Does a car speedometer measure spee zleh2(1e6l3fjp :ne* x)jmzxd, velocity, or both?

Can an object have a varying speed if ithx2 go ybyti3 f0p:+7ls velocity is constant? If yes, give examplegby7+3 2 yh opi:0txfls.

When an object moves with constant velocity, does its average vel;i: t6dfels5 hhd. ru7ocity during any time interval differ from its inst.h hs:d 65;d7ue ftrilantaneous velocity at any instant?

In drag racing, is ite 4+wbitkb44a possible for the car with the greatest speed crossing the finish line to lose the race?wia 44b4ekt +b Explain.

If one object has a greater speed than a second objec k.llfb9vi8 w suwi-n;e5 m*z+t, does the first necessarily have a greater acceleration? Explain, using ew wi+lev9bk u8-i l5 ;.mfszn*xamples.

Compare the acceleration of a motorcx+vmme: uu2h)ycle that accelerates from 80km/h to 90km/h with the hvmmue2: x)+uacceleration of a bicycle that accelerates from rest to 10km/h in the same time.

Can an object have a northward velocity and ae2s ,g76dcayj-yq f1m 0fgz8j southward acceleration? Explain.

Can the velocity of an object be negative when tvkhf.w xb o7fo(-j26 jd3kn+its acceleration is positive? What about vice vern7bk(6dof xt w3fo+.hvj2 -j ksa?

Give an example where both the velocity and acceleration are nega n 4imeuuz,p/po;- ua.tive.

Two cars emerge side by side from a tunnel. Car A is traveling with a spedjtchm4m/+ wt5b8inh7 9a3p nj;zu 1bed of 60km/h and has an acceleration of 40km/h/min . Catjz8tn1wm uhnc/b459m+pb;ih7a3 jd r B has a speed of 40 km/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 ac)x6 b )m2zfrm)kpi+ml-p sx) gceleration decreases? If so, give an example. If not, e-z )fxsbgkmr)x+ )mm p2ip)l6xplain.

A baseball player hits a foul ball straight up6jles0r) s, mc into the air. It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be tr0crem6s,j l)saveling when the catcher catches it?

As a freely falling object speeds up, what is happenia;suig6 r pd(+z.d6rr ng to its acceleration due to gravity — does it increase, decrease, or strd66z dsr+ragi p (u.;ay the same?

How would you estimate the maximum height you could throw a ball , psnbl(3cwj-jns dt *gt3mn40eg4vbh3:i5k vertically upward? How would you estimate thl*np nbk3n jt 54d:g ejsc, mgtb 3hs(w-30v4ie maximum speed you could give it?

You travel from point A tppg mkrskg-1*9g : .yho point B in a car moving at a constant speed of Then you travel the same distance from point9yrk .pk :pgggm* -sh1 B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical crqg.sr5 x4j8string with ten bolts tied to it at equal intervals is dropp .cq5sxrg j48red 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 gqbikzc0 4)k9 at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fzq)k9ic0bk g4 ifth floor making stops along the way, a dish resting on a table?

An object that is thrown vertically upward will return to itsq w8c*kgcs0s1 7h hs 7ao5th9c 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 accel9tghsoc07ask 751*c8 h shc wqeration due to air resistance is always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero accelerahsn,iru jkqev u3a yo i hp 227)a/i5z68p.c2ution at the same time? Give examples..iq /iy )o6s 2nkuveizr2,ahc 8aph5u72 u3 jp

Can an object have zero acceleration and nonzero jzx21ve x 0;nlvelocity at the same time? Give xj v0ezx2l n;1examples.

Describe in words the motion plotted in Fig. 2–28 in terms of v, apl z4wf qh(ll sh(8w6t 3w7wv2, etc. [Hint: First try to duplicate the motion hq( l2p(ws48z hfltl76wvww 3plotted by walking or moving your hand.]

Describe in words the motion of the object graphed in cl:l)67-znp hcgags,Fig. 2–29.

