In what ways is the word7k5tg*b, txg,micj ,o “work” as used in everyday language the same as that defined in physics? In what ways is it different? Give exampttcix*gg7 ,b,k5om, j les of both.

Can a centripetal force ever do work on,vy 2cjp xwr::9v :xczr qj 2wjjdh*z,) 8hb5n an object? Explain.

Can the normal force on an object1zim..q5 uzwk z:w4n 8h wzg)l ever do work? Explain.

A woman swimming upstream is not moving with respect to the shorelpka v9ezsrc8.0;g q 7. Is she doing any work? If she stops swimming and merely floats, is work done on hl 8sc.gr 70 9qazvp;eker?

Is the work done by kineti 6v qv*y,* np p9qugyud6gos85c friction forces always negative? [Hint: Consider what happe,p69 5qgv vd*sqo6ygpnyu8* uns to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall s(p-h ,xl. m:gxgs 9tg.ee/rd even though you are doing no work g.hdtp/em,9s.e -lgg:srx( x?

You have two springs that are idenxhua+fh.x8x,ifbk ( -tical except that spring l is stiffer than sprinai-8fhk hf, bx ux.x+(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 that i/ qk/qe 5p1 c48kxgngal7y am,s free to slide on a frictionless surface (Fig.6-30). The block pl,7 kg84 x1nqcya /eak5q/mg 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 youc.cqemt .;ige:x26 djndk8o4y k -.eqr gravitational potential energy change when you k qgi k4- e etd:m8jo..cyn.xqd6c 2;ejump as high as you can?

In Fig. 6–31, water balloons pv.;s t k*ter2are tossed from the roof of a building, all with the same speed but with different se *t.r t;pv2klaunch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched frm 1g0a( hg(nwbom a point 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 0 mngh(gawb1(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 compress the spr0*f,c(5kyo d p8f9pojt ygn r1ing by pressing down with your hand and then ro5g ry0pkf* cno ,d(891 ftypjelease it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hunh vh1y+as0s jtq54pz2hi2zod2/ c e f8g from the ceiling by a steel wire (Fig. 6–33). The instruc+2hyaqh2sciep/z4sh j o20dt1 8fz5v tor 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 gravitational potential energy when water at the tuf t3acnfi:oo7( m3+ z)/vidrop of a wafmuo ti+ vn /(:3)if37 rzdaocterfall falls to the pool below?

Describe the energy transformations when a child hops( z)3 w7u(m gt5f*pu+ isadcls around on a pogo stick.

Describe the energy transformations that take place when a s,atmkzn)fe5 g,w7-96 vduk cjkier starts skiing down a hill, but after a time is brought to rd7t 5ckeu,-nfa6 jw9)mz , gvkest by striking a snowdrift.

A child on a sled (total mawww i2m:a nh(;ss m) 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) the w2h;wn (aiwm:re is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log i .*5gwwdo 3utgod77fh1yyb - ln their path rather than stepping on top-lg u*wby. d d71h oot5g7ywf3 and jumping down on the other side. Explain.

Two identical arrows, onehihga; vw(n7nn8vc2 j 5p;b z4 with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictionavwgacn72p n4;b8v(;5h ih nzj l force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in88q yv. 3eu,s mbbqn rue)d*x6 terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clo .*q)8rb x 86ueey, nd3bvuqsmck has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than iy j kn:6rnn-r -a8ju-g9 r)peots original n8r-grn ujr-n )yj9e -:ka6 opheight? Explain.

Suppose you lift a suitcase fa*sfiuco4 + ,lb6yz.orom the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height6ui b,fs *caz.o+ly4o of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the pow(c e9azx*i +uder needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to cudh*1i zomjni84) 1yolimb straight up?*i 11 jyoidzu48)monh

Recall from Chapter 4, Example 4–14,vtq298f+i s,6ogkzy o that 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 energy conceptsykfv6o gq 2+t z98osi,.

