In what ways is the word “work” as used in eqt(x71 t+qu kfveryday language the same as that defined in+f( 7qxk 1tqtu physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on a ;:+b2*zk 0.dxgepknb.urrxyn object? Explain.

Can the normal force on an object ever 9ow7; bf9lcte do work? Explain.

A woman swimming upstream is not moving with respecc:gxi . (x.lipfb. ziz65 b0n bxlf9,st to the shore. Is she doing any b0xig6ix .. x(. llfbz fnszp :,cbi59work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction for yq- 429r3hgk c*) i19uoyem yelf(iqnces always negative? [Hint: Consider what hain3 rq 4ek (gyl9ifuy)*e- q2h ym9oc1ppens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even6rj*8 .n00drzxjgx wm though you are doing no 86 w0jdgr xnrxz.j0*mwork?

You have two springs that are idenbkl,8wc a 7 / ;wa3o1nlbhvg(gtical except that spring l is stiffer than spring 2hlb1gv/ aw8bl3k ;(oa wn,7gc $(k_1>k_2).$ 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 free toi xkwsn: 7mbe,;uc/j) slide on a frictionless surface (Fig.6-30). x,)7wnm j e;sik cb:u/The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potentialom xp+ fsq0tonl . d/;f9m15ro energy change when yomsdxof +lo1fqn 0rt/.9mpo ;5u jump as high as you can?

In Fig. 6–31, water ballok+oe vg7)/ zz e6um(usons are tossed from the roof of a building, all with the same speed but with different launch +(ekg)vz/u z7e6 us omangles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a po)q33omz ifetpm+b: f)int that is a height h above its lowest point in two 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 equilibriumfob3fep+:q3 imt)m ) z position? Explain.

A coil spring of mass m rests upright on a tablennp ol2jc tyjo9:ud7:2yw9 .z. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explai :9jy t: y2c7nzon2lo9pjudw.n, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The ii30pa su9bc 2w kj.(wxnstructor pulls thbx 3j(20wupi9 sakc. we 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. Why?

What happens to the gravitational -yx49cr qs cd9tyv8k*r zs3d x11a 3lnpotential energy when water at the top of a waterfall falls to the ponsrlz94y d9axk- r 3 y8cc*t1s3d xvq1ol below?

Describe the energy transformations when a child hops ar8+xsikp7w va ahb6:+xound on a pogo stick.

Describe the energy transformations thasru7prvsc(s- m) +xc i:0pxd: t take place when a skier starts skiing down a hill, but after a timerc-svc7 pxri( 0p:sud+)x s m: is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest ay1)6zt- ;u gqp9 soezot the top of a hill of height h and slides downuzz-qeg)t o p;6 yo1s9. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers pref* zww3jb7 9 g0iwn5xyber to step over a fallen log in their path rather than stepping on top and jumping down on the other side. Ex 3 0b*wgwzx yjibn9w57plain.

Two identical arrows, one with twice.99pv7/jwem)ul1 ig fz6 b hyjul(f4o the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the h9 ef fm6uuop7 )l1.yj( j iv/l9gw4zbslower arrow? Explain.

Analyze the motion of a )z*+ivo ebr w* o5un)msimple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a gvi+u mne *b5*woor )z)randfather clock has to be wound up.

When a “superball” is dropp y l3j.yd:vk/wed, can it rebound to a height greater than its original height? Explaj/k wy.l: 3ydvin.

Suppose you lift a suitcase from the floor to a table. The work youj *ut6fvx46/ ftl3unz do on the suitcase dept/ux6*f 3 z4ufjtnlv6ends 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 needed rather than the w trh70j of;2ajork.

Why is it easier to climb a mountailxvw b-9rb70vn via a zigzag trail than to climb straight up-x r0bw7v vl9b?

