Does a car speedometer mea( zd4al vuak((;kln1 xsure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? Ifc*27umacsk1*drg0b( xxu: x i yes, give examples.(xx rd1cgiucsambk**u0 72 x:

When an object moves with constant velocity, does its average velo6ag- a( bk4ifygf*l 0,bp)emhcity during any time interval differ from its instantaneous velocityp-b)g(y a 0aik bl4ffhm,e 6g* at any instant?

In drag racing, is it possible for the car with the greatest speedhpct bq,w8u;5s 3-agaio jis,j7 hy ;: crossing the finish line to lose the race? Explain;y8csuaqi7;-: hoj5tb j ah,wisg 3,p .

If one object has a greater speed thanwz+ hb(w:kh;wawhu oz1gr +;: a second object, does the first necessarily have a greater acceleration? Explain, usir+1z;z;wh a+o:w( hb:hgw wkung examples.

Compare the acceleration of a motorcycle that accug(.we0bjdtt l k w42,elerates from 80km/h to 90km/h with jtg(l 2,bd u.wk0etw4the acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and a southward acceler n(uqp3,bpvs:ms + 1wqation? Explain.

Can the velocity of an object be negative when its acceleration is posit)xaaszk (d km9v-ioet57dxnh 0j:e12ive? What about vice ve-2j1o ev (dshez) mn5ik9ax :xk70a tdrsa?

Give an example where botz:nabnu:1pko (jov:g7j) i4 s h the velocity and acceleration are negative.

Two cars emerge side by side from a tunnel; +8j:gejf otvujq6npq vc996. 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 kj; fn9p 6jqj qe96tvgoc+:v8um/h and has 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 decrzlfy56i192 1sgl olereases? If so, give an example. If not, r29g loi5y z e1s16llfexplain.

A baseball player hits a foul bt9.x sso 3fe0 **ktiwnall straight up into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will .* xsi0t3tk9neo fs*w the ball be traveling when the catcher catches it?

As a freely falling object s9x1m x;y :zdxspeeds up, what is happening to its acceleration due to gravity — does it increase, decrease, or stay the ssxzm1;y:d x x9ame?

How would you estimate the maximum height you jsosti/2i a-l h* *guj r((n2fcould throw a ball vertically upward? How would you est (ss2rf2i/n(lu -i *aoghj*jt imate the maximum speed you could give it?

You travel from poin5wy3d;apdnq6-bj i* pt A to 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 ;d-6 *w dpiq3jp5anbyaverage 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 bolts tied to yt1. s8wjv( ipd7 1pqhit 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 beq(1 s7y1 wth jdipvp8.tween 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 constantb cw1n2l4uc 8 r/,zfx fa/gdl; acceleration: a rock falling from a cliff, an elevato/;a 4nud c,w/8bzxlrl1fg2cfr 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 r n(vv*tx; o.reg1 cy5leturn to its original position with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, wil (trlyxecvg. vo*n ;51l 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,o l9n 4wwzvy,rlp 61hp5 (oqw and nonzero acceleration at the same time? Give ex9o wl, 1 4,zpow( 5nlphrqy6wvamples.

Can an object have zero acceleration abbv8bn,:bxqt8*km w/gqvg uu 02y8 f/nd nonzero velocity at the same time? Give 28b u/ /mtbb8fq yg8v:b *w,qxg0 nukvexamples.

Describe in words the motion ug4 vizb u)w9btl6( *iplotted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted by walking or mozi(u6bv9l4iwt*)b guving your hand.]

Describe in words the motion of the object graphed in Fig. 2–29hf/d6i5dw) 9 wn2)a*sxmvwh d.

