Does a car speedometer measure speed, velzvn;-cp+ m m) u8qj8sur oi+ kfe/d/h3ocity, or both?

Can an object have a varying speed if its velocity is con17uo2llzi 9v 1w-qfy0hu * hgnstant? If yes, give exa-*1wq9f li1 u7lh02zgnyu ohvmples.

When an object moves with constant velocity, does its average velo-)zq3-oi (/ zn)h eme qpyuh2mcity during any time interval differ from its instantaneous velocity ao3)2yqzz qmu--e)/h e m(phi nt any instant?

In drag racing, is it possible for the car with the greatest speed crossing the b:qp nwxt*z8squm8 9t*7glr1 finish line to lose the race?:s9qlb* tm*t g8 ru8wpqzx1 7n Explain.

If one object has a greater speed t) *+wpe9k.dyxa x/yho1+sb dhhan a second object, does the first necessarily have a greater acceleration? Explain, using exa9yak)dh+/ps1y* xxbohwde . + mples.

Compare the acceleration of a motorcycle that accel ow,av e *n;4zz*osv,4 yzgrq,erates from 80km/h to 90km/h with the rz*,o4gevo q*a ; y,v4 zws,nzacceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northwgjgkac 02;e1 b 6v/fomard velocity and a southward acceleration? Explain.

Can the velocity of an object be negb5*9iy,; k 6chr :v;vhk lvbjiative when its acceleration is positive? What about vice versa?hb;, cvv 9y i6:bivlrkkh;5j*

Give an example where both k *wwt.n 2/owqcfd87nthe velocity and acceleration are negative.

Two cars emerge side b/:uti3i y- gtmerq lp g/6;vje:hv1f9 y side from a tunnel. 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 th:upri1 vey:ih9qlt ;f-/3eg6m t vj/g e other as they come out of the tunnel? Explain your reasoning.

Can an object be increasinwhm47tu n ,k6ng in speed as its acceleration decreases? If so, give an examplh6nm47t ,uk nwe. If not, explain.

A baseball player hits a foul bu xq)nve -q.v8dg;,;wk m,tszall 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 v), .vmxq8 ;etnskq;,gwduz-be traveling when the catcher catches it?

As a freely falling object tj9 )owm x7av+speeds up, what is happening to its acceleration due to grav+7w v9axot m)jity — does it increase, decrease, or stay the same?

How would you estimate the max*br16r( gyonqv9xr) ximum height you could throw a ball vertically upward? rg 6 x()r*byq v9orxn1How would you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a constan hdu/a-zd a4c7t speed of Then you travel the same distance from point B to another point C, moving at a con-7dad4zuch/a stant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string wi yei3jugbkxsn,v,x1 : x/c)w2th ten bolts tied to it at eq1b/c )g kusjen3,x:xvw,2 xyiual 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 coinz,ch9v* :x j1 iev)6iq ka)fnstant acceleration: a rock falling from a cliff, an elevatoize )nkji) xfi6:ch*v q va19,r 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 return to its o1o:k;t cv9mgpzprm n/o z(3.priginal 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 tot./k o 91r;npmp gmpz3czvo:( air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero a,whr7-rz u2y b:i is2jcceleration at the same time? Giveu,- i22ry :srwijhzb7 examples.

Can an object have zero acceleration and nonzero velocity apwq7 bz(* ,iluqn;j0wv*e gy)t the same time? Give exam, qjwbw*0)g*vli e pz(q7ny;u ples.

Describe in words the motion plotted in Fig. zxi 10key oq.s5zy+l;2–28 in terms of v, a, etc. [Hint: Fi; yse k y.l+x1z5oz0iqrst try to duplicate the motion plotted by walking or moving your hand.]

Describe in words the motion of the object graphed i gvz p3p66e7n3 r6 qv;xtci-gpn Fig. 2–29.

