Does a car speedometer measure speed, vex/t) bg51zj ui;cqvgr ljj50-locity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give exa3a 5u3cao ,+yr5a fhrrmyhfac5 a5or+ ar3u3,r ples.

When an object moves with constant velocity, does its average velocity during 0xl 3+j,q+xog/ojir:c w l-osany time interval differ from itosxg : cj r/q0ol+o3l xw-i+j,s instantaneous velocity at any instant?

In drag racing, is it possible for the cara,le-jo 8 ae6z with the greatest speed crossing the finish ,ea-elz j o6a8line to lose the race? Explain.

If one object has a greater speed than a(4p8 y;3;8wcy f wokc7r w(kz uipn7fo second object, does the first necessarily have af( kyww3ir4z877ocpk 8c w;u( onfyp; greater acceleration? Explain, using examples.

Compare the acceleration of a motorcycl jpd,58oii d,0zyf8hp e that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accfp zh8i5,,odp0 yidj 8elerates from rest to 10km/h in the same time.

Can an object have a northward pe:z )0t ae*+ 0zohhlqwv: x(yvelocity and a southward acceleration? Explain.

Can the velocity of an object be/c6b;x4e4rp aux cx 9cy ,rk:d negative when its acceleration is positive? What about vice4:crxd byxxcp9,a6u4 ce/r;k versa?

Give an example where bn: pl+06 obln2g mby4voth the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is travei6 hzd:cjvxqi -88mu4a /8x fqling 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 the other aihf8i6/cz4x8am vjuq8q-d :x s they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreases? If so, give b*z/lxf gm4.*dhvu:ran example. If lurgx: dm h*/f.zv4 *bnot, explain.

A baseball player hits a foul ball straight up into the air. It leaves mso vm60r3s3m the bat with a speed of 120km/h . In the absence of air resistan3rmsm30v sm6o ce, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is hap9+i cuv;s:;ov+; pipv hqg8nfpening to its acceleration due to gravity — does it increasp cqp+vv +h;g8v;; o:ui fin9se, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball vertically upr;m3av;i1)-q ioxeyi .c dl.uward? How wo. i;e oilay-3v) ucrd; xi.mq1uld you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constant speed o0ypcjg m*pz4hy91;y wf Then you travel the same distance from pointc;4jzm gyh 01yp9 pyw* B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string wit2j3elm a:-i0d(ot of/ nqee2w h 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. Why? Will the time between clinks incree0w 3defqoeaj/:notmi(l-22 ase 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: a rock fal/ots lc+g vv;mn; pfm+3a9w2lling from a cgto3 f/nlslw2v9v +;m amp+ c;liff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upwargc3 +k l0hxz:rd will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to t:xgz0lrh+3k c he motion.]

Can an object have zero velocity and nonzero acceleratio*xy9,c3gqwratv. cx/wo 4 g+v ,*gyxn n at the same time? Give v4t ow*xcng y3v,r9q, +g a*wgcy./xxexamples.

Can an object have zero accelem(v9c)ne5, k6ywv f(8 p e9nsn9lbiriration and nonzero velocity at the same time? Give examples.6 nw (b cfik9r9vv(e n5s8nle,m9i)py

Describe in words the motion plotted in Fig. 2–28 / tm;dd nfh0mrhx.h92in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or movin9dhhtmn/.d0rm x h2;fg your hand.]

Describe in words the motion of the object g 3v5m*cgs3vygraphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.25 h?: +4ggffao y. 1vjvfij*1;0:jdyd eme    km/h

  A bird can fly 25 km/h How long does it t*gcys5h 4 zu ch01;xlsake to fly 15 km?    h

  If you are driving along a straight road and you look to 6a xm(a x-w rl7;6artzthe side for 2.0 s, how far do you travel during this inwt-6rr(6xl ;m7axa azattentive period?    m