  What must be your car’s average spee vdyiy4f7nldropq-+m (e c4*5d in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h Hzkpam89vn.i /ow long does it take to fly 15 km?    h

  If you are driving along a straight road andtyz3 m+cn j hd:h4hd99 you look to the side for 2.0 s, how far do you travel during thisy9t 3n :h9hh4dd+mc jz inattentive period?    m

  Convert 35 mi/h to sn ;7xhatjg9 tpy.8h ,
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves froakz-1 6sbm;xw m $x_1$ = 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 steadibzcr -9s+t+j lrpb s ()ha7iv.ly at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after driving 3 hours and 20 minute lh+(zrij7prt bsv9.ca+b) -ss.
(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 seca/:1yepomg(k3x v: b wonds between a lightning flash and the following vm xp( aob:3e:1k/y gwthunder 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 arounr+wb f3 fdako(.yl8xg qy y, 09xw(:atd a quarter-mile track in a total time of 12.5qxargy8a ywf b(+f 03w(y9dko:t,lx. min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight l-t9 dhhy j13suine, moving 116 m away in 14.0 s. It thed93uj1 hy ths-n turns abruptly 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 parall61*wyk rmkv dls:p0/y el 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 be before they reachwmk v6/d:rks1*ylyp 0 each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 1 jupvs3hthj a5901 gnmm6k6u+10 m behind a truck traveling How long will it take the car to reach tmu3husk1j g0hv659a+j6mp t nhe truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , anfsx f.kqzm k/78e*x w6d then encounters a tailwind that boosts itsx.6w*mzs7 k/ ffexk q8 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 comple +qm zrj/z* m) ) fyho.anhfv6sjja405te 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 250r+zja6a oqv)5nm)j/f .40* h msfz yjh km is covered at 55 km/h.    km/h

  A bowling ball travel )+w;)6rs igvqtyov0lt-l/w hing with constant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of thevy)tl t)qs grovw-+/0;iwhl6 ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 9;z)-1 0t tgy*jaggy -za )puzyjvp1;r 5 km/h in 6.2 s. What is its average accea;u1v;-gtay1*yrg )ygtj 0zjp) -p zzleration in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is paq 0(r9eat:m her acceleration q( 0rtaam:pe9
(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 accel;eo zis-/ rmy-iv k9 p(m1p8mleration of about m1m/; - yvi-(mlei9k z r8ppso$1.6 m/s^2$ 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 5.5digp0jn k0v6i2 si4l0 s. If it then brakes 5 kvgj6s iid0n 4pl0i2and 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 xm0)-eoiwwt*7ou*zugu7v p6. 0ber hstarts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a functo i b*gr wpv-77w).0 z0euoehu*m t6xuion of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. Wdzdhges4yyg)k:a,p 8t3j+ c :l9c;xa hat was its acceleration? How far did it travel in thydjyal:3 ch ztg:8pgesdx4c; ,)+9 a kis time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. What was itsvp p2s;)g(,pgy5zmw d acceleration, )pvd(2wgpy ,pz ms; g5assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeofs d7vv(.jm0:+ ee zabuf. How long a runway is needed if the (constant) acceleration isubzsej:m 7 +d0vae(.v $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essen .wmao+cs(; lntially top speed (of about 11.5 m/s) in the first 15.0 m ofln.o+ sc;awm( the race. What is the average acceleration of this sprinter, and how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How;ag9 0 r go:0s)gov9eswqi6m xwo21nx far did it travego1is:g9xn2a0oxo;0ww ve6sr g9 m)ql in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Ass;a qwf)92vx-tlt l ,djuming a deceltl t 2-d qvwf)xa9j,l;eration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h s591ugr*c)(xuwd *f thnt hzo8 trikes a tree. The 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 collisi 1tu*zuhrdo wc)9f (x5t*g 8hn 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 initil-6rf o o)p;wil0-sajal speed of 95 km/h and human reaction time of 1. ;--wioj 6af)0ollsrp0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a car is w,bz xaevwxe.:qlj/ +(y6j w4 $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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 onean,nln qy3m/o ( c0l8yt3ro ) the highway. The car’s driver looks for an opportunity to passyaqec0l 3ro, y)mnnn/ (o3 t8l, 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 comx jr2lgp(rcw4:l c-. ,mnz4eu plete the 10,000-m run in less than 30.0 min. After exactly 27.0 min, there are still.ucc-g4, pmr4z2 nlewxjl :(r 1100 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 car at 45 km/h approaches an intersec26 m le+ x:2,zanyx bbuytrs+z+jv(*wtion 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. 2v: xbwy6m2j lxz,yrzsut n*++ (2b+ea–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from th3ec,cx bs rb99e top of a cliff. It hits the ground below after 3.25 s. How high is the cliff,r39 ecbsxb9 c?    m

