In what ways is the word “work” as used in everyday language the sa*7s laa1uv( *rih2ren me as that defined in physics? In what ways is it different? Give examples of 1ir*s 2a7rnuvl* ( heaboth.

Can a centripetal force ever do work on an object? Explm4pkt9bj pz60 hnc;l,ain.

Can the normal force on an dm6; wgx8d) b2axpxu+object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is32fkh n g)osd*w,ur(z she doing any work? If she stops swimming and merely flo2 3 gn(s*fwd, z)uhrkoats, is work done on her?

Is the work done by kuw7.3u. oxj+izya 3lul-x1 y dinetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a t xyl13y3w .-7z u djuil+xu.aoablecloth out from under them.]

Why is it tiring to push hard against a solid wall even t:af )k6j-g3hul y.u rnhough you are doing no woru -u3jnh :fakyg) rl.6k?

You have two springs that are identical except that spring l is stifv0 g haw,/osv9*)qlfsfer than spring,ohsf9q/sv0 )*gwl a v 2 $(k_1>k_2).$ 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 constc,2v7sqg0jo ih 12 ksxkvo1,:;rckj 2edg1s tant horizontal force on a block that is free to slide on a frictionless v jj0 o;x:sc7 dksq,sh1kir g2gte21,c1ov 2ksurface (Fig.6-30). 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:fktjtgg 6)cjjeg8i +) 3x37(m qm ikz much does your gravitational potential energy change when you jump as high asmmtif3 xk)zjg+g qej38 kg: i()j6t7c you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wit :+8ovzs 74 jna-szzaph the same speed but with different launch angles. Which one has the highest speed on ima:z- +z 8panszoj4s7 vpact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lov kg8. -dyrup(4o)bft west point in two different ways (Fig. 6–32). During both launches, thv-ob8 4rudy.( t)pfkg e pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the 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 upright ons1zx r +y62fhvo*cs0 a a table. If you compress the spring by pressing down with your hand and then release it, can the sza1c6 r2 0+oxvh ssf*ypring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a +w3h qoliu1.x steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball again oqwx1.+i3 uhlst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when wate;sl dhv+r 7/3 dmeblk-r at the top of a waterfall falls to thel d7vs/k +hdlm r3;eb- pool below?

Describe the energy transformations when a childqv+of ,1fe.s8 s5zk. oyqj5yr hops around on a pogo stick.

Describe the energy transformations that take place w86toofreumn0a,( r 0t hen a skier starts skiing down a hill, but after aotr8 0m fr( eoa6n0,ut time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts mijan 6y sq 71f*yzwz,j)a;w(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 (a) it is icy and there is no friction,f jys 7*1)anz,awqjz;(w6yim and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen loguv5c1uf2z;r c; kdze7 in their path rather than stepping on top and jumping72cvufzec ;z r;15 kud down on the other side. Explain.

Two identical arrows, one with twice thuwr ;:q9k3.tb qdv 3nie speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the akur3i bwn9td. q qv:;3rrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a s+h1n(f aw .x-x v)gswuimple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfathf w+gwsnhvxu)(1a -x.er clock has to be wound up.

When a “superball” is di -1o3k0arczuz,x1li ropped, can it rebound to a height greater than its original heigiia1 31k-rz x u0,olczht? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the puan 19s2h8oi)ew x(*o zv1losuitcase depends on which of the following: (a) whether you lift it straight up or alongho1)vo enal o(zu*1s8wx i p92 a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neexu7q;p 3jc bg*ded rather than the work.

Why is it easier to climb s n /un3iu74 4h,sdefblps ,v /h0diw*a mountain via a zigzag trail than to climb straight up?n40in4v/ih*fs,3 u / eld s7h,bupws d

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropedxn sdrxb* y(/.pr;*d s to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every mes/r* y ;*p(dd rbdxnx.ter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by wq:tcy/5 5qvpthe gravitational force when a 265-kg pile driver falls 2./qyc wqpv5 5:t80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. moky r.+t djt 1s::bn 5x+z7mx rh, amczh59b)How much work is reqazrmco:mz91:h,sh5yt j nbt7d 5 k++ ).brxmxuired?    J