  What must be your car’s average speed in order to travel 2c+ v 9e.rtjxiocvz,2+35 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to flrt (2 /7 pvs38hro1k- ksoxkipy 15 km?    h

  If you are driving along a straight road and you look to the side for 2.qar v+ 8p;d7wy0 s, how far do you travel during this inattentive periry p7d+av;w8q od?    m

  Convert 35 mi/h to 5cqa5ahf28v j
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves fa4 y57wiv9d;i uu tgw:t zz0)srom $x_1$ = 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 fo.zi (2 .v(us9 8 trugeivhruw)r 130 km. It then begins to rgvt. 8zw(29r) .suh i(vurieuain and you 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 se rvu:7cjd7m4. d 5xfikconds between a lightning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sou 5.7dcmf4dkj:v7xir u nd in m/s from this rule.    m/s

  A person jogs eight complete laps aroump otmy-bhf+ty797a 8nd a quarter-mile track in a total time of 12ympoty7 hbm-a 8f9t+7.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trai f9hmz3md5 bik8l)u6 wner in a straight line, moving 116 m away in 14.0 s. It then turns abruptl l m khd3bwfu86)i59mzy 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 tracks. Each hp ),c*qs + *)(wv+haawbkidh tas a speed of 95 km/h witv swha* hqbkt*))ia,+(wd+pc h respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m beh 9 wserf6me;kz 1(ct07x ar0h(edu se5ind a truck traveling How long will it take the car to reach thrd6emeca1(ezft5e 7(09 ;hxw krs0u se truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , anpfr v) 0hhm.ti4qb+rs -sv:r*d then encounters a tailwind that bov*. f ti+ 4hrrmvh):q0- sbsprosts its speed to 990 km/h for the next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a com2 d8hm1bnaw4splete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the rea12sn8b m d4whturn 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pins vl8oo2o4-z02e4 d w kig -grpcat 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 his h- 4-4iwork dz8co l2po2gvge0ands. 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 a mw (4vpir4mb./fx2ris its average acceleration in f.m4r xwi/ma4(2prvb$m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 sqk(z wx(ka1n e 5s33ab. What is her acceleration nz3kw5x akq3aesb(1 (
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particulare-t mzarjp l.6 8;tgt4 automobile is capable of an acceleration of aboutr jt6l.etmza8-p ;g4 t $1.6 m/s^2$ 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 cong/i xhe5f t+u(stant speed travels 110 m in 5.0 s. If it then brakes x+(guthi5 e f/and 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 qjl1x1 dhup9: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 ti1:luxd1 h 9pqjme. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. What was its acceleration?vo6mzoc-5wo -twey9 4j71 mi8ptt(z e How far did it travel in this time? Assume constant acceler ti 58zpeetwvc6 -o yw1m7z49(mjot-o ation.    $m/s^2$    m

  A car slows down from,xf ek( akn9:t 23 m/s to rest in a distance of 85 m. What was its acceleration, 9 fxtkk:n ,(aeassumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How l2f5; t.l) x ol8w utgimyog1i)ong a runway is needed if the (constant) acceleratio) )go5u.f t82myitgill1;wox n is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to k z k)55pccp:wns,rci:ho;p 9 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 sprinterhk cn)9p: ;ipo5 ,c:srw kcp5z, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. Hkv;9jf*(vz,-4hdyirmq u( ux ow far did it travel in u((id 94rjk;fxmv q -v, huyz*that time?    m

  In coming to a stop, a car leaves skid marks 92 m v/1ed tfuk,oj i1*a1clong on the highway. Assuming a decelert dv 1fu aec/1kioj1,*ation of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h stan+taq/cyxiz)r6 kzj ,h +.x*rikes a tree. The front end of the car compresses and the driver comes to rest afx)n,*a +tq .h6zkcx ar/ yz+jiter 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 an initial speed of 95 km/h anu/+ aqdo3jb x3d human reaction time of 1.0 s, for an acceleraa/3qdb+ xu3jo tion
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car is xw*bi 6;py 7;rn .oijp. b-upl$d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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 lo,4c8t:-ce sxwm s dq4cgqcq3,oks for an opportunity t48x4dq,qwcecs gst- :mqc 3,c o 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 tl0 2p,4 meethdhe 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The runner must ttle d 0e,2pm4hhen accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h appro7 1ylkuj4zqh(da yk66 aches 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 inters67u lkzqk1d4(6yah yjection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the grou 52o(1akp/ q/nlkvj mqk;o ;xand below after 3.25 s. How h /2;ooakl/a(qjp;k xmqv5k1nigh is the cliff?    m

