Does a car speedometer meako:r4on z 6wdr/y9 *nbq1cxb 2sure speed, velocity, or both?

Can an object have a varying speed if its velocity is constant? If yes, give exs)t7eg dxenv*;v8 o vx/6xy2-kf/bh kampl fv*vk7boeyx)h28 xgxnt/ v6e;/ks d-es.

When an object moves with cok7o548 :zm xsbp1g ,ya*mx4zn ux lqv0nstant velocity, does its average velocity during any time interval differ from its instantaneo50nam:ykxvo 81x,s4 ul4zqbpgx*7z mus velocity at any instant?

In drag racing, is it possible for .wnha. v ;t-kuthe car with the greatest speed crossing the finiun hvwa. -k.t;sh line to lose the race? Explain.

If one object has a greater speed than a second object, doe5sry: fe4csv9 s the first necessarily have a greater acceleration? Exp45s :cevyfrs9 lain, using examples.

Compare the acceleration of a motorcycle that accelerates from 80km/h to 90kmvro/1i1* oibh n+nv ,n/h with the acceleration of a bicycle that accelerates from rest to ,v/i o vhnr i*1+bo1nn10km/h in the same time.

Can an object have a northward velocity and a southwaropm3r8bm8 8twd acceleration? Explain.

Can the velocity of an object be negative when its acceleration is posi,uhf 2pj gqrpl1/h59 qtive? What about j ,p/ rphfqg5hu129lq vice versa?

Give an example where both the velocity and acceleration are nev 4x8 zqmeg7g,gative.

Two cars emerge side by side from a tunnel. Car A is traveling wi*sv.*7/oow7k n jslxnp cl2i 3th a speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the other as they come out of tnx / o*7 *j7ksv3lilons2.wpche tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration )zv19xp3sm)8i3;ieii6 imc n: uuorb decreases? If so, give an example. If notux iv:minis3ecb 3i9zoiup 8 )m)16;r, explain.

A baseball player hits a foul ball straight up into the air.ptosr.: 5e x;tgci1y 4 It leaves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be traveling whytt4c 1x5er .o;:gsipen the catcher catches it?

As a freely falling object speeds up, what is happening to its accelerah54swc1xjgg +h4b r)k lh)i0c tion due to gravity — d4l hc1 j +4g))w krhihg0csxb5oes it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball m xiwn q6r9plela+/7+vertically upward? How wol9i+l mpr6 w7eax+q/nuld you estimate the maximum speed you could give it?

You travel from point A to point B in a car moving at a k1 fyyhz8 rz,m19evrp ,4z,v ,cjwlt /constant speed of Then you travel the same distance from point B to another point C, moving at a cons1v 8zyvr,e kr9y1ctm p4zwh l fj,z,/,tant 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-longvl*)-1e mhycm vertical string with ten bolts tied to it cl)ev-1 hy mm*at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or 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 motc- q-zyq(t1(jry c l(bions is not at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops yr1l(cb jzq cq(-(-ty along the way, a dish resting on a table?

An object that is thrown vertically upward will rr lccpiblf;5x 1l -67zeturn 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 dire;1 lc l5fpcz -r7ibxl6ction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration at thewv7rnj wfe: b-g u8/u; same time? Give example 87wf;g/e -uvjwrb u:ns.

Can an object have zero acceleration and nonzero velocit(t(ygcj nw7i +y at the same time? Give examptg((7y wcjin+ les.

Describe in words the motion plotted in Fig. 2–28 in terms of v, a, etc. [hilr 2uf(dm0 97b7 kmgHint: First try to duplicate the motion plotted by walking or mf972i7m0rbud (k hglmoving your hand.]

Describe in words the motion of the object graphed in Fv2/mjuboxh o4tk q63gz.ju20 ig. 2–29.

