In what ways is the word “wor pjfgce: u:3*lk” as used in everyday language the same as that defined in physics? In what ways is it different? efc:3p*:u jl gGive examples of both.

Can a centripetal force ever do work on an obje- gh+/ z-linvch cjjlfe(,y //ct? Explain.

Can the normal force on an object ever do work? Explainga0hxjyeeb(+ u8 p /q9.

A woman swimming upstream is not moving with respec9yspp 75p 7mmrcw7 gs18vwx;bz y)i.nt to the shore. Is she doing any work? If she stops swimming and merely floats, is work done oryp;w.1 vn5g s 8)w7x7zym7bim p9c spn her?

Is the work done by kinetic friction forces always negative? [Hi* :9mzm/x/ rh ka9fmrunt: Consider what happens to the dishes when you pull a tablecloth out from /r9: kr*uha/ fmz9mxmunder them.]

Why is it tiring to pu8on0-c)-swjq i w tvx3sh hard against a solid wall even though you are doing no wor-wcxn803t io w-qjsv)k?

You have two springs that are identica fmm78j,fkuoe v97k3 vl except that spring l is stiffer than spring 2 f7o39fv7kjkv eu, mm8 $(k_1>k_2).$ 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 consk0 gqbrs 9(-pftant horizontal force on a block that is free to slide on a gq9s0pfb-rk (frictionless surface (Fig.6-30). 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 lb s.iq 17rkjfg85(9( ,trt uh.ewfayyour gravitational potential energy change when you jumqjhuri9rt a8.1be . tfyl(fw ,sk (g75p as high as you can?

In Fig. 6–31, water c0w4k. wom.4 j*ljflaballoons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore ail0.j wa4 ojkcfl wm*.4r resistance.

A pendulum is launched from a point that is a height h above it-abas2:a0qvgh (uqtj6y/4 lj lpgp8g 0l8/ons 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 equilibrium p8 q8ogpllapl2a (h/a/-6vqbt g j4jng: 00usyosition? Explain.

A coil spring of mass m -0+ 3eej4s zwy cu,myzrests upright on a table. If you compress the spring by pressing down with your hand and tz 04+suczyj-eyewm3 ,hen release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ce o-blndd5k g/a,u8h30jcyl.7d xz fg6iling by a steel wire (Fig. 6–33). The instructor pulls thef h0a5gz jc,nk/g3 l.dbu 6yd- dlo78x 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 potenwxzs * bbi+8q) vmawm0h01d3ttial energy when water at the top of a waterfall falls to the pool bei01bvs*)t aqwdm z+ xh0mw38 blow?

Describe the energy transformations when a child hops 1w tk*t8k5tf htx5,ivaround on a pogo stick.

Describe the energy transfovi) sp 9n.mj1yde (:wirmations that take place when a skier starts skiing dpd1w.(:)m 9vsiji en yown a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from retg ky/euam9 5l(6n-v9oqvy 0p st at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle o0 y o-ym9/ean9gv(k l 6tqpu5vf 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 their path rather :; .4ns 0v 7lh:qdtplql..41kitpiuu4 beitg than steppind .eh.itupui. :7lv0pk: qtibln l4gt4q ;s14g on top and jumping down on the other side. Explain.

Two identical arrows, c 7dny/(y elfvqxmie9 -,9 :waw-kx.r one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a cony c - qf x-.kad(e9/7ewmyin9xr:wlv,stant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging6rt(2n26tbrthw t065pjw sqlsar4q+ pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock w asrw ( t tq22r40 j6+lh5rstnq6tp6bhas to be wound up.

When a “superball” is dropped, can it rebound to pg/swkm/ u j(orc3t((mdtyl+* 6s 9cea height greater than its original heiy ccj* os p9+ms tugkd(mlr//tw( (63eght? Explain.

Suppose you lift a suitca7n/yybslvcb/1 w to,l2 r4se-se from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated p4lnv/t2bswo ys7er 1cb- y/l,ath, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power ne.o9s) y qlfo8meded rather than the work.

Why is it easier to climb a mountain vi av)hlela7: 8fa a zigzag trail than to climb straight up 8lf:e ah7l)va?

