In what ways is the word “work” as used in everyday language (c.:/ cokr q/vcgahg4 the same as that defi(:haog/qv krg.c/ 4c cned in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever dc fr/tda 8a/-lo work on an object? Explain.

Can the normal force on an object ever do - s .o)*opqeeczocpq6/a 1d/kwork? Explain.

A woman swimming upstream is not moving we,da mu.f9 ,tor) p,reith respect to the shore. Is she doing any work? If she stops swimming rdp am)ree t.o, ,,f9uand merely floats, is work done on her?

Is the work done by ku00hvff1 gqsjzsw9 *0inetic friction forces always negative? [Hint: Consider what happens to the di0 s9uh jf0g wf*qvz1s0shes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doinffirwfg 90 7f5v cxg12/c6wrdg no work?w5ffgr/6c07fi2 wdc 1g9 rf xv

You have two springs that are identical except x0edr llt/(.o that spring l is stiffer than sprinle( t/.xol dr0g 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 constant horizontal force on a block that is freeb/q wd0-/tem cp a5o4l to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A,wt cdqmpol5/b0 4/e-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 much does your gravitational potential energy o r wmwh;45y8cchange when you jump as high asm8yw;roc 5w h4 you can?

In Fig. 6–31, water balloons are tossed from the roof of a bu/; h yvq gtn2.gw4kackq(+y (uilding, all with the same speed but with different launch angles. Which one h+(gkg q. kvuynyt2a/;w (4hq cas the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a hmel*bk v:e6i2 ev++ uneight h above its lowest point in two different ways (Fig. 6–32). During both launches, the pen:mvbv 6euk+ie +nle2*dulum 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 on a tabp 24 /ut0mep , l5;: pw*wej nhrga2p+kgb0cjble. If you compress the spring by pressing down with your hand and then release it,g; 20pk:ep02cj+ wmrb bh4t5gpeln/ wup*aj, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a stef :j.5c r7umdaqpj6) tel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball agaia5tj) 7j q:rmcudp.f 6nst 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 t9wd2eu7x;swi2 ;xrze he top of a waterfall fal9;uw wz27xx;seir2 de ls to the pool below?

Describe the energy transformations y+w+ixk*xm ep5j1 5 zowhen a child hops around on a pogo stick.

Describe the energy transformations that take place when a /m wc:.-w*bfr:egyxu;so w ,nai5 1p w 4esg;cskier starts skiing down a hill, but after a time is brought to rest by striking a snoybfcas4x/ .*i w, mcog pu5:g;-;1w e :wnwserwdrift.

A child on a sled (total mass m) starts from rest at the piukzlejf+*3: i m+ lz0ie*l6:g)hh ktop of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of tl+ u6k ifg*+ kz):pimee :lljhh*i0z3 he hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefe(eqfb1bzc5 (2d,zu22u g*dlusg;oqi r to step over a fallen log in their path rather than stepping on top and jumping down on the other sifugolcd2 b*;q2qb2zz,(5de u g1 ( uisde. Explain.

Two identical arrows,yb/p:xa* 7cgl2d)8 x yo u6trx one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constantl7x)xp8 ructd/ :y b*62xgaoy frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) i-nn7 /1zd xjjegnoring friction, and (b) taking friction into account7 1-nezn jjdx/. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it9t 60jljzhnw2 rebound to a height greater than its original height?znj 6t jw0hl29 Explain.

Suppose you lift a suitcase from the floor to a table. u zxi8/6a7 )mpaj)tes4r0lfs- xw ke: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 time it takes, (c) the height of the table, and )kxflx)rm07pee4zt6 :wjau s8si /a-(d) the weight of the suitcase?

Repeat Question 22 for t 5spe)7hedds4pii(hmn 3-r l610tpb k he power needed rather than the work.

Why is it easier to climb a mountmjlft/8uq01-kez, dmain via a zigzag trail than to climb straight umd q-m 8zu 1/j,tekl0fp?

Recall from Chapter 4, Example 4–14, that you can use a pulley anasp3bu 5hbnz h:ro..+d ropes to decrease the force needed to raise a heavy 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 c .3pza bosbr:5n.+hhuoncepts.