  What must be your car’s average speed in orderc)zr 9 7q2 1)kmk5m+b uey;z tszgc c6b*qpyp1 to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it takyu5r x;ws-,sjdic 14 o.hp w+ye to fly 15 km?    h

  If you are driving along a straight road and youb ay vf/ z(vifgog2zf3 m:.uu.sx52. a look to the side for 2.0 s, how far do you tr.sb3afx gz.azf2.f: yvi( v/oum5g2u avel during this inattentive period?    m

  Convert 35 mi/h to ntfc t*d.07x 8)dlybc
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves frol8 -iejly, j:hm $x_1$ = 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 scho47pjz y+k :r.lf8mgm zk- einh9 j7c9uol steadily 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 minut9jp +z-:h 8iummfy rnlkzjeg47c.7 9kes.
(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 liudq+ 5ck.x(raghtning flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives i(qc5.u+rkd ax n 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 totg1u9(gfc a 1rusu;f)/c ye1e dal time of 12.5 min. Calculate g1;) ( eu ceg91r1afcdyfsu u/
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its traineb 8xl83p x3j3ahng+rzbw :px;r in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfw3 rw8jl3pb x8;:nhp3 +abxx gzay 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 ovrcvfmz mqx 0 /5h; :x06t;zlwther on parallel 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 reach each other? (See l;xv :t;xr0wzc0h/z fq65mmvFig. 2–30).    min

  A car traveling 88 km/h is 110 m 2f4a8m im hkx1behind a truck traveling How long will it take the car to reaci2km4mh 18axfh the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounters a tail;8 q,uip*p 7yc11o.n2fkq wjfcx bq2ewind that boosts its speed to 990 km/h for 2bw qxnp kc28uy o,jq .f;epfi1*cq71the 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 c+s c2k,hjvjh6u+mr8*7qlt f pomplete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the rsq8kl27vc *,jpmf++hu6jr h teturn 250 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits the pinsbdx ;va4k.r9x5qmze)d5 p r9y at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his m9d5.54brz yv);are xd 9qpxk 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 average acx66xw*tj41d9 )ate pxm o ffx4celer 4o1f6 mpxw)4t aj *xxd6efx9tation in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 1f+ vuug.vc):pc9 tk js:;r bb60.0 m/s in 1.35 s. What is her acceleration:c)tuf:.p bbgkj+6; vvu sr9c
(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 acceleration of aag94:bm brfuz.y(fn scr i4fvq:e282 boutb(es r92ifb: yfz8 4:v2 nuq.mcrag4f $1.6 m/s^2$ 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 constan(r*ot,d(d4e 7zrc arv gtyu+9 tj97 p/ji lh1tt speed travels 110 m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleration injlr(rd g * i(749/oj,t97t y dapet+t uhzvr1c $m/s^2$ ? 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, huv:sr8u,s yx*rg o9)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 function of time. Display each in a Table u o9, uy:sgr*s8) xvhrand on a graph.

  A car accelerates from 13 m/s to 25 m/s in 6.0 s. Wgmfrim2 2av1(oc5/3 z /alwbdhat was its acceleration? How far did it travel in this time? Assume constao23bv/5l dac2 fm m/zaiwg 1r(nt acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance 9ti4zvob )5rsb: 4zkj waw/9pyl/u3 hof 85 m. What was its acceleration, assumed const zl:at4r9s p/w4ki 5whvj/ub3o z9)ybant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How long a runway /d ag/mjcxqi zff0- ,(is needed if th, 0j( fimd/g/qzc -afxe (constant) acceleration is $3.0 m/s^2$ ?    m

  A world-class sprintec9wklsu nda ;c :kr7u +g0s2 78ug4dvkr can burst out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how77nku42skvud8rwg:c+a;gl s 9k cu0d long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down unifor p0y mi6if(yd2mly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel in tha2yid0i 6(py mft time?    m

  In coming to a stop, a canwoafl+/* *ic b83 dbar leaves skid marks 92 m long on the highway. Assuming a deceleration3b nbi+8 f**daalow/c 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 car compresses andbt:wqo hum5 le7i1wm :l yb(2; the driver comes to rest after traveling 0.80 m. What wasut:my:l2ow m ebb5iw 17l(h;q the average acceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial speed of 90b ig29( +sfrrq2 lrz nm*qoh15 km/h and human reaction time of 1.0 s, for an accelerat(s9h0r n2rqo qz1gb* i+2mlfrion
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for th dm-vlkw q)+g-sypoyr -c:v(4e stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck goi-)ux4 vl /qxrxv3g 7lkvd/ bz0ng 25 m/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his ca /gluk0xvvbzxlv/34r7dq)- xr can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000ke4.9br ktmk( d 3i6tw-m run in less than 30.0 min. After exactly 27.0 min, there are still 1100 m to go. Th3kidtk (k4 erw9 bt.m6e 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 aji :i48s8 jd8)y (ztkpmtxuj +a 2t)id-vis8pt 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 decelerationz8xit8ajpt4t v2-p+8km jiu ) yidsi js):8d( is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below aq*mx00j dlb.lqmph c:a)c08tfter 3.25 s. m :j0a0d8l0phb)xc*qt.ql mcHow high is the cliff?    m