Recall from Chapter 4, Example 4–14, that you can use a pulley ajh*ay65u yl 0dddtf1 4nd ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raise jhy1dt5d0a4*du6lfy d, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationaqoi1x-qll4ekcr0 2z p 1pvx+2 l force when a 265-kg pile driver falls 2.80 xc1p kl2012izxovq erq+p- 4lm?    J

  A 65.0-kg firefighter climbs a flight of stairs tefm/k lz-q2;mxxy/+ 20.0 m high. How much work is re-mxmfty 2 q+elz//;xkquired?    J

  A 1300-N crate rests on the floor. How much work c :x, fbu e1 lh0p:sk8q;g1vme7f1ckd is required to move it at constant speed (a) 4.0 m along the floor against a friction force q17kvxgu0ckl11 m;eff8,es:bhdpc :of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mov4r. 5a(t.vy;duo 0e+pi kuc ncers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of fric ;kuy.rde5 04n( acp.+ civotution was 0.50?    J

  A box of mass 5.0 kg is acc f5629wew7flpt i n*.ayp :mhfelerated by a force across a floor at a rate of for 7.0 s. Find the net work done ht9mf6 .i 72fypwlaw5:fn *pe on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How much w+7psesfrf8pe lt( 8.q ork is required to stack them one.8le87espf ( strq+ fp on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff n9wl:,p;: wximp ffo2;h ):h aadwi,u objects we might not otherwise be able to liff. Show that the ratio of ou ,u mfloi; hwa9:fx: h; pipw2n:)wd,atput 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° in,;e5 unf6e /r*z6ksebx- euipcline and is kept from accelerating by ,6 x ps -*e;rukb/ifuee5ezn 6a man who is pushing back on it parallel to 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 requir6 m1o7tce gwo /r*fqi:ed to give a helicopter of mass M an acceleration of 0.10 g upwart6or:e/mw 7qfoig* c1d.    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 iie6,8xj7 *rbii mh u .mqm9v.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 )dh+pu 0un(j3rp9 qwpin Fig. 6–37. Determ ) wr+d9j pu0u3hpnqp(ine 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 ard.7fl *j6w bs 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 oa4si jro))2r p(v+jzjzg knljf+)h8-51nq hexygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has l(0u xd/jub5r 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 stop an e-.udjdmmq/6;a:xqk, )ojl m.ne;r v p lectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 stoh3la2pg)g+;h1-kczhvt* q ay, vur;qp a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 N v0f txo zm 0/moxx;z37r* v*yron the arrow over a distance of 78 cm. What is the speed of the arrow as it lea0rf/7*m m xt0;*xxyo r3ovz vzves the bow?    m/s

  A baseball (m=140kg) trav 3vpur.r+j/sf eling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught.p v+fsj/3.rr u What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will0q0j,pmy m(b a its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s bapy(q 0,m0m jreaction time.

  At an accident scene on a level road, investigators meas w:g-mps((wcjxm5tn-qz6 .xns/vzw. ure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic frmwgqzws:.tcxn5p.ms-v- /n j w ((z6xiction 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 pcl6jst/9 q: ptp5)do+h2 wvvat By the time it reaches the plate, it may have tph): q52owt9l+ sc pvjv/ pd6slowed 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-gnma g30y .ot7kg rock go if thrown straight up by someone who does 80.0 J of work on it? Ne7 gmao. t0g3ynglect air resistance.    m

  A 285-kg load is lifted 23kq (3*avkdav e j1llgls3m :32.0 m vertically with an acceleration by a single cablgsm3kevj( d *vla 3l ql1a3:3ke. 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 stiffness constant, k, of 440l5e vvl;x6kj6 N/m How much must this spring;kj6v 5lxe6lv be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1. 3fbv n4n/(6rz2d7oa hk* iris2 m higher. What is the chang/ 3i*k47nn2br da(i 6r ovhsfze in potential energy?    J

