In what ways is the word “work” as used in everyday language te-v,)w l 5sr6hb4nim 1;( nw9kal4he8hkotaxhe same as that defined in physics? In what ways is it rsb8h5 4h 4 le)1(wn,v mta6x;woeilnahkk9-different? Give examples of both.

Can a centripetal force ever do work on ez+ iprj).(3pk7wcbe an object? Explain.

Can the normal force on an object ever do w +p;o*gbmp z00sw ut*jork? Explain.

A woman swimming upstream is not movxi7q ej9jij+/kb .b l(ing with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is wlbq/j (kje+j9 .7ib xiork done on her?

Is the work done by kinetic fri5 34xuceaf r/pction forces always negative? [Hint: Consider what happeaxrf/ p5u3ce4 ns to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wals(z/+fh;hnc ocf q4k:f-w 35 eyb fht,l even though you are doing no wohh fshq(wnf by354f:;cz k,/f- +ctoe rk?

You have two springs t8ri*(k tal l7xk2:ijuhat are identical except that spring l is stiffer than spr:ik8(a*2 xtu i rlkjl7ing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force onbi0v1b 4 +qzcj a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distancj b1iz4v0b+cqe $d$ 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 poten4;xl* e/ye ;rpt(at zatial energy change when you jump ase;r/ 4at el z;t*(xyap high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with , v4nl0gfq4ongxj7k+:6w tt 2f7sp0ko a/w jkthe same speed but with different launch4:fwg0knv2noql4k6 as 7 jgf0/ttoj,w p+7 kx angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a pointzm)mzqt5n9ntg / qeu4gk 47.m that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given ang/ g4t 4n.qk95mnzm)tmqe zu7 initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compresbz6 vh03 ifr)ts the spring by pressing down with your hand and then release it, can the spriz6tv fi30rhb )ng leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instr;/e1 mmk;pv:y3 ;k fmly0drtuuctor pulls the ball back and stands y;l;:vu ;p/edt0rk m kmm31fy 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 potential energy whenkwktea 5-xff idcp.t *ajy726 ,0iq) m-ekw(w water at the top of a wa5taty ifdq2-. a)mipe-,jew k 6k0wcxf*7(wk terfall falls to the pool below?

Describe the energy transformations when a child hops aal;u4yuuo/hnfgc4 f hs 4l();round on a pogo stick.

Describe the energy transformations that take plp mfxeprs+ ;h51 n -hjm66csz:ace when a skier starts skiing down a hill, but after a time is brought to rem-h;6zc ns p5x:jf ep+sr1h6mst by striking a snowdrift.

A child on a sled (total mass m) starts from rest at lu2e c9 mz-lj3the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and c29jle3-mzul there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path r +rzmd(y an (5rwas- .2o-n;wl6hgdw iather than steppin- wz siadangrl;mw nw6d (. r(yho5+-2g on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the oth/rdjlt+g,0mi er, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fati0j r,dl+gm /ster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simplerhqd- f8f4;vt swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into 4rt; 8h qv-dffaccount. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a51t hdtm z,d5a height greater than its original height? Explain.1thddm z5a5 t,

Suppose you lift a suitcase fro5qa puc 0w((8gj mmggms3l 5/nm 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 path, (b) the time it takes, (c) the height of the table, and gma(qj08wus3/gc55(n mlpgm (d) the weight of the suitcase?

Repeat Question 22 for the power need (n co 8kfhyv+ltqm9 usg(;6;ned rather than the work.

Why is it easier to climb a mountain 6nkph.o qlb 3v,k+9vk20gy1 /sqxy fnvia a zigzag trail than to climb straight up?bs3k2pknholfn6qq, k .yg/1v y0 9+xv

Recall from Chapter 4, Example 4–14, that you can usc-3s5v4poh ; f: nyrzbe a pulley and ropes to decre v-nop csbhf;r3 :z54yase the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done6*plxrz1l7 ki by the gravitational force when a 265-kg pile driver falls 2.80 pi 1 zll*7rxk6m?    J