  How much work is done by the gravitational force when : v(/bdro9 is dvb73gaak5r:ea 265-kg pile driver falls 2.80 v:d e3ka sr/bg9rv5(biado7: m?    J

  A 65.0-kg firefighter cl7xo kq nu,4g;e0oi buw03f;gtimbs a flight of stairs 20.0 m high. How much work is required? kiug 0,fq7e43 u;o;0gwtbox n    J

  A 1300-N crate rests on the floor. How much wojv s2g kwux2rw,k7m**rk is required to move it at constant speed (a) 4.0 m along the floor against a friction force ofm,2 k2w*r7*x uwsj vkg 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do xsw66( vjsp-j (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wj- (sj66pxs wvas 0.50?    J

  A box of mass 5.0 kg is accetxb/(h c)v86 ixkv0 txlerated by a force across a floor at a rate of for 7.0 s. Find th/)6h vtx (vc0ib t8kxxe net work done on the box.   J

  Eight books, each 4.0pq : 0udz-gs92yzr6i s:f rcv3 cm thick with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on p-qru fiv 0:dy2z690c : rsszgtop of another?    J

A lever such as that shown in Fig. 6-35 can 4u,)x hagkw)pbe used to liff objects we might not otherwise bgh) au,x4p )kwe 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 3.3h qogy/ /9heax5dtt c78ovd -6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculxa 58c dh3qghtetyo/7-o9/v d ate:
(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 a5fa4vs) zpxb(ru1di 0 n acceleration of 0.10 g ixzfpd 1) 0a45svrb(uupward.    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 distance axis is l3 -ngyg+xw,iv inear 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, actin8wex w9l 67 -e:5l ahdav3ljrjg along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0jxjarelw:laew l v79- 58 h36d 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 b4 eb*dy niy5z 7r*.*rgbw;w uparticle 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 molecule, with m*exs0t)3kuwwn ho lnh7kr.70g*z 7w aass 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 ha i7bjh59woaly: :fg6js 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 s d5xnza9uu qr9wh(5 ;utop 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 1059x*o eti7:epn km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firf(t3,grxbu.uzs;8s w3 6s hz bed from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow6gs3ubs;wbsr8 z,x.f 3 uh( zt as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s mo0: /*i eyu0dphyegb9 jves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the g dg/u hpey:e*0y09bjilove?    N

If the speed of a car i+fx eq2zgq5zp:f p 1(ws increased by 50%, by what factor will its minimum braking distance be incr( p1f5ezzqfp+q2 xw g:eased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roqbv5+)sodru9 k,ic -uad, investigators measure a car’s skid mark to be 88 m long. The acco b,s5kuv+ iuc)9-drqident 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 b +p5r6lct/sa mass 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 t a /ltr+cbs5p6he distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go inb3 .c,jrqdwe (fluabg ddv*du9.1+ - f thrown straight up by someone who does 80.0 J of woru+dgbwe1 u-b*nd ,jdf.a 3(cvl d.q9rk on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a0 +r s11i+ j bwycb, 72dxu8zwmbsmd:l single cab +z1mlbw:1ybm c,x70 j+s 8drb2 udiswle. 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 stifw*5/hw*ivg, ds a:7u bcn/ mer4u+wykfness constant, k, of 440N/m How much must this spring be ehwkm //uwngy+ *icuw b7vra : s5d*4,stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to ano,zsd k8-tom 9)c)smt:n lq ab,ther 1.2 m higher. What is the change in potentiol a zs,m-s8 m:b)dkttcqn9) ,al energy?    J

  By how much does the gr)qrcn9ozryyc 03a0w/ avitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the j0)qa3n w9yyo0r/ r cczump?    J

  A 1200-kg car rolling on a horizontal surfmnb 3l0a 6r4/xa/sglwace 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 stiffl/ arwlg n b03xas/64mness constant of the spring?    N/m

  A 1.60-m tall person lifts a8/n6fb td8izu 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energynu/tz 8b6i8df 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 16ftzfk ,2wr0w3d0pqwcp i3d,/ 00 m and climbs to the top of a 3300-m peak. i3wfdwdpq/t3k0 rfpcw z,2,0
(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 end of the spw:h8: wo7+nj qjwsfms5ln7o 7ring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attachehs7o58:f7 onqs:j7m jwwn +wl d to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at t/dvgerky.n-v8 6 i xbv63 rzum6- evz3op speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swinmv6nvg 3dre x k yzrue63ivbz-8v6./ -g upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slidcsl xt;pqo 7-fv4e/5aes down a frictionless 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 y uff/ q/5bqhff)1lvhst 8)urasgw5 pc)e1; *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 kinetijt/-o ns-(r,gjwc ti9 c 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 0.7m-r,og/j9 tc( ts i-jnw/s.    m/s

