In what ways is the o jswr8/qq w8:.jw2s sword “work” as used in everyday language the same as that defio w: j8 q2.8/sswrjsqwned in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work r tg72u 5en7ston an object? Explain.

Can the normal force on an object ever do work? Explain.7v +qg5lngnv) (r r ac2e/6rooy6f3tb

A woman swimming upstream is not moving wit9g iyrt6m9 wi1h respect to the shore. Is she doing any wtir y9m9g1i6work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consibpv 6;;,k mfo d:5htmhyvqy ,8der what happens to the dishes when you pull a tableclothy ky8; m6b:ht5 om ;,fhvpv,qd out from under them.]

Why is it tiring to push hard againsh(arsa 3rrm2m)oi 4s6g 7s/ kxt a solid wall even though you are doing no woo(32mhrkaisxa ss4r rg)/m 76rk?

You have two springs that are identicalg2bc:vh3 n.sh-mfaw/(t*qka except that spring l is stiffer than sprinmvc* hw gqk3t/ hns(.baf: -a2g 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 that is free to:n1: hrmht bqvf/3y+w slide on a frictionless surface (Fig.6-30). The block starh+nw :mbf /v13tryqh: ts 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 gravitatio tbofr ygjb 89bv6n4/2nal potential energy change when you jump as high as yofr6t8 2 4ov ybjn9b/gbu can?

In Fig. 6–31, water balloons are tossed from the roof of agz b +kkzjht. )c mxc 72o*9igg1ltzil;(-x .x building, all with the same speed but with different launch angles. Whichztc.z*+bmoz;l- g gj iik9 hx t21l(ck)g7xx . one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a poi f yiz,;wkq3ou4p ek;7nt that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium positio4;ky7piuow ,fk ;q3zen? Explain.

A coil spring of mass m rests upright on a table. If you compreaf c66h g-spaq *.sqxrt /6c16-jeoxh ss the spring by preha a/j-xc*c goqe 6f61p hxq6ts6rs.- ssing down with your hand and then release it, 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. 6–33). The i+f bbyfy2gymy:zh z818 +m8otnstructor pulls the ball back and stands against the wall with the ball against b fbm+ z2hmy88 1oyfz8:ygt y+his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy wa-vuy,96 i/*w cmbuli hen water at the top of a waterfall falls tom u/cyivua6 b*, 9il-w the pool below?

Describe the energy transfo7kz5 266dfkkm kksk2*uf lee +rmations when a child hops around on a pogo stick.

Describe the energy transformations that rq5e )4qsv tj*1:z/h gl(dbidtake place when a skier starts skiing down a hill,:vr*j 5qidzl s/g)q1deb 4th ( but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of5g2z qfe vq81 rb:k(oa height h and slides down. Does the velocity 2:evo8z1bg(k qrq5af 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 stexhnl ufkduf 79- -64gqp over a fallen log in their path rather than stepping on top and jumping down on the -xugdnhkl-fq96 fu47other side. Explain.

Two identical arrows, one with twice y4kxd t mg(u8zq;.bo3the speed of the other, are fired into a bale.;dk8y(tbxz4 o gq um3 of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinggq) tipk:-1axing pendulum in terms of energy, (a) ignoring friction, and a:gp-q txi1 k)(b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” iekazl0s+i0 o6 s dropped, can it rebound to a height greater than its original height? Explaio0k aez0 +6slin.

Suppose you lift a suitcase uem9xm758j9ofeh 6yz from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time9 65ofyu7ze x89emj hm it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needef,is ;9 e v5texx3sye7a;r/r yd rather than the work.

Why is it easier to cj svaek3//wf ,limb a mountain via a zigzag trail than to climb straight ueva3k w,/sf j/p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to k jv c2o,+ugz6decrease 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 t6vozj,2 +kcughis, using energy concepts.

