In what ways is the word “work” as used in everydaye. nlw(e*my. w language the same as that defined in physics? In what ways is it di(wy.el.w*emn fferent? Give examples of both.

Can a centripetal force ever do p /vl/p x7dio(work on an object? Explain.

Can the normal force on an object ever do wory l ,3)u0u+v,e vlym 6wql+iaqk? Explain.

A woman swimming upstream is not moving with respect to the shore. It2c4 fstasc-p g,bgs; f+.g1h nb8r.ds she doing any work? If she stops swimming and merely floats, is work donc2t ,rsf8p.fdga 4t ghbn.b+sg;-cs1 e on her?

Is the work done by kinetic friction forces always negative? [ 3*:iglydg* lx*d6x.w b4nh xpHint: Consider what happens to the dishes when you pull dy3bp*lhxigx dg*6*4 w: xl .na tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though h;5f (o+ouzt:z 6bdxo)8jc m byou are doing no worm)+ctf8d(o zj b:6xou o5bzh ;k?

You have two springs that are identical except that sprjgb jaayve*8k5(;cbbc 2p82jing l is stiffer than spring 2 je8*y 5gab(jbv ccp22kj;8ba$(k_1>k_2).$ 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 ont0w/ q:f0hz bn a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distbh: wt f00zq/nance $d$ 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 grqu+ 6mk;z2ik yavitational potential energy change when you jump as high as you can?;km 26+qyuzk i

In Fig. 6–31, water ballooerwo m6g7.zy w(v ,p4d)/yeapns are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the hig er.mzpwyao,v d/ep wy)(64g7hest speed on impact? Ignore air resistance.

A pendulum is launched fromj70ikk e2cy h( a point that is a height h above its lowest point in twcj(y i7khe 02ko different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of 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 mas)vbi9,t .b)5y )aj ikdj7n zzis m rests upright 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 conservati)zzkyav.bn5jd,) bii 7ji 9) ton of energy.

A bowling ball is hung from thc/ur 2:vrp m8se ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it:rsv/8 urmpc2. Why?

What happens to the gravitatw4 eipc7)bs46p-. s*ajk yu b q5*qwghional potential energy when water at the top of a waterfall falls to 4ycks*wp 74*wubq 5iqa-jegbp 6).hsthe pool below?

Describe the energy transformations when acvdn7* . ny5pvu 6(ghb child hops around on a pogo stick.

Describe the energy tran y2m-gbzj 61d/ ug,kpjh( npnm8o8w6nsformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strik8p 62,nmdon g z8wpm6hnu(jjgk 1 /by-ing a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of hein2shsj h 5i30rght h and slides down. Does the velocity at the bottom depend on the angle of t5jsh s2 03hnrihe hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather 3 -opwyfe88qts sy0+h than stepping on top and je-+yts w8py30o8hfsqumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the othe r,kga1he8y idbd;m6 )r, are fired into a bale of hay. Assuming the hay exedh ek)miay8dr,; 61gbrts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple 8/ v ra1b6lfivswinging pendulum in terms of energy, (a) ignoring friction, and lfvari 1/6v8b(b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it ;t yy 9ky46ky/n)eqfk rebound to a height greater than its original height? Explainfyeytkynk y)q46; k/9 .

Suppose you lift a suitcase from the floor to a table. The work you do on t+ -dsoma(n1g pw;bf8 hhe suitcase depf domsn+-hw1;pa 8 bg(ends 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 (d) the weight of the suitcase?

Repeat Question 22 for the power 7,r; b.2g,deu vtwq-k, u)bxiff0vwyneeded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straigh cnzbte 7f..xb8p4u2gt u.z7 bfn 4eg.2put8bxc p?

Recall from Chapter 4, Example 4–14, that you can use a pull1eooc,d h*(aobip/a9ey and 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? Accoun*h91ob,/c ad opi ae(ot for this, using energy concepts.