Recall from Chapter 41xhq:hrjo;l l-dp(+m8vy qb(, Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Figoj (lm(+-dy pq1hhb8q x;lvr: . 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by th9(,w hlm8nvty, z9zxe:i s.rm e gravitational force when a 265-kg pile driver falls 2.80 m?t(8h9 . ly z,rs xi9m,em:zwnv    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work ;x 2y4ygc:mqris reqyc; xq:mry24 guired?    J

  A 1300-N crate rests on the cgqm c09k (* r)oslfynt o7;)xfloor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a fricti com ;y0f*c(o9r)qg) s7tl nxkon force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg c sk.x *l,dr9ierate 10.3 m across a rough floor without acceleration, i.l,e d9 rkxi*sf the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a fof. t t6mt0oau aef6,m7rce across a floor at a rate of for ame6uft6t0.7,afo mt7.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on ab6sv i4gruo6u:7 ni)q table. How much work is required to stack them one oi74r vgn6u:s bio)6qu n top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff object26(l x ,rfu ,juaufmj+s we might not otherwise be able to lifl2umf,rj6j a(f x+u u,f. 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°/ 8h . p0ex4krr6wppso incline and is kept from accelerating by a man who is pushing back on it parallel to e 8spwh6.r/ok4 r0pxp the incline (Fig. 6-36). The 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 of mass M an accelerationyax;g+zq+yl 3h* g 4x+ ntiw5m of 0.10 g upwam +q yw+3at+g x*hlx; iy4gz5nrd.    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 tfm(m 3k2; )xd-i cxsymhat $d_{\mathrm{A}}=10.0$ 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 alol/0 - 1vo;fkqh +opkz-m hjq6nng the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m mofhph6; zk j1/vko0-n qq-+lto 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 pafh-zm(o;j+ g ywfhx */rticle 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 oxy vkwg1a4 dc ho;cv8v k 6dhdv-28):cmwgen 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 ux7r os07 -s**d grtkxarrow is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to st y: 07.x+bmotqosw5xl *w( ltjop 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-kgck1z3 7pbcjk5-pd;/ wkcwc1 t par traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose stringr*: c ;j.nx+b m,k lew(.njkt fj5wu/h exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the* xkj:wf+c.n lekjmbnu,rtw/ j .;h5( speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moveia ,rfe1wycm :.pbkhc9 +:ct ;s a fielder’s glove backward 25 cm when the ball is caught. What was thwc:p cmr, y;f c t1a:ki+9e.bhe average force exerted by the ball on the glove?    N

If the speed of a car is increascdpjqjo60a 0iy: lqw:80z13n5suuy eed by 50%, by what factor will its minimum braking distance be increased, assuming all else c50unq u:3 o w dj0y spal1i86z:jyqe0is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measuregn8dk3 ea -wkbh+e/s8tzjf2)2 - h waf 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 tf tj3 whgfena-8/dkbhe2+8w ak )-2szhe 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 time it reachece to;a7qg;gb bj*z7: s 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 tgje:;acqbbgz o 7*t ;7he pitcher is about 15 m.    N

  How high will a 1.85-kgqiq1p*m h2elu36f)3 .c.8p sei ppdki rock go if thrown straight up by someone who does 80.0 J of work on it? Neglect 8qi hpep36pd2 .fi esk.c)*q1umpl i3air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelera-mhfp+4 6s i im)r(zdtih4c e3tion by a single cable. - (3e4pish4rchf6t i +z)mmidDetermine
(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 stiffnesac 2qh.2;qc5clo lknp 4 0+hoj dv93pvs constant, k, of 440N/m How much must this spring be stretdov02hpnocal q.qc3l29h jv;pk+5 4cched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What ioz8fil;v5d:r13beqz byssu928w7e is the change in pre3ib:qzl;18by5 9du sev ow82 7fzisotential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole 3gf0mfew +(-m 4wjbxg vaulter change if his center of mass ris-0b +(jwxfg fmgwem34 es about 4.0 m during the jump?    J

