In what ways is the word “work” as used in everyday language the same as thats7ypks,8lrydk ox 31mh5 n,e. defined in physics? In what ways is it 7,ep r3lx 1,k yks.o hsynm58ddifferent? Give examples of both.

Can a centripetal force evi8 x.o + gjhzvvik;rm:piz6 70er do work on an object? Explain.

Can the normal force on an oom* 0-mgiv c:kbject ever do work? Explain.

A woman swimming upsc+r(d zk54etptream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floaed +ptk c(zr54ts, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Cons99wgr) ;uy5 9s8v4hrbny m.kcx yzb.zider what happens to the dishes when yo;b)huyrgr 54. yx9vw98.m 9bkczynszu pull a tablecloth out from under them.]

Why is it tiring to push hard against a so6 et;5(yw lhkxkd-v 0clid wall even though you are doing no wk0 (xe5 cwly;hv6-kt dork?

You have two springs that are identical except that spring l is stiffer2d5xqkoxws9 10dq7x*fvxu6c than spring 2x2s607d9dk*w51xx uqoqx cv f $(k_1>k_2).$ 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 forc +kk23w nr;y7jmio wn1e on 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 2r k3wmy1; + wnjnkoi7has 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 youryo-* iow acn(5 gravitational potential energy change when you ju y(i-nao ow5*cmp as high as you can?

In Fig. 6–31, water balloons are tossed from thew.rt0 *io3upiwb)d2 z roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impactdw 2w* ouz. b)t3i0rip? Ignore air resistance.

A pendulum is launched fu bhl za,y7a:gdev:) +rom a point that is a height h above its lowest point in two ybvuade 7,)l::a+hgzdifferent 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.-c tj 6bibk8 2bydf3nygk65es m rests upright on a table. If you compress the spring by pressing down with your hand and then cgtbf 86y-3bb2d5jney 6ik.k release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a s d bhll/.z;qabkwri7+9tw r1.teel wire (Fig. 6–33). The instructor pulls the ball back and stands against . w+ta./1kb q h;lwl7dbr9irzthe 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 potentialz 2dravz3lo// energy when water at the top of a waterfall falls t3l a/z/2 zorvdo the pool below?

Describe the energy transformations when a child hops aroueiz. ch6n: 6v r:)kuevjs+d0 rnd on a pogo stick.

Describe the energy transformations that take placs 4y5oejix31zg i ++e; 0yttbie when a skier starts skiing down a hill, but after aozti1+gti+ sy5xee3yi; 4j0b time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top o (gk1r bqgx8lr.g(bv4f a hill of height h and slides down. Does the velocity at the .gbx ((klr84vq1gbrgbottom depend on the angle of the 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 theirmn 6eibm.1mfpti0 ihc3xr 4 -4 path rather than stepping on top and ju01t 4i6 m-bimfhn .im ex3prc4mping down on the other side. Explain.

Two identical arrows, one with twice the soif ;cr(tsoypyt+8rmah9234x zjq 6 4peed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fa698fp yor4yo 2xcm s 3rit z;t+h4aj(qster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy,kwt( e:gflq9 9e,lok 0 (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound upf0 9:wl q(9geke,lkto .

When a “superball” is dropped, can it rebound to a height greatz ohx pwlygc yk a 7)0z1t,074lw9htt(er than its original hlkh( 9l a oh74,z7g)w wyt1x0 cptzyt0eight? Explain.

Suppose you lift a suitcase from the floor to a table. The work 7u9av gn3.eyz you do on the suu g.vn3e ay79zitcase 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 (d) the weight of the suitcase?

Repeat Question 22 for the p ectg4 smsg nma.b5;)4ower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to c ro8b y5y cox)a-4un.jlimb straight upo noya 4j.8br 5c-y)xu?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes tuo 1fsa;x :5hko decrease the force needed to raise a heavy load (see Fig. 6–34). But for eves hu ;oka15:fxry meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by h hf*ov3i2coqd+ ;let 0eawd5((tq q+the gravitational force when a 265-kg pile driver falls 2.+5 o3*hfe ed tqlv(dtaqoqhw(2 c+i; 080 m?    J

  A 65.0-kg firefighter climb0;:-+ byjnarin0 vm9:euntx bs a flight of stairs 20.0 m high. How much work is required?r-a nybmn: 9j+ xun0;: bi0vte    J

