 -.p/jmncmwsj1r b $x_1$ = 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 t6bb(i/uha)qy1.t5r iwrgg8z: a iw;qhen begins to rain and you slow to 65 km/h You arriv yg(iaq )gbu; r6:za5.hqi1tw bi8wr /e 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-thumbz*+dtq oo/g0c 03 vrpc, every five seconds 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 tz+v0to*0r3oc / qcpgd ime at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quartebt 9rk0mvb- *1 hsx9fer-mile track in a total time of 12.5 min. Calvbbfer -k mt91*90sxh culate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer i. +zh/mwej()(guz ra; :n/oamftnos 7 n a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfwaygtf:+z.m/m(wa/h;sj on n auo(zr7 e ) 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 appr+d jdb79i*xz dz+k- arr);ottoach each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be befo-ak+ *d 9)+zr robitxddjt 7z;re they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will it t*,htjxm,: lvz+*ezs o ake the car thtzs vxz+,:, ojm** leo reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/r1)2scv)rz kz t,4xjk v,*vaxh , and then encounters a tailwind that boosts )jac 1x4kvz,z *rrs2,xk)t vv 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 and average velocity of qm6ne ;3it g5a6)ffwwuu4yo ,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 returnyfew );ofn6,qtu 3 65maw4iu g 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hitnf iv6pa7ndg9ux buv0 k;4o,/bj 0,wws the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.5buivjf0/ ndbw9vn6w , x4kug0 7,pa;o0 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+xay2 4ht0tfm 6.2 s. What is its average accelerathaxfy+2tt m40 ion in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 0ls q 8ts(x2;ov2/ h rd0e6iymzsw+ nds. What is her accelerationhy0q; v/edzsi680xond + r(2wtsm ls2
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acceleration of abou+8hvz q6 a5jnw+og ts2e;/qcclk(d z7/q+v k2ca6j;8znz7c hl 5qedt(o+g swt $1.6 m/s^2$ 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 consi,8/rgc: gguhtant speed travels 110 m in 5.0 s. If it then brakes and comegcgur/:i8 g, hs 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 starts from rest at t = 0 agv3al7u n6xg(nd moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration gvg6l x 3una7(as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to3b9 b/z og:n.*emupbx 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant accelera9xp/:gue. nb*bob3z mtion.    $m/s^2$    m

  A car slows down fromnb xkvanw +*q kbyu,u nr7l5n+6)4qy1 23 m/s to rest in a distance of 85 m. What was its acceleration, assumed n*+xu5bnq)k7 1y6nbn w u4q,va ykl r+constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for ta-hd.s rp9wth xn6/(yn9dodk (keoff. How long a runway is needed if the (constt9d d.owrdn6 n(/p9hy(sk- xh ant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially lm+ 3lc- wtpv vfgf/73top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it tp 7v wcv3fm l/3gtl+-fake 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 edi6tx8 w- 86yl+ rnxrs. How far did it tr6+ry -xxeri wtd688nlavel in that time?    m

  In coming to a stop, a car leaves sogen-o5 v98fr/g5huekid marks 92 m long on the highway. Assuming a decno u55 ggfh8oe9ve-r/eleration 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. Tho5ts;yyqj un/ i28flhxo6 5v)z y5; gle front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of th ;/fxysz 56hqy il825)5ojynt u;vgloe 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 initial speed or8kc+l) (dn6.v -rekate k+g zf 95 km/h and human react e6den +ar()kc+-grtk vlk8z. ion 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 stoppings on7 -bctdh9cz4ds9. distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The cawe:/te d-r(4r4rtg zur’s driver looks for an opportunity to pass, guessing that his car can4-4rtdtez /g er:u(rw 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. After exactly7ifo3 b+h gic; 27.0 min, there are still 1100 m to go. The run7cf;h3 go ibi+ner 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 te*( yxc)d(qs as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 yxcs( )(qte* dm away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below ai1uabqy 7 :6x q2c,6bb3e;hjuo(jvf zfter 3.25 s. How high is teyqfuc 7q j(;3j,6vuz h1o6b bi2ba:x he cliff?    m

