Does a car speedometer measure speed, velocj3oxy612cbaw (es.p lp mb-a*ity, or both?

Can an object have a varying speed if its :; xgxzfj-c fx) nd2m/velocity is constant? If yes, give example xxxn);c:f2/fz m- dgjs.

When an object moves with const- i1ywr5 wln,pant velocity, does its average velocity during any time interval differ from its instantaneous velocity r5p1-w,ynliwat any instant?

In drag racing, is it possible for the car with phy210o o0.mum g uot2the greatest speed crossing the . yogo2huo0up0t1 2mmfinish line to lose the race? Explain.

If one object has a greater speed - da82m ax)jovm26 rua/t7ia ethan a second object, does the first necessarily havatrj oai )-m82e am d/x276vaue a greater acceleration? Explain, using examples.

Compare the acceleration of a motorca ebf/hgo6-l hm,(ef:ah5k,:ckp3 jo ycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle thath-:oaag3k f5bepo hh j/l:6k ,fc(em, accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acce-b jlr*pb9 oc7leration? Explain.

Can the velocity of an object be negative ;y7 sz2*b brj3ae*xpbwhen its acceleration is positive? Whab b2x 3j;7yp*z ae*sbrt about vice versa?

Give an example where both thma-aumg 1kc 8w5k5;fkz-pql(t;8m/4 nwz icke velocity and acceleration are negative.

Two cars emerge side by side from a tun7qo.y b44nzgt4/i kq, pz7vw nnel. Car A is traveling 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 ko 7q7, /z4gyv.n4 wpzi4q btncome out of the tunnel? Explain your reasoning.

Can an object be increa:yvb a0pvu.nz +yt grp3zvs :h;( pg8+sing in speed as its acceleration decreases? If so, give b;3.(v8 uppyv: gs+ gny r +th:az0zpvan example. If not, explain.

A baseball player hits a fa ;dzu 93p7sdsoul ball straight 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 catcher3 d9ad ;zuss7p catches it?

As a freely falling object cwugajid8 6s)h 3ez)0speeds up, what is happening to its acceleration due to grzgiash6) 3 )ced j8w0uavity — does it increase, decrease, or stay the same?

How would you estimate the maximum height +k ik dzt4+1i*yudz2xyou could throw a ball vertically upward? How would you estimate the m+1+izx2*kt 4dkuyiz daximum speed you could give it?

You travel from point A tzkadh 7+8cb b/o 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 youzk7 8/ac +dhbbr 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 with ten boltsvlwj 99fvuj85f p/e5u 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 increase or decrele w5pvjf8u99j v f/5uase 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 m t6i*zftrwl3u a).(facceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor makitmw3if)a z*.(tru fl6ng stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to its o gzi f46xumc93riginal 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 resistfgc4i93zx m 6uance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero o qkw,5a7c)ql+bfle9 acceleration at the same time? Give examplesk+,bf5l )ac 9 eqqw7lo.

Can an object have zero accrcf1em v-b5,veleration and nonzero velocity at the same time? Give1be-v rmf5vc, examples.

Describe in words the motion plotted in Fig.t:kt 3,c. pivi)5i kbv 2–28 in terms of v, a, etc. [Hint: F5p:kcitv )i.iv k3, tbirst try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the mo (p/-vtzbz3 p9tkt5(qodkptd( djr; (tion of the object graphed in Fig. 2–29.

