In what ways is the word “wc4;mikqcgiug y +ui0h 8*4 )cmork” as used in everyday language the same as that defined in physics? In what ways is it diu8c0*4ihgiumm +k;g ci4qc )yfferent? Give examples of both.

Can a centripetal force everzdy- )3m(mfwf do work on an object? Explain.

Can the normal force jzsdq9w1 906x3u+adrp inf9 s on an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she do5u4akv9 - syiping any work? If she stia4kp-5y9s vu ops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider w3,l. iebcs hi2hat happens to the dishes when you pull a tablecloth out from unhclis. ieb,2 3der them.]

Why is it tiring to push hard against a solid wall even tho0owe9-y6ghp w 9; dvhuxefn;6ugh you are doing no workd;0wvyepn-hw h f9ox e 66u9;g?

You have two springs that are identical excepxln +;bswcskx . a5s55t that spring l is stiffer than spring 2s.nsa5kxx 5 ;+sc5bwl $(k_1>k_2).$ 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 constant horizontal force on a block that is fr lqo(.a*e811wmuq jm5nijej odu 7d8;ee to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and qjuem7lm dj oq(na8.jo i*5ew81 1u;dby 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 much does yok30xdn x ;lr/*uk+okf;3paekqo v7y ;ur gravitational potential energy change when you jump as high as yx;pe;kk/ vku*07anl dqx 3frk3+o;oyou can?

In Fig. 6–31, water balloons are tossed from the roof,;*x z;g-zm xs,slqu w of a building, all with the same speed but with different launch ang ,;szl-*zxumxq,g ; wsles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h ot yz,;mh8a:tabove its lowest point in two different ways (o, yt:;ta8z hmFig. 6–32). During both launches, the 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 ups 9dwhk8j+pjx8yz30vk hu 2- kright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.ds9 yjw 02u hjp+3kzhxk8 vk-8

A bowling ball is hung from the ceij:s.sdp-rr /bdn4i juc e75i.ling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands again sjp7i .j5 d/4rnre:bs.ic -udst the wall with the ball against 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 water at the tohzjs-79/aqpjj41 is gp of a waterfall falls to the pool be agj 17pi z4qhjsj/s-9low?

Describe the energy transformations when a chil 8nbt hzvnfg 5b8ypb +92y/ qg4otv:+id hops around on a pogo stick.

Describe the energy transformations that take place when a eqgyl h9: cbm2px* :fgoiu*14 skier starts skiing down a hi y *2 gp:ifxc*:qmblg4 h91uoell, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of afalq0hzt7; -w ac. kjzx).f(u 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, and (b) there is friction (deep0zlftq;- zcx.j fa(k.)a 7u hw snow)?

Seasoned hikers prefer m.3 (gm39zhq gor/ jobto step over a fallen log in their path rather than stepping on top and jumping down on bzg g3.oqoj3 /9mm(hrthe other side. Explain.

Two identical arrows, one with twice the speed of them;:nhyd g zs+- other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain m:dns-;ygh +z.

Analyze the motion of a simple swinging penyu .kg jhy(x23m :0sbev,jgm tn)do.-dulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has tjgnvum,yxmos. eh2-( )kby3j0 : .gdto be wound up.

When a “superball” is dropped, can it rebound to a height greater than k/ hf;ko)9 lyr./g , qjt)iqwj;p 1ck ejceo82its original height? Exjc;kfrk). lq p )j ythkjo 1/qiee,;9c 2go8w/plain.

Suppose you lift a suitcase fro: r+ljhkyq 8fuhj: c(oo43.tom the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it s oyo(.hf43kjoj u+c th r:lq8:traight up or along 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 needed rather thana* w8 wu -/-jne*wkpdg the work.

Why is it easier to climb a mountain via a z9 e ibth.i tie;z ),nfgr6v()pigzag trail than to climb straight upvhpf9. e ()it,;ntb) e6izg ir?