  A 65.0-kg firefighter climbs a flight of 7vi)u*u9*3c;edlb u(puckk7uz 7 sr m stairs 20.0 m high. How much work is require9zk7e* )bu3ic mku7 rs(v*cl ;p7uud ud?    J

  A 1300-N crate rests on the floor. How much work is required to move it at ck*rthypp pj.g-0o5 b ;onstant speed (a) 4.0 m along the floor against aphtr ppgbkj*-5o. y0; friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (h : ras1+rj8x9qhcyw-c /ee8 rlorizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if+e8ej a ryc /rqw8l1s 9hx-rc: the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelera4tp n1cas- 5s q7becg6xn*+ej ted by a force across a floor at a rate of for 7.0 gn cx6t7e-s eaj51q*+ bsnp4c s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick witb;0. hmfb2rbmyx) g9dh mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of anotheb b 0)2mh9gydbxr m.f;r?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we might zz zj1f, f2 qe3f-qx4gnot otherwise be able to liffz4gqzx1q,z 2jf e3 -ff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept fr y oia)n7z)m)dom accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. )noyai) md)z 7Calculate:
(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 opto+)p)l jmx9h18 j rhf mass M an acceleration of 0.10 g upwphxr lhjtm8)) 9po 1+jard.    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 di45njujb(2 l .iy)sysel* r4h bstance 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. 6–372kh icw ffnj dq2wqy(6;3q*a (. Determinw 62fna3qcwh(jq 2*;i(qyk dfe 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 exerted4of57 4 wcxyjq on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, ir2wv las /l6ip kn8 7jl7*yp9with 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 i:3 nyb/*z3x7el rdf,vc0 ydc tts 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 dbq32upd y 9j (x-lf,t*y/vdhelectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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?w:scpy3 b :s6gqd1+pq$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exg oz.jy2t nry 29( guf:xnt7)serts an average force of 110 N on the .o jn) g9y:gf(2 z7r2ustnyxt 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 a fielder’s glove backward 25 cm whe blm/hjsn(33an the ball is caught. Wham3/s3(lb jna ht was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%w).u5o+ cr plc:- htih, by what factor will its minimum braking distance be increased, assuming all else is the sameh.-c p h:+5w otlri)cu? Ignore the driver’s reaction time.

  At an accident scene on a level road,)oxn v0;; zzst investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car wh)vs; ;ozt z0xnen 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 isc,e 0vyle(l*ub48gas s 6fj2s pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, iu cg,y4ls20bl s*fj6vaes8 (e f the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does h.feh8 0vnuw)9m rw(g 80.0 J of work on it? Neglect ain mf80r()u.h w9vwh ger resistance.    m

  A 285-kg load is lifted 22.0 m vertical+ cq90z:mdw bjpmu1v .0v+c gxly with an acceleration by a single cable. Determine j vmmxwbpqd9z0 .1gcu+0+: c v
(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 sts3ioxk( ck,t-jduaz llk 14b6; .td :giffness constant, k, of 440N/m How much must this spring be stretch1ujia ;k-ok6tdkgz :3,x(4ct dl lb .sed to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is tb*r1. sapj dy2he change in potential energy? *.dj rbp a21ys   J