  A 1300-N crate rests on the floor. How much work is required to mijyl1t ,u l 0-xs8rx7vit95 boove it at constant speed (a) 4.0 myu 5 sv1jt9iltix b8x, 0l-7ro 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 (horizontally) dn(mi,md3guw5i3h5 y:g mf1u pushing a 160-kg crate 10.3 m across a rough floor with:5(w3hn3 d gmi1,fm 5 dgmuyiuout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerabur. alu3d*w2ted by a force across a floor at a rate of for 7.0 s. Find the net work done bduu.al 3r w2*on the box.   J

  Eight books, each 4.3 cm thiz ms33lqk(* knck with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of as*mn kzq33(lknother?    J

A lever such as that shown in Fig. 6- ld*-32eugaolv3n98bz ( nl*i dqef+w35 can be used to liff objects we might not oth+(g we 9ufol2bqvn*ie*n833-alld dz erwise be able to liff. 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 accelhp 9a ,fx5*( unxzyn1+x p.jukerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient ox* upy(u+kpa j9fxn,n1 h.zx5 f kinetic 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 required to give a helicopter of mass M an accec591+fmwa8x*zk u5m e c9lwakleration of 0.10 um18w xc ka+5ec zf5m*a99wkl 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 the disaj7 os 68gffi5db;uc/ p j-ld8tance 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, acting along the x axis, varies as shown in Fz)8jwledtuq m :w 9) kqx7y8;dig. 6–37. Determine the work done byt)l)8q jzwdq;xwe9m y u 78d:k this force 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 onbe3w5zciap 1 p g:a09/bicel)z. yj+ p a particle 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 mq 9 6to*ave0mqolecule, 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 doub4s der,w 6i0;nlbcj;xled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an ela.ef )tfs6bx8 (zmp*f ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 donkpmym (q7qe *kpvi(l0yl-n.a-o n9l.e to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an av 8 )tvurhehn.a/0xiezi+2 lm9erage force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leai+n e8t/lah )zxri0he m v9.2uves the bow?    m/s

  A baseball (m=140kg) zhqxk6h qpquku+ 3rq83 ld+cs i7vx3k9t f)5 ,traveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was th +xzc6s8f q75kdqx3k3r ik9tu3 pvhq)ul+,hq e average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor 5twblp5kb77 h m3lq7iwill its minimum braking distance be increased, assuming all else is hl77b3 qwb5mp 5ktil7 the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, in )) j2hef xm7zb7wq1hu8c ne,rvestigators measure 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 driver slammed on (and locked) then,r)exz)8c12h7fm7uhq j we b brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched j0,dz: n,kvrp 94 atshat By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average fh dk:,jt,srz anp9v40orce 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 rqi(u a:g6djp ch2v4+p- b3pvwock go if thrown straight up by someone who does 80.0 Jp wud(+-gp2 bahqjvi6vc34p: of work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by ab *nkxp 0q)g 1g7k2fiw single cablew 07x*q2bfpk) g ni1gk. 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 constant, k, of 440N/m Howbdpb zom4)u+ a-el+5k much must this spring be stretched to store 25 J of potential energy?ao+-bukbd) +m5z 4ple    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the clxi2 z *y7vamn-4gac6 hange in potential eneriy*zl- m6na v24 7cxgagy?    J

  By how much does the gravitational potential energy of a 64-kg poll:qxt51/m dgw mgey8 mh/;c; ie vaulter change if his center of1q :8 xm /dwyg5mi;gem/c;h lt mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizod0(n) /hab-5kyn 4l h g)m6jfucu5anm ntal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the sprin hn)bnmg5(h4-lud uk )cafa/05nj6ymg?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it 8dam: lf4exob xt6b* 5i3jl:a is 2.20 m above the ground. What is the potential energy of thtaa:bmx:6e5b 8 ol j *3l4xdife 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 to the top of a 330f:3*/ pmexggujspy 9 6a.kx-x0-m pp6x :s./ xu 9ay3gkjpe*m -gxfeak.
(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 vertically next 86xe8-2m)qjfm2llhr2 mlvp i to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-klmli 6 h)mqx2l -2vfjre8m28p g mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, bu j7s9mt0 crdu.x1/ vis running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high cans 1 tcmv.juu90 b7d/rx 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 frictionless q3 7 fsegux5rr,5-gdb 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 ;pvl oa3 rl6rq6 k)ho428.0$^{\circ}$ 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 a rdntb:lj(s j:o a lt53h-s(9jlg+1 gkinetic energy is transformed into gravitational potential 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 0.7l1s t+:ajhtlgngjs a(ob3:9 jr(l - d5m/s.    m/s

