In what ways is the word “work” as used in everyday language uvyra8u0m: 9ce n,2bxthe same as that defined in physics? In what ways is it different? Give u: c0a,yu v8e mnx2br9examples of both.

Can a centripetal force9gdx *yd 8z3ck ever do work on an object? Explain.

Can the normal force on an object ever do work qyx( jg/l-g **hzz,zw? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doq;.0u8f 9nvfj5tnntza t;a 6w1b tf ;qing any work? If she stops swimming and tb. 5aqf8t90 w;u;navnt ffz6t nq1j;merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consi:tmmh6*o 5ui *gz,ln0 9sely eder what happens to the dishes when you pull a tablecloth out fyemli,*s5t*o u: nzghem6 90lrom under them.]

Why is it tiring to push hard against a solid wall even though yy*uu:pfqv4dl1 f3 g9 .v3up pxou are doing no work3 9:p.gu yuuvl3 q*pvpffx1d4?

You have two springs that are identical except that spring l is stiff u iiqg22s axrb :pi4z3urp/12oh5em)er than sprinrqp i:eo51z2iu g3 m /4xu 2sh2raipb)g 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 on a block x jynl2x 2eg4:;g6 s y6zh9nesthat is free to slide on a frictionless surface (Fig.6-30). The block starts from h6;e:lns2g9yxn 6 y gj24x zserest 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 gravitatio-67c tuj; x: dom(gsxfnal potential energy change when you jump as ; x-s7ut6(omfcgj:x dhigh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a a7 r94avoxd +o dsptjk2qy lo8c6601rbuilding, all with the same speed but with different+oa cd 9k lra6v4pr 0yo782sqoj1xtd6 launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that za3s /nozke:1is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downwaz/n:ea osk31 zrd 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 tablehfzmu6f e hg/ 7jdy/+1. If you compress the spring by pressing down with your hand and then release ihjy71/+mdfe hguf 6z/t, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. ce*dhjic 0h1nw2c2zsq57 * pi 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose 1w*pnsc icdiqz* 27jh52c0e h. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitatul ,ui/ qu1u6 oj(/mmiional potential energy when water at the top of a waterfall falls to the pool below?/l6 uui mu(u,im/1joq

Describe the energy transformatin+tt / ;bdzsa+*q: rtaons when a child hops around on a pogo stick.

Describe the energy transfo ya2 )pti:kl4nrmations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strk2n)4: pality iking a snowdrift.

A child on a sled (t*f e:)9ry96dp fplwqqotal mass m) starts from rest at the top of a hill of height h and slides down. Does the velfp69ql*) dyfp9 qewr :ocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pat)s6j(mru.ic8,mko clx4 r cek:ym ef0 q987 omh rather than stepping on top and jumping down on the other side. Explfsuo:mmkmr 7.ex4l8c 6yq)0 e m,jc9(cr o8ikain.

Two identical arrows, one with twice the speed of the other, are fired into a 9iehd7)p2r b pbale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster ar9p)dbi7h per2 row will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingi 0sbc/ rg3*2agtv tehjd6 q,5ing pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grand, c haei63/jg*qr2 t5 sdvg0tbfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its origa.g+wpsb od,d.s tgv(9ak+b3p7lsu -inal height? Exad(p u+b-+ p9.k g7,3 a wdbsot.vsgslplain.

Suppose you lift a suitcase from the floor to a table. The;lokjo60t . *p5iie ys work you do on the suitcase depends on which of the following: (a) whether you lift it straight up orjo ;i.ilk yo0s6 et5p* along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the pow -gxr 0f.tf0h)ukw6lr1 +fr6jxi.log er needed rather than the work.

Why is it easier to climb a mountain via a zx 0z26k 9pn2 o/rpk 3gslc6gqgf +5pzrigzag trail than to climb straight u26g c g0op6 skp r zz39r5+pgfq/k2xnlp?

