Does a car speedometer measure speed,j4 nm9iia +5mq xa;9no velocity, or both?

Can an object have a varying speed if its velocity:jofh 6t yjlur+z g-sb -:)edj1v,f ,b is constant? If yes, give examples.,:lr6-)js h ofvgt, d: z+jbf1yebu- j

When an object moves with constant velocwu d*c/.zbj 4glu0r j/ity, does its average velocity during any time interval differ from its instantaneous velocity at any i*ulucgjj r /.zwd/0b4 nstant?

In drag racing, is it possible for the car with the greatest speed cro-:pmd2 2v*5px khgv ntu8v/u assing the finish line to lose the race? kvm*:a8 -h vd tu/v2pgx2pn5uExplain.

If one object has a greatlw6 9k-lt1:hq :i hh dgaxyxm,/a.7mqer speed than a second object, does the first necessarily have a greater acceleration? Explain,th:q i,:d7ha l9kwq amxg1- l x.6/mhy using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to mbhz6u+t1; z;l ki) otn*emo590km/h with the acceleration of a bicycle that accelerates from rest5)ei6u lhzmn;tbo;m o kz +1*t to 10km/h in the same time.

Can an object have a northu9: odelafg 69r 8wu /j9ule19tot5mnward velocity and a southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is jy3 ,0tdnzao* positive? What *ojz03an t,dy about vice versa?

Give an example where both the velocity and acceleration are negativekyel6i5q*;yn6 o z: bh.

Two cars emerge side by side from a tunnel. Car A is t( 1fr :xy)doderaveling with a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and yoe (d r)fdx:1has an acceleration of 60km/h/min . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decrease wz w61xcq/ px(i2yuu3hz+qd4s? If so, give an example. If not, uqh q1 d6 pywxuz4c2(iw/3+x zexplain.

A baseball player hits a foul ball straig8.hc eoic-by2r,w t-ae; vv,n.ul cj0ht up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling when the;ocy 0vb8,.ciaj -. n vte,-elu h2rwc catcher catches it?

As a freely falling object speeds up, what is happen 60m fk/;unqm j(ffi;9qefgf *ing to its acceleration due to gravity — does it increase, decrease, or stay the saqfff/ e jmuf06 *i(;qf;kg9mnme?

How would you estimate the9hhjc2z2r/ hk maximum height you could throw a ball vertically upward? How would you estimate the maximum speed you could give iz 2 hh9ch2rjk/t?

You travel from point A to j*/nb -nyp+iwl w/ok0 point B in 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/h ? Explain whypjl /yi n-o/kww0 +nb* or why not.

In a lecture demonstration, a 3.0-m-long vertical string 7;q-g rrhx -hhk65iwawith ten bolts tied to it at equal intervals is dropped from the ceiling of the leh5-; a6xhrir wh-gkq 7cture 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 constant acceleration: a rock falling fz 8 gad,4oh -yd8ubzcb.p;b5j: pv rp4rom a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting on4ad,uj5zpdz .p c: -bbh8y4bo;p rgv8 a table?

An object that is thrown vertically upward will return to its original jel, aoaijsaz -.ot:, ;li3k3position with the same 3jaejtli i.lo,,kzaos;:3a-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 motion.]

Can an object have zero velocity and nonzero acceleration at the same ti*kgioho0 fkt29c dm7+me? Give ex0t+7o h2kg o midc*fk9amples.

Can an object have zero acceleration and nonzero velocity ym /nc qq4,w45pv2hm1 )/ psjr wkj*vzat the same time? Give examplep zqs/ck2q4vrj,4 j)1ym 5*hv/w m wnps.

Describe in words the motion plotted in4.- m0 v qrrbje42iatd25vad b:p/o mq Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walkin:b4qrvmj4/qvaa2bi5d -dp e 0r omt 2.g or moving your hand.]