  What must be your carg-uix*l/ n0 ay’s average speed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How lonw10kbdh3 zua 7g does it take to fly 15 km?    h

  If you are driving alo1p) g 74ubynnf.sm /(wbmch 4rng a straight road and you look to the side for 2.0 s, how far do youubh.4 /sn74( rgmc nyb 1)wfmp travel during this inattentive period?    m

  Convert 35 mi/h to *s;y;1 dxpbnwcug:u7
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves,ay4 ,l-e9 truff 6qcb from $x_1$ = 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 begj*6 b-a w ln6c0kz ab:ujci,7pins to rain an 7cjwlab*pi , :u 6kazcj0-6bnd 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 seconds between a lightning flash ;geodhooamglgm/3c f-gt 6)fg 0f508 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 sound in m/s from this r) f 05;-tg3o/fl 0 da6mf g8gcohegmogule.    m/s

  A person jogs eight complete laps around a quarter-mile tracm 7j;d 5expc5jk in a total time of 12.5 min. md7 ;5x jcjep5Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer in a str/07if-tlj wi raight line, moving 116 m away in 14.0 s. It thenw-iiljf t0r /7 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 approaj6fhz;x:*ysulpo z,o1g- : shch each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially zyo h:lup6xog fsz1;j- ,sh* :8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/t vv8 1n,(mefvh is 110 m behind a truck traveling How long will it take the car ttvv 8fve ,mn(1o reach the truck?    s

  An airplane travels 3100 km at a speed of 79p7+ s3u iyvp;n0 km/h , and then encounters a tailwind that boosts;7u+3i yp vnps 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 complete round-trip i *qq:jcc /6gghs wjf+ ;8il1 bh;i5tagn which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunc;6gltgwh+ba 8 :gqcjq/; 5ih ci*js1f h break, and the return 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with con4a 9lm8*,uppd6 ftuqqstant speed hits the pins at the end of a bowling lane 16.5 m long. The bowler hears thd* ufq8l,q pu am69p4te sound of the 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 95 km/h in 6.2 s. What /is,2ufs (esz is its average acceleration i /eu,s(issfz 2n $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35x;,* pc2o tur;hrtnt+ s. What is her acceleration;*+h;o2,pn x uttrctr
(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 acceleratio0z dtdmkv, 71an of about0ad 7mvkd,z1 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 constant speed travels 110 m in m(x/;)tde 6 ssm acjl /7dn40lylj9wa5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceymw /l0xsdjd ;cta lj )ls7(64n9/maeleration 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 najiw2m0av )j)ze7f8k vg6*t 5;rvls car, which starts 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 functio a6m ae2jg*8s)jwz7vr l)5ft v0kni;vn 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. What was itd0nlhmc6t5r x 9ubb, 6s acceleration? How far did it travel in this time? 6,dbh u5 9x0ntlmrb6cAssume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/n m/gk*x sxah8sa0 r +d3b)vo,s to rest in a distance of 85 m. What was its acceleration, assumed constado /m xxavr0a), 8s+ *bg3hsnknt?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. 2hc*zvk9o5 thHow long a runway is needed if the*t9kvh hc 52oz (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of the blocks to essentially top spez plyij*r/ 5g3,punu vpea/ vl63a(;wed (of about 11.yl,pr/vgla;/e3*5upnw6i uzvp a j3(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 reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniforml0iw ab :*mvnx-*tef+7 dg9 o2w0enllt y from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel iv9in0fdl-e 7atn 2l:g*m0 *ebotxw+wn that time?    m

  In coming to a stop, a car leaves skid mark98kknk9c8g c ws 92 m long on the highway. Assuming agc9 kcw8 k98nk deceleration 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 w1m+p.q :ex,kezxn 8k cs :fv*car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleration of the driver during the collisi vn 8.x, k+fqpkw zexs1 :m:*ec 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 distancexnve2-lv lmd df14qwe dm so44k-587ds for a car with an initial speed of 95 km/h and human reacti541sq2ek -4lmmn74wv8dd-vddl e fox on time of 1.0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the stopping distance of a cac3axk jm5veb )m 9zw;dpd+9+er is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on the highway. The car’s driver looks fovw+42-+z tm ae2f l+ 6jzkxfhdwh 26qzr an opportunity to pass, guessing that his car can accelerate at 1d- x am kwlz fjf 22w+z6zv+q+4h2eh6t.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 mi*n:96 vbnfqiqz7 *opfn. After exactly 27.0 min, there are still 1100**opzq6 :i 7nfnb vqf9 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 intersection justpkl*ed7wluh w o+:97 i:g.g dq 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 intersectio*o. p +ldl97q::d7ei gwguhkwn 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: gd)b cib yi*t(.rvp7 jy)c23qsiz.d of a cliff. It hits the ground below after 3.25 s. Hoi. 3yii7 q2 )(zcb :b) gjv*ddy.trpcsw high is the cliff?    m