  If a car rolls gently (ggwu39)l c;wei zk 32ko3ul0s$v_0\,=\,0$) 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 odc w,67 u1fbvt+psc.k: (ivnut :pef ;f 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 l a16jpvfm.pyzl g;ma+gow he2k9 *18r throwing it vertically upward. With what speed digy2kh +e a11m apojwvzp*ml6 .9fgl8; d he throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influedy.+-)ydtel td yr ac2r 3a+qopw:0x4nce of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a func wqe:dp dl23or a)-y.x 4tt++ adr0yyction of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertic */4b7z zfapxjq39prvally with a speed of 5.20 m/s. At a height of 125 m above the Ea 3x4b97zzq*vp rja/ fprth, 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 equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the distance trav6b)6)6xfdra cvqs -ieeled during each successive second increases in the ratio of successive odd i-ecr6)xa)i6q s6d f vbntegers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, sh7a+wye5 w:ckg ow (algebraically) that a ball thrown verticalc5ag: +wywe k7ly upward 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 upwar 8, x0ztsmsz/fd 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 of the apple in2xeg bsy k./zx.pwq)( Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not b)s.pw/zyg.x x 2kq(ethe unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.2877plue(ompj , s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the w7(,uplem7jp o indow did the stone fall?    m

  A rock is dropped from a sea cliff, andf ,z( dubo 4hszebbtgj9 9/l;4 the sound of it striking the ocean is heard 3.2 s later. If the speed o /4jfzbtze;4h(od lbb , sgu99f sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your gardel a26seydmj* nr64;ehn hose nozzle 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 2dns 6yh*e4ar;6mlje, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/s from the edgezl)9ms ik n:bg tfqq4kb(j:d45*okg. of a cliff 70.0 m highstl5bb)9i.qqk 4 z*kkog(d: 4ngmjf: (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 wi29.5vdm wn: equpry*endow 28 m above the street with a verti dm 5v9:qewupn2 .ery*cal speed of 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocityl 1vo1q6/49oyblkzy a of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if 4o1lb16ql 9yy av ok/zany, 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 td;.9fb :v 0x(p 0b)kugpktob+skc n 5iime is plotted in Fig. 2–28. What itdgvokcbk5np bk.f 9u 0:i s+ b;(xp)0s 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 approxima(isj(dhhz a9 -1 dno)lcn*rg0tely as shown in the velocity–time graph of Fig. 2–35. (Thsn)-zohl(gd r0a9h *1j cidn( e 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 acceqi f 0 hzrq :viuwq3orr+(.c eu6l6+t3leration of the car in the previous Problem (Fig. 2–35) whe+z .reufotv:iuq ic3h 6q+ rwql63r( 0n 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 objec:. j 2v,xm*pn 2u(dscxqze a o09j,lqst traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a function of)(js mhvcu,a4 time is g)(u,aj c4svmhiven by Fig. 2–28.

Figure 2–36 is a position vert5 nn;e+ti *assus time graph 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 posi5;tntse * ni+ative 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 time interval from C to D.

