Does a car speedometer mjel x*ojb1b* o77(meoeasure speed, velocity, or both?

Can an object have a varying speed if its veloccx+o s7-jmqp5(g 81m bo/ pepa-atc*oity is constant? If yes, give examp * j( qe pbms5po/cg78 1-o-ca+omptxales.

When an object moves with consup / x 907inryujpxtxw1rb3sm7*x0u0tant velocity, does its average velocity during any time interval differ from isr p9u xu*pxw7x1/i 0yu3xr njt 70b0mts instantaneous velocity at any instant?

In drag racing, is itu3wzbd: *,x sh3(pz0apyn4 jje2ay *l possible for the car with the greatest speed crossing the finish line to losa*wznya30uj3p ld ,xp(2bs*j ez 4:yhe the race? Explain.

If one object has a greater speed than a second object, does the first nechcuoajc :;riz(; :rg* essarily have a greater accelj cocg:ir:haz(u ;;*reration? Explain, using examples.

Compare the acceleration ens0 di3.p rtuvotpo )ja(hg vs 6,8*9of a motorcycle that accelerates from 80km/h to 90km/h with the acceleratio( a8h)sdp3tv o6e9pisj0o v ,.utg *rnn of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and ci.i rw.r-p1qg6- ijca southward acceleration? Explain.

Can the velocity of an object be negative when its acceleration is positiveyp/g(g ildj2y p 2u,j(? What about vice i djpuyy(jglg,( p22/ versa?

Give an example where both the velocity and+xw(ge 3dvibx:porethf ) sfv,703 .z acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling w k+i1orf ttg3,rf;cf1 ith 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 ,fir r 3k+gc;1tft1fo . Which car is passing the other as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in s *fjp* mk8y0mepeed as its acceleration decreases? If so, give an example. If not, e*mk8j ym0pe *fxplain.

A baseball player hits a foul ball straight up 2.7 m1dl kz.0bzv)v w jva:yfninto 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 catchervv7dk z nla2jw )0.yf.:z1bvm catches it?

As a freely falling object speeds up g)he nl z,(bsl:( +wyo3z0mx-a oimk5, what is happening to its acceleration due to xob(g iek0nm:y -aw35 hl(z) lsz +om,gravity — does it increase, decrease, or stay the same?

How would you estimate the maxim si7+m d2o0tzfum height you could throw a ball vertically upward? How would you estimate the maximum speed you c70sitd mf +z2oould give it?

You travel from point A to point B in a car moving at a constant spee;g 3:ox9g jvyt quu65cd of Then you travel the same distance from point B to another point C, moving at a c9g c gy:t v;5j3q6xuuoonstant 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 with ten bolts tied to0o h1of4a s2amdd/:df it at equal intervals is dropped from the ceiling of the lecture h 4ah dd:d/0s21aomffoall. 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 motr au0)m6f:j z2lo eib-ions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish resting onuj)io2a :berl f-m0z 6 a table?

An object that is thrown vertically upward will mo9 qipf3sa4yc3s;p1u/m 6usreturn to its original 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 resistance is always in a direction opposite to the motionufqi4 msc9s s3a3/;1uoymp6p.]

Can an object have ze nh+zchir1dz8g8m l,dj5 r)r6ro velocity and nonzero acceleration at the same time? Give 8 czz)l dh6gr1dj 58irhn rm,+examples.

Can an object have zero acceleration and nonzero velocity at the same ti,mmb p g p)):gr1gct3xme? Give example ): rgbg1gpm)mpc,3x ts.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, ekeleh 0b kpqak;1e.u -k 61m94ybo5 mctc. [Hint: First try to duplicate the motion plotted by walking or mo0buh6k ;1- b1 pkk54e9kayoe. qemc lmving your hand.]

Describe in words the motion of the object graphed in Fig./b/ :g o:guw0 cawf7pileok +2 2–29.