  What must be your car’s average speed in order to travel 235 km in 3.25 h )j7utniz-6 uh?    km/h

  A bird can fly 25 km/h How long does i uueg1c mfe86;t take to fly 15 km?    h

  If you are driving along a straight roaos ;/c6vkcl y9d and you look to the side for 2.0 s, how far do you travel during this inattk; sc/9v6ylo centive period?    m

  Convert 35 mi/h to avkakif1db q +wl((-e 51t3xg
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fromn8xz f((a 0rb d wk)ckqfy0;b; $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home wk8p (m 99spanfrom school steadily at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h na98mp s(pw k9You 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 betwpt36n2(zpv bn een a lightning flash and the following thunder gives3nbp( t2nv 6zp 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-mile traca hw82b;13o-zy btppobu-i/(glq2 iqk in a total time of 12.5 min. Calculate 1wgah /2 o23zou8qp -i-;qp ( ltbbybi
(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 m away inmkc g4)b1kz dp 2m7-jvaq n2c, 14.0 s. It then turns abruptl,vnk-27 md) a2qpc41jmgc zbky and 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 each other on parallel tracn;cc+cm qu -o;ks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be beforemcnoq +ucc;- ; they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck travelibbrkv- k5hg8ya6f3ht w1wh: -ng How long will it take the car v3w h rhybhw t-1a6g:f5b k-k8to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encoub q7.h /cucnw0.j- lnanters a tailwind that boosts its speed to 990 km/h jaq n /-wu0 .hnc.7clbfor 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 ang,fr4( vz1pyaw-ahi:o:a2pj e.ty d7d average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is covzt :7fdag2o.1a -rp4:ae ,pwv(jihyyered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits)o)jb.kxc+dk 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 ball is released from kjkco +. )d)bxhis 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 i p+q6s28edt -cr gbw+;ug4rd,vzt oc5s its average accelevsqcz+ tw8beg5 r4 gco;tdrdp ,-2u6 +ration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s ix)c: ka(3feyi6r1-4 e gexc pgy8arq;n 1.35 s. What is her acceleration c6qexgea1: ia)4 8(rkfpcex-3y r;yg
(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 7;i wty,d:ms)eu d4+ 4qykbqdbn9e1pan acceleration of about yn4: ee q1dwqkm+ ),ybps94ti udb7;d$1.6 m/s^2$ 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 brakes5pj529whmjjb h 3bv y- anpj95ybh3w j- h bj2m5vd 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 rest at t = 0 and moves in p flqi l(s* jggo:ac.-84u,d ua 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 o d 8 g(lq-j*:.,iufus lgap4ctime. Display each in a Table and on a graph.

  A car accelerates from 13 m/s toes4ti3t f+6nwyi +y.e qcc1g, 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assumwt3i.,cnyg+6 f ys 1cte 4+ieqe constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rwb j0144pbeubaui+( k est in a distance of 85 m. What was its acceleration, assumed cwp au(ub1+4 04eibbjk onstant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takl*ob9b 7: glwreoff. How long a runway is neededo7b:l9gw * rbl if the (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the block(ibta)mlsw6myg: t: ysc8s:5s to essentially top speed (of about 11.5 m/s) :sa g( yiy5tl:8ct:bw)s msm6in 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 unig)c( 4q, 36k+n orhiqxgadnt7 formly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in that timx 6q7dgo(4),hr3 kcnq+ia ntg e?    m

  In coming to a stop, a car leaves skid ma* q xblp8rc1m,-dj5ne rks 92 m long on the highway. Assuming a deceleration of r -jqd xbmn ,p1*le5c8$7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. T2qji d2rlm0o1c/p9y n he front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collis 2r9 ldym/2o pi0j1nqci 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 f o,1uu1mnkd) ck7 odr9or a car with an initial speed of 95 km/h and human reaction o9d)domk7 1u,1rc knu time of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of azzy)1l-j21k aj+iyuk 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 cy6sca+4kxbkfy43+sh /s q +pj ar’s driver looks for an opportunity to pass, guessing that h3++/sh4kfpj sqsk+4x c6y a ybis 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 ce3iwk u1u .4oug2wr/u5ff g230.0 min. After exactly 27.0 min, there are still 1100 m to go. The runnec4 u2uuw.ekgu i3 o1f25rfw/gr must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km-s;9g;b7 2s bldimxyv /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 t29gl;isxsb ;7 byv- dmhe light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits t9k4mfxz1g2 ) qa 1zlifhe ground below after 3.25 s. How high is the cliff? qg fz4l92m1k)1z axfi   m