Recall from Chapter 4, Example 4–14, that you can use a pulley and gl )( t(s pwg.peghs lx/7+hn3 gu6.doropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every h6g3glp dt+o/ es .n7whpul ((s).gxgmeter 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(tdb..(o g*ndc*x ypz 265-kg pile driver falls 2.80d tpn(o(yc b*g.zd*. x m?    J

  A 65.0-kg firefighter climbs a flight of stipdfz* :g 3i:lairs 20.0 m high. How much work is req*:fzp:li3 id guired?    J

  A 1300-N crate rests on the floor. How much work w8pm* tjn03 fntm5/reis required to move it at constant speed (a) 4.0 m along 0jt pnnm t8/5wfer*m3the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-fu fs7rkmm-;6kg crate 10.3 m across a rough floor without acceleration, ifkm fmusf; 67r- the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg isz-oylg4 wv z()bw19ew accelerated by a force across a floor at a rate of for 7.0 s. Find the net worv- w9b)zez (wyg1lwo4k done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flalhdw3he91nl *5wn d-ze m59wxeh,k m:t on a table. How much work is required towe-* 5l:19nd3hwh , knmze5emd xhwl9 stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we might n 9qxe. s.5+ocxdor(et2 m;tonot otherwise be able to lif e9 ;s. toteo rx2xc(5nqmd+.of. 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 ywn8*fq9i z2w0xj3ovtj/d( uaccelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic frod 3q0ix8j2tj y*/ zwfn9u (vwiction 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 g*pvjls, 2 pe nfx66l zlkz,0+a helicopter of mass M an acceleration of 0.1jznpzx 2, 0p*lksf,lve6g 6+ l0 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 cx+(*im5f isq.3mcl v the 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, acting along the x axug6a4j,h )e vf;htg p f1c7*ekis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0gvfe 16hacjgf ;ehp4t ,k*7u) 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 part lcfrtb5v ,a6i) 6m dnk*s,v0kicle 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 oywt42*re y*1s iw3yrexygen molecule, 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 itobh2k r4nw ;,te0 pb+ts 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 ku eh+kfaa 7 nxu:l10c8cvy;dgh.3ze;( v2hvelectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 o ,mg(51l7w.q opsmm5j. bx psmxqm+0stop 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 :do m;dcvyyuj 510pz0exerts an average force of 110 N on tj0zpuyov0d5 mc; dy:1he arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves awim u(ap6 ee1 3+txp8w fielder’s glove backward 25 cm when the ba+8w1xwe 3u me6iptp(all is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased la7o oo9.d9hbby 50%, by what factor will its minimum braking distance be increased, assumia .doob9ho l79ng all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a le i ,:ky:4dhagcje)f3- g mpbf3vel road, investigators measure a car’s skid mark to be 88 m long: k, gfyi3:befjdc3pmg)h a4 -. 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) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mbcsje u9s /8ku4whd5 k3c9j a)ass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance betwes sb3 cd4e8u5ja9kwucjk/)9 h en the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone i /snn( 4ggjo o, /+tgoj3)pf5 iisp,lwho does 80.0 J of work on it? g/3(5ol ,n i)sj+/ ipfnosp ggj,4ot iNeglect air resistance.    m

  A 285-kg load is lifted 2 sy :ppa2yxq7jvv 4*ui jo avgnc:)+ca5.f(s92.0 m vertically with an acceleration by a single cable. Determine9i4:jyfagv*xasyscuv n2. 7 pqo a+(:)5cpj v
(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 How much must j-s3 4aj5f k0lt 9h3;uznkgqkthis spring be stretched to store 25 J of poteskaf;34-knk 5 jhj039qzglutntial energy?    m

  A 7.0-kg monkey swings from one branch to anotlwszgez.j* n( a89;awher 1.2 m higher. What is the changes ge.*zwl;z(a9 wa 8nj in potential energy?    J