  How much work is done by the gravitational force when a 265-+u1m f58qu7bfr rvv i6kg pile driver falls 2 1ri+56 mv8uv7rff uqb.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high.q7a(q(wzdz ,k xe( +ya How much work is requ( yz wa kqdz,(q(e+7axired?    J

  A 1300-N crate rests on the floorj nt*+8zt2pqx:x;e1b ohs2b u. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forcuj:o t qbszhx28t+;b2*x 1pe ne of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) 8y030bduz2fo6rst lq5f zz+ipushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 3yt 6uf b20rszo8iz+lz d5 fq00.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fbq .ortc 1nim7+g;2e oloor at a rate of for 7.0 s. Find the net work done on theoit71 gon be+crmq2 ;. box.   J

  Eight books, each 4.3 cm thick with mass 1.7 5-esk3m5m etakg, lie flat on a table. How much woram-ts k5me53ek is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be dmlw/ )qhc1met ;q9e 9used to liff objects we might not otherwise be able to liff. Show that the rathqm19d wt/);cleq em 9io of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelecyut-f /1 s+b .z3 xsdtu;xjv+rating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficientu/xbctsvfy1djs+3.z t x;+ -u 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 of mass M an accenz4z6;j8ai 2h p4z .;7j a2h cncqxmuileration of 0.10 g up2iaphc n2uzc;448ji;ja qzz 6.x7h nmward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linerbrkx lc0zb/ jh4 -qutf/ln f qn.709)ar and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fi i(-me w2j,fw2 fpsjjx-08i/tq d0rlog. 6–37. Determixeqi-wj/ pisfm2j002 j( ,8t ro- lfwdne the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a partir9j0sk* (hcv9,niibm m +na*w cle 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, atxm-;sn5nnig (6n9vff s,p ,pn oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what fact vec;/0. )-ve 5 avjliuu,co(oyqw;swor has 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 stb.k mh6v5llp-op 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 stn82 mmxdp ).yhnaet1yp15 ue3op a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts at 9whg*q,aemris96 w, la2jr:n average force of 110 N on the arrow over a disr:9rhm9* w,2,at6esji lg wq atance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove bac1s.xq 3 j94u-chzh lfjgq n)v8kward 25 cm when the ball is caught. What was the average force exerted by the ball on the glozqhsh-3j1n f9 4xj )vgcl.8 quve?    N

If the speed of a car is increased by 50%, by what factor will its minimum b*t fy2imdytv6 f7/r,u raking distance be u /,yvtmidf6 *yr f72tincreased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a leh5+0m: hv6 ig xa/udepgj+s) jvel road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient o emhj:/id x a0v+hp)gsgj+u56 f 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 rezq45jbqp9ga n72 fp( qaches the plate, it may have slowed by 10%. Nenq9p7pq j4f g52 bqz(aglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does o07u or 09itad80.0 J of d0 u 0o9a7irtowork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singles (mk12 8ibaer cablesmbrk (e18i 2a. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How mu *5yp rrhj9 hz1+(jkdxy/mr4w jo/j4dch must this spring be stretched to store 25 J of poten+rwj 5*zmd4 xkd(9j1yhj o/hyr prj/4tial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wha()flod/ixvu/nk,w) r t is the change in pouv )oi/d)(f/nkwxlr,tential energy?    J

  By how much does the gravitational potential energy ov :q guzk97dh,f a 64-kg pole vaulter change if his center of mass rises about 4.0 m duringhu: gv9qk ,7dz the jump?    J

  A 1200-kg car rolling on a horizontal surface has smc go 34uy83tdpeed 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 constant of the sprc33u8t odgy 4ming?    N/m