Describe in words the motion of the objl:w, * fk rb))5geicadect graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 k iaa gbdi54 uavn1 5wxjs.6o+:m in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly6svwkki; eyjw.-8q cgv u7,w / 15 km?    h

  If you are driving along a straight road and you look to the side for 2.0 s, 3n 2q sc/d:wbqhow far do you travel during ts cwbq3nd:q2/ his inattentive period?    m

  Convert 35 mi/h to fml .26kxg1;nl at.ut
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves 22nx+ai:y)lpqndlq sd )4a-rfrom $x_1$ = 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 fornp8c 7ej,432 izj0hbdoqn i/ o 130 km. It then begins to rain and y,jd/op2z eii8c3 4qobjn 0hn7ou slow to 65 km/h You arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightning a3lv,zb:re 6 zflash and the following:zlva,6z e 3rb thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mn cq4j 9e4rws+ile track in a total time of 12.5 min. Calculate r9e4c j4+nwsq
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight line, moving 116 mtd 4f4.hicawk* b2xm7 away in 14.0 s. It then turns abruptly ab. 2 *h7w dki4x4caftmnd gallops halfway 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 w9q.tn,-en5f5 xjb nw 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 bt- wn59f eqxnw,5nj.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 wil4bwt x8)zumz4jod9p ,1d+ vsp l it take the car to d4tsvpmj+1)d z,4u p 89zxo wbreach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters a td:g p5dsjz 4:bw s2m2cailwind that boosts its speed to bz2: ds2msp5j dw4gc: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 completc9d0j -2qhvt ff40u ape round-trip in which the outgoing 250 km is covereh09jfft 2 vadcq4pu-0d 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 speed hits the pins at the end of a bowlgqt* kh6sk9uti 634 rning lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands.s6iqtg6*kt9n k h4ru3 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 averaka3pl,e(i lr6ge acceleiek(l3a rp,6 lration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. Whati*qjme q 7b*1d is her acceleration i1bmqq* d7je*
(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 accyjd1afn12mh kx ;9(jp eleration of about xjmn( 192f da;hjy k1p$1.6 m/s^2$ 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 5.0y s+43p*ckjdr gkrl,* s. If it then brakes a3, c+prjk4*g dy krs*lnd comes to a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from resuc2 u /0mtyyp0t 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. Displt u0uc2p/ym 0yay each in a Table and on a graph.

  A car accelerates frik/kiyyrd88 -a,:vy oom 13 m/s to 25 m/s in 6.0 s. What was its acceleration? How far did it v:y-8 koi,8y/adk i rytravel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23yb bxsv3;8,ef/lo g (q m/s to rest in a distance of 85 m. What was its acceleration, assuyxlb ; se(8f/3obgq,vmed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for 8k*n0tgm1qsj y)hkja1xu*(j takeoff. How long a runway is neededa *nj0g(k1*yj81 xuhq sjtmk) if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter cae8o t,/w+1chzw y)my r6*4qyyr me3py n 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 acceleration of this sprinter, and how long does it tak r 3*yy/yyq1mewe6tmych wo,rz48+) p e 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 6.0,kbb2s) a msbd2i+j( s0 s. How far did it travel in mb bs j2+(k2s)d absi,that time?    m

  In coming to a stop, a car leaves skid m gai.sb i,,:bearks 92 m long on the highway. Assuming a dec,, b:biia seg.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. The front end of the car compressess36co ldy5vmidnp690c ythdt )e.n/ 1 and the driver comes to rest /ecmys0pny )t6 cndt36di5 lo1vdh 9 .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 for a car with 2xxn/u z w)j n+7al)zxan initial speed of 95 km/h and human reaction time ofznj x)x al+)u2nx/w7z 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 distd+)nkao6wth aaf .afmi2-c41 ance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver lookk xeoou svp n+b.h 3u;.qf/h66s for an opportunif; uh3oo6vsu . b n6xe.h/+pqkty 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. e * 9 zrf3abhzq7 *2ff8y0idxlAfter exactly 27.0 min, there are still 110 a28b z70q*9efry xf i3lf*hdz0 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her :lg dh554l npdcar 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 h4l 5gn:dlp d5maximum 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 hits8zyuvuri53m/: 5lj z n5yn xb0 the ground below after 3.25 s. How h uzi 8uyn: lm0jny553 rxv5z/bigh is the cliff?    m