  By how much does the gr,17t rg6iok0j *8bkxlkt y)s javitational potential energy of a 64-kg pole vaulter change if his center of mass1y tik 0gk8*)7jblstrxj,k6o rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a dv t (+ :+yujufwjwt20horizontal surface has speed v = 65 km/h when it strikes a wtdjut+w2jf0(v :u+ yhorizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it 95 dq-w1f1bj8u eyxj8asryt7is 2.20 m above the gro -f xsubq wjdr91at5y j7881eyund. What is the potential energy of the 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 1600y x(g73:me;v(4iq jv vujbh;ub 4 32a,twt imv m and climbs to the top of a 3300-m peak. 3yv i4vuutm;xg he(qb,(7; ivwvb 23m:tj4ja
(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 to a ruler. The e navjds;ps8bb( ..b8xnd 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 spring, ws( b bd8 v.jnsab;8.pxhere will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at o)xbp 6t q)fbyp3h+g8dz h*s.top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high c y).hpb 36oh) zqt*8xgsdpb+fan 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 35.0h ,j1fiypvgfxn5 -)z* $^{\circ}$ 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 urv+u ob5j3nil 28ym.a frictionless 28.0$^{\circ}$ 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 gravitationa0+w dblvmpv 1mm;t(9s l 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 cro09sv (l;mpbdmvt+1mw ss the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform witod;leyw.dcs:hwq+ym52 f66.tj, vnt( e*ir sh a speed of 5.0 *t6(s5dcwy +s e;hmoeqi lt 26w ,dvjrny..:fm/s. ($\alpha)$ 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 constanmv ofvgvwez3tqcc 7-73z )lwoe ;2s 11t is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg bwzq171s 3zw)f2ev v ceot-g7 m 3cvlo;all 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 sho 6tol 1ptt8a)twn in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius istpt)ot t1a8 l6 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 stiffneeisr/fq+skv/ ;b 7 b0fss constant k), Fig. 6–40. The block is given an initial displacemen7s fe /bb;fvqr 0isk/+t $x_0$ 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;ut88 j+hp llz cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness88 ulp+z;ljt h 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 t2lmh(dgy *k -ko point 1 where it is released from rhlk-2mkgyd (* est. Assuming no friction, calculate the speed 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 at 3.b4 odoa o+7yrp rrx;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 be placed at the botto4s7 gcuxu) rn 6+ryb8xpae bke)*ml.5m 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 brought to rest. Let M be the totalkerb)5* bx+6us48l 7gen. mp u cy)rxa mass of the elevator and passengers.

  A cyclist intends to cycle up ;u94r 0e5j r35 shviu2vmckcma 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, /via9uma4qeing 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced i,/9vmq 4a eiuan this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hie6jl/3zrw+m) s uy,hk f:(xq ogh and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this procexwj3e6+ofuyk l( r:qz, smh/)ss?    J

  A ski starts from rest and slides down a*.g/vg 6xysl(:l 2jrhe3zi. r;gnetq 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 7epe*c) pz)8u cpdl hy j :n,7syxp18f13.0 m above 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 2.0db5114 *ynqy+n eg qyl m, and it bounces back to a height of 1.5 m. gy b4e* nyy11+qldq 5n
(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 acrosxij8sk+8heri cr+ p5lp av+1:s a floor with 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 friction is 0.30. What is the final speed of +lke ia+sipv +:jxh88c rr5 p1the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of Ibp91 jj7hi))c tczzm;oh x 4c)f the average force of friction is equal to one-fifth of its weight, with what speed will it reach poi ib)9om4z c)cc1;p )jjh t7hzxnt 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the fo f-wszbz; d87zzghcp773t;4 kmd5qdoot 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 sprin sn 0w1d9)- pieh8cao7qkv9mgg (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 beyond the equilibrium position before stopping and turning back. What vg-pa )w 7cds90hnm 81o9qk eiis 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, Fig4r-l- y z-gqak k)uf(l. 6–40. The block can slide along a table where the coefficient of friction ka4)-ul-lg( qry fz-kis 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” y cb3ldobp .d.87g-cj(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) What would its ladcb7c-3g. d.ypl8oj bnding 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 tonff* a 8nc)y9 44g,kdazicp*u lift a 315-kg piano to a sixth-story window 16.0 m ca*znk4a,yp *uif94 fcd8)g nabove?    s

  If a car generates 18 hp whe-ge(*y.qbwbj n traveling at a steady 88km/h what must be the average force-.wjeb* (ybqg exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates+sa ov3 ,mayn4 from rest to 95km/h in 7.4 s. What is the average power delivered b3+mov y4as,na y the engine?$\approx$    hp

  (a) Show that one British horsepowe/u 8kxwf ow/n8r$ \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 in th.gc sglb* tpox(r+g0 bza(0,d e 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 0;l +zbfg+y6g;cam mlher 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neml;; b+l6cga+0 yzfg mutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1 w+fsez7r(jp)9wcmg, .0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fxiu nqta* :)a n9h18vvrom rest to 14m/s If this motion takes 1.5 s, what average pow9*na:) 1vvix8q nuha ter was developed?$\approx$    W

  A pump is to lift 18.0s70+h c:rzt 1t.kutwhu hooh/9 z35bk kg of water per minute through a height of 3.60 m. What output rating (watts) shoc 71r :wuzhzs h3+k5h0t./o9 kuob tthuld the pump motor have?    W