  If a car rolls gently 4x)m my /u1d1xttn:ma ($v_0\,=\,0$) 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 ow r,rpeuw:v)qlggy zf)9c016f 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ballz+quij*u 3n2w vc( ft; 3.0 s after throwing it vertically upward. With what speed did he throw i*cw juq3nit; +v2u( zft, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Drr vjo+;tewb)a* 07rk gaw graphs of (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.b7*e;)+w jov ta gr0rk

A helicopter is ascending vd uo..c:szht.g; oq8p ertically 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 timedqt.8oo :ucp;z.sgh . 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 /z9mka)9 lz w81jwgnxadwx2/ rest, show that the distance traveled during each successive second incrz a axd zw1/8jx w9/n9k2)mwlgeases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, shq9jaq 3gn zo/6r0wgr(ow (algebraically) that a ball thrown vertically upward with a spee ronz r gqga039/(6wjqd $v_0$ 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 *pyc8 7isyd2m18.0 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 in Fig. 2–2vel5z4 7 wm0n:efo klyw* 1hs18 (or number of photoflashes per sn7eez5holv*ywk : 4fl20 w1msecond). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takesu 0bp3f2uc ,iq 0.28 s to travel past a window 2.2 m tall (Fig. 2–32). From what height above the top of the window did the stone fq0, p ubufci23all?    m

  A rock is dropped from a sea c(oz-lw.8p vpw z, 0frxliff, and the sound of it striking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s ,fr wvl (ozp -,xp.z08w how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard k- m0. gykif, op xz5zhb8);kastream of water. You point the nozzle vertically upward at a height of 10xypf;a,i8zko.hgzkb-)m 5 k.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward wmo 0*,n jqy2sv5w, fodith a speed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2no,vjm, yw520*f dos q–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 vv w/ll:*n35kfg u -s:lg pie:window 28 m above the street with a verti- e :g* givw:5l ls3pf/k:nluvcal 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 velocity of a*tgp;:8: nofnux-t b t train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was th*: x u-tnpt8; fntogb:e 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 time is p,nud5l nb +pd y49+(bgo arrp+lotted in Fibr adu(5grplny+b pn4 ,9do+ +g. 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 acceleopsj n5( ibumu 95(o)xrate approximately as shown in the velocity–time grap( ui5pu5 js9on) obx(mh of Fig. 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 acceleratix,sr7/ m5q fx*qam23bopat /r on of the car in the previous Problem (Fig. 2–35) when it is inrr ,s/qao* xtqmxp/fb5 a3m27
(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 th+xn7+3 ::tyf7vc 3ih pmpmxwlyyq8t(e distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose d kkf d9/r+qv9t1v* e8e,kw moxisplacement as a function of time is given by Fig. 2 w9xtqo dv* m vek+89e1/,kfkr–28.