  Convert 35 mi/h to 4,emx/ *no)x + i2lzoen 7xjrq
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fronuolpsagsd5qgz 2 656xb y465m $x_1$ = 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 steadilym n 7hb0m/fw5f at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after dwmh07/5 fnfb mriving 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 flasi,. wwuop0x :zh and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at.p o:x, uzi0ww all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile trackg0/v x i5u (wcmxh7z(x in a total time of 12.5 minxw /u(vxm507( xz higc. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trai 7mj 4rkf:1/ef shq;h :x4evoxner in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in1: /qexe;:sro hvj mf7k44fxh 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 kfxl: 2.yv;xxws(: bp-) horgother on parallel tracks. Each has a speed of 95 km/h with re:.f glxo)kh(; b :wpv xx-2ysrspect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long wike43sh 62ldqb3-ya1 i4 hetzd)3xs z hll it take the car to reach tzbe hhd3 ta2zl6kyi1d4e4hs )3xq3-she truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encountevdyixvz jy 3y65 gn4;8rs a tailwind that boosts its sj y4 v8ngxd;5yzvi3 y6peed 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 a complete round-trip in wh (ixaatny ju6ih6p--7ich the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covanx(aj-ith-i yu67 p6 ered at 55 km/h.    km/h

  A bowling ball traveling with constaw za,fgs54 /awnt speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the balzs waaf/w5g,4l 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 + yb:hm)ujzn 6zi6+9jbgyu x56.2 s. What is its average acce +yj )6bjuy:unxb6zh9zi+ gm5leration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10o8r1hah2qkr6s w5wymy6c 3 e..0 m/s in 1.35 s. What is her acceleration.csoaye 2y6wkm5rhr w13q 6 8h
(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 accub n j)p:k eahbh1hft+ (kgo0 w-:z.*weleration of about kbwt:) hahg*0zkf-o :w(ne.b+jhp1 u$1.6 m/s^2$ 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 in 5.0 s. If it then brakes10 whb9 (dsv muqt/9jo and co1o smudqj( 90v9w hb/tmes 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 a c 0* eaqd1tbr 1i9uh7:mu-jaht 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) i7aj 0huh:bqm *1crit-ud1 a9ets acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates fro3jo*.*lp /uw l-y lyqom 13 m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assu-3l p/o .jowuqly* ly*me constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of kuo9:3rnp;xo/ xxw.j85 m. What was its acceleration, assumed3 /nou;p9x w.jk:r xxo constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How 5ie:n esmkd 0/o1kwf:long a runway is needed if the (constant) accewmki:fdsn5 :/eoke1 0 leration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst;wp )j w+ky3z)duis;u out of the blocks to essentially top speed (of abskzu);3)w jy;u i+dpwout 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to reach that 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.f7ubx 8sop- v(g) 4oxv. *chml00 s. How far did it travel il.fob) * vg4(uph c-8xxom7svn that time?    m

  In coming to a stop, qy. - mt y/*k4df o1oq)be9fw9 -l wku,7aqqwja car leaves skid marks 92 m long on the highway. Assuming a deceq 74wb fkq .*9eaqdfouywk/om,) l1-ytqw- j9leration 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 treesgsc4d mj-m0h. o h89t. The front end of the car compresses and thgmcj0-. 8s4h9omsd 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 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for2y9l ddqkugs. p1,7d f a car with an initial speed of 95 km/h and human reaction timy,g 9d7dpd1k2sfulq .e of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car kzsya xs3h1+ z:rds :ff5x6e 5s b14ucvb2 k6wis $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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 looks5iik+hsk2it )pq l5xgy ; 6*h48mnlgy for an opportunity to pass, guessing that his car can accelerate at 1.0 lhqnihgg8yyp26ti5xk li )4 5k+s *;m$m/s^2$ 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;3xlxv3*f5 l ugw)1v +qqsg jm. After exactly 27.0 min, there are still 1100 m to +)xvxs1u3l53;gmjv q qwlg*f 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 heror.8sp3f mjg c yqv07. car at 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum de3 jsqmo0 r7pc.yv8 fg.celeration 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 theo soz 8l74o8nb tv o+i+a,nb8r ground below after 3.25 s. oo 8bo7 t nv4o+zbi+ar8,n8lsHow high is the cliff?    m