  During a workout, the football players at Stat qljh8x)4 x rt4i0xks-b+d3nye U. ran up the stadium stairs in 6b344jr )k tdxslnxh-i+ yq 8x06 s. The stairs 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 climb a 6soon,am 24.zu .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 steep a hill cs9w umsn 4ouv748zg r6an it climb at rsw mo8sv n4g 9z4u6u7a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able l.s-1c-f, vm8u gaxuv to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fri vu1s.a, 8vgm-fu xlc-ction is 0.45?    hp

  A bicyclist coasts down ltc4iv(4hv 9la 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 “5zfvd2sw2e v8uer9*g,+tted :mi/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 bumpersetd8z*9eg: tsd+v2r f,e vw2u 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 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off t( m boq/1vpgzmni1tj f24+qc;he 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 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 floorzco g1v/n1mq 4imtbjfp+ (q;2 to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 10 2-/ha3uqiuw-8ch st;m pa 1h/ -+vcxrznocs936 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 launch if he wc-aas+ihs c/phw;-x3mtuqvr0n-81 /c o2u h z as traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction alpnsuf6h4 1)h:; rkzilhg +2zbong the looped track shown in Fig. 6–39 is to r2zsi up:+;z g nrfk)h1h b64hlemain on the track at all times, 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 withoe+ us euzl 42vng:/o- jor*d/eut his parachute opening. He landed in a snowba 4e*uou-zlr2njeed+gsv o // :nk, 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 whose other 8)7k5 dg-khtze dqm lgvo5rdj,7-a)nend is fixed (Fig.)-)lekr5d, qdh7v75an-mzjg d 8 ogkt 6–43).
(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 to the top of a 3700-m-high mountain. The climb is made m sq2lt6 )(vpmin 5.0 h starting at an elevation of 2300 m. v tpm(s2l6) qmCalculate
(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 elevatt5, ml*1v4dksn5d w ixor 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 area9).pigd zcxiebro w4(rofma 7m7 2- x; in California claims that its lifts can move 47,000 people per hour. If the average7coi4rwaoix b2.mz 7f)e9 mxp(;-gr d lift carries people 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/s and f/mm*jnos3( 3rv lu7qj alls vertically 81 m before striking the turbine bl3q7j rnv(*o sl/ju3m mades. 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 c- .ozbeh)q;9u llcl6 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 answer doesn’t depend on the size of the loop or how fast;ol clz- .6c9uhb qel) you go through it.    mg

  (a) If the human body could converx)c1:v/ gd1h 6: q51d xwuv7kcw, m/f btwbvbdt a candy bar directly into work, how high could an cdg bhtcvw 1f x1w)md/1/ 7x5v d,u:qbvk6b:w 82-kg man 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 fire scj7t6mn)0kc d at an upward 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 s-n*+wem) ll jqpring 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 w q*- e+l)lmnjof 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/cg,3wapmk- hjc .qq.y 0l2y/t dq8)b vs grabs a rope, and swings out over a lake (Fig. 6–45)c. yw38d)p/lh2mg qq b q.yka t-c,jv0. He releases 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-kge3;kra- 0:mxz dlw)dfmye szg98a ; f- athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish -0we8 gs-d x)z9rk zymmd a;fela3:; fthis feat?    W

  Some electric-power companies use water to store energy. Water is pumped b+dic.7 nm 5ppby reversible turbine pumps from a mpp.b c75d+in 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 constant k is ca, k(1ba207g.acyj j b0z piz7icp k;zut in half. What is the spring stiffness constant for eac pa j ,7aa kcbz.kpib zj;i(7gz12c0y0h of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 mvfvp mxy*lu8rxs, 3- 0 up a rough 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 can2u03tu)kboe v accelerate from 35km/h to 55km/h in 3.2 s, how long will it vo 32k0ebuu)t take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patie8h (xasek(k0 vnt walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patienekxk vhs8(a(0t 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 ro)/vu-g v55w6ncw(lfu*oin nr ck vertically upward a distance of 500 m, what w5w/(or wu) *5-cnvfln6g vnu ias its velocity when it left the volcano? $\approx$    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 95kg/s (a)5+ 1sljht il/x4u.4ojhm7 0zgf2 e nxq If this water wheel is set up t eoj /4j7x0l1ls+mhh2 .utnxifgq4z5 o 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