  By how much does the gravitational potentiag)7 f2 p 7 rv ps-c9ic5vyz*wignwl-m2l energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the ju5 7- if-cp9ns2rygzgv2wlpic m*7 )wvmp?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h bj 9-bqq xk3s(when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring st-sb(b k qx9q3jiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book mc*en. re9kgy6mgj06 from the ground so it is 2.20 m above the ggem.09kj*m6n gce ry6round. 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 toi-+;yy pb*3 bd ul a4kis3eft)p of a 3300-m u43bd yyii;3- *+f lptb)esakpeak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next togqevh6scp / 4vk)rbu4cv306 k a ruler. The end of the spring is next to the 15-cmgc p366vvrk/)kb4v q4 hus0c e mark on the ruler. If a 2.5-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, ibf 3vsb-ofi k4mo80 x(s running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How 8s-(xkof4 fbiv3mb0 ohigh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startin7;k x5pso pu6og from rest, 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 g8dgj ; 75vfdcuiven 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, Fran’s kinetic energy is transformed into gravitational potenx-9uc+our cex:08 nol tial energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass:cruoln0xeu 9-+ o8cx 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from th c()het l+fr2ae top of a platform with a sc thfle+2ar) (peed 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 (igno +4f h;a7hm 2oswqe/ iu;yppk4re its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressk7+mp ;eshq p2yuoihwf 4 4a/;ed 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 loop l*pl 254aye to4;ds)mj*olgsed track shown in Fig. 6–39. If the block is to54yl*sdg)os24 * jp; ml tloae remain on the track, even at the top of the circle (whose radius 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 (sprin.s koh+h kp))fg stiffness constant k), Fig. 6–40. The block is+.h)f hkp )sko 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 arp6g s+k(n us6h 7t:rm bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungeesmrhr+u( k 7tgn:s66p 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. 6–4wh yr:b/fz6mm wjp,nc-;i, 5o1 is dragged up to point 1 where it is released from rest. A/opfcr:-m 6zyw, jb h;n 5miw,ssuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throwd zsne9x1 a;/mm; ,axwn with a speed of 12 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 spring to be placed at the;s /wrw;(ovzdr ui1id)3)o ca 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 elevatcov o 3dw;1r/;)wuz isa()irdor and passengers.

  A cyclist intends to*sjjgjr8z/ 6qzc n/v) cycle 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, each of mass 7650 kg ay:(in rb nw9qkw6;)ql8v9qb m nd traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in tb k q6qrl8)q9mn;v:y9wnb( i whis collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the /+2fmxzpioi y zi5 1s+bottom with a speed of 2.2m/s How much thermal energy due to friction was generated inxiz izo+5y+ 1ps/2fmi this process?    J

  A ski starts from rest and slides n*f,f fkjd 7jvz.i::hdown 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 j+/knzk 1jyv :p 5.fqba 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 back to a height ojbo ypbz w:,vo78v:(of 1.5 myw: ,vp:oj87b(zb vo o.
(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, starvueq l:a)3tp- p8z(9 (efztfmting from rest, is pulled across a floor with a constant horizontal force otvftuz(fqlp) p8-9z(m3 e:e af 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6:liq, e-/hm6mjy pb9c –41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance travepm9hm:ib/6 - c lej,qyled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a stg51 i.au7m 2r5ur8dai3clss+ e-sfqc;b xkq7 eady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal sf):i9ls uy 3dc* :0hxflxi1f)m9n:tn : eknhgpring (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 stoppil* nh: fyk3n1g:: 0x):ime)d ffu9x9ntlsch ing and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig. 6– k8c (awt1,; hsyefy*spug(-g 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 posif(y*p ce- ,gy1w(gu a t;8kshstion, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (massdzs/vedupa:3(- ;, p:reuxmg 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 ludgm3 esv:pa-(z,;/e pxd u:randing 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 a9cq9o cv4)tyc qd5bm( 1750-W motor to lift a 315-kg piano to a sixth-story window 1q mc5v(49)y9tbc qd oc6.0 m above?    s

  If a car generates 18 hp whg1/mszev-1 1qxshgz :g)t:cwen traveling at a steady 88km/h what must be the averag h11:/:gzsvw-1c mggxetq sz )e force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95bm2l57/a ed ktkm/h in 7.4 s. What is the average a 7b/eld5t2k mpower delivered by the engine?$\approx$    hp

  (a) Show that one British h/n4) fptj, xn u7eu.g.0xnaehyg-p3j orsepower$ \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 of0*n vh2im8 2xfcskabxgq (1o; “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 6gas vp.m/ 0 oigi5zmak/ie1.55km/h in about 6.0 s on the level when it is img gi miz5p/e is01aavk5.o./n neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? )zyoj+jb97 x .2qrgp0 t-orww ck6x2 c$a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-+ x2p cj .ujnz,7iublbc56x+zkg shot from rest to 14m/s If this motion takes 1.5 s, what z7i2u+u jj.x bzl, xpn56bc+caverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a hfxiq 4 t5g28l rv;4gvheight of 3.60 m. What output rati8g4h fg 4;lxt5ir2 qvvng (watts) should the pump motor have?    W