  If a car rolls gently (.y t +cf4 a4ynor-devrktsypx) a4588$v_0\,=\,0$) 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-g a l 8)(d vesbrc;mzbl4x5myun123g air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s afte e 0vqi:a(8vu5g9z tq w*c8axar throwing it vertically upward. With what speed did he throw9qxq:auc i g8vtaa58 0 zwev*( it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls rbpgfggop3* e09f 25itonh:s) 0*yh dunder the influence of gravity. Draw graphs of (a) its speedd9ng f3:r fh5to0bph)g i ogy*20 se*p 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 verticall eino9b,xpf .q l*ooyt25 *(wn *+jjrzy with 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? [Hint: The package’s initial speed *b 5(pjefzoowl t+qj*n.o92 i,* rxy nequals the helicopter’s.] t =__ s

For an object falling f /o 6r612dp3rmdaj* 7 pry+mw1jgjmcvreely 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 firmmypd 6rpjj 3o/1rcw a*7 dmg v2j+r61st shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thronsj8q7rr(c9 ikc* h 5ewn vertically upward wsq hi85c(e cnj7k*r9r ith 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/b0ffoq. yqn8el: sonh mm;0,wj 8)z,rs
(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. 7 -+ -nlbnkfs +ysi;fg9n cv6:0yqiwuplje( ,2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear oln +f sn7v-+lec6yupfb:0(-n,w ik ;9 yigqjsnes at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window h,xd ok*e;o dphhse h2s5n34b-p:z 5q 2.2 m tall (Fig. 2–32). From what height above the top of the window did np235;he*qd:ksb ,shx5-h dz o ehop4the stone fall?    m

  A rock is dropped from a sea cliff, and the sound of it striking the oc5njlpc8+ml(dh3x:e/ s rh 6guean is heard 3.2 s later. If the speed of sound is 34(em ph hn+x/su 5ljcd:638rg l0 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzl kuf5pvu- i4.he for a hard 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 ground next to you for another fh5-uu.ip 4kv2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edge of 0t ( vk.g2f-om n*3hk fa.ejvxa cliff 70.0 m highkv.0fk3 jf(ext* - a og.nmv2h (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 streetq1puc.z6 o 0ucrze;5y+n m knh/vql -4.ih vu8 with a vertical speed of 13 m/s If the ball was thry54ep8q/vlrmk +hziv - .. c;0hc1nnqu o6 zuuown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train a g*x3 p8prt-93se,akvpj5 ezss a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) Durin*e gs k3t 3r9jep5-pxps8 v,zag 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 ofvc9ovicwav3p q d h +d;3+q22l time is plotted indh3v3 aovv;wq2 2+i+qcd p 9lc 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 accelerate approximately as shownv )upumnnhe 2* dwp;u+/)q. dm in the velocity–time graph of Fig. 2–35. (The short flat spots i um *eud); wp/ n+pvmd.unh)q2n 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 t s6hjye1bn-:m he previous Problem (Fig. 2–35) when it 61yj :s-mneb his 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 wny32 s z*vt5dmo)/cu v :zyi(the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement asme /+ t(p-hzkfk. ,twv a function of time is gihtp+. -kfkt/ m,zewv (ven by Fig. 2–28.