  How much work is done by7dw-o0p ge2( wkhf 2jy the gravitational force when a 265-kg pile driver falls 2.2jweo-gw27dkyfh0p( 80 m?    J

  A 65.0-kg firefighter climbs a flighycj4( xi.p/nogy3m13quk69 a qlt0klt of stairs 20.0 m high. How much work is required?qym /u 0j9 .c a13gni4xpy3lkq 6klot(    J

  A 1300-N crate rests on the floor. Ho4utkt++4z mg;xqn 28 b tj1:o cp+uezvw much work is required to move it at constant speed (a) 4.0 m al qot+kpzn4u+c e+1:4tjv ;2bzuxtm8g ong the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontaq(* ,jxjq5b1 eiwng 03gzyag9lly) pushing a 160-kg crate 10.3 m across a rough floor witho0 egn5*ibg, 3wqyqzj1ja (g 9xut acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg isqj*ccg;a ytib075 g7 u accelerated by a force across a floor at a rate of for 7.0 s. Find the net wo t c5cgygj77 i*uaq0b;rk done on the box.   J

  Eight books, each 4.3 cm thick withmhtwo47 8/nkr mass 1.7 kg, lie flat on a table. How much work is required to st74/rm8nwok h tack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can b5 4 4tg-qmkjafj4 c:ple used to liff objects we might not otherwise be able to liff. Show that the ram: cajj5gt-4plf4q 4ktio 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 x/ti f,ao 3rqq*jt.b: m down 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 effective coefficient o:q *t./ir b,tofa3xj qf kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an accelerati: r;xx ah297jh:zpiwcon of 0.10 g ur:;h7zh x i2jp cx9aw:pward.    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, assumejejtsnhyn+*8v2- 0e h v0ar;q the distance 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, evu qxnz 7jpu7:j3uk n84c*g je 1ai53varies as shown in Fig. 6–37. Determine the work dngv 1a*cj 3uu8 j3e7u :xie7znj5 qkp4one by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a pad5hrl0it5io , rticle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mam35ot jem)-e fss 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 its speed increased?uzxa x* d9q9 f)(gi3qk $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an ele hylc fa8537 3vq/nh l p23hr..ktvicrctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 avkde bw3 h9,9+ eqrv0q 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an ave)hmyez6l r-6e5o jz 3prage force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it le zloyeh3j) 6mr-ez p56aves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s b23bz (a x)ydq+bnz7pglove backward 25 cm when the ball is caught ynzpz3qa 7+2xbbdb(). What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%,o; akt /u n1tpc)o ,2xc.igt:u by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the dr:c,1/ uiongto. k ;ta)pcu2xtiver’s reaction time.

  At an accident scene on a level road, invzp/y5- d)6c8eg,trw)n ydd glestigators measure a car’s skid mark to be 88y cdr)g- we6gtpd5n, z)y dl/8 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it g1zxftyzp. o 3o l4(k9reaches the plate, it may have slowed by 10%. Neglecting gravity, estimat9 k p3oz1zlyo4.(fxgte the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doef)6g amy4d 3obs 80.0 J of work on it? Neglect air resad34 gbmy)f o6istance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by0md a5bjg4m p)p(ph .v3y, 9kqloj2 ej a single cable. Deterpbme ol5 j jh)mp(3p9ad 4v0 .,2jkqygmine
(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 must4uu(d 3u k+b5wyl+ova1 /(6i4nqzzn1kdj mko this spring be stretched to store i4 +4lkvz1mbqa u+zwo5( u(ud3/jkn nd1o 6yk 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hiyz2+a, +xzqsxtf16 -co eaz: ggher. What is the change in potential energyzg+as t xz, z2-1o6xy:fecqa+ ?    J