  If a car rolls gentlyp5ce k* 8,jsejz*vfw6 ($v_0\,=\,0$) 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 spe;fo /. 0msawxu nrx;8hpn- ,weed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throw7h5 pl1sa oep8ing it vertically upward. With what speed did hel8o5 phap e71s throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and fall,zwpc1m. kuo0fs7u wo.v,xl0 s under the influence of gravity. Draw graphs o.m,pf 0uzko u0x7lvw1.cwo, sf (a) its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a height of 12xtf4f i(l 6bxq01fi,e5 m above the Earth, a package is d6fxb0,4 xiqft ( f1ielropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show thatc(wltoz 422 mzahb7 o: the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Fig7b4ohw 2za(l: m2ctzos. 2–18 and 2–21.

If air resistance is neglected, show (algebraicall dbzn5g xj+*m2/(j8r wh /-yc9 ptwgnqy) that a ball thrown vertically upward with a speed 9zd8r+/y*jg(nbx n w t/j-p 52mwcgqh$v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown ver rtupd4)cxl (5f ,z(gztically 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 photoflash odx7v2 2mb2-t mr-dgdof the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple i r-bddmg2v2 xt-27o dms 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./ bcddmk c8e b*clb*92 2–32). From what height above the top of the window did the sto*clkedb*m9/d 2 bcb8cne fall?    m

  A rock is dropped fromu./oc,z ci g:q a sea cliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sou:g uzc, /.iqocnd is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream n-/n;4diu ;kwyni9f; nr tnrn/+ mba0of water. You point the nozzle vertically upward at a height of 1.5 m above the nrnyin4kn;n+ frbi9;w-ua0d/ m; n /t 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 water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 msr3-se t4wux3/s from the edge of a cliff 70.0 3-3te u xw4rssm 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 mk; x 9ee3.qwdrwk+- pwith a vertical speed of 13 m/s If the ball was thrown from the streerp 3x;ww+mkk e-dq.9e t,
(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 vtvdy/+ga/c- 8w 9 tgvfelocity of a train as a function of time. (a) At what time was its velocitv-tf/tdc y8g 9+av/gwy 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 greatest?

  The position of a rabbit along a straight tunnel as a function of ti +f+u4u)sp.gcyk 3p+f7m y bpzuxp,+rme is plotted in Fig. 2–2 z uu+pfp+kpyyc)g7+s + .,x3pu4mb rf8. 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 nq5;o x0y lx2caccelerate approximately as shown in the velocity–time graph of Fig.l0 xox; ynqc52 2–35. (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 in the previous Proe51 ac fe)9bdtw:.bz ,f*f: 91w rxyhsigom8xblem (Fig. 2–35) whenhs f9r:,wex f)fc9ixb5:1doe w .*mab y8gt1z 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 theu71o gui(,hg z object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose disvxeapx+q zhud3/w 1 hm1:(d 4bplacement as a function of time is :amu1 (dv34eq/zd p w+1xxh hbgiven by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an objec-al,jl7*1uhtauhn 0sl q2l2 mt 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 dirml*-la20u1l n2 , qalhhjs7ut ection? (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 firefighteqiu/:ss 2fu*s+wxxf.,f-8u3ofmz gur’s safety net. The survivor stre3 2z+x*f wsiq:sxu,f-mfo.ug sf/ 8uutches 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 y 0 ,;dtzk*rlwMoon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assud0*rw yzl, k;tming the same initial velocity?