  A 1.60-m tall person lifts a 2.10-kg bookk7k+ m p*y7kixd e.p/w from the ground so it is 2.20 m above the ground. What is th7ip/7kdyep*+ kxw .mke potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker startszi9k /sex8/1n8r r1ndd 0 tdzr at an elevation of 1600 m and climbs to the top of a 3300-m pea 08dd8nrreksx 9z 1riz /nt1d/k.
(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 r r(f+78cm*bakg5aim)xb *lalb u*la/ uler. The end of the spring is next to the 15-cm mark on the ruler+(a i8xaalb*/ c*b*fmu7m 5 ba)krgll . If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/ya ;k)/sk5- ialzn5 kms) and grabs a vine hanging vertically from a tall i ) 5y/lk5sk a;mka-zntree 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, starti 1qreu sy.y(v-ng from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove updm3d xlxa885s z4,a jo a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s -jg/8pd0bcl*vxvx5r s:kx ( nkinetic energy is transformed into gravitational potential energy without the aid of a p rx-ngx0l *:d/vbs5kj( vpc8xole. With what minimum 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 m.pvx d1hgde; ax5q)9platform withx);gdxv19 amepdq. h5 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),opxa8: gq uvyjj*c +(; whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30 (aqcv+8xp uj yg;o*:j-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 lhda5 8imhysg :bzu2 mlc1h1 /3ooped track shown in Fig. 6–39. If the block is to remain on the track,z/8ds 3huym5ac1: g b1l mih2h 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 jvgj s1/ p,xf4k), Fig. 6–40. The block is given an initial disj4 gvfp, 1jsx/placement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungeue5n w i-8 oq8uc2h- krct:rq/e cord whose unstretched length is 12 m, and falls a totq8q2:or8r ue tkuc-wnh-ic5/ al of 31 m. (a) Calculate the 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 nn+da, -3rhf(jc/s b b2qs *fupoint 1 where it is released from rest. Assuming no friction, calculate the speed atdnb s/(h ,bq2jc*su na-fr3+ f points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s jm2hc *4:wp csy8ibl*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 .93x i 4o-c8s,meuw1bj:tdpue(zxyv h y3s(aat 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, calcjb-h .:x(3s vicyw3et( u4xy , 1m9apde8zousulate 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 5 z;erwm; wd+ba 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 ona4sq *v5hc8vf :+nkr f mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal ener fhnvk* vcs+rnqa85: 4gy 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 the bottom with 7ru ik80-gsksmf;6*uc-a ibocyh+k/ a speed of 2.2m/s How much thermal ea7yssrk; /ioic--k+6fkc uh b 0u*8mgnergy due to friction was generated in this process?    J

  A ski starts from rest and slidstcy v0d0ks86 l .cug7es 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 f,jae6k*srk7f 1 ae9c o*zsyg08kp i w/rom a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to vzr.19w 2yen6rzm7ag imgk7, a height of 1.5 m.kr 7g.76 1y9w,vminzz e2gmar
(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 co1fv.p tfk /bj4nstant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of .1/fbj4 f pktvfriction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes pointg- mwk4.1tfmy 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance -kmmfygt1 .4wtraveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady up u5p3xi(fyhdo(sr x- 4ward 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 vlyc j n6f3h:t-ery light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficienjthn 6f y3c:-lt of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal 5ilnbt69/ani2jp n. tspring, Fig. 6–40. The block can slide along a table where the coefficient of friction it6/n5i ap.nt nl9j2b is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glidsg7(dmx,zt*xg8w8: o + kilp rer” (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 absenwxt( 7g:8+zl*goid pkm, 8 rsxce 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 motx ak-9 +to68m anr0kyjor to lift a 315-kg piano to a sixth-story window 16.0 m ajm+0 txk-ayknr6a 98o bove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the ao-kq/yyi c(6q:k4 hr(fifdn(* zbr(rverage force exerq (f fd(nii/q6k *zy- rrho:kbyr(c4(ted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h0zdtz+ ncp.lnoxx.pax.l 07 4 in 7.4 s. What is the average power delid. 4z .7cxn +l0n0txxlzappo. vered by the engine?$\approx$    hp

  (a) Show that one British 5u*-eqv enqo,d55urp 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 y dv,vhd1 *iu- cqxgy sa27c30often 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 slyjtrr.fr 6a7b.i . 6m(zt7xtuows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approxyb6rt6xjif7..(t urr 7maz.timately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.o/+(8 owrm mu4g*q0ow9lddqv 0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg 7/g5xqrb i3uen3q 9ejshot from rest to 14m/s If this motion takes 1.5 s, what average power was deq7ej33nb x eg5rq/i9 uveloped?$\approx$    W