  If a car rolls gently(tqxs)o b*4r(d:e2g*biz (t xslsc v9 ($v_0\,=\,0$) 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 of:z qkms3ern;e loz *rr+ps04+ 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches t 3x dx7zhodw94a j jf;6jg,9xa ball 3.0 s after throwing it vertically upward. With what speed did he throw it, and what height did it reaf o43,jtxg96ahdj7 9j;x dwxzch?    m/s (Round to the nearest integer)    m

An object starts from reb)-mbh) cf/wd(yf e,y u5kc.mst and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time frby,fw)bhy 5 (dfcu/m)- ec m.kom t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically wajf)x 4xjcx i4h:51/x zt8kosith a speed of 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [H zj4kfxto5/j ixsx4c 18:a)hxint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object fallingk(jelf /wi /7i:kdwy : freely from rest, show that the distance traveled during each successive second increases in the ratio of successivee/ d (:yj7:wl/ wfkkii odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebrai,yliwe ka-j99znu: ,np0u bb 3cally) that a ball thrown vertically upwn bkzyal39j0:e,p9un b, iwu-ard 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 a speed of 18.0 680vg xu6v42 f ghdjtc:zdd8pm/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 ea f3m2jdwlh40.t(e p 9u gmtw.wb+yr5 dch photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is ab3w+y b2..w mlm pwd jeghf4(5tt09ud rout 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–32). F k( 7xbuezike*3 i8mgjse cm/zny 58:5rom what height above the top ozmz my5kxe7*iu enc5b:8gj ik 38e(s/f the window did the stone fall?    m

  A rock is dropped from a sea cliff, and the sol5 yp n:y 8;n;u+t .lpgruu.ixabjm.4m er -3kund of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the cliff? H ybuu y;:.t4+eumn pgrx-r5k.;im. l3 jl8nap =    m

  Suppose you adjust your garden hose nozzle for a hard+dvr*oz.vox 0g-v.b.0yu1 qxuyd+wu 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 ground0g+ -wzx u yqr 1vd+0vd*.yxbuo. .vuo 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 o 5 9y+oo;w3aiyh(sgminn9wd 1co5j012.0 m/s from the edge of a cliff gmo 1cs9oiaj5;5hd0y w 9 i+o(on3wy n70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the street wivmd+m nb8, ;5*m crrhdq,j4fh y*r:gw th a vertical speed of 13 m/s If the ball was thrown from the street, ,rr4hn vymfr;h+:d , *g8j*bqw5mc d m
(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 timd *usqmvvwven4i* 2u.b:f 5/z e. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration i:qvue/ n.d2 vb*zmv ws45f* ugreatest?

  The position of a rabbit along a straight tuklkt5c/- ci a) nd+rk.nnel as a function of time is plotted i.cni tcdk) alk+/rk5 -n Fig. 2–28. What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can dd :su*wx1 g0zaccelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The short flat spots in the curve represent shifting ofgu:z 01d*s wdx 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 the car in the 3 v. xw5da8shatz );4kewzyv:previous Problem (Fig. 2–35) when i hw3a v;4vd wa.yez5tkzs8 )x:t 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, estimateoc xd/gw .m/;w the distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the )kmjff3gc6z l i2 r*v2pa(9 efobject whose displacement as a function of time gm rf2v fkpaei*9j6c f) 2(3zlis given by Fig. 2–28.

Figure 2–36 is a position versus time graph for th2 kl)lyoyl q6vusbt- 3o00 qyn; 5shz)e motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the objv qnl5 loq-z0yy)o yhst 20l ;bku63s)ect 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 firefighog h6guv*vp 34sh i4;kter’s safety net. The survivor stretches the net 1.0 m hi6phvgv4u 3 4k*og;s before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on r9qy q iq0q5mw0 0b-ugEarth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it w r0biqgqym9uq0-q0 w5 ould on Earth, assuming the same initial velocity?

