In what ways is the word “work” as usednc2(.iiy 1xfp in everyday language the same as that defined in phyf.cp i1yx(i2nsics? In what ways is it different? Give examples of both.

Can a centripetal force ever 9a8yy4(ehz6 cjmu8ktdo work on an object? Explain.

Can the normal force on an object d91hz:c qgg/ym :v(jtever do work? Explain.

A woman swimming upstream is not moving with respect y/pvaw/(.wp r w wil0 o9)qsx5 ;eyjf.to the shore. Is she doing any work? If she stops swimming and merely flre(spyo w /5yi/ fawwv)xp9w. .l0qj;oats, is work done on her?

Is the work done by kinetic friction forces always negw4ka.qqd j7s9mn+*veative? [Hint: Consider what happens to t4vsnw+ j.eq79k*aqdm he dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are d) v;bxv; pp, wjubj4jk;6wp0roing no workrj4 x;,)ub0jw v bj;wk vppp6;?

You have two springs that are identical except that spring q1.jk3m29ltjlxne6 a hf7 a2 ul is stiffer than sprxtqau26j n9 l37 mjf.ea1hl2king 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 )sinz9: *hygahorizontal force on a block that is free to slide on a frictionless*:si)yhgnz9 a 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 your gravitational potential energy change whev+2s/.4z gs m4comkkrn you jump assrm+so 42g4 k z/mc.kv high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building7b6hismsct6 3.2ap jm, all with the same speed but with different launch angles. Which one has the highe 3hc76sp am .tbj2m6isst speed on impact? Ignore air resistance.

A pendulum is launched from a point that isn.zbp9j-7j-5t pq nek 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 upwar--5 e.t nknbjzqp9j7pd 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/j vxftn2s.s0 fd..uf compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using t2n.j.ff 0sut/sdfxv .he law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instrur4,7y 0bditr wcb4w ri0y,r 7tdtor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitationcl)ii(bd+zhe* w(i 3 val potential energy when water at the top of a waterfall falls tozc*+bl i dh3vwie)((i the pool below?

Describe the energy transformations when a rqm7t5rq4; yh0d2obn child hops around on a pogo stick.

Describe the energy transformations that tg(:x giq7,px l)fko+;y;pbum ake place when a skier starts skiing down a hill, but gqg)y bf,ix7p:l(uk mpo x +;;after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m.mmizp,x10 m g) starts from rest at the 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 there is no friction, and (b) ther m,mz.pmgi1x0e is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in udhs59 ;+ bd4mkd;m tdg4; gr6trns/ztheir path rather than stepping on top and jk;n;6t g9rss;dur4 b5mtmz/gdd4dh+ umping down on the other side. Explain.

Two identical arrows, one with twice oiro*aq ,ud4; the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fast*4oq,or;adi uer arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingince01y0(rl5v b5o byl hg pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfathhl0oyb 1cyrbl50( v e5er clock has to be wound up.

When a “superball” is dropped, can it rebound to 9:k4 h dov7nira height greater than its original 9konihr :d7 v4height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the su4nsp gvm;)v f;4+ znf3v;cg.g y,fwa uitcase 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 heiv,cu+;4;mnggpg. f3nas;fv )fyw z4 vght of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed ra m* fzgnuv6 +g(nd8nkpcx:*+ither than the work.

Why is it easier to climb a mountain vi yge e89h )7chcum uv*6o/ v6lrhz03oga a zigzag trail than to climb straight upum )yc68h oc3gg*e 6 /vlv7u h0e9hroz?

Recall from Chapter 4, Example 4–14, th0kw r;:/hmpy rat you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energ/wph:; kymrr 0y concepts.