  During a workout, the football players at State U. rzg.nb -l+ ;jbkan up the stadium stairs in 66 s. The st gkbjl+.-bnz ;airs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 mgb*sjjg1 /mfs2 6/wtl2x0a +(hpj dv$^{\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 steel,ob i98 fvkbv(a 6sblgw/ 68ep a hill can it climb at a const8 ivb lwgl/b6s(aoeb,86f9vkant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dra9htyjqa :k 0w/g a 310-kg box along a level floor9y/:0qta jkh w at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a ) ocipjijw5nzu*vz r 4:,/ j:v7.0 $^{\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) yu/n:dd i- 9rw-fe t*sbumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffny / d-rf:9i-en*dsu twess 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, ;w.. 6s clyct4,sko eliu 9bq1and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are al9 kuo;yc1 scle,q isl6.4 t.bwl laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) s gub)shwl/87 ,8 ,)r)fznirbwe0wyn in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?,u s8 w8lwn/,i)nhb7 eswb)0f)gryrz   m/s

  The block of mass m sliding without friction along the loopzz7 n(.2q*(y ,nne-hfqkj m duix 8jx-ed track shown in Fig. 6–39 is to remain on the track at all times, even at the very tmxz.d q*qnn(fkn 8zjux (,7jeiy-h2-op 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 afteoz 7xw7g: ;sbfr jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep;7 fxbzs:w g7o, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fia1na8x9x hes7xed (Fig. 6 h9na7x1as8ex –43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The c5sv7s vi+urz(fds41yazml4: 9s bqf , limb is made in 5.0 h starting at an elevation of 2300 m. Caly zssbda45 1(+rzumqf ,f9i:7 l 4vssvculate
(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 br 8i9ho:88xz(i4 ppe woat dtrn, y3u5ceaks when a 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 ;b dyn sc*:ke;in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higheen sy: ;d*kc;br, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the i(i4kn3 ap *i, eipv3yrate of 650kg/s and falls vertically 81 m before striking the tpiape (iikvn3 4y,*3iurbine blades. 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),vd1- 7rbc*p+ ftnje*g 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 youbj prcfe-*d 7+gnvt*1r speed is above 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 a candy bar directly into work, how imk,:r*shxe3p: +wu lhigh could an 8*xlk: +,h3iemupwsr :2-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired w.r 456ysz+)zlau 1a tp rh0cpat an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring insi j.k .6/w41fcgc- g0vqi vqirede the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a hi .0-i.qc1cg6rvkf4qg/ jvw eeight of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lakea j;td0udy:o 59p4vde (Fig. 6–45). He releases the rope when his velocity i0od 5 9:e4 j;uatdvypds 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 kou*95z4o c(mm:o hkwin 9.0 s. What minimum power output was used to accomplish this feat?z*hom:wo 9 k4uk5cmo(    W

  Some electric-power companies use water to storeo21:jiua6,wkcmle8wvt : zk*5duf b, energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour b :1v 6bul,w5jewcfukdi8 zamto, 2:*ky 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 stif4+ q4jxxaca; efness constant k is cut in half. What is the spring stiffness constant for each aa+ ; xx4qce4jof the two resulting springs?   k

  A 6.0-kg block is pushed 8.086mzo 4uv;hz r m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in ts 5v8 .,cqwnax: (mid/4po yx3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglecttw5 /v(x:a4xdpo cym n,i.sq8 frictional losses.    s

  In a common test for cardiac function (the*nb ni+z,mda ;/hv y7tog2.f 2ds1szd “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whdn s;2hd/o mag. syb vzz+1d7,2ntf* ien 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 u55 )1ucy u +yccbk6b6uil5oj500-kg rock vertically upward a distance of 500 m, what was its velocity when it le5uu651oy5c)u y u+l c6 kjbcbift 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 5dl x- np we99vq/wrty6 *coq(wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power output?oc6 y( *- /9vwpelqxtd59nrqw    W
(b) What is the speed of the water as it hits the wheel?    m/s