Figure 2–36 is a positq /s z nmgz09-afa, t8mzd04lxion versus time graph for the motion of an object along the x 8n mx/l4 za00d -,sf9gamqtzzaxis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 mlh tm2ha;5)k-nh:i k4f mht18zgmlg: above a firefighter’s safety net. The survihi mhh:k1g 4nlhtlmkg-)f582azt m; :vor 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 abo l2 5zv- z57 itbuyxpl*)veee;ut one-sixth what it is on Earth. If an object is thrown vertically upwarpxzeutvy- zl* v2);l 75eib5 ed 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-shoufe ;e.c+9gmfglder seat belt has a good chance of sur.mf fge c;eg+9viving 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 bripb-qp5(wmmh- c0 9iet0r788sz osn l k q,6zuhdge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the tru i89epc,l70uzh qwbskz8prnm t5s-- o6 qmh(0ck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions by hauli3f6 .ktbd4hfwu.9akj sr0; t tng them up on a crane and dropp3w. s.bthfu 0 trkdf9 jt6k4a;ing 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 tram cz;u:d4c,de vels 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 front of the trae./wajfq(-f dzfapv7a020 br in 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 i /aaf(d a -2.qrfbe zv0jwp70ft passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving board 4.0 m above the wam4y;q j )-e cal/i0 8cbpkrc;nter’s surface into a deep pool. The person’s downward motion stops 2.0 m below the surface of ty;ace4c/pj l-ir 8 m) cb0;nkqhe 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 system, it is necessary to balanc*v ow. z-/blv95e ryj; s0aijne the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average/e;s- o*bvz0 .vwrij a9 ln5yj 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 for fish. Supp5tc 2ncpge)lo:wb 7pgca96 2fose a pelican starts its dive from a height of 16.0 m anct2)op29wn ac6pb glg:7e fc5d cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is planned h3o 6xemp8w8c so that the ball will stop within some small distance of the cup, say, 1.0 m long ox pec6h w8om83r 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 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. (azn-nn*eaj:4+ 3,vbozr qql3g d p.ubd k4b on a freight train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him,+3k4-egd v ( 3*z4anbo.pz.ndrqjlqbuab,n: 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 buildingf/wwti,l3eu(f/ pk ww9y7l3x. A second stone is dropped 1.50 s later. How far apal9w3 (k3ywfuxwe7 ft,pwi/ /l rt 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/*wg 3 b9oo xysk+ .2p6ksbrlxp8zio* *h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained fp*x oy* k8 *kow .2zbbo+sr9sxil3p g6or the last lap?    km/h

  A bicyclist in the Tour de Fran(jw.w,b77 la27ggaznn+bgz fce crests a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his average acceleration (ijana bbwzggg,7+ w 2f(7.ln7zn $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first child can boun6m nfns8m:))l06 wu5 sz vzsb i4xqjl6ce up one-and-a-half times higher than the second child. The initial speed up of the n6xsn)s 56jsif4qzmmlw:zv08u )l6 b 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 travea.t+j7 ltx sdo1:eb k c+e1gm.ling 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 pas te7 1b +staemk.d1l:.c+jxgos 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 3hp qrwq. x9)nIn 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))x hqpqr.w39n. Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerati*h6f fqf. wer/on 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 F7 -5wg hf72,boltmh6*m pxcwg lam7v)ig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. Thl)c7a6hpvf*o2x 5l 7wm,bg7t- mhwmge 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 taky:ym hx((.cjfes off in hot pursuit. The police officer catches up to the speeder inj yfx((c:hmy. 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 sr9ore4etc cs qq(0ii1k+)p+g l ty mm7/r5kd 2econd stone is thrown straight down with an initial speed of 25.0 m/s and the two st g79m4)keiro q qyr10kd+r5 /tmstc+2l (eicpones 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 thmg43z)im3ub ae same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should the second s u mi3zb3ag4m)tone 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 pahe;ei7 jo*l9h*j5z gp rachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What woul*j5ehoe9h 7i zlg*j;pd 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 burgers through a gri,7w+s tb xpah2 4-goyalling machine 2ag y-whsoap+,4x t7b. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times faster than Joe c(bb e olihc ,xg(*j;r-an. How many times higxg ro b(be, (hc;lj-i*her will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on -dfp u10a266 r,c. zlf;reqio;oqwai 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, suchic0f , -aqai.;er6u lz21 pq wfoor6;d 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 *n/ y b*gai7mldawq0p3yel.i,34d stof a particular 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 it off, timing its fall. One student reports a fall time of 2.0 s, and the other maie0ia , b7.ld*g/3yw* ps3ydq4nl t, 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 fo8d -n wb(x,hkh(o jfi9r two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous nw8 ( ,kfih(hd-jox 9bvelocity? (e) Which bicycle has the higher average velocity?