Does a car speedometer measure ss9t;wf09rmwlg 1 6 yacpeed, velocity, or both?

Can an object have a qtta;by+x2dv6w ; 0s nvarying speed if its velocity is constant? If yes, give exanq2dvat s6yb t;+0wx;mples.

When an object moves with constant velocity, does its a ,,ddj; hkic6everage velocity during any time interval differ fr dhdc, jki6e;,om its instantaneous velocity at any instant?

In drag racing, is it possible for the car wit1:hd1g5yd3b4 vnv3 )m l6p)pnufnvxoh the greatest speed crossing the finish uyn) fo3mnp41gv35 :6v )nbhpdx1 dv lline to lose the race? Explain.

If one object has a greater speed than a second object, iiv3d1 7gyv*ksi.zjz t6x(4 ldoes the first necessarily have a greater acceleration? Explain, using ek*i 3idisg 1 t4zz.6xl(vj 7vyxamples.

Compare the acceleration of a motorcycle that acceigp0l-cjt (pz myr 3,,lerates from 80km/h to 90km/h with the acceleration of a bicycle rc(3p -t,0lzm gj,p iythat accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acs1kquc ,yh 8(q-ay:ye t3w 9dcceleration? Explain.

Can the velocity of an obj4s7m:y*ag.lf(k2w iie xus2m ect be negative when its acceleration is positive? What about vice verss.e flw:sa7m gku 4 i(x2i2my*a?

Give an example where both the velocity and acceleration ar,k+)vl2 t-whc* pjr ume negative.

Two cars emerge side by side from a tunnel. Car A is travebs( :zzgt2h/t 985boycw hj s3ling 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 as they comtcbs82b9z z3/ht5j (gs:oyhw e out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decreay:*hj.ds c +:wvr hjd3ses? If so, give an example. If not, explai ysd:hjj+cr3 .*w:dhv n.

A baseball player hits a foul bal,f kh i dhro/)0 eagfm/d5oap)p95 *dal straight up into the air. It leaves the bat w d*f5 0 f9ordhe/d/)pp5imag koa,) ahith a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the catcher catches it?

As a freely falling object speeds up, what is )3dmq/hlyz 0l happening to its acceleration due to gravity — does it incre/q03mz)dly h lase, decrease, or stay the same?

How would you estimate the maximum height you could throw a baleswig- /(df4;q4zqn/i ru:h6arpgh2 l vertically upward? How /4/f(ag:q 4ui zgp2sh i-nedh6; wq rrwould you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a const0phx4 ;xhap(l ant 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/h ? Explain why or why 4phaxxlh (p0; not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tr i*01 iqz(twdied to iti t( rqd*0z1iw at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at af7w*2/d0e9(u f uthqhlwk78f 7gqr pconstant acceleration: a rock falling from a clifuefd r pk7wtwqhaguf809 lqf(*h/727 f, 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 upward will retyh5n(, 5 sxqkp ;1b :uf7(/tctww lqadurn to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will t,7thbksl5wu(ty pwxc51;aq: n d(/fqhis 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 zero velocity and nonzero acce1a3 dmgplc6t8tq70jb leration at the same time? Give dm673 cqtp10t8a bgjl examples.

Can an object have zero acceleration and nonzero velocity at the sam ynb0r+p d2 *k*qtey6oi1wwq:e time? Give en tdpw2ir*+ y bq :y1w*kq60oexamples.

Describe in words the mz7a+1pj 9ul odotion plotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or m91 7lojpz +dauoving your hand.]

Describe in words the6e6 ptedj. n5q motion of the object graphed in Fig. 2–29.