  A 1300-N crate rests on the floor. How much work is required to move32z0guaf3 toxq0 +uatx7winbe) g, c 2 it at constant speed (a) 4.0 m along)z2fn0 w3,g qc+u0 bxa3i u2xgtoa7et the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a o 3)bmeahbh(n2 mw*0 k3 gz7xk160-kg crate 10.3 m across a rough floor without acceleration, if the effective coeokag7 b 20hn wm (3xb*3me)kzhfficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor q(mkrxi e 8b1gfeyq8i h- k*17at a rate of for 7.0 s. Find the net work done on the bofymb1x7 h iqq*8g k(1r8 e-eikx.   J

  Eight books, each 4.3 3t-:2e u7pko adlf. amcm thick with mass 1.7 kg, lie flat on a table. How much work is :fk-. e mla7 2uptd3aorequired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-3z . htanx(g6,.p wq*bnac;ylk9 5)ye:ms2 ozd5 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of out. eyz x:*,tknz5qd2; o 9w6 p mchbgsay)n.al(put 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 ap(91 n-og( zdzqlk9 lcmbc80n 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). Theo 9k809qm1 -z(pldc(l n bzcgn effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter o 9 :f5firw+f,twm 6ghkz8c*pwf mass M an acceleration of 0.10 g upwardmhrtci, fwf +85 wk6pgf9:w* z.    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 .nyuep;ef+ +x axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig.a+aalie2;:i y 6–37. Detey ila a:+;ei2armine the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in the 2n8d5lv:uyzysi,m;l ,c5 kf(ggrn / v$+x$ 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 oxyga2j8 zy8h, -jhsodf8 ken 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, bpgcf3t0,3clu h h s800xn3mmy y 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 requiregz+tm(c9 be 7tbqt2 :yd 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/h?s rvv0j,ezq-,; :e sih$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average wv6rdkk *6uc;h/.2xto,sdp j force of 110 N on the6wd v u.cpdx k*t,jr/;sok6 2h 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 ,jv(9 g1xr1j3w1at-gh z8pjwke-yjs -fz -a ra fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on w 1(g3rjz,a98yajgx--tjph1z-rw1fj - e sv kthe glove?    N

If the speed of a car is increased by 50%, by what factorr)saymw6okm , :yaaes 7cq 7 9.jx;bf6 will its minimum braking distance be increased, assuming all else is the sameqra,;7 6fyy oemac smb7 .6xs:w j9a)k? Ignore the driver’s reaction time.

  At an accident scene on a level roadz9 ow9mq58o of, investigators measure a car’s skid mark to be 88 m long. Them9o 5w8z9 oofq 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 mass of 0.25 kg is pitched zmjxochp /j*re onf*; : +tm.9at 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 between the plate and the pitcher is jf+z mr:on j.9pe*m/*xo thc;about 15 m.    N

  How high will a 1.85-kg rock go if thrown stra.pez c(vnzb,sy(+y 4pight up by someone who does 80.0 J of worc4yey.(,pz +( nvs zpbk on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single ck5j qtjy50 6gbl fvn1;vd46xi ablel5xv djf4vjn01;y5i bqt g6 6k. 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 stiffnmj3o;4x 8 teie6euu ,mess constant, k, of 440N/m How much must this spring be stretched to store 254 te83em,uxiu;m 6 ejo J of potential energy?    m