  How much work is done by the gravitational force when a 265k3l .5wofxvs. /bq rdi:sj(5s ov xb90la ca05-kg pile driver falls 2.8i/o olq.(j5xd w aa50lxfr bs 0k9cb3v:v5s.s0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. fo 0t-bun .d4,*nom*t s sv6lbHow much work is req fnlt m6 0ntub.s,vo*s*dob4-uired?    J

  A 1300-N crate rests on the fltbvpl4 7bfall p7sw5myt),22oor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230bl7tv w)527pt2 b ,mpfly4s la N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontallym/qe/3vs d;d goy6: xk) pushing a 160-kg crate 10.3 m across a 6y3 /;o:qvkx mdgd es/rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated oc+5lyfpcqb(.3 o 7aw qd n,*fby a force across a floor at a rate of for 7.0 s. Find the net work cq*l+bf .opof(w573ad y cnq, done on the box.   J

  Eight books, each 4.3c 2.zo kai2ezij0g28t cm thick with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on topik2.2 0zt jcoez2ai8g of another?    J

A lever such as that shown in Fig.i;6z9x+erbpfuo qovko95 c1 v-/c6s p ekde: , 6-35 can be used to liff objects we might not otherwise be able to liff. p 6e-k zk eco16v 99u/erxd,oob;qvifs:cp+5 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 accelee5bwe wx2k r 9*cpwn6ua+ga43rating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of g *4ewn+ w6ecxb5upr93k2a wakinetic 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 o;pv2fgq4zu, f * 4qlruf mass M an acceleration of 0.10 g u2ru v l44z*qp;qu,fgf pward.    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 linear and )wgq1mc 4smw7that $d_{\mathrm{A}}=10.0$ 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 shmuvatp9z* 5jt( *c svs,1o9pkown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=5 as1topztmsu 9(9c *vpjv,*k0 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 al kl.. x+b/fuk 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 molecs f7bv4qp bw3 ovlg3mr( e-)0tule, 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 doubledvxdz2 ifi*;;5- +abe-fqtlf d, 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 requi- jz7uzy w:0dzred to stop 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 105km/7v(.kmbj vl*zodm h2;h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow who jysfu akh:95;cek:qqd lvgq(+m)7+l se string exerts an average force of 110 N on the arrow over a distanc shkvlkm 7;5++ujyecqaq:gl 9()fd: qe of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) trav3ood++qpmdmo f2 /rk x 2y-e4qeling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by th f/ +kp3 x-yq+e2ood2 mqrd4ome ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimux*i0idjm jasy 1 )5k,xm braking distance be1 )0km5j*y, sijxidxa increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level rosts srg ch (.n38ib2co*9qx i*ad, investigators 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 the8t bco9s cs( g3iiqhr**.n2sx driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the ti2o-mmmzbt v 1lrn5 -53dxxoo3me it reaches the plate, it may have -odbm-3x rl2mvzn5mo x1 to35slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does pgy m*4per.n*80.0 J of work on it? Neglect air resistancemp pe.4ngr**y.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratil6orcr/ h. 9cqon by a single cable. Determin/qcr. r9ol c6he
(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 muchb5l ;:)u v.4bpn5fxwfcvr wo 8 must this spring be s5 op8:4 rf)5bwbnx.fwu ; vcvltretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1:8en+ecrn 05cnj3tb h.2 m higher. What is the change in potential energn: ejhnbr50 e+c8n3tc y?    J

  By how much does the gravitational potential energy of a 64-kg po; zv7c5kd;o4r/ qc. 2wvdombl le vaulter change if his cenm;q bo/57zv4dc ocl;r2dv.wk ter of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on kfvsuo)qko,(s -brsp1c1 w :/a horizontal 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. Whatuc- p1s bfo)qk:(or 1/ swvs,k is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 9am9vrrpwk0w ;8 s ;vv2.10-kg book from the ground so it is 2.20 m above the ground;r 0; wvr9wavvpks9m8. 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 1600 m and climbs to the top * 2i9o hcshh:5x /2ebx*rnw qyof a 3300-m peak.y w9 e*rhxhxq2*5:in bhocs2/
(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 nvl1gw vfix0*1 ext to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached 11lx ivfw*g0vto 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 top speed ( : y)1ab vxp38qtu.knb5.3m/s) and grabs a vine hanging vertically from a tall tre .auv:nx1pq)3k y8bbte in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest,gm3ibd:mi 7k/rs7 y2n slides 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 qy3zox xd24 i(( kb(+/+ebmqcry -rny28.0$^{\circ}$ 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 o:dzyi:.f9t 9s.ped f transformed into gravitational potential energy without: to.ip9fe.f syd:z9d 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/s.    m/s