  A person who is properlye5w6y56tav dj constrained by an over-the-shoulder seat belt has a good chance of sda65j6t5 wvey urviving 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 standibfqaz t u61vr3p6q )+- wt;vfong on a bridge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is pa6 6of1rbt3ta+fp uq ;)-qvwvzssing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end coq*3-5qjiqcxfp2au k.2bow ; kllisions by hauling them up on a crane and f uqo *3. wp-aq; 5b2qckk2xjidropping 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 abouihd.--yy 6jmxf h7f laxw/pulv)o*ej6 3n w-/ t $10^9\,km$ 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. The front of the traict f9+gc ;blr6n 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. 2–38.9;fb t6clcg r+)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into uvvh 7sj+vcky )7b//kh7s /bta deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the avert bvvh 7uj vkss)+//k7hyc /b7age 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 7l dx 5 p8qe/bei(tl tl7mv,k*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 tal 7bpx 5el8,* vmq/te( dlk7itkes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight down when diving w ew l5ssg0)e-for fish. Suppose a pelican starts its dive from a height of 16.0- lg)e0ews5 sw 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 planned soa0*2xzc pn: rsbzt .hb-gm ye9z6*zj 2 that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the pr*bnh9b j*t26zp z0-zxas c .2me yzg:utt 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 hop6bb7 ,8py;r5qi zgr ;tdrz.hf on a freight train traveling at a constant speed of 6.0 m/s Just as an empty box ;db; rrpqrfiz.,h75b gt 6z8ycar 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 swc(09 zr3.7pp,h udyycijsc9 econd stone is dropped 1.50 s later. How far aparcwpuz , (7i h0jcrdp93syyc.9 t are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must av*gn)k p5rmu9y erage 200.0 km/h over the course of a time trial lasting ten laps. I rn*p5yug)mk9 f the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mount*tmb0kezu1 9gq uy j73ain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed i10 mj9zb7tqeyku* 3gus 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 firju+;;f,4) udulttq;w9 dis ry st child can bounce up one-and-aqsi);9f+;ud t4r dju; ylwt u,-half 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 overtakes a 1.10-km-long train traveling in tj7 (ag45wzl 43rggo o(ze xbt-+ik,nthe same direction on a track parallel to the road. If t4zwo gjg ri x(+ lo-5bae,g(k73n4t zthe 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/spp32vspg 2o.jyuf2o/p;i in) In throwing the baseball, the pip;p2 /pii sgop2)uvo2. n3fy jtcher 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 acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from restjt*b9hf9d ;4hsrb9e r, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a traffic agx6b,qir rxtok4; 80 signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, alli,qt6rr0a ox ;gk8 bx4 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 consta e;0 3m6xaihji7giy+rnt 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, mainij6a37h0eix;+ig ry mtaining 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;4 /96bvftd nly 2.00 s after that, a second stone is thrown straight down with94tn/ bvy l6df 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 verticalhktm4 nxj0tg4: 9o x9qly 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 anqgmx449jtx :tnho90kd hits the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long wouldol rbn fy2( r)iug295h it take a free-falling parachutist to fall fru2yhb(o)2lirgr5fn 9 om a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses v(tytw fq/ 8+eny( mvhao*-; usm 9g:ia conveyor belt to send the burgers through a grilling 9m vf*yy8: moe-+tvagu/w ;q ns(thi( 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/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a7kk 8x w2ocwiko(0 :rr speed 1.5 times faster than Joe can. How many times higher will 7rkxk02 (wr okc iwo8:Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff whil qyvu7;jl hv o :9d5n8ly8bc0be your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and h byqync9vl0o85 djb;8:u l7vthrows 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 barm4 yj0ec(sa 20w3nj zsometer. 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 fal0 mez(c2w04n3js sayjl. 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 th-j bsakkkjc)xne2:a. ; +bks0e position vs. time graph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing th-s :as ;ck.j)k0 enxjba2b+kke other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?