  A 65-kg trampoline artist jumps vertical:q :r2pjxwha56pp/+yprrr by2k9t c5 ly upward from the top of a platform with a speed of 5.0 m/s.559ypjrk2b rw /p y:tcqpxa+p h6r: r2 ($\alpha)$ 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 (ignore its mass), whose spring stiffness constanhud9upo zop8am1dm4 n5e4+-f2yy;o pt is 950N/m is attached to a table and is compressed down 0.150 m;zh 1m5aood p o4 u+unef-942y8mpd py. (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 along the looped track s)0nwo f1newo d2ak3mjv1 m9 )uhown in Fig. 6–39. If the block is to rema1v0 k )3enn1w9md ) f2owmaujoin on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness cotv4vr ( tm((vpr(7plm yeoppjp9b9*9 nstant k), Fig. 6–40. The block is given an initia4pb (t ev9jo vl(pmv 9ptp(y(rm9p*r7l displacement $x_0$ 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 fromv2fd18 /xi*w mu+kq*:j fjkw m a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hook kvm/uf kq i*d82w1w x+j*m:jfe’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 poinxw+x4zsb 10gdt 1 where it is released from rest. Assuming no friction, calculate the speed at poin g4+dxxbw z0s1ts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spee,g ycyf,p9a j b;+4vfvd of 12 m/s 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 designin (y3fjo1yx 6v)sa*zcwg a spring to be placed at the bottom of an elevator shaft. If 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 broughtj o c(xay6yfsz)vw1 3* to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to : zspi4lhdy ymcuve cj2x m-qc9 7.51*cycle 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 8tgeh m4,ppd(wbmk k. 4759udrc2sxland traveling 95km/h in opposite directions, collide head-on and come to rest mbdu dr8x cg4tew,h72 s.k kp49mp5l(. 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 ree6 pcqh8cm 14taches the bottom with a speed of 2.2m/s How much thermal energy dueq 14cmcp 6teh8 to friction was generated in this process?    J

  A ski starts from rest and sl+, qtm*ir qlt84b5y zbides 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 abovm;;zo:tku-k s e the ground.
(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 height 0 /kcb5 86tizgakclf4 of 1.5 m8f5i/tkzg a l6ck0c 4b.
(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 from rest, is pulled across a floor withoqu; 9kxqr5:1 2w qradrhpm 65 a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictionr5rqhxw 1kq;a2 m9oqr 6 dp:5u is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coas2zt.lvgx+z6 c ter in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speedlz2 tx g6vzc+. will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s res)i8 zm2o j:y/oufp4 lxb(/pl, codd/ aches the foot of a steady upward 18.0 $^{\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 horizontal spring /jyio40 *3diaq kp 6nd(k=180N/m) 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 beyo nik0a /p* oj634qdiydnd 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 sprijaye, uk vvyu,s., m f3k*mp,4h pu46ing, Fig. 6–40. 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 spring is released from this positmupjis *34 .u,pye av4 u,vm6,ykhkf ,ion, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980h p-q3eou2/7pkf fhj - kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glidfpfjp- eh3- q2 k7u/hoer eventually landed at a speed of 200km/h (a) 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 a sixth-story wikvwj 2rkcspq76wv-g l s6yrt-0 y5z1s uk0: w9ndow 16.0 w-r9w6vs k kus:s1 5tvgzwk0q2l76yyp c0-j rm above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what musthx3 ubnwct-cx3 :8 3fp be the average force exerted on the car due to friction and air res8:w 3xc ux3-3ftpcnbh istance?    N

  A 1400-kg sports car aclhh9 +,j/fm0 bx0kl iacelerates from rest to 95km/h in 7.4 s. What is the average power delivered by the engi,9xb f+hmahl k0j0/line?$\approx$    hp

