In what ways is the word “work” as used in everyda1l z *u:ad4dbyy language the same as that defined in physics? In what ways is it different? Give examples o4b l*da uzdy1:f both.

Can a centripetal force ever do work onztt3+) thut2o an object? Explain.

Can the normal force,xjumg hnn6f 9d i2gzv d0:2)v*9duxa on an object ever do work? Explain.

A woman swimming upstream is not moving with respec)g +ln 0.p+yi6wms iiut to the shore. Is she doing any work? If she stops swimming and merely floats, is w0l .imu+g w)py+i6n isork done on her?

Is the work done by kinet emopv30sb fo96;lkz(ic friction forces always negative? [Hint: Consider what happens tob0op;6zko vefs l(3m 9 the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid walusftnkrnys;8w vex .e+,f6 03 l even though you are doing no ws snx;yr,0n.+ff8ek u3wtv6e ork?

You have two springs that are identical except that sp 2na:.j qjym*boc 1.etring l is stiffer than spring 2me:q *b t.yjna21 joc. $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constan2ndm )l g)i8-d ux;rgnt horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30d 8dux;gi)ng) 2-rnl m). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how muchdld mfey;iu2n4;u 8y : does your gravitational potential energy change when you jump fi :nmye;2l8;uud4 dyas high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildinu,0mxadbt(i)(ob l /4mk j+gg g, all with the same speed but with different launch angles. Whi4ixd(mj)m b(/bogaukt +gl 0,ch one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point ig2ej1o51zqkusi00mp 7t 3e dz n two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of thepmjuszgz2to710ed3 i qek150 pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests u4/hhi)dum vo 4pright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Exp/hh4u) vdio 4mlain, using the law of conservation of energy.

A bowling ball is hung from tgpgws,4jwz c7wr825p:dp j 1 hhe ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injuwp7,w h j41p zsdrp gwj:c52g8ry the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational pxz n++aks* sb;otential energy when water at the top of a waterfall falls to a sbnk+z;+sx* the pool below?

Describe the energy transformations when a child hops around on a pogo rac 9z3;bbuy0(iuu :1 r0zmupk1 oby6stick.

Describe the energy trw:fmyy ztng(:337p s zansformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by zmy fs3g 3ynz:7tw( :pstriking a snowdrift.

A child on a sled (total masoc (: 08 qges:uw f:ges2;fpcss m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if s2 u0gfqc w:(soe8s::f;ecgp(a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over afgl65xx:t9qx1k cc m) fallen log in their path rather than stepp fc5 lxg:1qxt6xc9)m king on top and jumping down on the other side. Explain.

Two identical arrows, one with twice t s97l1okr07q(e.mrf;wu.(axv lrm qahe speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows,1 maelu mk;09a.7vwq7qso (rxfr(.rl the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in oxj hh(h*a0f9 terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a0fhhjxah *9o( grandfather clock has to be wound up.

When a “superball” is droppaw fae)c52w*t ed, can it rebound to a height greater than its original height?c 2aw5fte)w*a Explain.

Suppose you lift a suitcase from d n fwh.i:9nxr02pp3pthe floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the tinxwn 3.p:ihf92dpr0p me it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than ;mtnrcey( g+: the work.

Why is it easier to climb a mountain via a zigzag trail than to clim xam ;4zz0jmo)b straight up0;)z zaxmo 4jm?

Recall from Chapter 4, Example 4–14, that you can use a p1)5o xmq : ctzf )xcw0spxz;j*ulley and ropes to decrease the force needed to raise a he1xcs5pm*)txzqcxfoz : w)0j ; avy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 69dq:khd0 hj t265-kg pile driver falls t6k hjh0q:d9d2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wog57( s xwcbe94/xqalb m2k*tcrk is requba9 lt2bqg5cm *wce/ k x(4x7sired?    J