  If a car rolls gently ( am3dx cr)3fkn wnkg- j1;30nz$v_0\,=\,0$) 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 straio x5b /wtdtq )5rt)uf)ght up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after throwi f oihnydj44bhrf+),uj0ik (5ng it vertically upward. With what speed did he throw it, and ndr )h(+5kfjfb o 4u0i,4jhiywhat height did it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls under the influence of gravity. Dxjnrfn h6wo.8 w/)6olraw graphs of (a) its speed l8/h r6nfo)xo.w jn6w and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed of 5.202y 3*5gs btlsi m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much ttyl 3*2bi5sgs ime 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 t9ir4q 68 wpvarm,k5 fle- mk*ihe distance traveled during each successive second increases in the ratio of successiv kfp5i*v 9lrm,4qa k6 we8r-mie odd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglectedrp**at8 7tq5p5kw ogh , show (algebraically) that a ball thrown verticallqp5*twhk85r7t *poag y 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 upward with a speed of 18.0 m/s o0a )t38 lb(hsblqd )x
(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 ae :)u7t,i3wju) ei.tt7uiypi9p h9x dpple in Fig. 2–18 (or number of phi7,ui9u:tei)x7p y et 3 w9)tp u.idjhotoflashes per second). 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 takes 0.28 s to travel past a window 2.2 mvfis2 bj 8m:v 230poow tall (Fig. 2–32). From what height above the top of the window did the stone fall?8o0mb3 p:w2j2 vo svif    m