  A 1200-kg car rolling on p e0mb)31i,t3udpu 84tjp:vupsem . ua 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. What is the p. ipu:1uv30tb3d,psu u pe4mt jm8e)spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 223s)t d y xalcp3yl6a).10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the bt ysadx2y33)pa 6)cllook 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 h- skzk3nh6rxx-5tx +of a 3300-m peak63ht rn+-x 5shzk-xxk.
(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 han90 7lq muqp;/eie+sio+dso )ugs vertically next 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 to the end of the sprin 9 oouepqdsq/m+i)u0 e7s;il+g, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at topwha 2jo+db2jf z66f +tk)v9s3fuya (i;/yjku speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jung29i/)kud ;kw6 jbvjy yf2 fo+s t za6+f3u(ajhle. 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 frictionleg. f:aknih6 cgu:um2p9b)qx+ ss 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 givefbft5 4 7th:aln a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fray)b: h6r, hcbgn’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order h6yb):gh c,rb 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 vertica67e(z1 xzz vjm8u,gv glly upward from the top of a platform with a speed of 5uz1vmgeg x7j(8v6, zz.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 iyy l; w4o 818pux1czypts mass), whose spring stiffness constant is 950N/m is attached to a table and is comp8ly1czpoyu1 8x;y wp4ressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown in Fig. mycf,a-) 4r,jkf1u ht 6–39. If the block is to remain on the track, even at the top of the circle (whose radius1mah y)j,,4 furckf-t is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness constant i. h 47wg/2jyrdyj tq+k), Fig. 6–40. The block is givhjjy rwt.+i g/27y4qd en 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 jrd cw .v+9v5 j,bwp-oj*pxvh2umps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s2pbp.rv wjhvv, o +cjw*d9 x-5 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 dragged8 mey0z,o9(m/5mpsd;a bs kam up to point 1 where it is released from rest. Assuming no friction, calculate the speed0bk5 mam;msy,p/8de(o a 9s mz 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 ang9(pzwwu e 5q2iktu7u/ le 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 poxuu/e;mvmz wf 48n ++pl2 +yclaced 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 mass of the elevator ane+mf/+;m8xp+ 4y cwz vou2lnud passengers.

  A cyclist intends to cycle up abc5ov97qz 0pv 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 76.84lgmn1u -uzvj s ) j;xscjc+50 kg and traveling 95km/h in opposite directions, collide head-on and come to res;z sc u8u v4sxcgmj+1-j)l n.jt. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the e8g2j7p aeiwp vna0 mznf16 +5bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this processi2nvg5f6pnp 8e1wzam e0 a+7j?    J

  A ski starts from rest t.wra-4hao/l and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m abovek (j.qm4j8z ot 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 hefa50ck/asig(/ o1hgyq :yl2fight of 2.0 m, and it bounces back to a height of 1.5 m.a5i 21lay(h /:ky qsfogfgc/0
(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, startinoq0bg r(o8o +3 *zthrlg from rest, is pulled across a floor with a constant horizontal force of 350 N. Fo8or0( zhg*q l3 +orotbr 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. 6–4qmf , foklf,5.f qnw/ qwd oqqg n*3.52iv,l*i1 passes point 1 with a speed of If the average force of friction is equal to one-fiftl lfq/vq 5.5onqf.fmqfq, *,*w,3 k gwdoi2 inh 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 6p mfp f id,7+wj4zsq ;lt05xl:rkc1 +kmbow.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 tok3g0 3 jzwga8x3 0e: oxy0eau wq(gk*p 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 stopping age(aqx8wuo ek x :gag03kp00yj33w *znd turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attm)b8 i: acex*sached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where ths 8mi bca)*ex:e 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 its first swing?    m

  Early test flights for the sp1(btgxvf*o z2cd tq l ,oh 5sso:46ud9*bvv.oace 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 the absence of air resistancet,q h2zbb6( tsdxo5uvf * ldo:* o4cv19svog. ?$\approx$    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 sew3 t lnsx+c9axc) ako- 99ay0ixth-story window 16.0 m above? a )wkanc s+-9y30l ocxx9 t9ea   s

  If a car generates 18 hp when travelincu-m lsw4752 zwt-ns gg at a steady 88km/h what must be the average force exerte-u7sw z g-4 wl52nmsctd on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from r t;s1mk+f lflo8b3 (iwest to 95km/h in 7.4 s. What is the average power delivered ktw (f;m l38+1 ofslbiby the engine?$\approx$    hp

  (a) Show that one Britisxr1 9zwc bsjz/ 8ti/*mh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form ofu4 kfkfm0a9fi de0/w3pn. 01k45matuh z0bo k “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-k):y0m8p;u7y t wjr xwn v+q:e-ubfn s+g car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed tnew+umpjt )r f 8y:uw ysqn- 7:+0;bvxo keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp ;q(3t*c gndt jn4- zwimotor 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 motion takes,+ ssg5 ye+ m--bzd nwgv7/kto 1.5 s, what average mw,-v ke7/bz -5d+ggs y s+tonpower was developed?$\approx$    W