  A person jumps from a fourth-story window 1 momkm4vwqkq*d3xja* 75 ;)q r5.0 m above a firefighter’s safety net. owq; )jq* mx7r5qm4md k3vk*aThe 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 tnq -w7o8pr/kv o gravity on the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upward on the M k v7rw-8/onqpoon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by e,blt0h-in+irk5g 8 qan over-the-shoulder seat belt has a gooe t-l0qib5 +ik rn,8hgd chance 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 abuwfck4x;xqar) t+. +vove 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 cw+4t+a;xrx f. ku)vq truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end colliukq;1qfl vz,ba q;+tc r7,t3wsions by hauling them up on a crane and dropping them from a certain heighvkz,w7lbctu;q tfq3 ;,1+rq at.
(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)ak91zxvzcxfa.gy;; kd6 r3h 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 f2jme9;2*2nvwbiklgacou:/yqcx)j/ n /l -qe rom rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the tram;/2 g ayeixnj:nlcc v kel q*)o/22j/q9u-wbin started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a d2p -9imszid4zttrm*ems ii78s 6a ,d.iving board 4.0 m above 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 of the person while un*d29 mz7i4i.i6,sms t peas-t di8rzmder the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessyn95vv k3kb/ag oh+ i8ary to balance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate3bi 5 9y+ /hko8gvnakv 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 for fish. Supmc o hrl.p0 srd5-1yj(pose 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 heigh5s -dy lpr (.h1rcjo0mt must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which .la i2j /xjr.aa golfer strikes 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 fr.2 ja/irx.ajl om 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 travel3pa 2d7v5camtkcg g ,7ing at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accele t25 ,d3c7ca7ggk vapmrates 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 stone is t2kuqv v/w7h)xc8 p6edropped 1.50 s lath 72/wqtku8v )epvcx6er. How 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 2lfr-advmg; kd n++q1qx8) mq3 00.0 km/h over the course of a time trial lasting ten laps. )mx3+8gqlkvm;rq 1nd- ad+f qIf the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at 18 kmpu.*h )6eoym2 cbk)d:lmr hs 5/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average ae .:rsmpl2yok)dh )*b 6hcum5 cceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The f)txps3mnx/6 d o lba.8irst child can bounce up one-and-a-half times higher than tp n3btl/ao)8s6xd .m xhe second child. The initial speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1.10-km-long tzx2 0* vyivmg, ad8d x f*v:w1ivev03vrain 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 d w,avv0e 3 xf20vvzx*y m:vvg i1d*8iare 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 n3e1mz; pzd/u3qhs h; 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 z ;;1d phz/nuhs3 e3mqthe average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, wit,ij ad5 )9a7uhjxxl iamx+) 3sa18a foh an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection has a traff53mghc m v3ijg+vjt nx - iv*1*9hqmf7ic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10gi1fj3 mv mt cvi5+3g nxvq*h *-m9jh7 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 speeps:+qw m wpo-fxi3:5hmk. b6jder traveling at a constant 120 km/h takes off in hot pursuit. The polhf3mk-. :bo6piw +qx s 5wm:pjice 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 (qy oh w k,hg4txp1i2*a building; 2.00 s after that, a second stone is thrown straight down wt (qw*h, yhpi1g k2o4xith an initial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The f 0pyh31brt9*e-jqv lsirst stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocityythl-jp ve*q0 13rbs9 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-fafmmm kd4z f no48:k8s5lling parachutist to fall from a plane at 3200 m to an altitude of 3od5 4s m4f8fkn:m8 kmz50 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 beltp; r lb4sw*ba d.g/ci0de-u*t to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spac4d/t*;c0i- spaud*br gwel. bed 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball verticb ucx 93ts)n8ually at a speed 1.5 times faster than Joe can. How many times higher will Bill’s ball go ) 9s n8uc3tubxthan Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your frieh6gbg.icy98qd bi (o ,7owa5*h6xnc ,h6 hojnnd 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 the speed with which yo6i xb,,9yo7g5h6q*hdcb8o in.chhgn(ja6ow ur friend threw the ball?    m/s

  Two students are asked to find the height of a particularke):pord,s -v,g ed:z: hcfvlag ,7e , building using a barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop ik,-: cde)f:os:, ev,d,a rgl7 gpveh zt 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) Is 81/),m m:ykc8 yzt nqbn;z hfg8: wcsethere any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) Ayzns: bw8gh ,1:qcm8 e/mk t;8)cynzft 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?