  A 1300-N crate rests on the floor. How much work is require b6qs; 6xhfwd-/;;st )gnako sd to move it at constant speed (a/go6a ) -;s;qb;fk6 ssdwhtxn) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do 39.dh:higm4 lohox67p cezh6 (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wascxl63 miho hpo he4dgh9:7.z6 0.50?    J

  A box of mass 5.0 kg is accelerated by a nsyhiux p-9+d m/5l ohnk(u;. force across a floor at a rate of for 7.0 s. Find the net work d-hi9no5+xs .uy plhdunk/m (;one on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How ;l nq go+ gmgw,dh+g0.much work is required to stack .hlwoqnmg 0+; ,g+dggthem one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used tgt1ge;q*zo t(4ds*.na:c2 mst+c zd2 m gc b6io liff objects we might not otherwise be able to liff21 + gb*zs4;: .dgite6qs 2ccon(t*cdz mmtag. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acce jp4p3) (5siomt 1en9zey4tbvlerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kineti b1mpeoy4v4n ej i(p5)9 ttzs3c friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force rpldh7b mt:2 5:k.g azjequired to give a helicopter of mass M an acceleration of 0.10 zjpm td7:2ga:bk5l h.g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume vj/gs *thns0*fzn. rw /b.cz3the distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object,c +na2f yi/ 8i3gff)hj acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this /2yffhg 3j8a)c+ni ifforce to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a parti ,/v or w:y;8dfmyfc1ccle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen mol id jqsgg8 ,k ,; 2bjbrzqqc tcu,)d9-an,r/9wecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its sp)n6q4 2jcb bleeed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to tqtu d8vw dp+zw;(y58stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at m -2tn3ozlcf6 e/c uo-105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an ,evdqcjbz7-ms f;:4 iw 2 7rfgaverage force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves tw7, e dfsqmz-4fgc7b2i :jvr;he bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm wheehu*z/ u6em m6n the ball is caught. What was the average force exerted by the ball on6eeu 6z/* mhum the glove?    N

If the speed of a car is increased by 50%, by what factor will its mz-7 lve7, dnecj 75n-.dqapka inimum braking disda lk.7qz57n - pec,7jdae v-ntance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measurgo6tlj op:3 1 nc5c969p tqdzrrg 4,nxe a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the dri ln3 tj69n 1r9 xo4c5dto:g,zp6r pcgqver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time itlzn h.y(t.0 bj reaches the plate, it may have slowed by 10%. Neglecting jnzt..b l hy(0gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if ( a/1nne7;h9q :ktnblzxb6cgthrown straight up by someone who does 80.0 J of work on it? a(t/lcq;96g1b xnz:h e7n knb Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically withhr.(4 grzeff u +cstg ye,u/4 nea+wr:dx3 41h an acceleration by a single cab4e4w che zuyxaf1u+,grg(:e. 4hrfsnr t+/3 d le. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness c 7ng thyj cp37yx/cn0j+(.i -o avluxe.fm/6r onstant, k, of 440N/m How much must this spring be stretched to store 25c/xh.t o(yij lga7p6 0/y7juec+rf3.mnn- xv J of potential energy?    m

  A 7.0-kg monkey swings from oney:jlcs j4g:c2sd ad/ 5 branch to another 1.2 m higher. What is the change i4s cjdcs::dy/2a j 5gln potential energy?    J