  If a car rolls gentlyp mkh3 +k*l,zlzm6:kpimj /-m ($v_0\,=\,0$) 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 of 22 mqk:yku( mxk8 p)(nf8z/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3fd6a2 hi4+h vb.0 s after throwing it vertically upward. With what speed did he throw it, and what height did it rhh6vb+ dai 4f2each?    m/s (Round to the nearest integer)    m

An object starts frok,6gd 5sgs 2ysm rest and falls under the influence of gravity. Draw graphs 2ks6s yd s,gg5of (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.

A helicopter is ascending vertically with a speed of 5.20 m/s. At a h/rfh -53ox 7zffd u9ifeight of 125 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] tzoir79/ 3dh- fuffx 5f =__ s

For an object falling freely from rest, show that the distance travpd(13bds vf*w76 rz,iq b.sn6fp lax3eled during each successive second increases in the ratio of successive odd integers (1, 3, na(,dwl3s6p d p*xirbv 3fsfzb17.6q 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, sh; *jjs/ tg-elmb.z85wyel: qzk;.cow ow (algebraically) that a ball thrown vertically upward with a jz.o gq5t wc j*lys/mk.b:;8el; we-zspeed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vert95g0 i.9fklby eq)cl qically upward 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 photoflas7vl *pz.bxrr; h of the apple in Fig. 2–18 (or number of photoflashes per secz*xr;b7 lvr .pond). 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 wiu8vx-ccx)nxo;iy,9mb *vq d:ndow 2.2 m tall (Fig. 2–32). From what height above the top of the window did *-xxm b;uvn:idc o)8cx,qv 9 ythe stone fall?    m

  A rock is dropped from a sea cliff, and gph:i0 4t**v sramh.othe sound of it striking the ocean is heard 3.2 s later. If the spe.vm hah4tg ps0ri**o :ed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle forfv;kbo g2 vq;yb.af .9vii 0v- a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground nex-vybo 2. kiab90g;fqvfv ;v i.t to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed o1x,xprw: l6vm f 12.0 m/s from the edge of a clifr :xxwv,16pmlf 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 by a window 2tti)-o(ckgx 68 m above the street with a vertical speed of 13 m/s If the balltx )go6-c(ikt 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 of1lw4 iqmn ,mz+xpah o8j:3f*y time. (a) At what time was its velocity greatest? (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 acceleratiqw py i+x1f,n3m* omhjl:48a zon greatest?

  The position of a rabbit along a straight tunnel as a fun ,3)yqw *y1j,rc eiaj/g1mr tmction of time is plotted in Fig. wy qg y3mt,*m,)e1r1 /rjijc a2–28. 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 cah :p4bf4*wrt5 y rvel3n accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The :rw3btyer 44 vph f5l*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 of the car in ry* 830ovos6fr1 obgy the previous Problem (Fig. 2–35) when it is ior6gsvy 8o0 3yof*1rbn
(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 th3o, fxuod wj4.e distance the object traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose displacement as a de;ew2 -fasdz,8:: ,kqn9h vopc mx:gfunction of time is gix z,o8a: g,2wkmeedfdvs-; c pq:h :9nven by Fig. 2–28.