  A 7.0-kg monkey swings from one 4wt.co0.rwmuv,b* o, i3 el9zag,lqw branch to another 1.2 m higher. What is the change i,zwq.3,oo4*wt,c0lg m a we .i b9ruvln potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chan6w -rt7h85jk rylags rq(/x0.-cckidg7j5 6rkh 0crglc (ixkay8 /sd.-w-tq re if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling ons0l( .da:g )3jy7ipzprn-d qc a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and i(-ci.qgjp )n7 dadpslr:y3 z0 s 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 ;qudqgd /(c 8tk8+ kg ,z v9gp(yk-yme2.10-kg book from the ground so it is 2.20 m above the grouukg qck-ym/ve 98 kzqy(t8g( d+g,d;p nd. 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 of a 3300-ms;auy3z ux(spjye /tdeb+ 54- gh01td pea5ztp1d uuha/;s3 j+(y-y4 s0 gedxbtek.
(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 ver+5m1jxp .jigpnw 82 dqtically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5.p2 8 xpmjwd+1ji5qn g-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (lwj5do lec ((7 v5lpn-5.3m/s) and grabs a vine hanging vervcled- l(j l(o75w5np tically from a tall tree 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, slides down a fl2hs4bs,u -. .hk1 ofkw(m2rievmn+ erictionless 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 28.0nk.6kht;n) c*hi 8fft $^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational pol0+2u tmz)g1xi/hfr;vxrcd) tential energy without the aid of a pole. With what minimum + )0f;lx2 h1mgrru)/ctxviz d 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 jumps vertical.5i r.mq3 lcqply upward from the top of a platform with ilqm3cr5p.q. a speed 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 ma4j3qqkw a4 5*c)hcyyv ss), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give t) yy q*q4a4kwj53vcch o 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 frijjb kv9/2fc /itsy t-m9zkx91ction 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 is r), from k9t-c/t9j kj1 myxb /f92szivwhat minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring sti7b,7ft d4g v w3 s,(vlvjd(vrgffness constant k), Fig. 6–40. The block is given an initial df7tv7 vvd,jr wv4(lgd (gs3b ,isplacement $x_0$ 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 wha3ln64hbq 7xpy y1omo7:)mv+ l- whdeose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring s+xq ml4:w3m7ed7 loa6)nvpbh1 oh-yytiffness 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 d86 9z.dsufkl8kre aic *:7doa. qjy4is dragged up to point 1 where it is released from r8ysadruodk9l:jzk6*7 qei .fda 84 c. 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 38m or t/+dzuu12 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 designing a sprin4 *kxlmv8 ;o6cb0xsuna . ve2lg to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a h;vx4 a*cl8x0vsn .elo 6b2mukeight 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 up a)thi+t:d l etv- c0)4 ffhefhyp0q6t + 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 in7bdyacdl 9mj7 t**p7b a18 jyy opposite directions, collide head-on and come to rest. How much thermal energy is produced inaca yy p7j 1977*ty bb*ddjlm8 this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child desc 27ojrww. btaz4i b8z;ends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generateia o87tzbj2 ;w4 .zbrwd in this process?    J

  A ski starts from rest and slides down a s:16nf3erufa )5 vzub22 $^{\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 13.0ant:e blbz* bxty,s;a j2*/j: 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 ba8uu xd5bdelp sj*cf-7ms ),w-ck to a height of 1.5 mu-*s7fmp8bxd)5usl-w, ecjd .
(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 acra /b6y:uk p mbv.j,lp+oss a floor with a constant horizontal force of 350 N. For the first 15 m the floor im6: ,k abl yu/+bv.ppjs frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pas6hit* 4jw gek*ses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what spk6jtw g4ih **eeed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwaratk7mk- 5q t/ibdb06dd 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 fihg,dvzam1,sr gt po-py,v 4 4.rmly attached to a very light horizontal spring (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 stopaopyr p 4,v gg4v,.,h-dsm1ztping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attxk ) d2rbb1q-xached to 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. d1 bxb2x)-qrkIf 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 tho9k40rk*qyl o u7a2xs e space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height l4x7*s 0o2yka 9ukorqof 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 motor to lift a 315-kg piano to a sixth-story .s(3(k3xo,ifyjvl 6l z x9rivwindow 16.0 m above9i3 os3 (6lizvfkxx, .rljy (v?    s

  If a car generates 18 hp when traveling at a oh2.fm5r :,pqkjen+j steady 88km/h what must be the average forfnr eo5,2+k:j.j qp mhce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accel bpcht 4q:k3zfuhp8 m74r .5gzerates from rest to 95km/h in 7.4 s. What is the average power delivered by the engine?rkhc4 u mz fpg3.btp8:475h qz$\approx$    hp

