In what ways is the word “work” as used in y tdc5k3w4tnh-j2h gv c 04ni)3il+ms everyday language the same as that defined in physics? In what ways is it diff -ci+2t4nmh l ts3dh 3v5ci40wg jny)kerent? Give examples of both.

Can a centripetal force ever do work on an object? Expn/11ph *bib hblain.

Can the normal force on an obx+g;88 agn6hh(n ja*gp i wlp+ject ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she5fmxt8vfo5 z sc0hwk0p4kexp / - jrat;o(,b7 doing any work?fb phkvs/erft8,t0x7czoma; w o 40(5kjp-x5 If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: C1;v jkmk fu8a9onsider what happens to the dishes when 8;amfj k1k9 uvyou pull a tablecloth out from under them.]

Why is it tiring to push hard w)) keneh k,sgyj-)yn84zbn3against a solid wall even though you are doing no work jyhwek)nns)ky-8eng z)4 b 3,?

You have two springs that are identical except that spring l is stiffer tt8u-g2zpj0cwv-u7n nj pw ;d+-4sdn zhan spring-;2n 7 -ntu8j-z+0pvuzwnjg d wdspc4 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 free5j.fbjz t g 5 -mt*aa;at1c4ba to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has trav;4at 1j 5tfz gmb.a-5bj ac*taeled 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 muchdnq 7 wysio1t n0. o: ,:v*r5eqkg)ifw does your gravitational potential energy change when you jump as high,y7d:itovs q01oni:. 5f*)qrekw ngw as you can?

In Fig. 6–31, water balloons 5vespjq ib,-48i5se r are tossed from the roof of a building, all with the same speed but with different launch angles. Which sji, pq4s8e r5i5ve-bone has the highest speed on impact? Ignore air resistance.

A pendulum is launcheii jz jx84i2j))u.ry hjsv629y-w )mzww)ud nd from 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 vewzu.rj 9nh wiwj-j ysv 8mix))di 26)y24u)zjlocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upvcl ; ;mtz00q;w:x ux7uyyh 5mright on a table. If you compress the spring by pressing down;vw;50y :z7u;mc h 0mqxu xlyt 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). T-* aax0 6uquaohe instructor 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. Whqa-0 u6 o*aaxuy?

What happens to the gravitational potential energy when water at the top of a wl7 :(1wq 8gy +zu(mnjtzo5cu taterfall falls to the pool below?8+tlc7 t(5um :yjqw(uozzg1n

Describe the energy tr4x5kxs(nju)idlx+ -6n xb5kvxi g;7cansformations when a child hops around on a pogo stick.

Describe the energy transformations that ta kcp3.n) jjnoal+u so836p h2uke place when a skier starts skiing down a hill, but after a time i26). u3s3 oonjc+u ph8npkjlas brought to rest by striking a snowdrift.

A child on a sled (total mass m 03/u l6rilqxe) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom dep6lrxie30/ lu qend 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 overhei njvjfor; ;l;ukz;o( 2*v ; a fallen log in their path rather than stepping n2v;ujkjolf;eoiz* ;rh(v;; on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speedhzxhj ee- ,,fra2278,aih erz of the other, are fired into a bale of hay. Assuming the hay exerts a constant frice hi,fxr7a2ez, 8,ha-ehrj 2ztional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a sih6 0)cxrkgvun :. 9nhemple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. c:.9ev 0n)xgh 6nr hukExplain why a grandfather clock has to be wound up.

When a “superball” is droppedrg+yv/q .s8hq, can it rebound to a height greater than its originalhr8s.vq g y+q/ height? Explain.

Suppose you lift a suitcase from the floor to a table. Tr qpye/,6)yo o;un zx,he work you do on the suitcase depexyo;r)ue6 z /q,noyp ,nds on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather thk;hu bf, ha p35*nqp*san the work.

Why is it easier to climb a mountain via a zigzaxbou 0 y6 f,5jmjxz:l;.rawy; g trail than to climb straight uo;zfr .5bjay0y:ux, x 6 ;wlmjp?

Recall from Chapter 4, Example 4–1o bk*v gxb)x -z4yv)7f4, that you can use a pulley and ropes to decrease the )- vbyvfzb*k)x4x o 7gforce needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is donec 26 bfo,7 cyse;o u4vnz24mtz by the gravitational force when a 265-kg pile driver falls 2. zzs,e2ucbnc4 67fv2oo;m4t y80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much u b 7sq(t0 y/b:olda (xc5hbv/+ye2g dwork is require0:d bebg7ouhyy a/v(+t2b5q/d( slc x d?    J

  A 1300-N crate rests on the floor. How much work is required 3euqc.mkt g n f0,;;1; yqvoxzto move it at constant speed (a) 4.0 m along the floor agamcy;;gk, z ;.neu o0tfqx q3v1inst 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 crad ;gmgmm hyx.zv; ruh ge;-)1+te 10.3 m across a rough floor withoutu1g;)grhm e;-.md;v mhgy+xz acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at n*5rb1 fj)/5ri.evtfr e ,vws a rate of for 7.0 s. Find the net work done on e es5f/,r.1*i5 fbwvrj)tnvr the box.   J