  How much work is done by the gravitational force when a 265-kg puvz rmf3g4q.fu a2,(vdk(. plile driver falls 2.80 mzg2k(3pfumu 4vrd,f(.vaq l .?    J

  A 65.0-kg firefighter climbs a flight of v7n4,fckzm mii) 9.hwstairs 20.0 m high. How much work is require7,viw cknz i9mm4.fh)d?    J

  A 1300-N crate rests on t j v:ut-+lxgo1rg,s:2 0p1r2 rro. gv,gek htqhe floor. How much work is required to move it at constant speed q1pg+ rjgrsle2:xk,.,vo - 1v20ht gruor :gt(a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizon jf ,8sybrobrg /g (s(1p-me4gtally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effectip8rg,o sf4s y(jg 1/-mbbegr (ve coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of q fj pcf ;a6)osd+e6t3 for 7.0 s. Find the qf)f+sd ; eoj36c6 tpanet work done on the box.   J

  Eight books, each 4.3 cm thick wib-otmzp 18l s7b-, lxvth mass 1.7 kg, lie flat on a table. How much work is requ- 7txpom8z-blv1 l bs,ired to stack them one on top of another?    J

A lever such as that shown qe:. yeg xoojt;u +6-uin Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show thauxetu:e ;.qo+yo6 jg -t 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 downlvfx8uv+ sw j6,1chj: a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The efcsv,8f:ujv1w +lhj6x fective 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 o9edr 2s5 r4(w rki6m zudf.6kkf mass M an acceleration of 0.10 gdkkum. 26kzr 9we5r4(6dfsir upward.    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 isum2 oiq.. i 7l,ggve6b rf*2ha 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 show:svb98,, xdh tdu0qfs n in Fig. 6–37. Determine the work done by this force to move the object s,hvub 9,sfxd dt:0 q8(a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle-qssf4ke+pamw h( 5- q 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, with mass of m e,u 8uwnq)( (zxulmlzr.e5($5.31\times10^{-26}$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 has3rve 8 cvvrx-ehk91q u9hv 86v 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 stop9ntavejv ;l5ek*4*. s 9vkktcc+ d4h* md7gvu 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 ex 33q,*nu akvc;jxx) done to stop 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 s0nu :ttt l3oneb;; 3gbtring exerts an average force of 110 N on the arrnet:;3t;b ug0 nbtol3ow 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/s2lh r jo lxs-n:h gen1bf;s,.8 moves a fielder’s glove backward 25 cm when the ball is caught. What was the ajhnoxg:fehll s.8b1 2n, rs;- verage force exerted by the ball on the glove?    N

If the speed of a car is increa3e 0m*dta +xnksed by 50%, by what factor will its minimum braking dista mde0n+a3kxt*nce be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a lev qg9hel/hgm7g ;a 6 sljf8bl+1el road, 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 wasl+;6gebs7f 98g /glhhal jm1 q 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 (n;y 2 ;fr1xk u7uujqw0.25 kg is 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, ifr 1;7nw(xu ky2j q;fuu 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 who8f,kh 47ofiz z: b*nbf does 80.0 J of work on it? Negl:f 87fz,4inhzk fb*o bect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with am -z)r2 j/rguyn acceleration by a single cable. Detr2-)yzjm gr u/ermine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much pr v6rq.u0rfcz ../dhp 09kcemust this spring be stretched to st zhupf0k.0 r dc/9qcvp..6r reore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one braebg; 6ek 00cymnch to another 1.2 m higher. What is the changee0cy ;0 b6ekgm in potential energy?    J

  By how much does the gravitational potential enepi5fse ;k; sgp;7ao: brgy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump?;sia5gf;b s7pp :eo;k    J

  A 1200-kg car rolling on a horizxzx, 8rg;s i(,.ov bvpontal surface has speed v = 65 km/h when it strikes a ,(vs, gxrozpbiv .x;8horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from tqrv1 8,xeomlvywv4k 8*8ttg45f ngb :he ground so it is 2.20 m above the ground. What is the potential energy t q8mx5e 4bk,8vtgnwolfy v g*41r:8vof the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of a 3300aim 0+/s+ jh5p03e furtyjgl *-m pe/hlm0 i++aj *stjer35yfup 0g 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 r:8sjb nhxurz y6b62(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 spring, where will the end of the spring line up with the 8:hrbr sz6j6x(buny 2ruler marks?    cm