  A 65-kg trampoline artist j6*mm ((ic7t xua+fbbhumps vertically upward from the top of a platform with a speed *ut6im(b mh(fc7 xab+of 5.0 m/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 5q 1i7.u4cnn8z2ua rxbyzgx7s a;w5z stiffness constant 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 ball when released? nxi15 5zzu7 aazw2nb ;c8srx g.uqy 47   m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides as,i4m rm+ 2iqw1ymc )without friction along 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 imq i,i 24+y)mm1s carws 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 conn2:t -t*tsibf2 vj b-zstant k), Fig. 6–40. The block is given an initial displacementt* t2iv2tj-:nbbz s -f $x_0$ 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 t:u9 j bx8qu 5yjel n(.a*ennsizl. 0b,o a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring*l:u89zex.ne.u,injbnlaby qjs0 (5 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. mg*bue m9 .1ycu2h l849,oha dcz9up q6–41 is dragged up to point 1 where it is released from rest. Assumin.92 lu 8y9ahpezmobqg dm*4h 1c,cu9 ug 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 9e axmlo2f665wq/a (+ghto1; nphanb 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 desigil**dl(: w 9trbx jvy+ning a spring to be placed at the bottom of an elevator shaft. If the elevator cable should b*wxlldbt+(vi j r9: *yreak 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 cycle tjunjp3.+ 1hlj ye8w5up 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 traveling 95km/h in oppq6h lmhw3lcf dy/;u5 0osite directions, collide head-on and come to rest. How mmy 56 / hhlw3udq;lc0fuch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slel e l(0bvt2g0 .j8hzjkvvx9u9w:q e1ide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much the(8gqjve 9u v 9evl:z1.jkh02twb 0xlermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a6iq/fe4 6ubk2otz ,c k 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 abgc0 , pcmqs)m8ove 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 hei-de cgn 44-v0hw6ufirght of 1.5 m. -6ing e4-rv4hu0fcd w
(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 with a r(re 7( *i+hmgni f(dtconstant horizoi h (+ greir(ntf*dm(7ntal 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 the crate?    m/s

  Suppose the roller coaster in Fig.g t:9 (gmfd7jg 6–41 passes point 1 with a speed of If the average force of friction is equal g7jgfmdg :9t(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 st .69,t97c )gfn mob ;cwebeehweady 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 (k=18b- 35,w. ky(dpodvce nd(y+pr 0N/m) as shown in Fig. 6–(bny-5ecw dpp,ddv+o.3r y(k40. 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 spri +vanm 3 -rn7gx-pxcvn(mfx.: ng, 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 position, how far beyond its equilibrium pgmrc :(3xf--xavmnnn p. v+7xosition will it stretch on its first swing?    m

  Early test flights for koz b31 bac+ 0,ver)ckthe 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) What would its landing speed have been in thkr+ abk,cbo 3)e vcz10e 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 l eq0vmv3tg7t *c2l6 ieift a 315-kg piano to a sixth-story window 16.0 mt7c6gteq v3me l2i *v0 above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must beqc,5;a +zpqw f:dsz9t the average force exerted on the car due to friction andcst5:;qz pzd, a9w+fq air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h i yktvbpm pu+p5sb.d9l u,2tb s+ ;vr*3n 7.4 s. What is the average 3 bsbp tm.bul 5tk2s+9uy p*+d;v prv,power delivered by the engine?$\approx$    hp

  (a) Show that one Britiss0/ qzw dh)9bah 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 ))9m1es8.pzxs, uw b 49z( rptdglyecare often expressed 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 car slows down from to 65km/h in ad4e denbimw1i64eb:2gpdf (uz/.k g9 bout 6.0 s owm1fi:e bgdni( g bp 2.dz9ku e6d4/4en the level when it is in neutral. 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 1.0 hdn.h3sgom jx;5zlb3a i.jo z0gc.0 n84is0tr? $a\times10^b$ J a =    b =   

  A shot-putter acceleratej o 93zy7ro9xxs a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was devel xj3x7yo9zr 9ooped?$\approx$    W

  A pump is to lift 18.0 kg o b:00zbavgb2h 1.z:qcdn vh :uf water per minute through a height of 3.60 m. What output rating (watts) should the pump motor zq:b .zb 02u: vnh0hcvbgad1:have?    W