  If a car rolls gentlyj /)eo .*gltds ($v_0\,=\,0$) 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 straig zcmt1+t1y*mo ht up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s aft skglb p-*q,s,er throwing it vertically upward. With what plsks*b, ,qg- speed did 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. Drb w sgrlx2e343:,oe 1yhfj;hx aw graphs of (a) its speed and (b) the distance it has fallen, as a function of time4slx3eb :w ohx2,y1 fe3 rjgh; from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending ve :)soy kbww k(gbj8bfg86)s6t rtically with a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from b8g:g66w(yf )bo8 bsw tkj)k sa 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 fallin)c c( /gg x,5/wvymg4xk)s, zejscqv)g freely from rest, show that the distance traveled during each successive second increases in the ccgs/ 4x q 5, xvkg,c )se))wym/gvzj(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 neglectoi*/8+ iiixlued, show (algebraically) that a ball thrown vertically upward with a speeiliui*x 8/ i+od $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown veui fx2 +pm+): p-xxxabrtically upward with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photo)ef1qeu *jf; v-(j7vsmx lsn9flash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Uq-elxn vm vje )7(ju1fsf;* 9sse 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 m tall (Figsozl6j/*w v 145jwb du. 2–32). From what height above the top of the window did the stoneb s1zw/uw*64ovl d jj5 fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking tsj(((hktwfs+a 8ccq s4 4t22e6qxx johe ocean is heard 3.2 s later. If the jh4x e2j ws862 qf(c4s(t+(socaqkt xspeed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a ha(w2de0zcyp8:yi)i 92mcbvc g,3g cpurd 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 movb p( g i,pzcuwc22: d3 gycy0v)ecmi98e 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 with a speed of 12.0 m/s frx22ard+ z9+vqedyo 0pr7+kvw6e g 9zqom the edge of a cliff 70.0 ma++ z09eezxdk p q2vrv7q ydr9o6w2+g 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 2d2 o mu/i ocqdq1:x,eg) dywe0k0vai7e 5*f:w8 m above the street with a vertical so2 ,e diex:didw:mv/0 7kq*wa 1eq5co)g 0f yupeed 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 velob/ j-b,ywe)mi :mszz;4h9-l sl )b iopcity 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) Durings )li bj/bszmo;-bp,z:m y9e)ihw 4l- 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 timet.t2v5 srpjuom0pl0 5w/.9;o r oi gtup+mvd1 is plotted in Fig. 2–2o2ov ios;ru0 lgtr1mv+ t m/.5j95tp w dp.u0p8. 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 the v4k x7yu d1ma6lxq96e,rh l;ooy 1az 9telocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting of the gey61h1xou9 a47qr6 l,x 9; l atmzoydkears.)
(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 previm 8b b/fy(jb6+5ixc wly-v:f dous Problem (Fig. 2–35) whev8xyyi +5b-jw f/bc:d fl mb6(n 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 trz8v:7 a3v k,t /l iuf.dhazf-r9:gig mjnc/m)aveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a funn+sc se 8v)sieun r (szaxo9)3b b00r5ction of time is given byasre9bezv0 ui) 0cn r 8b5()xsno+3ss Fig. 2–28.