  What must be your car’s average speed in orde8 1c f2lwh1xk5 h1qpvpr to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long dah 3;l5b+7iy - kqavbroes it take to fly 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s, ha(o xx.)*wzs tpnk4d 2f* bz(9;nvcfdow far do you travel durixona(9w f4x)n ;f dzk *d.zb(vcp*2st ng this inattentive period?    m

  Convert 35 mi/h to j4 2g+ thzidvg9sj+ mlxrsd/ i2x:v 09
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frdu(leu4rus -6 3p)cz8tx0ms pom $x_1$ = 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,w: a)s cm;xyzcz7v,wo5 hu5v . It then begins to rain and you slow to7vw ,5mscwh5zc,azyouv: ;)x 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightning flash andj n*-q9cpp8 m ad-zg3:uwp5gt the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estj3mw-:9u pzp8ctna5-ggp*d qimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps aro/jguvi z0(h. fund a quarter-mile track in a total time of 12 j.(hvz0 /igfu.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight t+ u-wlzrby 3.line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfwauzbrlt.3-w y +y 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 has ajcyrnr j 4ts (7:d35+stjt:oh speed of 95 km/h with respect to the ground. If they are initiall s r5t7(3 4y+ndj:tohj sc:rjty 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 +)xap sm;t/v z9v4cx n9*vptq is 110 m behind a truck traveling How long will it take the npztx;m p/+v c 4tasv 9q*xv)9car to reach the truck?    s

  An airplane travels 3 wma13x9aw qsa+ ,ga d*4ijwru);cib5100 km at a speed of 790 km/h , and then encounters a tailwind that boosts its aju d9 1)qgi*a5 rawa+ x4sic3mbw,;w 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 spe 42fmyzl s-o(c* y w p8w*dhc+qoek(j)ed and average velocity of a complete round-trip in which the out* ch- z*w(jopoq8kld +y4fwyc()2mes going 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant sr2rwt, tv/0 u(s, qzgfpeed 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.f,(02 uqtwr gzs/ tr,v50 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 average eip.gantr va3jqe*9t6( 7;f sacceleratior6q tne*(pg9iv;s3ae 7 j f.tan in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m:wu yuj93ohw o0h+ rs9/s in 1.35 s. What is her accelerationo09w:r3jhu uy+so9 h w
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular 1tp :)fvtu*dvmbgx + ;m,d6g4x8ewjvautomobile is capable of an acceleration of about 1;t ) *gb6xm e+uvv8 j4gf:xmp,ddvwt $1.6 m/s^2$ 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 spf 7:z6cpxei:h eed travels 110 m in 5.0 s. If it then brakes and comes to a stopx:h7ez: i6fc p 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 hrh iyep6 h-03from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a rihp-e0h y3h6 Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its accu5p/6 w.:jt co-unhmjeleration? How far 6/wujonm tcp5j .h:u- did it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was ittft6z 9id; o6gdk8 w7ns acceleration7k g6n6i9;8 fzdtw dto, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How loh1doe ks 3p4g9u pd7pr* k;(xwng a runway is needed if the (constant) acceleratdk94r eopg7 x ;1d(wp3*ps ukhion is $3.0 m/s^2$ ?    m

  A world-class sprinter +o2sipck7f;q can burst out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleratifqso 7;2ik +pcon 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 uniq/fl1z;03t( wjp7 u oza uaff/formly from a speed of 12.0 m/s to rest in 6.00 s. How far did it ta j1/ 3to z(zu/;fffqauwl07p ravel in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on tpie 2c(*r 9(laort )9t ddhcz,he highway. Assuming a de9pl cze rc9h)(d(t dator*2,iceleration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the card h 7l v/l2qh5i8/+lhmfcwg5m compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of th8w /hl+m7dqhl/5vm c2 i gfh5le 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 wgje2)okou k, 5ith an initial speed of 95 km/h and human reaction time of 1.0 s,ukeogkj2, o )5 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 distap *-pgg ln9smnn/b,hv u,6nf9nce 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 myi+ zd6coh:6the highway. The car’s driver looks for an opporicdm hz: o66+ytunity to pass, guessing that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. Acbbfp9e )-mw )dp++9zl +bk zafter exactly 27.0 min, there are still 1100 m to go. The runner must then accelerate at c+w9 b+mp bbp+)azk-l9)df ez0.20 $m/s^2$ 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 tran40mp d/ xw4gf( xo4cj ix:e;cffic light turns yellow. She knows that the yellow light lasts only 2.;fcj:ex wo nm0i4(xc4xd/p g40 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 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 tjew q0e6ch+o;qc0i1gbj0r2 uop of a cliff. It hits the ground below after 3.25 s.q6h coqe uijc ge00j b21rw+;0 How high is the cliff?    m