  A 65-kg trampoline artist jumphah/2ll rd(+ ws vertically upward from the top of a platform with a speed of 5.0 mll/h2h dr+ (aw/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 itswp 45q/ao o3(ffmhoq7e- s qi- mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwarqfqs 3(45 -phq-i oe7foaw/omd 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 frict2m7yx,k*t xkftom41l(ae+hr 9y h5hk ion 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 rao5mxt(hka *txl e km72k+ r1 4hyhfy9,dius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a sc xkxuf ,2j- 0s2kpm0npring (spring stiffness constant k), Fimk-s0cj0f2x k x2 p,nug. 6–40. The block is given an initial 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 from a bridge. She is tied to a bungee cord whose uuq nrm;(7.hva 4pmo;x ecm 6tzdq/)1enstretched length is 12 m, and falls a tota cv;h7.qqe r xnmpau4em d1)tom z/;(6l of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is drp+y;z yz* thy i(3v)vxagged up to point 1 where it is released from rest xh3 ivzytyp z(*vy);+. 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 an anglexga-8 u5)b ubezns2 v7eiu(0v 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 placed1+ iuvi0t/ 6kecxbfr 0 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 brought to rest. Let M be the total massb0t/+ifxk er0ic 61v u of the elevator and passengers.

  A cyclist intends to ulaghx81z(b8hl2w 7 wcycle 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, edi:uf-+h4 b2cf g8d vdu8+ grpach of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is progi8+4 vgcfdbrfd -udp2hu:+8 duced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches .c*pnids+ g wi*8e6a b*upn l4a;iu*i the bottom with a speed of 2.2m/s How much therma ;+*di. nil*nibcspe g8aa pwu4 i6*u*l energy due to friction was generated in this process?    J

  A ski starts from rest and slidesa v*zcr)h5k s8 7cow/a 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 av3 gs 63w b/v07vdbtpc tree 13.0 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 2.0 m, and it bounces backh7rxqii65s v (r;.el6iaj c8 7kwa,bh to a height of 1.5 m. ai.wk7;q 56s v8h(ex7r 6jcrli ihab ,
(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 acrossmop(rt+hxg x3)z, ss q*:rrw1r +zss: 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 fri(x)+w3px:hr, szt z*rss qm: ogrr1s+ction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes m*lo, su+nk4n+oxw6lpoint 1 with a speed of If the ave4ow* +knns llux6+m,orage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s r0e*jcc8 4xd-h0b;o9o i 8/phjjjln j aeaches 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 aul2 zy*/ o1sod very light horizontal spring (k=180N/m) as2 sdyu*/lo oz1 shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached ;/r ntcff sl/qr d2s60to a very light horizontal spring, 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 position will it stretch on itqcr6 sf 0rnt2 df;s//ls first swing?    m

  Early test flights for the ) ;k-gcce *ea 8zanxb*9f fyd7space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from k fenz*-xy df7c cag8;eba)*9a height of 3500 m. The glider 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 mo 0oz6e-vyc0t*3dij xztor to lift a 315-kg piano to a sixth-story window 16.0 m 03yde 0i6zj*tzcoxv- above?    s

  If a car generates 18 hp when traveling at al wymm+r3s8,0 bt)naud7 7bna steady 88km/h what must be the average force exerted on the car due to friction and air resistance? ylt7n70a3+ )drwm8bmbu, ans    N

  A 1400-kg sports car h - (re(wrb:mld*.fqx accelerates from rest to 95km/h in 7.4 s. What is the average power deliver( . rqh(x*b:me- dlfwred by the engine?$\approx$    hp

  (a) Show that one Britis /pn ,nxmto93awo kv,3v+;saih 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 ofte5c 8ahmw-ok:aivmi h,3;uc1r n 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 6 orw5lkrh76w0;yfysj adv:5 6efe()fpnj.f -5km/h in about 6.0 s7offenj fy56yw ( 0:d;r jsv6 ) .5-hflwkaerp on 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 3.0ov 5q9c pkz,9kr5n5x j-hp motor do in 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 motitp z;1td hmfng7g2iq2e;3mp: on takes 1.5 s, what average power was dze2t;ggmqpf7 1n: m2p dt;h 3ieveloped?$\approx$    W