  A person who is properly constrained by an ov/oksg4unv.k k4k * v 4lsi8q;qer-the-shoulder seat belt has a good chancekun8 l.o;ivkk4 k gs44 q*/svq of surviving a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and hisz .nsm+ 1u jpev ;wm53*(uuqysa4ep*q 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 polem+mvu*wuqee(q4 3n;j*.ysupp15s zas 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 collisions r;-)c ;grhqr, hw.hd,t koz g*by hauling them ut k*dw -og.h)rgr,z chqh ;,r;p on a crane and dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth16f v)ukoea(p travels 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 uniform acceleration from rest. The fronwsgtja:3j v-zxj4:2uy e k pr8ah :+*jt 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 speedjv+x s :*8k hgj:j :uaj43ztr epa2-yw of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board n26(t * ttiyn-w3:j)kkfv msj z7ip0m4.0 m above the water’s surface into a deep pool. The person’s downward motion stops 2.0 m below thm)kitvsw*j n(0mn62 7 -:3 itpz tkyfje surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit systemi 5vuj0m0 a nf19jb4ds, it is necessary to balance the average speed of a train against the distance between stops. The more stops there ares v 5bfnua94j10 imjd0, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wings and free fall straight down when diving fowm d28z7lv se4r 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 perform evasive action, at what minimum height must it spot the pelican to ew v4demlz7s28scape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planny ,godie-8d2z8dz. oh ed 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 fro8 . ogdh82d zdyie,o-zm 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 aewzvipd:ui)l1 b4d-( o 5 bpz;fee78 constant speed of 6.0 m/s J (a:p7bpfv;4di b- l)ewzdueoie8 5 z1ust as an empty box car passes him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stqdw. nun; y 3ana).a 3u0eeyu.one is dropped 1.50 s later. How far apart are the stones when the second one has reached a speed of 12.0 m.ea nu.w;dyy3 uu ena0n3a).q /s ?    m

  A race car driver must average 200.0 km/h over the course of a t h,x:vu dgw1v.ime trial lasting ten laps. If the first nine laps were done at 198.dvx :hg.v uw,10 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crestgos1t)x:imv8,) ge 8bzth r5bs a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km) g tzmo1t8gxbe5,)8:v brsih/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampoline swctt vxm11cpbb)z m(mtl a4lay0 .53 57k.zgs. The first child can bounce up one-and-a-half times higher than the second child. The initit 0m4b5wm gz1 .zcytlb73) lx5ak1cvm sp .a(tal 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 ins y60x3lknlk0ws -61(apy tqw the same direction on a track parallel to the road. If the trwwspk6lnl s t0y10 3-6a(xq ykain’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/s Inh,z;jfwx,i7u 7qxode (uip8: 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 duriuziipu e xo:87d7w (fqhj ;,x,ng the throwing motion.    $m/s^2$

  A rocket rises vertically, fromtqb.b3prn5t4+t) qab rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–4/nh6v--yvxj/q, j-5m 4 h o g6yzrsmso2. Each intersection has a traffic signal, andjs- x-n 6q,- /rogy m6zhv/mjo5vh4sy 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 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 constant 120 km/h taken .s3*+ikfhsebb-nv:s off in hot pursuit. The police offic+s:invnbf sh 3e- b.k*er catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s after that, a second s8zni31 an,mpwyq v ok70s3s w.tone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same y a3iq3nvw1w s mks0n.op,z7 8time.
(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 throwug ly se.*60qkn vertically 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 u6sq0 eyg *k.lbuilding and 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 would it take a free-falling pi+ nrfhy35 2mparachutist to fall from a plane at 3200 m to an altitude of 350 p+ fhr532mniy 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 a conveyor belt to send the bz)y g6jx.enwtb*j8 g*urgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers**yx njbg6tgzwj )e8 . 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 a speed 1.5 times fasterg, ,eygee:5cxql::fy zk)4sd than Joe can. How many times h fee4s y,xl y cz):ked5::gqg,igher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a clbkz+ spprcss;7 *;ji;y/j3mniff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is pp3b7 jksz;;n/;ij smsc+r* ythe speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particula/uq ck(lfzc;; r building using a barometer. Instead of using the barometer as an altitudeczq(c /;u ;lfk-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. (a) 9;.mpy0k wusf Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At whichu9m0; pkwyf.s 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?