Recall from Chapter 4, Example 4–14, that you canle6 k*pcqd /t w4eg06b use a pulley and ropes to decrease the force needed to raise a heavy loae ek 4dl/ 6b0*tcg6pqwd (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 done by the gravitational force when a 265-kg p +7qr2udafyh81lx(ao:0zwn r ile driver falls 2.80 my n7au8xw or:1ra f zd0q(hl+2?    J

  A 65.0-kg firefighter climbusn9)t8ynh5wd o )mz( s a flight of stairs 20.0 m high. How much work is requir5(t o wusn89m)yz)dnhed?    J

  A 1300-N crate rests on the floor. How much workj eqh.10 tjs.p yj0yzt /gf-f1 is required to move it at constant speed (a) 4.0 m along t1fjyyt-qj j.gt 10hsez f.0p/ he floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1t2hb, l s50uh d-wxpp7ie(6 zl0.3 m across a rough floor without acceleration, 0hhdeztlp56 ,sx i7u2b(lp-w if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerate ih y pu02m292cf6we,krlo4opkom5:o d by a force across a floor at a rate of for 7.0 s. Find the ne w42pirok029m efuycl:6o koh2, p5omt work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on anx r 1+(qnqyp0 table. How much work i+nx0r1 yqp(nq s required to stack them one on top of another?    J

A lever such as that shown in Fiuggyc)o, w d0+j+xvy ,g. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that t+yuwg 0 ,xjdy +cv,og)he 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 downc-vr/8ynzn l4 / +o+gw3yejoy a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the ino8/3yl w4vzr/ -ec ynoyj+gn+ cline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required n +in:(wrdw(oto give a helicopter of mass M an acceleration of 0.10 (n wro:+n(diwg 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 distaql/8 g(i zlmz31zw4s e4gllp3nce 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 hp13((y m;h esdza l4ex axis, varies as shown in Fig. 6–37. Determine the work done by this force tom(le;ys3 z(1 h ahdp4e move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in tc3b -v*ytk(k 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 ) uta dilqm*-3mass 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 is2qq xf 8i.1n+bvg0d is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is reqk0l51 )rpch9k0 gqia4lerci :uired to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 120wqrn lui32 e150-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 ofdk*7nzz()p1zw f bn1 s(mk)tg 110 N on the arrow over a distance of 78 cm. zgz fskm1zp* nk)()b17t ndw( 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 backwag9a0xftkz b ,go4b8wjs2,qhg cf/2 v2rd 25 cm when the ball is caught. What was the average force exerte8 gf2bqcs0z4 ,a 9/,vgfhtjw2bg k2x od by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its mj4;igioiyju. :s yvvfuy ha12l.r)b7r4 m.c4inimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction:usu iv44f. 4i)l7 v2 i.r;1 cyjbr.agjymhoy time.

  At an accident scene on a level ro4fdv ho m:1g1nad, investigators measure a car’s skid mark to be 88 m lod1fm4o1 hg:vnng. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when 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 pig3gq r qi2c/r1tched 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, if the distance between the plaq1qgcr/ ir g23te and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doesrx)w4boya) ,q 80.0 J of work on it?r)y)oqaw4 ,xb Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelam;d4kna 7 f,geration by a single cable. Determine ,mkdf ;an47ga
(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 stifflnjl e ;+9g6rz,vxro;4yf4va ness constant, k, of 440N/m How much must this spring be stretched to store 25 J of4xfe nly+6j olg4zv,9v; r;ra potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What *uck1 8xj o3hrn1ax v:is the change in potential ehj8 x c:rkox13n1 auv*nergy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaultl.i95i il ): w(yss-vbra9k8fze5zcp er change if his center oilav9i :(re. i 89wfk)slb 5-zzpsy5 cf mass rises about 4.0 m during the jump?    J