  A pump is to lift 18.0 kg of water 7h, cok492o nj7ma-ky lm* ojkper minute through a height of 3.60 m. What outpcj4n*okk-ao7 mjkl, 9 y 7mh2out rating (watts) should the pump motor have?    W

  During a workout, th.-crk. stk d+w)y 5qoc6wq+ fqe football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an ancr )s q6k.cq5fo+.qk w t-+ywdgle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 imci,w77(aep $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a h*o 8hy;imzu c2ill can it climb at a constant speed of 75km/hi*u;m chyz2 8o if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motolf *:x9sv+34r k hiokpr have to be able to drag a 310-kg box along a level floor at a ohsl3kv 4+:*ixfrp9k speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7 slvgm) dir3yo1 g:c a6a,(ye wb6l*t;.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 buisb2e da2s8l *tlt “5mi/h(8km/h) bumpers” that are designed to compress and 8 *l2sbasedt 2rebound 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 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 grounk,. lmyaix4, i(ksk7t d, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves,k4i tk y7laks, (xi,m. assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42s,1g8 aq ( dtd*dfi-2p8zv t-k* unltz) 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,tl z(t 81 inpaz-u*kdvqtdd8 fg-*2s he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction alu3d tfz ::aei)ong the looped track shown in Fig. 6–3aet izd)f: u3:9 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an airch,ru 3 a/ ,vsgk5h/ywvraft 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 vy//k 5uhg,arh3v sw,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 horizonta. ji sb h1q/;5obpb* tyhq /k4se)qpj;l cord of length L whose other end is fixed (Fig. 6–43).q i bqjhk4.p)b5t/johq y /;1sp; eb*s
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The cleh*e0 tpd:/j aj- ww6gimb is made in 5.0 h starting at an el-heg*ed6j /t jpaw:w0evation 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 920kim-xrb6kqt 5l a 3j8ngn*d, i g 344glkf3ju;-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 California claims that itl )ep13xi:qras lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.e a:p ril)x1q3$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before100jev h5glxg striking the turbine bladesgl 15e0g xvhj0. 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 verti9r zn+pk*n 77yiy ox/ncal loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, thiryn7n+/ix9p7 yzon*k s 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 1zvyp( lev4nv 7 g:l eja7uy8lj*s+ v*candy bar directly into work, how high could an 82-kg man clim*81v7ln v7yjlaupv ( +*yv4jg:e zsleb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward anghjio951ny;6t)w 3q m vlbm6bkle 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 0h:tj0e -ms d p.ttygl(s( kv,iae3 k:,.60 mm, and it tells yea km0l3h, ig:ytkptv (sj-t se(,. d:ou 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/a hpk,)i )g)szzfwk dt0w3b: ub;+on*s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his vez0g) k dwib;f k3uz)wb*no p:t h),+aslocity 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 ve6-z3x 2tjzmiertical distance of 5.0 m in 9.0 s. What minimum powerz meitxz26j3- output was used to accomplish this feat?    W

  Some electric-power cohb1an1c qkl e2 wnof 9;5xk-g.mpanies use water to store 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-MW (n gxw ak9ch2f5 nqbeo.-;l1k1$120\times10^{6}$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 cons7zf sm) hrxki9ym4a4dlg/k* 1tant k is cut in half. What is the spring stiffness constant for each of the sgl/7h9 axzd*k4y kf i r)14mmtwo resulting springs?   k

  A 6.0-kg block is pushevic s1r5 bgh7o4kno )m :z0ap6d 8.0 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 accelu)gazi +cum:2rh5 b8 nerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75kmuu)zb5gn8i+:r 2hac m/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (h ik5h03voc,ue/x hn6 h-v ny.the “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 avhun0v,n -ho3 xke/h 65chi .yn 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 spew,0n1ojcl(b2 dwum c/ es a 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volc , d/cw(en12mj0lbcouano? $\approx$    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 p1ygq2o( *ma40dld x4yvv+l rm at a rate of 95kg/s (a) If this water wheel is set up to provide elvml4 x1p2d4l+do( vr* yy aq0gectricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s