  If a car rolls gently j-t 9d,an+j-5bk,uqu+ 0jk6ac z qbjj($v_0\,=\,0$) 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 22l91a2+ngvco + e+,l 3;-dggy plc izgn 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 upward:o0v4xd:lwwsq2w vp /. With what speed did he throw it, and w4lwqws:02 vw/op :xvdhat height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and f)fzz)9e rpem8 alls under the influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 e9r)mz)f p 8zeto t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. Atpw ny) 6db0t+g a height of 125 m above the Earth, a package is dropped from a window. How muc ) 0p+ydw6tbgnh 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 freely2-xf(k; -l xr4l ,-gnkgxhrbu from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown ,4f2-rl(k;n-b x-ugh kxr xlg by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show9f r fkrqi 8z35ay5qp; (algebraically) that a ball thrown vertically upwa ar pqzff5yi3985r k;qrd 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 m/s c ndtc a/yu/7b,u;ta m; mattbn(5z*7
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflash of the apple in Fig. 2–18 +t: digjm+ 8swcizp+7 (or number of photoflashes per second). igt +sw+zpi8+c 7 j:mdAssume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–3efm xhbb4;o k/xb0s: l, /ail72). From what height above the top of the window did the stone :/i0lhkxf/m;a bob 4, l7exsbfall?    m

  A rock is dropped from a sea cliff, and th4;uxwl 9((kajh p8jk c lai9u0e sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , how high is the 4kkw ulcj l9 piu; 0a9j(8(ahxcliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of watery-9rd t tg2n)uu0c(s d. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the watd9 ut2t)uc(y-0 srn dger 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 ofx 6ni*z,. (fy5emfcwe a cznfc5yiex6*mw e,(.fliff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the street with a 2eaev x0r da*endf,djk9.l .3wujf56vertical speed of 13 m/s If the ball was thrown from thejr6 u*n2d fe.d9ak elx,df5av w.3 j0e street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a function o ml2ej*hl-i*q f time. (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 constai*qhllm* 2 e-jnt? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a functios-i9s8mfr,3a kjye(n.h 2yue n of time is plotted in Fig. 2–28. What is its instantaneous yke( ,fm8j is-hn as.e92ru3y 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 au3/mqyz/8a;w0gzp b eg tomobile can accelerate approximately as shown in the velocity–time graph of Fig. 2–35. z ;pae0q3/y8 g gw/mbz(The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car ix54 h6/z ql0x2*grdg4uh*fs6 b xb ewyn the previous Problem (Fig. 2–35)ugrwd y*/fb 4x0e* s6zbg2x5 h4hl6q x when 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 traveledleuqr v(i0vkhn ;kx44n:6im 6c zx fuw)y4o 67 during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement aa fsxt3tt/)2 rs a function of time /)t x2 tfsat3ris given by Fig. 2–28.

Figure 2–36 is a position versus time gra7k+o 0r ;*tfef 9iaoze.as d:dph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the timtaiedaeo;o .+0 szf7fr 9:*dke interval from C to D.