  By how much does the gravitaj7dvx*ok:-lk-h3 n vx en5/ nttional potential energy of a 64-kg pole vaulter change if hihnnxot-/3*kvd- : v lkjex5n 7s center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whennig cm ,y w,:b55gof9n it strikes a horizontal coiled spring and is brought to rest in a distance of 2.ig , mgco,w9:nb5y5 nf2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.brp9nx1hf ys1 rn ,/ po3j;3u6pbme s)10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of theb ub oe sy sfxm),31n/r9p hrjpp31n;6 book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs th:8mvweht .. uo the top of a 3300-m pm he:w.h8 tvu.eak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertidfc+m ,:pr5tx)6 r)hntp k1j ocally next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the shmco j)r+p:6 n5ftrd,p)kt x1 pring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vih 5(lj1a bpmc:ne hanging vertically from a tall tree in the jungle. How pbja(1m:c l 5hhigh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a f97:p:0mcohzxsn; ynfrictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless , 17d6tdd eykw28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational pnp)/4 qcs0wn3nfh(nm6 an cz(otential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 4pnsn(fn/nz0wamn q(c h c )360.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically8 0wk.a3dmi)yl4o kbh upward from the top of a platform with a speed of 5.0 m/).o w0hikd kbal y483ms. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore8 z 9:1srwmes6s fa,mfmd+ f1p its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.+ 1pf1 s,zsd f8amw6ermf 9:ms150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction al4mjdv0-rf .o+k6 k eu:-) krmen(im-qeyi)imong the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be releas )rm :d- . kre64mvyioqjeun--mm )f(0ei+ikked?    r

A block of mass m is attached to the end o(2p gaxi9 :zi .fpunttq(,lh; f a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial dip (uhg,p qzi;tl 92fxa(.:tnisplacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord s.pjwkp))g4 if-hy;h o 6wcazg(8 1qgwhose unstretched length is 12 m, and falls a total of 31 m. (a) Calcuq6gf a kp.sch4p1h jozg w (8w)-)yig;late the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to p4awg:wq /au4 ctots 7-oint 1 where it is released from rest. Assuming no friction, calculate the sp4s t-ow/au7 tq agcw4:eed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s y5jbbecr::re/rg; lb;ufw (+at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to bbb8xr. p.5d w,0yy .nq1iyt gke placed at the bottom of an elevator shaft. iq p ,dt85 1xyy.. wb.r0bkgynIf the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyuev a9:,:/ (iq hxcs (qy,owyycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and travel srwpe*pu22p amy4 q)-;m+ skjphxf1 x2t(*w ning 95km/h in opposite directions, collide head-s j)4 2fu1 ka* xsy+wpw(;p e2rq2phn*pmmtx-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wig+ .fjs l+hw,lth a speed of 2.2m/s How much thermal energy due to friction was generated ihj+g.s,l+ wlfn this process?    J

  A ski starts from rest and slid2upa y5o9 t6.3sglr hles down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the gr+*rv2,ytg f1 ls-ocwsound.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a h1n+( g zylzczqa.+cc/7q ai:p eight of 1.5 m.ycz + cap c.(l1zna7:qg i+qz/
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting ljq046bzy7z kfrom rest, is pulled across a floor with a constant horizontal force of 350 N. For the f0 4qb z6l7yzkjirst 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 withea)poz um7n 2* 6-8-hkrk x8bzuh-ddy a speed of If the average fo -8*kaeu7pn6 dh 2o)-uyr8z-bxhkd mz rce of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18n/b; tch. nc4o.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontct. phr -4:*z:kzxyyp al spring (k=180N/m)*zzph kctxp4r-:. yy: as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig. 6boi hv7 6hmh5ycgc; g4qya13;–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the sprin4c6ig ;vb1oh ;maychh5qg7 3 yg is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for to,o 8fna3i7(fq*qpnthe space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a,(8*fp3i q7n onaf qot) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to aikr0h -)+egby sixth-story window 16.0 m abovebhyk-reg+0) i?    s

  If a car generates 14u6-yw5b:+nl omjilu 8 hp when traveling at a steady 88km/h what must be the average force exerted on the cab 45lujimwoul6:n- y+r due to friction and air resistance?    N

  A 1400-kg sports car accelerates fy(iu 3dov 7s+q 7:qzesrom rest to 95km/h in 7.4 s. What is the average powerde+z 3:qq uvs(oy7s7 i delivered by the engine?$\approx$    hp