  A 1200-kg car rollingn:6 ezc.xoicsa5z . *u on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constan.ne xuczai:s .65* zoct of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the grounmxy/n72ffx yz7- g1 snd so it is 2.20 m above the ground. What is the potential energy of the book s2m77nn1zx-fy yx g/ frelative 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 kitz+ ;xnf9hbxuhf033 rjy :0 1600 m and climbs to the top of a 3300-m xfhy0:kj3fb hx ;93 0runz ti+peak.
(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 spring z7. vb5as +agkx5f;viis 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 endvb+5g;a.kaz xv7 5fsi of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is rungkg*q5w6frg ;g*ic f*ning at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jun*g6k5*rci;g qf *wfgg gle. 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, sli.k4( obhswc v i;d6 phvty6**i ed1j(xdes 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 shove up a fq3iet33hyk : z5v5gj erictionless 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 gravibo5 ki non:a6v h+8xn9plpvdwv ;5d),tational potential energy without the aid of a pole. With what minimum speed must Fran leave the;xnnkoa d 9)wvo5b+pndi6v v8 5,p:hl 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 art wn 3btcj0 *qeac4h+kvy/9r. xist jumps vertically upward from the top of a platform with a spee*qyrb93/waj 4c .kx h+c0ntved 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 stiffness constant is 950N/mj+8ys (u2ha9zp*0rokjc rv*i is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.3ir8o rj k*yu*z0j(2pcsva+h90-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 nu,yy c)u59y gxvc9u7xc.fo -g the looped track shown in Fig. 6–39. If the block is to xy yvcxuy,nfo. g9c 9u5-)uc7remain 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 stiffness constant +vx6h8 p7i vx ordv22jk), Fig. 6–40. T22jvdvrx po 7+hvi86 xhe 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 tiedp7 a+od7 h(iw e6ta2)jzj wwu3 to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the swp+7 jzaa) iw thjed (w6o372upring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragf/md j4rzs ;9yged up to point 1 where it is released from restr/4mdj9y ;fs z. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed( kxl(w vk 63qwk5gh+h 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 sprin ko)h:p0kwsvsj8of :toat4 r2 +xt))tg to be placed at the bottom of an elevator shaft. If the elevatoossj0tok )t):ovphtfw4t 8k+xa2r : ) r 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 passengers.

  A cyclist intends to cycle up a 7. s26mye4l i:dx8 $^{\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 trav: *on*hh/ yjygw),dz, ffb4j s8yd*z weling 95km/h in opposite directions, collide head-on and come to rest. Howd8/j*:o)gy, *ysbw hzzf4nw y* h,fdj much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches th1 qp*hzru 75zs jq.2kpe bottom with a speed of 2.2m/s How much thermal energy due to friction was genejk. 1spur 2*hzz7 q5pqrated in this process?    J

  A ski starts from rest andhact4weow sw5r182 ze .9;bx f 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 13.0u.sj y:g1p bsm2ane;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 boun60f o :ejg *an-rzd0o2x;l knmces back to a height of 1.5 m. 0:mof6ade2 g* zlnknx 0jr 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, starting from rest, is pulled across a 64gx18iapa)a uklva* floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for thia1u4galv8 xk *aa6) pe next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster is5x1 kb wi(k5q7k .5/9pbi:tlr )pmsa sco/cxn Fig. 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 wili5lxapbks51o s cm:x(rpq/w k5 s.9k7 t/cb)il it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachdjn: q cvp(-: ;m+fvnles 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 mzg gyl*3nq;: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 rqm:n3 yl*z g;geleased, stretches out 2.3 cm beyond the equilibrium position before stopping 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 hoqt*i m h*,3ukorizontal 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 posio3m u*qt*i k,htion, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spac3 0c(hi.e4anoob ad *je shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of aic0 je.b4d(3i*n haaoor 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 *u*dh- xh-e+ teub d:o1750-W motor to lift a 315-kg piano to a sixth-story window :bdedh*u-- etx+ ohu*16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the aveeno)pkawyii):b;1n;v 5 x3 2wptx5 wjrage force exerted on the car due to friction and air resistance?p1i 5xx:5;ni;) 3 nkywptaoj)vb w ew2    N

  A 1400-kg sports car accelerates from rest to 95kmule spo 61nl f* ult7js;.-n(i4w-jsh/h in 7.4 s. What is the average power delivered by the engine?plhn ;71le-joft -inss.ju6w(*u sl4$\approx$    hp

  (a) Show that one Britik1w 1x cxz:(u0s-mhcp9y6 j jash horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the oah,s* l7o3 68mjux l l+a*xnuform 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 ;1hqg/ko1 c6rwtss x8 slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling atko 61;1sqhsg/t c8rwx a constant 75km/h.    hp