  (a) Show that one Britisoq6x 6h8wb xnrr(e(: jh horsepower$ \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 expressed ids:e *px 3p/b3(k1lfa0hly)j c 9xtjan 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 car slows down from to 65km/h in abobci9o,90rs xqlwsh1h)z 2 md -ut 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed s21c,0dbswhzl 9mh 9 ox-)qr ito keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in5j3 die,yjzm5 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion ,9vey0 jgv ur1h2ri+z takes 1.5 s, what average pezr u 9v+r 0,yji2ghv1ower was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per mp 0 fqj*v7ogv3rf3g8nxohk /nr e*r 7::xhwi6inute through a height of 3.60 m. What output rat3o/gvi ro8nvep73 g7* x6qnr::ff*w 0hjh rkxing (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran:d e4d9v:s yqj up the stadium stairs in 66 s. The s:y4sed:vqd j9tairs are 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 cl9f+/miyo,vpcjch 1wh97 e6 pjimb 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 maxms15+0w0 .oyd keudfximum power output of 120 hp. How steep a hill can it climb at a constant sxm5o.y01we+k fds0ud peed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a mot ywv:n)rdfq0,or have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/swf0q d) ,ryn:v if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down ahzu02 w, ,0iop9*d+id9qe r 0tqjxnfr 7.0 $^{\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 built “5mi/l0 v5i*y *8wyd;czyk,6 ptk mbh(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 poipdy6*c;zmt * b k,wyy0k 85vlint, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library thu5 5l0nrmi6aw e first shelf is 10.0 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 lwi6 a 5murn05of 1.5 kg with a height 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 los8z 9x4zsolx:3aie4sng jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from as84ozz i43xs :ls 9xelaunch point to the top of the arc. What minimum speed did he need at launch 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 looped track shown irnsb 5he+e75ln Fig. 6–39 is to remain on the track at all times, even at the+ nehr5esb l75 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 his parachut-niw k3xno y36e opening. He landed in a sno3 6-ynwni3k oxwbank, creating a crater 1.1 m deep, but 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 w3 awwu 4+xo2mdhose other end is fixed (Fig. 6–3wwu4x2+o m da43).
(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 to the ta3y +llme + zt-asw;d9op of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Cal zme3dlla+9+ya w;-stculate
(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-kgx,9k.bnl) h p4p irh8rc2b9 di elevator 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 that its l8es0f 0hy4 alsifts can move 47,000 people per hour. If the average lift carries l0s fy 0a4seh8people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/,sp5 uymhl-zc(4i wq3s and falls vertically 81 m before st3cyi4mzl5w h-,qus( priking the turbine 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 circ z1 o7u wy(kx16d e,q;ddybn1fular vertical loop (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 — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this a7oy,1nbd1ye qd ;f6 wzdu (1kxnswer 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 in+x7y +b;eo lteto work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)+lee+t;7xoy b    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 ups1 qu.ry7f3hvward 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 spring ink94vqw 6 q hsp/hbr5w x-fy+2fside 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 mswqw v4h2p/6q 9bkf -+h5fy rx, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, a*7lqk47,wn hh y4qkqp nd swings out over a lake (Fig. 6–45). He relek47q,qpl*w 4hkqn 7hyases the rope when 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 dmz*b2 ixn nb wm71,y5uistance of 5.0 m in 9.0 s. What minimum power output was used to accomp71wb inyu25,*zmmxnb lish this feat?    W

  Some electric-power companies use water to store energy. Wa o9mqjb257 s:pk mxau9ter is pumped by reversible turbine pumps from xs p7jq ub52:omam9k9a low to a high reservoir. To store the energy 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 codm)/h 2k)skchrj ;fvj c/- bh7nstant k is cut in half. What is the spring stiffn 2 -fkjr ;c/hvs cm))hbhk7j/dess constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough ydmq tys85 -n:37 $^{\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 accelerate from 35kmr7apch9im,( *j,/eqooz 4 r ed/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,a (9r7cemhr,,/ieo*pdzj4 qo and neglect frictional losses.    s

  In a common test for cardiac func rzn x0n02iq 4s6ic(ahtion (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patqn4x hasz02(cnr 0ii6ient 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 otbugx 0xv3komw/o3w11( 5d vvjr 1uk,f 500 m, what was its velocity when it left the volcxbx1or v v5m (twu1g 3kko3,/1vj0d uwano? $\approx$    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 ath :pbvh)*1jz+a+ x xuf a rate of 95kg/s (a) If this water whev fbh+xja 1hx:p u+z)*el is set 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