  (a) Show that one British .vmqm agf;27 g2dv0,wnf o:s1lz-pnk horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often exprezt4;lcx 802wr vtqfgh;q. +50ogbtfz ssed 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 thatw weay)/uo2 iv+; ulw,wutxo/jr s *)) her 1150-kg car slows down from to 65km/h in about 6.0 s on the level wheuw)v/twxau* rlwo e ,)s/o+2yu iwj); n 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 dooxljt b68h fw 86*3ejw: xjs9p in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from res0oy(kts9 ele )t to 14m/s If this motion takes 1.5 s, what0eo ktyesl )(9 average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of waterzqivw 1w(zjw go0. )3c per minute through a height of 3.60 m. What out g0wq1wvz3(wjoczi.) put rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up7xquumz5js8 a 7s(l 3j the stadium stairs in 66 s. The stairs are 13z 75susxl jqu7j8 am(40 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 cl+60s+;7 aywy2s ld krqiaw:tqa2 lp9bimb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How snqh m z nok2n)wcuy7fp+e ./5-teep a hill can it climb at a con z.2 7pwmf qy oc/)+n5nuhnke-stant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to 2 ubbd3(4ri : es4ae ae nhjwgq9u+n6*be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.454q :9j4u(6d+nbasiagw3 bu ee hr ne*2?    hp

  A bicyclist coasts down a 7r ;g) 47caj5xs3qa.r /z gdsyzgd p;z2.0 $^{\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’s45 vrq,tpgbo9 ekim9;s fdo r--0tl.f cars have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what m;biqf rortov.4,d ts gkfe9p059 - l-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 rema/e ssju9uv (3xt0y oa+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 iusja+ey9/ usxo(0v t3s required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump rafp: 8e1)tf g(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 a)f8tg:aepr f1 t launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the c2)alln9jr v.looped track shown in Fig. 6–39 is to remain on the track at all times, even at tjn v9)2r.llcahe very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his parh z; k692daw1e,stc ddachute 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 as c9 k1h 6edzd2;w,tdestimate
(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 rs bz.t im;x z7h+e;0flength L whose other end is fixed (Fig. 6+z0 s.fm rih;7bt;exz–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 the8 kd.kjd7 0,5ut cnl b7l,eisr clt48k top of a 3700-m-high mountain. The climb is made in 5.0 h starting at ad0 clb84 srtk 7jdn85 ,kk7luile t,.cn 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 y*s.q3nl m0fq qo8tij *i7 g0du;czm4a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Califg m0ktqj v-cg inf()4(ornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.k(-t g0(i cv m)gj4qnf$a\times10^b$ W a =    b =   

  Water flows over a dam ag5;v6 n2) muimgzkd:it the rate of 650kg/s and falls vertically 81 m before striking the turbine bl:k2igzg ; nidv 6mu)5mades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circ r y4vp cuipz+1uncn -;-+y/ifular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum rvp1z/;uy ic4 n+- c-pyn +iufneeded, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body cesoc9m2fqh;k hz86/ p7 k3vfcould convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fu/f2m6eqc fpo7ck z3s9vhhk 8;eled 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 angle 7bz-c ze7/u. x ra 7+x+gmpnziof 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 bathroomsyok5 vdj y xm69j0o53 scale, 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 pe55 kyvo6xjyd3s mo9 0jak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6–4r9 t//lgq2 k dipz4me+5). He releases th +2k/e9gprq/mltdz4 ie rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m inh5 j6dw3lxuw 8vzs0t;sl n1 :l l.1dbx 9.0 s. Whatz 0x1uwl ;hst:n3l1b lj l.5 dw8dvs6x minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to std: ) t;ulidc dj6 9huiu-m3f7n0ggtf)ore energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MWt6)h j0u nli-id9:m cgud3f; f)dg7ut ($120\times10^{6}$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 t*37g7sf1f-pwbtws :8ql qk hq,oicq9t,)aod he spring stiffness constant for each 7 l1qcs93f,ki pf,o dwgt-qbq)8qot*a:7 s whof the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m u x5wkwoy e llm-(ui:ea s2l1j+1ug+ x3p 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/h to 55km/h in 3.2 s, howkq4-(qzv*j rj long will it take to acce*( jz4vrqj-kq lerate 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”), ti8q7wki -n 5c7hy pjyjzp. 0*ahe patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg paty5*z i8j i7a -q7w.jkny chpp0ient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock verj mk9 8wn75 gfdc/hsr0tically upward a distance of 500 m, what was its vel rn0s9/75jhgf kd 8cmwocity 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 *l9 :5 du/nc2fr;2xnsqiq lkz2.0 m at a rate of 95kg/s (a) If this water r9kcz5n q/*lq2xild2s: f;n uwheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s