Figure 2–36 is a position versus time graph for the motion of an obje8lo /2wyg;x7yp v7kqu ct along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the posix8q7ygkvp wl; y7o /2utive 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 fourtyx)9i ae-8h1cb(rqb n h-story window 15.0 m above a firefighter’s safety net. The survivor stretchi(n8rq)a yx - h1bbec9es 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-sixtkxb/gip);t2b* :p iidh what it is on Earth. If an object is thrown vertically upward on the Moon, how many times higherd/g xk2i )pibb;*ip:t will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shog*g mfa9i5p y-ulder seat belt has a good chance of surviving a car collision i -*f gam5ipyg9f 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 below, and his purc f9po xf4iy, k4:;ey-0 flczisuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his gi o9pc,4i yzkx4:-lf e;c f0fyetaway. How many poles is it?    poles

  Suppose a car manufacturer tested n49ng sud5j.; emyan-i qq3x,its cars for front-end collisions by hauling them up on a crane and dropping them from a certain e4m5n;.,gqnn a9sq j-x y 3iduheight.
(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 travelgjy , 2dqiyc*6v4ks hmz37la3s 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 res dgc +whf0r0:jt. 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 thef0rgd w: j0ch+ 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 deep p f a2(28gg;gvcoj:bu fool. The person’s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the pers2ffo gj82 :gc(gub va;on while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapi71c koq4 bjw,d9rolm. 1tp pw:d transit system, it is necessary to balance the average speed of a train against the distance between stops. The more stops there w9. 7,wjcqkp4lp :drob1omt 1are, 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 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,bpn0+q7h)yvj+r *rai( gj o w down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20+bor jn*pjrg a vyw0h+qi(,)7 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 so th2rh:whag4 i+c at the ball will stop within+chi 4rg:2 wha 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 i)h s 9cexi1 -zw3(htdon a freight train traveling at a constant speed of 6.0 m/s Just as an empty box car passesdiezsx-w91 h)(iht 3c him, the fugitive starts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second stone is drozb5pkf e uxv60g, g6u+pped 1.50 s later. kpuf60vb+6u5zxeg ,gHow far apart are the stones when the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course on;+v7 iauj8gp;l 3 p,dft.i tdf 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 the latid .;p+adtj8 ,3g;up7n vlfist lap?    km/h

  A bicyclist in the Tour de France cres4c 0x2y.eqxru ts a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his speed i2e0xxqu y4rc .s 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampoline;x .)dgrx; zars. The first child can bounce up one-and-a-half times higher than the second child. The initial speed up of ) ;zagr ;xdr.xthe 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 traveli88jlrh8j t5htevz f03ke -8 isng 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 th tl0htk3-8h jv88sjz58 riefe e 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 baseeg/6d5slc1y bspd )b -ball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwi1)g-/ys5b6ddbecp lsng motion.    $m/s^2$

  A rocket rises vertically, from rest, wit.r858c9jpa x sy8 pan4gkux0w h an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Each intersection haz31k9 yu,qdbr+z4dyps a traffic signal, and the speed limit is 50 km/s . Supposk+d,prz4d y 31b9z yque 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 120 km/ay-hj: kyi;6gh takes off in hot pursuit. Theyy ;hai6:-jgk police officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a builde 569qja 5ux :ezt2woping; 2.00 s after that, a second stone is thrown se zu:5qojw 9p2a65xt etraight 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 fir9p:jz vh4wbuaiti* e1stqojb xg:c8*, . n5k3 st 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 initi:u8.ig q3,:*jvecnhbb s491jtaxk tw zi5o* pal 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-fu3 qa93clb wi0+0da ygalling 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 will restrict her speed to perhaps 15 yw3lcg3qba0+ a 0u9id0 km/h .)
   s
   km/h

  A fast-food restaurant use)hj8na 38ybaw* oebp/ s a conveyor belt 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 3waa8bo /) b*hepjyn 8spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vo1r4(66l xbu bymnxq *ertically at a speed 1.5 times faster than Joe can. How many times higher will Bill’s ball go than Joe’s?x1x ( bry6l4nq *uob6m $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while yo4.rc,bkp1 vz8t)xp,vrxt2 q) wp zz*yur 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. Your friend then picks up the ball and throws it up to you, such tha*q4 .xptz) tvwprrz,p)12zv8, bxkcyt it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using p3*y d n,usystze81)ua barometer. Instead of using the barometer as an altitude-measuring deu*yz3eu)8 ,td1y nspsvice, 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, 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 fsn e8hm--q)q yor 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 -y hq-)q 8emsnbicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?