  During a workout, the football players at State U. ran up t gst,c5oqdm8v4 wp:h 2he stadium stairs in 66 s. The stairs are 140 m long and s ghw,5mov: 4c28qtpdinclined 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 ay fwb*s22fo xnav3tj60 sj07b 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 sd :u)s w4p ol0u)0+eyaallno8 teep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N? ae n:w)d00uaul olps+8o)y l4   $^{\circ} $

  What minimum horsepower must a mulbgu.9h-nej6f*7izqd n b 0(otor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/she.-*07 u biu6j(qlfnzb9g dn if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.;2m 9dxsb:p8b3l )aqvcwzw0t0 $^{\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/h(8km/h) bumry**d)e8y b/zk j+cwi(a) ggdpers” 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 /kbge+j8* )y*ddc )gzyai (wr 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 1f6n.h..a49ou/w, hxcuqgw8 ;igw yo s0.0 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 height of 21 cm, and an average shelf9 qo.46whgx.w yin8 ;.wa, hfsuucgo/ 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 Owenslg. 2;*hw8f6 bccxpxz me3 x6p’s famous long jump (Fig. 6–42) 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 launch if he was traveling at 6.5m/s at the top ofplpzc 8326g xc;xmw e6fbh x*. the arc?   m/s

  The block of mass m sliding without friction along the looped track sho e.;r865dlkjqe m y c;dlu*u2iwn in Fig. 6–39 is to remain on the track at all times, even at the very top of thq6d y .*kulcd r2u;;elimje8 5e 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 atf25e*4 hqsii n aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only m*sthi i5qe42finor 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 end is fixedfgov k/yx; en+y2 s5/r (Fig. 6–ve gyk5n;+/o / yf2sxr43).
(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 tg p 1/gjkb4j0ahe top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m pk4b0jgg1/j a. 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 elevator is 28 m above a q8(o 0cg38fhu2mtzr qhuge 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 Calw 9d+nb 3 q:taae;yh9mifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) da+: t 93mh;qeynwa9bhigher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 8*tn()3-h vel8gg3xw3nmau.l( ft1yrm i(tf p 1 m before striking the turbine blades. Calculate3 vfn(tat1tyli3 mrflhx3gg ep)((m*. -uw8 n
(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 loop (Fig. 6–44), the a7k(ppm3/ehhd/n0+ l jjq :+y u* 6stwa z,yktdifference 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 nee/0lh :+qa k j3 sj ahk6wypd(+7n* ep,uttz/ymded, 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 into work, how h4 r;zemelu3x+lew* 5m igh could an 82-kg man climb a ladder if he were uewx;3er+lm4l *mze5 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 upward azs v.4a,t9qvga 8ol (zngle 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 inside the scale compresses gih;dt1nc+z;1v:ro;g:sk p h 0.60 mm ;1gcg o+h;:ztr:dpn; v k1his, 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 the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope1:d.+fxaoa+ / rjllt,v 9*bp5pscmj h , and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zf aj mvlp, r/5 d*tp9+axh+ .1:jlcosbero.
(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 disbw06y7 -f/brdpxx 2pxtance of 5.0 m in 9.0 s. What minimum power output was used to accomplish byd w672pr-xx/0 p fxbthis feat?    W

  Some electric-power companies use water to store energy. Water is pumped7 qy0(j4pq .3ezfl*6ghb fg zl by reversible turbine pumps from a low to a high reservoir. To store the energy produced 7 qhjgzelf*l.zqy3pg( b6f04 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 0mqqdz0oo 8n7is cut in half. What is the spring stiffn0mqzd8oq no70ess constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8uqxrt)v j.0r8.0 m 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 can accelerate fr)d aja qex0d98om 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 8d aja9q)xe0dneglect frictional losses.    s

  In a common test for cardiac function (th;b wr+(kg,rq v pev8h9e “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 1prg,b+;8 hv(ek9wq rv5 $^{\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 verthy b qqz1t;6o)q /lh 7nmx8u7aically upward a distance of 500 m, what was its velocity when iq1/)q6 a;bym7lq 7 ho8ntxzh ut 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 f:izn6x fm3+ /lrbt+m8 ca5r i.m j;kcxrom a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what zt+ if6k8 x;in xm/ bmr:m5+acj.crl3is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s