  What must be your car’s average spee(8kujl;gmcy9ui. ft : d in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How ig.f; i4p0 egxiau;m(long does it take to fly 15 km?    h

  If you are driving a avbg(kc p4q*2w,i+cc.khko:)dvp p +long a straight road and you look to the side for 2.0 s, how far do you travel during this inattentive period? b (o c:2d)wv4g+phk,vkp.*pi qkc a+c   m

  Convert 35 mi/h to u:b f(5bxtzr+n+,t, gyv pfv3
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves lls0mm uk;p8r)1f .c cgaxi 39from $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

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

  You are driving home from school steadily at 95 km/h for 130 km. It then b8 rjeh4:vraxp 9g: ,c9vh2cjiegins to rain and you slow to 65 km/h You arrive home 4ch,:9rh 9jx:re a8c2gv jvipafter driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightning fiwv 15 94xikn3+ ajktllash and the following thunder k 491x5a nvit+ijk3 wlgives 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 track in a totbe4444 jf nqjcal time of 12.5 min. Calcu4e qjnj44cb4f late
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a straight lio:vu,l5ex(: n5diwl x vkw:7rne, moving 116 m away in 14.0 s. It then turns abruptly and gallo(e:ordw v75x vx: ik:,ul wnl5ps 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 appr(io25acqhh6a d2 k 8rc7gzq d/oach each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initiallyi2z6q/ora87qckagh2d( 5c d h 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 (exx p 9;jc2eize h8o*h/(brub -9zga is 110 m behind a truck traveling How long will it take the ca b892e ozgp*c;(xeah/ 9i(hbjz-uxrer to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km w 9bb7+vm2m cvy:g,bt/h , and then encounters a tailwind that boosts its speed to 9 9b+7tb: vmw,2mcgvby90 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 complete round-trip 9 y8zdhdqz-0,gi nc i3in 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 covered at 55 3-ci zh0 d9qzni,gy d8km/h.    km/h

  A bowling ball traveling with constant speed hiv b/pch l5fo24 p7c.bnts the pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the bacp. o47 fv pnb5hlb/2cll 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 95 km/h in 6.2 s. What is its avcpl lxay3*e;k,pb 06pl3i2-fmt)uv xerage acceleration incu2 ,vy36-p )ml bi;f lxkpe*lx3tpa0 $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest tpz 1rzw-cq kwh2x -91vo 10.0 m/s in 1.35 s. What is her accelerationrphkz v12q1c- ww-zx 9
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a pardjnyv2* p zcmgoxwn,yjhv680zr(i+7-b9 b1 mticular automobile is capable of an acceleration of abou* ,n-6nj md0bgwh zjo+ybv 72c(8 i1vy9mzp xrt $1.6 m/s^2$ 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 r 64l*mdvev j5vzq9.lit then brakes and comes to a stop in 4.0 s,jmlv.v l*9e645qzv rd 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 = 0l6 y6jhb12ox e,6 rddj and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display eabj266 ydl,16dh xorj ech 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 accevf97s,ofa4vjxo - wd 6leration? How far did ofo,djsx a v64 9-fvw7it travel in this time? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distanceq62yln2a+ k ilvo uy2; of 85 m. What was its acceleration, au2vn26l 2kyo y a+liq;ssumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runway i9c)-4bw1 y1i9 gjgvhf rpg5hch if;0h s needed if the irc4jvhh )h9gwg10c y-f;gi9h b 51p f(constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to esv70u ; m3xlgocah0 u3fsowm 1-sentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to rea um0u l3x1;30sfhg- 7v oaomwcch that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from-wwsa loef* ax qs:/ y1eo:5)i a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in that time?ywea: se iaf-5sw/1x ):oo*lq    m

  In coming to a stop, a car b5. (n5zlkywz;: k9cmt;fhghleaves skid marks 92 m long on the highway. Assuming a decele;n :5fc zhy kk .l(zwm9gt;bh5ration of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of the c2b0 hf77ukep3 lkm, ipar compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the 73pb27hefmilu,0 kkp 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 idg.hvz ei j6/ov8 vk13xd2t4 zbj(e295 km/h and human reaction time 2v1ijd(j ek6t d3.zev o hgbi8zv24x/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 a car is5 unxb3 i x1ve+i)*lqe $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , 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(wxxaj cfe95 jc,h87h m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelej,jf( x w ahc5e7x8c9hrate 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 +8qwn.*ba8s9n t 1n6 mov acnyor0x*y run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. The w0yx+8rnon.*ntvq8n1mab9 * ya6os c 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+sgsr8(jgs.381k cva z yh 9tt 45 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is8s+ g tj .sh s9k(tcya1z83vgr $-5.8 m/s^2$ , 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 ground(y1sr x kqz,7bzg ig:9 below after 3.25 s. How high is the cl:kz7g9,bsx1rg izq( yiff?    m