  How much work can a 3.0-hp my)xupm:dv 0 :r4ugpv+m ulge328rl/botor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates acihy ws:5go u-ohxg;q9 5g)e6 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average pow5cygig-w uxh69: os g;o qeh)5er was developed?$\approx$    W

  A pump is to lift 18.0 kg of water x*9ik ,hji- g6.anks qper minute through a height of 3.60 m. What output rating (watts) should the pump motor have? kk, h.iigxj s69qa*- n   W

  During a workout, the football players at State U. ran urpy rfz b;9ej:h3vt- gi47vj( p the stadium stairs in 66 s. The stairs are 140 m j(9 rtep hgr4:f7- ybji3zv;v 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 cyclizr 5(pgp w84tym( ojg pzg-g38st climb 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 mz03rmko4w9of 1 f46rs 6u1e7 nd /trehy1zum xaximum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces adf r114s7w khom 3yzn9dmte1/6r0 xou6ru e4fzd up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg yw5 y;z0 gm,xu*1 iaszbox along a level fy 0 m;aiw5gzu*x,zs y1loor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down 2v hi zt: 64xs dj2vmx2;k)vieb-a;yba 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) bumperz:1ivmvxrz .5s” 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, bv1 r:v zmxi.5zut 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 emb(esc.: .qd the first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the pr.eecmqb( : .dsevious 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 the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in lnnsl 3ss+( h c/how29the 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 in3nwc9 s(/hhl2 s+ olsf he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along tnpc f g/5u22px2jfg k2he looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of tp/2p n52 ugkj gf2cx2fhe 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 37q9m8 6ij*qrgt0 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming th8mtgjq 6q9 ir*e 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 idm*oncnx7g: 9il :ir+/0s0.x yzuxaother end is fixed (Fig. 6–43).x:scii*d/ 9i:la yz0+ r0n mnxxug.o7
(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 mountu2s5/ 3nvaa,win 2jyn muw2+vain. The climb is made in 5.uyjnn, 2w+/svw2 3i n 2muva5a0 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//:kps wbou/r 67;hq :sepzy 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 in California clai2 +)houq (ewzqms that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estima 2zq ue(qoh+)wte the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 ,j 8;+,mocnfb sdog x7m before striking t,m7fn g8ods+x b ,;ocjhe turbine 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 coaste, lv4 v.xqp/dqstk,35keq(q xjs- 0u ar with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.04akvk pq3dx ,q(l- j/tsv .5q ,xseuq    mg

  (a) If the human body could convert a candy bar directly i+k7 ub (ni(kjbv ;i+odnto work, how high could an 82-kg man climb+n ;jki7 (dbiv(boku + a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle*jdp1fz +8 iar of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale comprh-hwikl: u*1a 11(nz sztc-c xesses 0.60 mm, and it tells you your weight is 710 N. -z:h*s i1(nlh aczwuc1-x t1k Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs84/k0,oylqjhq7 rmtmpe .o k* a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his veloc y,kj.h8p*lr/oq eqtk7o 0m4mity 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 v0bt2f-nn 4 ieklhq-b2ertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplit-f0b2q2ebhln4 -i nksh this feat?    W

  Some electric-power companies use water to stofs s7i(ic54-*u a xc:aa wfen1re energy. Water is pumped by reversible turbine pumps from a low to -1*se7f 4uca (i fni:xsaacw5a 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 constant k is cut in half. What is the springl.puq1 nv 1uq/ stiffness cons1 1pvunquq.l/ tant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up as+2hya,0kklzkl z t19 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, hm-ep+ m7u *xfuow long will it take to accexu *f mmeup7+-lerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient o1/tv jbipp9j(p+ d wc257ise walks on an inclined treadmill (Fig. pw+c os(pve7ji/1j d 59it2bp6–46). 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 vertically upward a distance of 500 m, b ,tk yer -q6a1pt:.7zz; skr*hvi se6what was its velocity when it left t *iq k:e7s6kr.set v ha 1;yz-,6btzrphe 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/s (a) Ifr4* ctah5iahxh1;73x y )wtcl this water wheel is set up to provide electricity output, what is ita*cx;x ht5l1 r3i4 yt7hac )whs maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s