  A pump is to lift 18.0 kg of water plyt;f -h dq1)ozj51h yer minute through a height of 3.60 m. What output rating (watts) should th fot1y)y jl1 5-;zdqhhe pump motor have?    W

  During a workout, the football players at State U. ran up the st2o8jp,nc e ggg2j8z/w*ryb- hadium stairs in 66 s. The stairs anjj8p ogy8 -b,*h2/gwe2zrgcre 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.8.ewpr *qq5:dvre u-q 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 ofg 6--sn v6qbgpfq u(*f 120 hp. How steep a hill can it climb at a constant speed of 75km/h ifgf6 s(gp-b6 v q-nq*fu the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able tpai:g x *j9rl7w-aue ;o drag a 310-kg box along a level floor at a speed of i-9*rp:x7a;lgewau j 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dyko+xx4m0ah4n,vaq f 5gm7l9 own a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars hamjix)*zrg (xb m;cxb/vuca3 vto57- .ve 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 compre;bxbma(uc.g* 7c3 x- /t j )vxvr5ozmission of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library )gisz73pysr7kg+i k2kf8d 0h the first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of73ghisis0 f) 2kygz8 r+7pkdk 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 lonpps5io lw5kye;:c az7,ryo() g 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 s k) ca,rlo(siz755ep y :;oywppeed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding witu7+ 5e;arneh od8 3kvqhout friction along the looped track shown in Fig. 6q7;+ee5kau h8v3n ord–39 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping fr5(av 6g(r)1eo fdwoxiom an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with (v dr() f5a1oiwo6exgonly minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other enhhxehm gq .e+goj+ 8tgy rb4,.p,:p n9d is fixed (Fi.thhn,gg4ro9: 8,x+m q p+pg ejeyh.b g. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountai78pvnki dm bly8x2a6 (n. The climb is made in 5.0 h starting at an ele(vb x2k 8iyl8ndp 6a7mvation 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 vfxx94sqb*b2lg9ovznmm ri(u.f + th)8r65 x28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims thatm.n n qwhk7hjs5 j-)0y its lifts can move 47,000 people per hour. If the average lift cark-m jn57h0n .s)qywjhries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate onprg7xxim ( rpx6q3 08f 650kg/s and falls vertically 81 m before striking the turbine blades. Cig 7 r0xn83px r6qmx(palculate
(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 coast+ wi*93p mqyjlfo9z0d er 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 — thy0m39iwf j + z*q9pdolat is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a cane7p )*f5l *r 5svwoe0kr ay;pcdy bar directly into work, how high could an 8evl5 f;esrrwoyk)5 *ppc*a 702-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwarm(nll3.jo. oz)pwl +m d 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 sca3 pnq):t fwt4cle compresses 0.60 mm, and it tells you your weight cfqt : 4nw3)ptis 710 N. 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 grabs a rope, and swings out over a lake (Fig. 1wy d;q16oy q3/+x8;o1vrnx lfl yjqo 6–45). He releases the rope when his velocity is zeroxlojxoyr+;11 1l q y6v8;yw qdf/ onq3.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s.whjkb c ;d.xss,t 4,j, What minimum power , hjxwkbj.sd 4t,s,; coutput was used to accomplish this feat?    W

  Some electric-power companic627 towixw9i a* fmam/7.s tq-zjfl.es use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To st qt2w7 a f s6i9/miwfa7ltmj.czo-*.xore 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 hal.w rv6/m3 :s voogrn,gf. What is the spring stiffness constant for each of the two resulting springn6g/v gm. ,3rr:osvows?   k

  A 6.0-kg block is pus jm wy w2oi9qv3ej2:.uhed 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 accele vr2 jrw21g (f9.pgvdbrate from 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 s g22vjrrpgvdb.1f ( w9tays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the p,( 5shopjdg1fx ,e 8* her7uuhatient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the trejr e 5up *8xhhh(sfg7,1 eo,udadmill 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 wn,b5s4n*x. iwa*ouh of 500 m, what was its velocity when it left the vu4*x 5wwibns h, o.*anolcano? $\approx$    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 (2s wl bx:vvs-73 (npmya) If this water wheel is set up to provide electricims7l:nv -wb2 v3ysx(p ty output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s