  (a) Show that one British horsepowe,khx k/.bnm m2.jka+ ajk7b1ar$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often exp. 9yipkv,vppts . yb0:ressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg cgq;l 3b+kxn,nj: oz2 zznos(*ar slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car tq(:l 2,zzj onns3nkb+ ; gxz*oraveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor de0*hjsb4a:u ar 8hw ags17+f so in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s Ifa.owoeg6q o3ts, 9 xpszf8 39v this motion takes 1.5 s, what average 6eqos, w9g fot8.3 va9 3spxzopower was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minb 0ei7pl j (q3rlc-5ba1lty8gute through a height of 3.60 m. What output rating (watts) shoul l3r1pi5 by -l78ejlqct a(0bgd the pump motor have?    W

  During a workout, the football players at State U. ran up the stadiu-8 fzse8d2- jqq(njnom stairs in 66 s. The stairs aq-djn zqo8 (f-8nejs2re 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist cm)purs-7bt7j limb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How sta zigb: -a- ))y6flzmqeep a hill can it climb at a constant sp)q)ibyz g:zlf-6a-am eed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-k-4qrjih zh( h4g box along a level floor at a speed of 1.2hzih4j( -h q4rm/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.cyg(1(ty sjctcxcg2q( ,krf 00n)0et0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have bui6xfn+rd 7:fqc8e tm5vlt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 k r7ftm:cf 68e+dxnqv 5g and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is sne3 et-555r uao *eyx10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a heightsua5-55 3yerxo n*eet of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42-5j8/ 52nkr kk;q 3p b/zkrrtruybw 0v) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at la k3kyn/;br /rb 02rkrqtk8u 55pwvjz -unch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopedall0 -hergts -ue3; ny)90y8f)kx ybz track shown in Fig. 6–39 is to remain on the track at all 9yb sh8yyx nel k;)taegr00-ful3) -ztimes, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hisw(x9vg+ x6la 0+ufuin parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, buu+xfwu9a6v i+0lgx(n t survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose otheraj: jn6wp9m )yo9q e+bxe)s +f end is fixed (Fig. 6)nj+s pjoey )+bx:fw 99qem6a–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs ,npmudh+wbb 5o/4 n+z to the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elem/nbo4d,u+np b+zhw5 vation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg thqjgl0 1d:r0elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims tha)k3dkil5 et 2mt its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the)t5 i3lkde2k m power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before hhmsff,y7 1xz.aj,s: striking the turbi ,1jhy ,sfahs.xmz: f7ne blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loope:ot.xc+w/j a uv/r j0 (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — u vaw+.:r/j/xcejt0 othat is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly )z-w 49zxcerd into work, how high could an 82-kg man e4d)z-c wxrz9 climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwcj;f :ljx;9uu(d7jfi ad79 gmard angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the sps)6zl 0ngw+s4 e,awjqring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does z06agw+n e)lsws4jq , the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a ropen ysh to x*17oe4*:ooh9bri7n , and swings out over a lake (Fig. 6–45). He releases the rope whnsbho 7o7 iery4hx*oo: t1*9nen his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distanceb a5::msfcml r dju555 of 5.0 m in 9.0 s. What minimum power5l 5mc5du5r fm:bsja: output was used to accomplish this feat?    W

  Some electric-power comp3qm o)vffq8g /anies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the en8f)/mqvq 3 ogfergy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the sprin g pflffg x9 6e*t.m) ((q(kdo()ratypg stiffness constant q6.dm( *o rfge)(y9g(t)palfpfk t(x for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3.nsjqza8z rn cj*-v:/7 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can av9 h), zmt2-ctg3rvmfccelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and 3 tfctmg)29rv ,hv-zm neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the . m1.mgykzov pi-jt(. patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg pati pmzg(.-yo1ktvmi.j. ent when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 m x bxwi 2v c2ddl4usu+7 5;fc eqo(b.,t6j,npg, what was its velocity when it left the volcan5cvj, 6d;db7 xopl4bft2,u2uqcs n+ew.g xi( o? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95auqsy u9;c8 -8sti u4sbg fg.,kg/s (a) If this water wheel is set ssby9 g8fci8u; ,qa 4-guu.st up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s