Figure 2–36 is a position versus time graph for thefktw 3fc 4sv-/ cyxvg :9w 8yxa)a;h;y 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? (bahsvw yf:8-fxy4 ay9c) kcx;/ vg;wt3) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s safey(8p8rlwf mn7 ty net. The survivor strel rw7my88fn( ptches 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 r/mu 7uuzj r)) w:gur2about one-sixth what it is on Earth. If an object is thrown vertically upward on mrgr:7ruu)uu )j2z /wthe 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 seat belt has a ggbd054c-f ofkjqe fl5 o6013 wm b4(kvcmkj4cood chance of surviving a car collision if the deceleration does not exceed 5fkv(1cw4b q4d4l 0 fkcb - 0mefmkjj53goo6cabout 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 abovlh9,xj3x pf,mt,qgk8(lw,l8z , t k abe 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 heq,38mlxag z(klhtkj t ,w,9lf, 8,bpx jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufact:7r5d:dvxjv6iorj9dgvb 4 0turer tested its cars for front-end collisions by hauling them up on a crane and dropping them dvr j9x05v gdbr7:4o dt 6iv:jfrom 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 travecz+z8w 4e +kpba iy5-els 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 uniu6o0c n( q28kl itjj9sform 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 worker? (See Fig. 2–38ku j li6s28jn0tqco9(.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a deep po /r p+.eiy,ybmr9 a 1vq6u2twjol. The person’s downward motion stops 2.0 m below the surface of the water. Estimvuj , i 1.+qtperr2m9w 6yay/bate 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 necessary to igw 7-ijk1t1u 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, calcj1t wg-i1uki7 ulate 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 lj whi(e,*f y24rd-( szzqdd0 free fall straight down when diving for fish. Suppose a pelican starts its dive fromldrwf(20h- z(yjd e*dzq4i ,s 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 g3cdd5t d u2;jplanned so that the ball will stop within some small distance of the cup,udgd; d 25cjt3 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 freight train traveling at a constant spee 1*j ,j /ds1/2oac tuytej+fjld of 6.0 m/s Just as an empty box car passes him, the fugitive starts from re/2tua f*cj,et/+ds j j y1lj1ost 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 ; .untsrl8a.co6w wd). A second stone is dropped 1.50 s later. How far apart are the stones when the secd t)lau8c 6.onwwsr .;ond one has reached a speed of 12.0 m/s ?    m

  A race car driver must aven, o cnnzx*6; yps;-berage 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at n; n *-6ocpnb xy,sez;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 mountain pass as he mov s3a : psm6s*y.iunxq:es at 18 km/h . At t*mxn3s. :ssyai:p q 6uhe bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampojufhw(+ 9vfe+e: lgp(lines. The first child can bounce up one-and-a-lfv+( :(e g9+jwuepfhhalf times higher than the second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakp*l*5csot mo, e/ ,070folh6qwp4 wdh m -mpoies 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 in this time? See Fig. 2–40. What are the results if the car ant/5w,sm7 ,q-6o*ph *oi0 mfod lpmoep04l cwhd 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 agz hl18z;0*.1 b twjsoi0u3raok( n ur speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is re *00g;1woa3 ltkz(i 1usr bonj8zru.hleased (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, fr*4wlsi sjkq(5 om 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 shpcj1nqgculwo ,033 fj*en..3mgb, so own 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..ebng3*gol0jc3 cou,3qn ms pw,1fj intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder travet + 5taynp9x bo78kg-,unrtk 5ling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 58gtxtnp5k ak+,-nb 79 rtoyum, 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 frr 0) ciz5l,lagh 9d8jbom the roof of a building; 2.00 s after that, a second stone is thrown straight downhz dj8ab 5c iglr)l,90 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 samo 76xdy: 04k h,4ixawino da3me 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 velocity should 0,7dd3 m6ax iyk4xwa: nioh4othe 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 resista6drfh(4vw2m:yxa71v dj9sjk nce, 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 yh:dfawrxkm6 jj1s47v vd2(9resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers0sphnup7f/a z d98 xy- 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 conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/minhs7d p/ xnpfaz0u-89y)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 t6.a n3uma /ic*yves6x2n,we g-k,pc vimes faster than Joe can. How many timev- iw cvgamke,ny6pu2nx3 sc* ,6a./es higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff whi*sjq)b1u5vbve y+0cf le 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 thq*+evvfcuy 0js b1 )b5en 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 hei muhd0nzd-jfb0;d9b)ght of a particular building using a barometer. Instead of using the barometer as an altitude-measuring device, udfnzj ;09mdh )d -bb0they 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 andh1vtc ;p-j s,7to8kd(y*j tkf B. (a) Is there any instanot;,ksjt-*h8dcv pyf t k 1(j7t 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 the higher average velocity?