  A pump is to lift 18.0 kg of water persy6e/h:y(:4z xam7 u8v i adum minute through a height of 3.60 m. What output rating (watts) should the pump motoruh eyau i8mzd4:s/x:76(y vam have?    W

  During a workout, the football players at State U. ra 78nhsmk-z3nl+ p8ng9hwvt / jn up the stadium stairs in 66 s. The stairs are 140 m lsh 3 znnlg -87/tnwk98pv+jh mong 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 cliv j5 nim8o(2seqq/5vumb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum powi,+mejin 9/ 3ka)nm pper output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if)+,pk j9nmimp nie /3a the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a , h 5k15sutzgw4 ppm.u310-kg box along a level floor at a speed of5 wh p.pu5u,m1 sz4gkt 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.x/cxxrxsq f qz/5q+ts9u353y 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/h(8km/h) bumpersu9z39auqt cdexa4mcph u ,*6: ” 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 rem,9z4a:9ec hcqtdu3x6muap u * ains 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 the ground, and the remazph)p g78gcv )ining 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 sgp)cg 7)8pz vhhelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famov3mxlr0 vq)/m us 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 )m 0 vlxv3/rmqif he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withou .c hn7;ng8xnvt friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius 7g .hcnvn8;xnr.
(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 a9n1my+womd8 l7 nclx (ys5 n6oircraft without his parachute opening. He landed in a snowbank, 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 18d(oll6x7+y5omn y9 cnnsmw
(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 mg-tnwv*9 i:z l6n ub*whose other end is fixed (Figgn*bl9*vmt: z n-w 6iu. 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 :arm9 bo)o3sq k31 llnto the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an)3o3 kl9brom q: 1slan elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator i)lilm 8.htpu rr7g+c3s 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 nvkr5jc-( cc( s/ifp/in California claims that its lifts can move 47,000 people per hour. -/r cic/kf(p5s j( nvcIf the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at b3h0chh p 6n 7qh*qjy-w) v exzyyo4*-x/5hgw the rate of 650kg/s and falls vertically 81 m before striking the turbine blades.c z w/gx-3o j*h4hw yqq)y*0nb7hevx5h p-h6y 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 loop (Fig. 6–44), thet dv4sx: fl661pu fk tq8 eg56tb4bvq0 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 abougkxtt : t4f6pb850seq1 64vlvdfbq6 ve the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert grc5it1g(t 4r vgg02 xa candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1045tcr 0r 1 ggi(t2xggv00kJ)    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 angle of 45.0kb58s.x+1 e zv-htj1 f oar0fv3 kesd0$^{\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 hh-5(ka yjkk 8scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peah5h8- yjak(k kk?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a l/ufpct 0 3z8rbp)t+ (x iod*uwake (Fig. 6–45). He releases the rope when his velocit +u0ip *wrotxzp t3(d8/cu)f by 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 distance of ia2 mrejz (nf6:+f(r.m8qpz l5.0 m in 9.0 s. What minimum power output was used to alaj8(eqz (mmf z+r n.i f26rp:ccomplish this feat?    W

  Some electric-power companies use water to store energy. Water ib6g2 1s-bsnb*- eghlzs pumped by reversible turbine pumps from a low to a -g* hbng6sl1z 2-bs behigh 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 cut in half. What is the sprin *g ahni)j.jz zz-p;fm.x87:kfu yv1f g stiffness constanz-j:v 8hf k zf7f.);ijnp1.ya*u xzmgt for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m :7vn:byn+. -iejufdzdw8kt 8 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 from 35km/c u9xo : f.oww:u)9vgc;/2z f 4odbrhrh to 55km/h in 3.2 s, how long will it take 9) 9h;/bcvww :2zucoffxudogr .4 r:oto 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 tetb .rdr u v;;p,xnu7m2:zas4mst”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whenn,u. rr d7 4;xtzmmsav:bp u2; 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 distance1,if7nl tvs 7 hduab92 of 500 m, what was its velocity when it left the vol2hdasu 79,in vf 1lb7tcano? $\approx$    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 95k )5 rr*1 k ckgc yl4tzk5zwj3 ,p3kbup)xa8tf,g/s (a) If this water wheel is setcp4kt1ta , bylx rzf* )wurkk8 c553z)3 pkj,g 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