  By how much does the gravitational potentnloit(3+ ua 9.v rats9ial energy of a 64-kg pole vaulter change if his center of mas t o3(in+au9asl9. trvs rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal h yelz.2;wecl o9, 52v uyzmo0surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brougzyve,m0 92 ;ulyez2o5 clwh.oht 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 the groundjc157z-jy h5xr5ru irba2i x +cih8;2 h otac* so it is 2.20 m above the ground. What is the potential energy j 8r2b ii a*c;r+ x7rxh5c2ju5oh czahy5t- i1of 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 toy7v-2x: kgyf6h,us iz zmg *6lp of a 3300-m pe:zvy7 hlg*2uy i6x6-gkf ,zs mak.
(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 h 3pv dh-hgb18uangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where w phhv8dg13b-uill the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runninrw 0 m55ww ck.5ch/i*4hri ic)qu/jfgg at top speed (5.3m/s) and grabs a vine hanging vertically from acwii fmcw5 4r0hwgurjh*/ik ). qc/ 55 tall 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 35.0li-+ahx:sn lzmu 7xkh59g;6u $^{\circ}$ 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 sc/:pn 3/iwiw2ldv:oa 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, Fr)h 3 zbmoc7mp9 9i6tbran’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minim6bo9 chr) pi7zmm 3t9bum speed 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 top of a v k6b qabi7j1b00ts*c asu 4c1platform with a spe 1as0sjbiq7 c*cb bu0 k61va4ted 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 stiffsfb,z4hoqx0u:5 0kujcvr t -7ness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwa 0cjtuhb,s- xzq 7u4fk05r o:vrd speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the loopedid7wt/po( 2ccj.ar7rlka.sb:t0 mm8 track shown in Fig. 6–39. If the block is to remain2l:wt(crkt8mbm7.i/rsapc .a 7d oj 0 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 (sp27eo +3wytikcw5kac;1tm 5n.yp6d x/op; qh tring stiffness constant k), Fig. 6–40. The c5+whk2m.;6;xtdi oqce7p t/y a1kt ypn3 o5 wblock 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 jumpst70mk1uol nagtvq d7 ; 9e)jc0 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 th k 1qv)ue to 7mlj9cg0ta0nd;7e spring 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 dragged up to point 1 where sj b;cpyyrw 7v r9 l0(;jls+h2it is released from rest. Assuming no friction, calculate th 0jv ;w yrlb+rshlp9s yc(2;7je speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a s7k;z a ;puw gtjz*:p9f-9bqqipeed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be place;z1)pxrr.tuqj ng sv9 ,,j8qzd at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passeng 8 rjzpuxqv,;1q g)nr t,.jsz9ers.

  A cyclist intends to cycle nm06n6z*pd/jd(8xd3 g/ j:gt kbobz s up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kjjj7 t 0mn jz4pwg,.vubr2,9xg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collisi ,vr b.jpjj24zmux9 ,gnj07wton? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wiou o1yq+- gip..b 4,x)llvuze th a speed of 2.2m/s How much therop4uly ,o-i)zq+blxe.g u1v.mal energy due to friction was generated in this process?    J

  A ski starts from rest and sxv) bc:6 tn4 vwq0r+uuqv.h x/lides 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 gr eu u:zqh*g0esdv4)0n ound.
(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 bouncesa 9/q8s,j,w:xjfujtn back to a height of 1.5 mfxj8 ,sj wjqtau ,n/:9.
(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 acb9w 6*n7xcm )f utb 4zw70gge constant horizontal 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 fiemx 7b6fg )u9wctwn470z*cbgnal speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of cn wo/j; n5cq) If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance travele;o)w 5 c/njqcnd is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a stguz i, kj/e-1knr3 - dz,fr-weeady 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 horizont.l3u +z4d-dm od7yqu ial 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 pos- u qz.ul7moi+y dd3d4ition 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 attace(p b r):lxnkp. i9a.cm8if v6hed to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 Nv p9kcipn )r.bmi .lfe:(8xa6 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 kg7z9 ;0l2t2 qcskp kz4dvfrk;a including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a sk29tqdl704 ;;c fvz rsk ak2pzpeed 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 piano to r)-(3q2ezwbib kwnb, a sixth-story wind2bb-b ke3z,)irwnw q (ow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h whn dxtj2pp umu81b;y*) at must be the average force exerted on the car due to fri;*pbu 2tynmux)j18 dpction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is tki/sv z0+qag7o ew/ n3he average power delivered by the engine //nzow+ 3siqagve70 k?$\approx$    hp