  If a car rolls gentlykv2*r.qfjauz, z * rh1 ($v_0\,=\,0$) 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 aix f70 0d w4r 2hogfxobyff46t2r 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 after throwing it vertically upward. Wi1; vp iwa 06(ulum7jmpth what speed did he uuvm6p0 pjil1mw a (7;throw it, and what height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under th:vwn ehy /fur2wc i4uz(n-7(6 fvhb p9e influence of gravity. Draw graphs of (a) its speed and (b) the distance it has fallen, as a function of time fruu r yib (7ww /42cvnnehzf:(-h96fvpom t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.nw* zvjv(;4g7 2c oqrl20 m/s. At a height of 125 m above o7v;* (lqv2nw4jcrzg 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 equals the helicopter’s.] t =__ s

For an object falling 3jjl8 z0drx1h freely from rest, show that the distance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 an jj0h13 xzld8rd 2–21.

If air resistance is neglected, show (algebraically) that a ball pm; ue52tnfzf :am-+o thrown vertically upward with a speed 5-pmfznou:a;m+t2 ef$v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upwar vtb3o)d vsw0o(o27: 7hzgomm )3paazd 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 in Fig*7w,lk6iwb(r pxp x7s. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm iwkp6 p xlb7 w(r*7ix,sn diameter. [Hint: Use two apple positions, but not the unclear ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (0c1*x nor8u9xpbbyq egqi 2/x785fq :mg6be yFig. 2–32). From what heigg qix fe 8bxmg91uonb * 7x085q/ yrypqc2:b6eht above the top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, anp517v/5 l2 vhcwgu ehkd the sound of it striking the ocean is heard 3.2 s later. If the speed of sound kh5wph7e1v /c2 vulg5 is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of wvg ,sm s16vjc1j-x du0ater. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground next to you for another 2.0 s. What is the water speed asdm 1 ,v jx6s-vg1sc0ju it leaves the nozzle?    m/s

  A stone is thrown vertically upward with lq3t7mh1avy9f2gu6c8a 9-y w8ux kyaa speed of 12.0 m/s from the edge of a cliff 70.0 m high (Fig. 2–34). y 6 9-y9k3 88a27xul qc1g mwthfuvaya
(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 abov6y(jdhx3ft1 a gkw2.be the street with a vertical spee21f3b w dj(a.khgtx6yd 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 train as a function of time. (ag;rvppe3q +kv.)o 9 re) At what time was its velocity 9oqvevp;r . r3+g)ek pgreatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a functionq7c i ,d0; kmjtn h/kp(0hup1e of time is plottedc eu,1h i md /pn0hp;0kq(jtk7 in 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 shown in the veloci.pw*hb:)*qh chljnf 2ty–timqn*b h:f.j* phh 2wlc)e graph 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 acce/qn1 .hchmkq j(q2o5u bc*q9u leration of the car in the previous Problem (Fig. 2–35) when c(n2 5q/m1 9q*qhjuhoqukc.b it is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object trav1d;zs*8diy zw9 q1ojveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the ou:sg 0).mdfu lbject whose displacement as a function of time is given bdm:f.gu0)uls y Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object at:. 1ciqw0 yvflong 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 dfv c1y0:t. iwqown? (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 fourth0yq0 99fasdg y-story window 15.0 m above a firefighter’s safety net. The survivor stre0 s9yya 9qgfd0tches 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 one-sixth wp4g3nm po a)4-b9n3,zhub c 9guqt/mo hat it is on Earth. If an object is thrown vertically upward on the Moon, how many times highe/a b3mpto )uoqmgc 4b3u 9z94-nphg,nr 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 beltt- 41gs*0 idoigb6kd a has a good chance of surviving a car collision if the deceleration does not exc*6sa-dtk1gd 4g iibo0eed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and mp:.8ang ydomec .. f8his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he mdm 8pa .o:nf8cmgye ..easures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end collisions g 7+xo/q81zhaw,a qex by hauling them up on a cra7,ga/oq xzhqx +aw8e1ne and dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth tra:g)q .puhgj-(sn+ kukvels 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 frov 8dun/-kb4n0l i4 tnhm 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 train started. What will be the speed of the last car as it passes the worker?ibn ukhn/0l844 n-vdt (See Fig. 2–38.)    m/s