  A rock is dropped from a sea cliff, and the sound of it st7p2q-nmw mh7 xl i5qd8riking the ocean is heard 3.2 s later. If the speed of sound is 340 m/s , mpwx25d -87m7 qnhi qlhow high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard streamy us97usaz-5j vg q/a9 of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water st z7u/9u9gq asy ja-5svriking 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 upwcbrmck5d a ou8ol)r, n,,.; xward with a speed of 12.0 m/s from the edge of a clir;,lu d, 8ko,bo xcrnc)w. ma5ff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward b45ccgdze3lxn,(5- o do+i r3 rjuomp4y a window 28 m above the street with a vertical speed of 13 m/s Ij5 ld5pm ei+drgzo3no oc-(, u44rx3cf 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.t-suawem; z4tnv6 o7)-y dei* (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocit--4 zy u);a7vwds nt eo*em6tiy 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 3,-p2 2ij qqiy btim1,fro y,+riz ,lrfunction of time is plotted in Fig. 2–28. What is its 2r 2 ti,i+ir1q-rmqly,i3yz , pbfj,oinstantaneous 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 n4fu0b sr,h1x the velocitu s nx4r01,fbhy–time 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 acceleration o/ 40)rvfh l58oywspahf the car in the previous Problem (Fig. 2–35) when it is 8 a/)hpl0o fv5 r4whysin
(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 trave .z+a(b 5 9axyminv3zpled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacemenu5.i8 a 0luwsi trzy68t as a function of trl ywu6 az08i5us. t8iime is given by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an object along 7ry1 yot(jbj.;+eqfbthe x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positivo tfyrq+ e1;b(bj7.y je or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter’s vw2wtkh x-;4h2 xdru; safety net. The survivor stretches the net 1.0 m4u ;;-kth 2w2h xdxvrw 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 on1rjydl5cz) -5)b xi7owujk;h the Moon is about one-sixth what it is on Earth. If an object is thrown vertically upw7zwk-j r b1x 5; )luoi)cdhyj5ard 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 constrrq .pkbgoj s:d189 r6 *ku/idlained by an over-the-shoulder seat belt has a good chan9s rq1d .8g 6lip/o bkru*j:kdce of surviving a car collision if the deceleration does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road be lw47uaaea e,:low, and his pursuers are getting too close for comfort. He spots a flatbed true7 4:aawal ,euck 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 truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacwiz m57l,uf-f lou m/r*)4tikturer tested its cars for front-end collisions by hauling them up zuf,7li5k woum tl/i)m*f r-4 on a crane and dropping them from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels a k/ c3nlcqf1/ ,lhef,mbout $10^9\,km$ 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 nvns7fkf(u l ,99tdr4from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m fn,vf74 dkts 9ur (nl9from where the front of the train 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 diving board 4.0 m above the water’s surface into a de sbdklt( 9ym6 fjn9pu; 5gl60fep pool. The person’s downward motion stops 2.0 m below the surface of the9lgbkpns(uf9 j t5 ;ydm 06f6l 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 trans qmcm 18r-p/wdit system, it is 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 mm/cdwpr-q 18 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 z9o.u; ;ng dt*(jij0 ufna jr;wings and free fall straight down when diving for fish. Suppose a pel9; uj it(ujnjf rdz*.oa0gn ;;ican 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 escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikeqvec+8 kae43wy 48ls ws a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult than from a downhill lie. To see why, aq ke wyw8e+c44al v83sssume 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 t(7noaz w8h 4vvoc-a8.h*f vw a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and aco-*(4tz w8 8voha vf7 awv.hnccelerates 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 7c(+w;hhwb ree. x /cehigh building. A second stone is dropped 1.50 s later. How far apart are the stones when ;.he(r we7b+/ch xe wcthe second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a time trc9v0 zk b4s,ck-3)homi v0()qdqu f sfial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last la cvq3oks4f0(kdf,q m)u) 0 v9ciz hs-bp?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves at l7;ba 8(3+m8at;yfsqifu uos 18 km/h . At the bottom, 4.0 km farther, his speed is 75 km/h . What was his avera8ful8f3a;+qisu o tb ma ;sy7(ge acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing k gvlyw (5 alrpkl9v,+:a2ws1 s1cqp1on two trampolines. The first child can bounce up one-and-a-half times higher than the second child. The initial wq92rl,plvk sagy(k:+w1 5 s acp11 lvspeed 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 travec 193o/,kkzcnqbjx 23 yzir7j 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 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 =,7 1jz2knr3ozxcqc93iykb/ j    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 throchsz ; 7rp(mj3ws a baseball with a speed of 44 m/s In throwing the baseball, thezmcrpj (3h7 s; pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises vertically, fr y--dwtx1 1ovpom rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each ia muc3ye* 3.kzntersection 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 intersection3uaz.me3 kcy*, 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, passedsm6w6 s hw -wwzq.z3/p by a speeder traveling at a constant 120 km/h takes off in hot pursuit. The police officer catches uphp q6wzmw-6wwz./s 3 s 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 fro 8xt m;mfde-/cbp6/ifm the roof of a building; 2.00 s after that, a second stone is thrown straight dowmx;pc tdb/ef/ 6fm8-in 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 samzywi,)7nep ( d)64pt )xe vxgze 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 stone be thrown frw)(4,tzix6y 7)nedepvx zp )gom 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 63jrbcqm445w 0o zw ulit take a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where sho56jm rbzu4 qw4l03cwe will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt:( d mrt8sav6onb1 3od 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 spaced 15 cm apart, what is the rate of burger production (in burgers 8vd bmnro:(3tds6o 1a/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a spera+ iv -tlh)2ods/a9 ped 1.5 times faster than Joe can. How many a-dri p+a2 hl)ovts/9times higher will Bill’s ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top o 1/qhro4 ga;f eh)f4zpf a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Yoq; efha14 )gfo4hprz/ur friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular buil38 y/ ntygth:gding 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 yt 3h:tg/ygn8 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 pbt:xj:,;ugocmqs-m sm b . 18uosition vs. time graph for two bicycles, A and B. (a) Is there any u:jm bmso;: b- .qcum8s1x,g tinstant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?