  (a) Show that one British ho;g; ejy(.pgql+:d fip vo;t5b uv)u,zrsepower$ \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 ofte oot: nes3w74b.ir:iwn expressed in the form 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 slows down from to 65km/h i jcjr; d-q8r i flx)+:(2pecntn about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the ca()fr+: nr-x 2cij;qpejtdc8lr traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? wg)s,gv 7r 4pu/(gxiz $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If ty 3y /6xebydc7px0 i9g-7zcg yhis motion takes 1.5 s, what average gcb7 6xyyyce dz /xy9i0 p73g-power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What oz4hw9w2t*nxhu y;-zm utput rating (watts) should the pump w;9uzh -*zht2nwx y4m motor have?    W

  During a workout, the football players at State U. ran up the vxp cy( 0zjq--stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle(-0cvzjy-px q of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a ) rof4b g xy sf,ag4pm05;ulh,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 l9o/ +te vat)vof 120 hp. How steep a hill can it climb at a constant speeoev/ ta+t)l9v d of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg1unf.jbki 8zg* )l/d.xfnhmemjr 179 box along a level floor at a spef/)9mkd niln huj 1f.r1xg e7*j8mbz .ed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down ac3ymtjq;7( kc 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’szjh ,iol puz1y222w.n cars have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains l wyhi.z ,n1uj222zl poike an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm offsv yu73nx0zr: z c5p4qev3e h0 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 h 5sn70033yvuerez q: vx p4czbooks are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owenn.* 1vm: y2i)trlzzras’s famous long jump (Fig. 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 launch if he wanrzr 2:m va1)l.*tizy s traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction alongl3w zr:zna5 iy) fh9)d the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very thfi wy5)z n9z3:dlr a)op of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fel8 gebzpi(8qg 3l 370 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 the pilot’s mass was 78 kg and his terminal velocity was 35m/spge8 iz3(g bq8 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 len:2 ea ijd8c,,4bbsg spv+s 7bvgth L whose other end is fixed (Fig. 6–4ebca,s,gvb7 i:82sbvspj4+ d3).
(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 topjq )8oohg imoa4qmdj ,)1fdvdm-*rl:w+r9 n1 of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calao4dlr9o+ 8:i)jjnmm q vo1wqm)fdhd r*g ,-1culate
(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 abovex cnq mni* o*huue;520 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 its lifts canp,xu:;j r: ad y-) +raeapm0mp move 47,000 people per hour. If the average lifpx-, emra:m upd:rj a+apy0;) t 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 8gi3(bz bd:ctk2h6r 6s 1 m before striking the turbigrh6 btbc i:d(s3k62zne 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*ah* w qsi2/hbr 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. *2qha/bh * isw   mg

  (a) If the human body could convert a candy b*/ rz3imq:e xuar directly into work, how high could an 82-kg man climb a ladder if he wem/ er z:u3q*xire 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 upwardx1;p 1zrlo 0,ztn :rpd 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 scale compres 9m onhog8zej+0et/40xqdfv*ses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height 8m/h0o4 vj9e0*qotndzef+gx of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a ro/c *x)aqkpa -spe, and swings out over a lake (Fig. 6–45)ac*q ask)xp/- . He 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 72yt kv jjg1/8*c7sfo1r-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power outjs1/ *8jcfkr 7ot1vyg put was used to accomplish this feat?    W

  Some electric-power companies use wa 9jt lwqr;,l2tter to store energy. Water is pumped by reversible turbine pumps fr tl q,w;t29jlrom 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 consggw.1hpx ud j91r0wq *; c)buutant k is cut in half. What is the spring stiffness constant for erw0uxg1u. ;c9 uj*hw1 gbd )qpach of the two resulting springs?   k

  A 6.0-kg block is pushed,7vi *8 ffxy: 4)ocfibnvvr+g 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate fromw+t;vldc8v h8cb(;0utu i a:b 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictionalcttacd+( i lvu8v:ub8w; 0; bh losses.    s

  In a common test for 31ow6q8t0dwl 0+em tx p5ehmkcardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power reqhtklo+8 e tw15d0m63xm pew0q uired 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 distang kst.-s+b(zn ce of 500 m, what was its velocity wh.nss+ t-z( gbken 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 2i1xk,sk( eu+m0 efg e).0 m at a rate of 95kg/s (a) If this water wheel is set up to p,e eif+g xm 1s0ukke()rovide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s