  A person jumps off a dik anid3chli m1tc0,wa;9;un-ving 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 decelermd;k;03ani acn -,hlc 9 i1uwtation 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+2mu yjv:9c as necessary 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, calculate the time it takes a train to make a 9.0-km tr 2c+a:m u9jvysip 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. S :eaxwk1/hapkrcwd;,34 l: eluppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to esca kh1epled:wakx;/r: ,4 w alc3pe? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ballzwyrk ::c:a,j is planned so that the ball wkrwj:z,a:y: c ill 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 constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train traveling at a co;iz qgs 4(bvcf bui1dy1o. fkqd .z6zh0g5 )p3nstant speed of 6.0 m/s Just as an empty box car passes him, the fugitive startb1p 0 hvi;zz u5)dqfqf4g g6o 3.dk s1zc(iyb.s 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 bf*w 0xr. ;qy s7xr;ugpuilding. A second stone is dropped 1.50 s later. How far apart are the stones when the second one har ;sr;*x ywpx.g fqu70s reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.01* 4 mw);jym*+ gyeyegjk m5ky km/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 for thw1y; mjkm 5gj+y4 e)m k*ye*yge last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves poi*qb;7lwp( mkx9 d9 at 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his a w9pbo9pmk* qd(l i7x;verage acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The first childjc va y/r-(rou-1 xcu: can bounce up one-and-a-half times higher than a/j :c(yvcu1o-x-rr u 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 overtakes a 1.10-km-long train traveliq pjc w1rjee84x(y6 8l 0gv ch.4pcy3(z bzzy6ng 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 t 3vy4ywcj1l8(rpe0z zyc 6he4zxb6p8gqj .c( o pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with a speed of 44 m/s In throwing the b)se 2igg fjkho* am +3t5pf(;ka4w zq:aseball, the pitcher+a ifgatokzwp) q(*4 mse5:f;3 2g kjh accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, wtw1 omu 5;1e bsvupcky8+;*b iith 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 v4u ptfzj.ybcu:o en j-2t:9)in Fig. 2–42. Each intersection has a traffic signal, and to n c:49yfzj)b-v2t .petuj:uhe speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a constant 12++iijb ejq1y-0 km/h takes off in hot pursuit. The police officer catches up to the speeb+ j1e+iqj-yi der 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 m3emt*nsx*ce81h;o,pv( 3 o2mmch sb s after that, a second stone is b,* pm8hmc voo; cehse3mt1nx*s3m(2thrown straight down with 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 first st;wur8od* fi3n4xun+f one is thrown with and+o ;finru*unw38 4x f 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 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-falk 8laut*m+)h37zj:c dl 5b a/ begzn7yling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance wilmhgduba 8tz 7kn z a*)7+lb3ej5:yl/cl restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conv*x 6 (art1eoieeyor belt to send the burgers through a grilling m1 o eeai*xr(6tachine. 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 h1;v- j qss5dfvertically at a speed 1.5 times faster than Joe can. How many times higher will Bif; hssqdj-5v1ll’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the grouno;pb ahnvxnj,r)5tcus y8d1p8 7;x7c d below you. You drop a ball from rest and see that uhrxxap) jbd;7,7tv;ncys881o n5c pit takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particularnx)go(ojt +mh *z i u8rhn77(u 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, timingh(uih7 87 xnmj gu*+z(rt)n oo 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. ( :mv5c8tr2e pxa) 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 velocity? (e) Which bicycle hpx:m5tv28r ce as the higher average velocity?