  Jane, looking for Tarzan, is running at top sp: jy;j 2fwnphq.o96xmb 9xq09x jn,dzeed (5.3m/s) and grabs a vine hanging vertically from a ox qn 9j,.zpdjby;w6h2q xn :0jxf9m9tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless ncp*5kiyb1gwfw)c: ;35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a 1pv9p;i d2f gofrictionless 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 transfo 0+pjthov)iv:u6qz(6514m bhxh7m ks k; ufiormed into gravitational potential energy without the aid of a pole. With what minimum speui( 5+ :v 1 q zht;7k6mfsohk6omhpvbix4u j)0ed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the to(io fm8v rjd ikp-+4w4,ofy5vxfsn*+p of a platform withif nif(8ovsk 5-4d,y*++4pxjov mf wr a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stix:f t u 0y6:1eyi7;)wwye r hv(i-exm4iw2caw ffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give wyue; e4xx wa6 eyr0-7 )iw im f:2:iv(w1yhtcto 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 frictiot; xw khx an,ds;bpd;2/qb u,2n along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle ( xtx;;k hd;pb,2s n/2u ,wqbadwhose radius is r), from what minimum height h must it be released?    r

A block of mass m is atta7b 8un dc7xy7lched to the end of a spring (spring stiffness constant k), Fig. 6–40. The blu8dl7x7c7yb nock 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 jum4jmpk69 .dugq au mv52 pgs-1sps 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 stiffg qms ag4vdu5p.9sk26mjp u-1 ness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig.jlstp5 yh s4 a;+29wlg,(nq ev 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calcunj5aleqyl4p vs,wg +2(;s9htlate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed oml917l3xu+- iktixsbvv; svg0y - )tt f 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 atzobc:b-k wa xj1:;w :t 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 b;twb:x: zw b a:cj1k-orought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle upg/(* skmi.- nzhk)ezes,buoj fbsf y53 1no 1: 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 and traveling 95km/h in opp b3a:9u oldkwkdc4zfw9t,:b6osite directions,bwd:: fk3tbcu 9od 6 ak4z,9lw collide head-on and come to rest. 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 andr i)s.grdygph26 41g f reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this procesigsgy2f p 1)4rgrd.6 hs?    J

  A ski starts from rest and xpwp:9kq73dh 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 grl;y*o ps/r tdptkw-4sq/* ek96a g6rlound.
(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 7sfm* f,(yws28 vovtxback to a height of 1.5 m. vv ,fs2 8sxym(7owf* t
(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 floor with a constant hor62 ivb9j b-w (ahim(rrezb3d00g8k npizo0r wdirhp026v zg(ib kbb ea j(-n893mntal force of 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. 6–41 passes point 1 oblc97xb2/ eny)oqj4 1ik,yrv+kk ke* f+vq* with a speed of If the average force of friction is equal to one-fifth of its weight,lb*voy2ck kb kq) e9n,i +o+yf1vr*q7 e/ xj4k with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12)cnly c 1 xkicid6kbol94 c(2:m/s reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (kr)j*e zdf8st .7bcz4z =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 frirs.f zjz4d)*ctz8e 7 bction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizox;a ilg:njp*y9:28 q-qyt gvpntal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this positioyyg i::a 28;tv*-jlx9pgq pqn n, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle od:rrikm0j 5( used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. Trkm0r 5 jiod(:he 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 31m 9/l bt *mxi3zno+r/lrn*b +v5-kg piano to a sixth-story window 16.0 m abovetmnbr+r+b*z lo9lx3m*v ni/ /?    s

  If a car generates 18 hp when traveling a0z6 4sbuq syq3t a steady 88km/h what must be the average force exerted on the car due to friction andbus q3s0y4q6z air resistance?    N

  A 1400-kg sports car accelerates fwwb ydy47k3b6 rom rest to 95km/h in 7.4 s. What is the average power delive3 b7dk4 wbwyy6red by the engine?$\approx$    hp

  (a) Show that one British horsd92ogk;u.m;z z(ji 45iq ie rzepower$ \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 of “kilowac+;u 2ghrzz,tf w, -mgtt-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 doop4ih:s l0o 4swn from to 65km/h in about 6.0 s on tl io0:4hos 4pshe level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 hxn jmv*2 qq-+sl( s(fy? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg sbk 9cl7uxw(oa+qx;27rg nj8y hot from rest to 14m/s If this motion takes 1.5 s, what average power was develox;ku9xjlgr7now7( ya+ 8cb2 qped?$\approx$    W