  A person jumps from a7dq3 d7x7imirsyi vv-:p uw85 k;t,c w fourth-story window 15.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before coming to rest, Fig. 2–37tk;8c 7msi,rpy7dwx5di qv37 i-v :wu.
(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 ism.b 5qrau9/y w iiuy62 on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go th56qyu9 2ram by. wiui/an it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over lcs d+w/5b- a ej-dfh1nmh6s whg8d96-the-shoulder seat belt has a good chance of surviving a car collision if the deceleration does not /h 1-gdljwh d mss+- 56afce869d hnbwexceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, e7o3s i7y ih/ s sgbs69q-accqfz5e:912 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 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. Hoh3:s9-q sis be cogceazfi9 s/576yq 7w many poles is it?    poles

  Suppose a car manufacturer tested its pp l53)y vqe58fg;oz g.x 1adfcars for front-end collisions by hauling them up on a crane ap)ex z fvf.dag3po;5l5gqy18 nd 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 ab dyakw(h03 lhf6f f d;ee6jive;u0i+:out $10^9\,km$ 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 tra7cf9 u6ie i-qnin 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. 9-i ceinuf76q 2–38.)    m/s

  A person jumps off a diving board 4.0 m a)n 9.ahhz0lr5tb* fckbove the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration off5 9lt)0anc .hhbk rz* 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 balance the a e,3izdbh cb)-mf1 li;verage speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train t);ibf,ebd1 mzil3hc-o 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 u*.6cm7i(u4fm u4 6xiiv zrvxfor fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to pe .v cmf(i viir4xu*6xu74mzu6rform 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 plaeh*cmr ,8,ke fdqw3ok y1nk27nned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is moy enkk*d,mc8f e1h ,23 wrkoq7re 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 trai,hrw 7 b44g1+sidqjnon traveling at a constant speed of 6.0 m/s Justgj4wi 7qd,4rb sh+1no 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 fnh)hhc .h 0)7upjl*sdrom the roof of a high building. A second stone is dropped 1.50 s later. p)hhuhsj0 c n7hl.)* dHow far apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h o o u7 zy6p2mqqyvy7zh*o)r3)tver the course of a time trial lasting t o37h)r7yqzp*z 6m2oy uvytq)en laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the T7vpie* z)h,3pbwjo l 1our de France crests a mountain pass as he moves at 18 km/h . At the bottom, 4.eb, 3)v wozp1*ipl 7hj0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines.s fpn+ fc)noxfe;du; n7/bsmm)25mh6s .h, mj The first child can bounce up one-and-a-half times higher than the seconsx+h/fj )m c7uspsn2mm e); ,6mo bdf; fh5n.nd 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 th:m 85b/dl5 vzntc5cqw3 ict8le same direction on a track parallel to the road. If vwdnim:lbql55 83tcz8 tc c5 /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 yz .g9 /zn;xpw5a -upp iius1)a baseball with a 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 released (Fig. 2–41). Estimate the average acceleration of the ball during the throw ap9-g.si)uzpy5 / nziw px;u1ing motion.    $m/s^2$

  A rocket rises vertically, from rni -4 apay7dn9juw7b1rw:t. best, 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 54cehdikj flv mv*an7 l-* u5qj7 5h(jin Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the nc h vl 5(-jk5lm*4j5fdja7eu7qh*ivlights 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 speb frk9cz,mk,x u)7l-av t;:njeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m,7k, )-ncau:vmlj,zfb r9 ;kxt maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s after that, a second sto .rft;2 sxjte .lv.v)ane is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same timerf x j.tstav .;.)2lve.
(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 v,;acxx0:vzz n/ 1ob9ibz dee2ertically up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. Wix 2vz dbbz :/e1co0i, ezn9a;xth 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 woul.p3 :t 8m1rbfd9rfwqfa 10pohd 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 rh8pbdm tra:31 fwqrf p1.9 o0fesistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send t92m:+a5 gq vael-ioq phe burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to coo-eqq l5:moaaip9 + vg2k, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster tha 0 qi65q+fym8gwd l5rsn Joe can. How many times highe5y0mqr+q85lw id6gf sr will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the tops.3ajg :5jrnn: oz v9q of a cliff while your friend stands on the ground below you.v:jjq .n an3or9z5s: g You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building uleh v,(uf,j5.dc rx 0gsing a barometer. Instead of using the baromete,fedg,0.xh5(cuvr l jr as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for two bicycles, A and B.5awt 3 zhl3nw. (a) Is there anyt n35waz3. lhw instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?