  By how much does the .xn /gl8lc- m6ipa3mp gravitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during c6pm m3xa8/il.n pl-g the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 659f: /bepya 9( cqofqbk+b46e n km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of tep/ y9 qfcbbb+a46ef 9(kq:n ohe spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 ig ic-z2wdm *a l6ohfm8j:)t5m above the ground. What is the p6*)5ltijmzh:-g io2 m da8wfcotential 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 elevatiolkvt. /8otlu7 x g*4nin of 1600 m and climbs to the top of a 3300-m pe.n tvx ll*kg ti4u78o/ak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the spri 9xbs 2ou+ r)xw+a0z ul1m4kq(lsr/ fwng is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached srllra+zx( kqo4uw+x) 910u f2b/swmto 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 (5.3m/s) and grabs a viqz 8qi 0x(a)cene hanging vertically from a tall tree in the jungle. How high can she swing upwa0qcei)a8 qx(zrd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from r,7 s(ifl ,b/sih1kzqoest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shggh1c3 ;mr i5wove 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 gravita2i )qpol amojx:44jm*tional potential energy without the aid of a pole. With what minimum speed must Fran leave the ground iniqjp4ommxao)4lj 2:* 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 vertically ugaiz8kkn:.e3s4a w v9 pward from the top of a platform with a speed of 5.0:e 389kvg zaaiwn ks.4 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose sprilgxn/z152tbm ((voo l7do 3eing stiffness constant is 950N/m is attached to a table and isbznlovi (3/5x dl7mog2(1eto compressed 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 alon fm-53)l gdamv-nauz:h, s.fi g the looped track shown in Fig. 6–39. If the block isn-a3a mf,f-slm.vdi :gh z)u5 to 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 (spring stifflo3v f:aq2(eyzmr9bagd h 7(3ness constant k), Fig. 6–40.arvy3ldb 39 omg 27:((aezqf h The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied*cc amh8mj5qys5zk, 1 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’s law applies.mc1hy ,qmsk5*5zj 8a c $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car show(h a tyf z-++v64fgo+ /bmplfvn in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculatah+p-m/t vyfb +zg4fovl+ 6f( e the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at a1jw 0p8kvy n4zn 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 bottom of an elevator sh;+mia8u 4bkrc0*f9 ezf, bh2u (iz yuwaft. 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 and passengerf 8b;u9 +kzia42c myf(zih* ,ewu 0brus.

  A cyclist intends to cycle up a 7..g a(fzb-:l db8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite9tw f(16b a1mil q*z y0*lizzc directions, collide head-on and come to rest. How much thermal energy is produced in thta1z6z0 m*c 9iyqzwf*lb(i1l is collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speedld2g0zuehlbzn 22q6;9mh x jh(4 l- nl of 2.2m/s How much thermal energy due to friction was generated in 2gh(ll-njz2hmn 604el hd2u 9zl qx;bthis process?    J

  A ski starts from restgxos --:r5kz z 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 above the ground. exxic,9nl*st4 jl99 k
(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 heightzup5sczo yu)t1 f./g) of 1.5 m. c u5uof/zg.)s1 zyt) p
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a flo+yfvpdn( r/q +or with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the nexqn(d /f+vpy+r t 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig7ub q;jdy5 psm pma+44. 6–41 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 traveled iss4m7yd + q45 buap;pmj 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot o+;+2ea)+ n-niu bugyzy hr0p if a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to ay 1t j (ytcs);kcg;+xo 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 and turning back. What is the coefficient of kinetic fsg;c t+jko )y xtcy1;(riction between the block and the table?   

  A 280-g wood block is firmly attached to a verw /+7ork rvff3y light horizontal spring, Fig. 6– 3vrfo7f/+wrk40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg 1co i+oo 1nkaz oaif +0d8--vkincluding pilot) that was launched hoa-z i i-ok+v d8a+nofo1oc 01krizontally 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 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 piant ,vduekq,hnvo o,u52z.p /z6 ni1a 3eo to a sixth-story window e zheut ao2,v /dzu5onikn p6v,13,q.16.0 m above?    s

  If a car generates 18 hp when travelin ajke 1w(mwnojg3)-htu6,svbp: nekr:lm8 ;,g at a steady 88km/h what must be the average force exerted on the car vleemk:6h3:bjws nt wj ;) ,-1krugoa( 8pm,ndue to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h integ63faowt6*v qm+st +j9bm* 7.4 s. What is the average power deli*ast9 qo6m*jwm+6+ gb3v ettfvered by the engine?$\approx$    hp