  A pump is to lift 18.0 kg of lv6hwc)lvz45 water per minute through a height of 3.60 m. What output rating (watts) should the pump zvl5lchvw6 4)motor have?    W

  During a workout, the footbjs ydc ujta9+( mp1-z7*s2xjaall players at State U. ran up the stadium stairs in 66 s. The sta9aap*-(1u jjzxs 2 tjscdy7+m irs 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 clim,. *0i ojw b2oc*hybnyb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hpp(r5n;w lz(y w. How steep a hill can it climb at a ;nywz((rp5 wl constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able t hjr bo+;63i,f csz;mbo drag a 310-kg box along a level floor at as ;hm 3fi c;6ob,z+brj speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a;d p bk6bswk:np3 l5;k3l2 vhv 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” thap p5t8tcl ombzh z.r;tco+f+ ;;7ysd.t 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 effez z+dcl+;8pbfso tcr;y ohtm7p5;..tctive spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remai6orqou2;tdf 5j/ ppb3ning 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 heigh5;rp duoof3 /jp 6q2tbt 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 the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig.6*s ui.)ihny u77we e i(*gjte 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at l* iue ij) (yntih.7*gesu76weaunch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sli m 3ny(l0u lmy+8-rgotding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of thly-30lm8+ mn(utgy r oe 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 1hlu-n*yo0 i ,,mny3ksoa+ay aircraft without his parachute opening. He landed in a snowbank, creating a y i osou1* ahyknl+ y,0mn-,a3crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(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 lengtxp1;vq *n o2.3zyx l5hwhu 4ljh L whose other end is fixed (Fig. 6x 5xhn; y 3u*4oj2zql1h pwv.l–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 t ye,7c zo,/dy 3q 6:sdipajcx8o the top of a 3700-m-high mountain. The climb is made in 5.ia o/37zx dp68cey,yj,d: qcs0 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 elevator is 28 m above a huge spxxv;7xff q5 +mj*f8bxring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 tha2z:ar eazzcf cc8c5eud2gn h)5+h x,3t its lifts can move 47,000 people , hcza5ce2)zr82h35d:c+gxe uf anczper 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 fallzan) ac)q x7 63ig hvrw/(v1ows vertically 81 m before striking the turbine 3rhnw aovaq(wc 6gzi/7)v1x)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), the :+o aq + ,fs)qp,vzievdifference 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 thfaqq)ovpe,i++,s v :z at 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 convertp/3bw-9tfs p. , wehtw1w(,qdb sy,zl a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one t-(9ww/wwss b,ydbp 3,z,fle. h1 ptqbar (=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 13dy *xpi8cigtdm6)+ , v jaeaan 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 inside the scywug lg)b(rdpt+4- 3:mu-u taale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read b- mu- ud( p+rw4ty utgl3a:g)at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out ozp algd9uq845 ver a lake (Fig. 6–45). ug8a 9q5pd4lzHe releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.uau k(ll/) n4 n,gd(ss0 m in 9.0 s. What minilk nsnd/,g u(a(l)4 usmum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water isrg 1 so;a9fvs/ir1(x z pumped by reversible turbine pumps from a low to a hs 1ox gzrr;9 s/av1if(igh reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What*8jmcnh,g5bw 2ga, j t is the spring stiffnesnbh2 jg5gc,aj w,8tm* s constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 mjeys ::,sy m.u 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 t,ub a9zn *ig tqsen70;o 55km/h in 3.2 s, how long will it take to accelerate frzu7 *t si,qnenb a9g;0om 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress btw, +w:gfxt3i* jk 0ztest”), the patient walks on an inclined treadmill (Fig. 6–46).0g* iw tjzfxk:t+b3w, Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertih.tu5w ckw-,i1mp w.bcally upward a distance of 500 m, what was its velocity when it lefpwhk.1.w -, 5 tucwbmit 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 95y;rfwy7e -w.)nkn m ;ikg/s (a) If this water wheel is set up to provide electricity output, what isy;mekn7 i.-nw);rw y f its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s