Figure 2–36 is a position versus time graph for the mot7g pvd qc;gjk ejye5zu;.0*a6ion 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 pgeau 7qjjc6dg;vze. k*y5 0;object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-cvwik:/ o74 oo1.xe rkstory window 15.0 m above a firefighter’s safety net. w/xkick r 4.7oo: 1oevThe survivor stretches the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about xezv 4+nadrx* d8a1;eone-sixth what it is on Earth. If an objecenvz;+d rxda 8a1*e4 xt is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat be1i+1 j oz5o/aov :7 qbd4 kgmuk,h*pyvlt has a good chance of sio q4o+v*vb5,1 op:7k amkzdhj g1uy/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 standing on a bridge, 12 m above th2wi2 6 iuqfpw-0xrd 7:nnj/rze 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 /d qp2fiu 6 2injwzxnr:70- wrthis 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 collisionss5 e17g5or jnl pl+m z--fo(wt by hauling them up on a crane and droppin morplj f57- t n-+zse5wog(l1g 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 abouug9gv *,sf v zoz++n,ht $10^9\,km$ 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 fr3(g /y,kfzyuuont of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as ityu( k zyg,u3/f passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the water’s surface into a deep pgi zgsslx1b75xq)mx 6b.x,,pool. The person’s downward motion stops 2.0 m below the surface of the bb xs x1g ,.6,7g m5pxilx)zqswater. 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 system, q0dbe --y9 hfnit is necessary to balance the average speed of a train against the distance between stops. The more stops there are, the s-dyfhbn- 0e9 qlower 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 wini l.kn0+pzql b88r7ck2 q4urzgs and free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it tak2l brqz0pu7i8rq+k 8nkc4l .zes 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 sp;ftgtk f uww1 +()4putrikes a ball is planned 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 more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantt tf+wp)k(g1pw ; fuu4ly 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 frbg4hv;6wjs,3uqj /r p eight train traveling at a constant speed of 6.0 m/s Just as an empty p wrj3u hjv, g;b/s6q4box 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 stondp- d5z6+ap j;-i1fefht9 jtrjn *w4pe is dropped 1.50 s later. How far -d p*9;epfd4ar zwj5jh- t 16i+tnfjpapart 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 over the course of a tim f- xopq+3/ 7a ekd6q-(gvwaeoe trial lasting ten laps. If the first nine laps we 6+fow ea3og(q/e- x-kdq7apvre 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 mountain pass as he moh) u- 2o gvlp3d.ic*enves at 18 km/h . At the botto 2-l)e c*dhv.giuon3pm, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can bouye7,bq1 ke.w -xrnej s4tdzid)6 -1 cence up one-and-a-half times higher thairx-wdte z) -1n6q deyej. ek7b41s,cn 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 ove+ewa r+6jn*mhrtakes a 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling wh6 nje r+a*+min 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 basebasi ;q 8x dz(5cc(bm5chll with a speed of 44 m/s In throwing the baseball, the pitcher accelerates th bmcx5isqhc (d5cz8;(e 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, fr0jza+ ls +slgx 1y(jmqd9 z,b)i.t(afom 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 -o/u;;h b6tep ai sc6n+e6tulpattern shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limitpo6+ 6cla;neu-esut i/th;6b . 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 sw7.st 7 h 1rb5cjhmvx0peeder traveling at a constant 120 km/h takes off in 70hr5mh .tc 1w vxjsb7hot pursuit. The police officer 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, dxa+4g)aud k.a second stone is thrown straight down with an initial speed of 25.0 m/s and the two stones land at the same time.aa xkd+u4d)g.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. Tmz54b. yz)r55fk ibh phl6z+ uhe first stone is thrown with an initpb+45 6r ky5.)umhfzh5libzz ial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second stone be 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 resistanc + +impmq(an.pebk:8ve, how long would it take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where sh+8m+:akp(m. eb vipqn e 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 top,(g 0pk;)b+qrlhqh8g oj vx) send the burgers through a grilling machine. If the grilling machin+g 80k(o) pxh, )gp lvq;bjrqhe 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 a speed 1.5 times faster than Joerr- suw5t+ vm/3v iqemd2b/l; can. How many times higher will Bi r v/e q;t23m5v-ilmus /w+drbll’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of aagi+hp) ,-dp-nge nmg:n4 cj1 cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the bal4, gg-pnn 1e+jihgc n-):dampl 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 using a1: st aqah4 /1g8lyea09ssdla barometer. 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 fall. 9y t lsae/d4g1q0h81als:a asOne 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. timezo e70 wb+u zw8+3loyi graph for two bicycles, A and B. (a) Is there +z zei30yu+8 lbowow7 any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?