  (a) Show that one British horsiv7rs ap5 -9bxepower$ \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 fxs.d y+c5u2 i6l/dei eh(z1g4 ric w*lorm of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car/ +9vd -wpj;+mjvltbb slows down from to 65km/h in about 6.0 s on the level when it is in neutral.bvljv+t j d+w;/mb 9-p 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 dwmgrjvzmc/(/*q7zvb/ wo1 c/d w6ot 6o in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a z354ni +ycxf)mbq+ ct 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what averag3) 4fxqc imtcyz+ 5b+ne power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heigh8h8ozlhc s245w5 yahbt of 3.60 m. What ouz55aw b4hc ho2l8ysh8 tput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stairs in bb; yyw-*fb,q3.:lju.lr6z7t rang e66 e bzat6;3 -ub.f wnb* qr y,jlg:ry7l.s. The stairs 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 cla 5. 69x vgft6xsqu/wnvtf 6;vimb 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 poweryac2,ou h0dz9n9 c fbwmo/4 o6 output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h ifb9u wm2d acon4h 0/, 96ycoofz the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor haveb(w wp1kkb(6dtky w05 to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction w kdk6w0(yk (pt1w5b bis 0.45?    hp

  A bicyclist coasts dowt ny;kr0ctt4p4y3,f kn a 7.0 $^{\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) bumpers” thatgq 5g ag/tr-9n 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 -ng5q a9t r/gga 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 cm6)+;9zcf q7sxh qorc l off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on 9+xqr6z cqh)o 7cs fl;the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olymptu2pvqa6 hv5f )) o,thics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What mih t,v )u2afpoht6) q5vnimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without fr* ;x*fwqmy; vxt4rx/gzx7 z- jiction along the looped track shown in Fig. 6–39 is to remain on the track at all times, e xrmy/qzt j;*xzwx 7 v;4x*f-gven 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 aircraft without h7x v cveijlj18: m338 ybdi/csis 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 anje/djv cmi: 8ilbx3 y 713sc8vd 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 w,h40wq; owl m,ee)gumhose other end is fixed (Fig. 6–lw4quhg, )m ,e m;0woe43).
(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 om5;chw3* op5ox kc1 o z msqt/1dhgt5u8;y2 ttop of a 3700-m-high mountain. The climb is made in w;o/3cxp o1 5moysm gudt5z28t qo1t;5ch*k h5.0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevat1j*x.n5 s*viip7age k1su2d dor 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 itsou3ziint 67-w5eh4n2 gvty6 z lifts can move 47,000 people perv z tu45g-n6n 2hto63iwyi7ez hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m beforyifax/jfh/nc8pdf7g - j *8 x8e striking the turbine blades. Calculate /di8xxh8yc7gpjf- jf a/ f8* n
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44),lcvpn,)9x ( fib))m1 q+azr rv the difference in your apparent weight at the top of rp zlcr)bi) +1m vq,n( f9xav)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, 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 high o6-q0gw r9r8gw*sxsxa hk) r6could an 82-kg man climb a ladder if he were fueled by one brr xga s86*kw-how0gq)xr9 6 sar (=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 of 4gb m1e-h::xdu 5.0$^{\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 scaaqo-yz;g g m0(,x -thwle, 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 doqz;gog tw -(yx h0a,-mes the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a c2k c1ufq.4xirope, and swings out over a lake (Fig. 6–45). He releases the .41ifcuxk q2crope 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 in 9.0 s. w biptb8,co-- What minimum o -it,8-pc wbbpower output was used to accomplish this feat?    W

  Some electric-power companu,oxzl/m4fs-kui(.0zf )hzx 0 k(euq ies use water to store energy. Water is pumped by reversiblh(-k,4u/u i ).fz ueo (zfklz xm00qxse turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness consts i0+xke-s2+ltn)ch aant k is cut in half. What is the spring stiffness constant for each of k-ssnca+0 )et+l ihx 2the two resulting springs?   k

  A 6.0-kg block is pushed d0wxji* u.r v:g ;co 8d-rl-ux8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long wi( m8 tlydfb3cc1vg8/rll it take to accelerate from 55km/h to 75km/h Assume the power stays the same, y c3(rfvtdm 8l1cg/b 8and neglect frictional losses.    s

  In a common test for cardiac functiu op r,,xsgz (.mnk f:ebbi+:.on (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 an anglbg:m x(iue ,k os:,b. +zf.npre of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a diy; dr9nj0 pg+sstance of 500 m, what;0r sn9yd pjg+ was its velocity 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 2.0 m at a rate of 95kg/gw. r4bt3p rj8le yr5:s (a) If this water wheel is set up to provide electricity o r5 .3pegwy4rt:lb8 jrutput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s