  Eight books, each 4.3 cm thi9mzpr6il os+dj) q 52zbb u2:nck with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of anot+pl6rb 2j2o mzs5 )iun9 qz:dbher?    J

A lever such as that sn6 48ovt*nd sfq9ne :( omjx8hhown in Fig. 6-35 can be used to liff objects we might not otherwise b *ho86e94fs:(tnd oqvj8nnm x e able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from ach3qlgf *w1tfkg3 o-xem:v 0y 2celerating by a man who is pushing back on it parallel to the incline f qm etgo 2-w* klhg:1fvx03y3(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 to give a helicopter of mass M an acceleye*a pm od.pfu-g1 zg8.d, i;vration of 0.10 g upw d-;.e.1gfd v*zu apop8yig,mard.    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 ojacp,rm arc2p n 94* mkp:/-nlinear 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 axihmlw8( 1wgu2w s, varies as shown in Fig. 6–37. Determine the work done by this force to move th(2wg u1 8mwhlwe 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 exerte,*e gxny,f; rci2ji) dvsl-p);rkf; n d on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, ani.nj) zcs,k* e 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 factor has its speea2iix4pex6o9ip6p k ( frrn m 0y)l(o,d increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an ellmzt80e v8s5dyfql-3pyc4z5x . su n+ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 stx ckonaviso:)4u:k)0e-j71x0 p um ykop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a s.,)2nc1e vemami xq31ip 6oz bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it1m31 .,6epzn2 v eacsqimo ix) leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm 3v1rbfkq.)pw when the ball is caught. Whatbpwqkr.f) 31v was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its min1qvk a +ehkby7c5 , bc7uoio(+imum braking distance be increased, assuming all else is the same? Ignoro+5, b (1+y h7bokavci e7ckque the driver’s reaction time.

  At an accident scene on a level roadu k0xt)qz)5+eo s6va v, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the catx s+a)u5v k)v ezq6o0r’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg3t5haoz.2dd l is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distt 2l5d3hadz.oance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock goozdhn:956 f+s gf dc0w if thrown straight up by someone who does 80.0 J of wfs 0dfc+onhw 5 6:9gzdork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertiu/rq8luh *5pg cally with an acceleration by a single cable. 5l /ug8p* qurhDetermine
(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 mus1/zg ocou1: ioi:uwx4 t this spring be stretched to store 25 J of potentia zo 1i4:ou:cix1uw go/l energy?    m

  A 7.0-kg monkey swings from x8 xlr 4v -1w2f+.cap aatiy(wone branch to another 1.2 m higher. What is the change in potent(f2x i.a-v wxclr4t+ 18pywaa ial energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter f bg.(ph k;kemh7m.*7u s7jqtchange if his center of mass rises about 4.0 m during the jum 7.mk.bgh jhk 77e; (ftspmq*up?    J

  A 1200-kg car rolling on a horizontan ny-(wz2:rn tl surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brougw:ynznt r(2-n ht 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 ground so it 88ju3h/m/ome/-lbji2zypbr) + znzz is 2.20 m above the ground. What ism/23h jz8rl/j eizn bz+uy/zp -)bom8 the 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 starts at an elevation of 1600 m andqy(euo* ;cmnan.0 vr.l7 y3c q climbs to the top of a 3300-m y 03v*qeq(u;l7.caynon m cr.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 vwsv+l. uv8bhm;e v6j7ertically 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 tm .v sl;ubev hw6j8+7vhe end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine hangvx (qujo h(i) 7cfb.m.ing vertically from a tall tree in the jungle. How high can she swing upwarjmhxv .7bif ( oqc.u)(d?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down xx st9 tcyt7ch v+dysze920*8a 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 ,-kv+ rs;ds;px,s hdr)wpgf3shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transfor ih (07a rw.hy y9uut6w5q:exsmed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 s w wu7i x6ay5r:tyeh9(quh.0m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertical. u;j qapgoe3v5oe 5vmq x2m44ly upward from the top of a platform with a speed of 5.0 m/s.pqgv4o2v j5 e4 em;m5ox3qa. u ($\alpha)$ 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 (imgt5xofho1e5q:t um7; c 4 fp8gnore its mass), 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-kg ball when releas8 efxm ftq pg5m7o;4u5oct1:hed?    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 loopedx8eh:b4x7ra50cav +2e emdf .z bilt: track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height +7axve: t d m:c.hxf5ea 0erz4lb82bih must it be released?    r

A block of mass m is attached to the end of a spril l5k:ixwwd(bpp k/j* - -oby8ng (spring stiffness constant k), Fig. 6–40. The block is given an initial displacement lj5-: ykoblwp d b-k w8/ixp(*$x_0$ 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 vl bop,7 v3sc nvm757bis tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the ,7ovb5lmp v7v7ns 3c bbungee 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 4ka/w6rt-98o ydwgkw 1 where it is released from rest. Assuming no friction, calculate the speed at poi-/kwy8wr w 4ao96gkdt nts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a 0nw e.;qvy yo1speed 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 placed*ildgnx. u6rs* 1rzp) 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 passengeruxn r* )p 6lzs1*gd.irs.

  A cyclist intends to w.*lxev7p.hk l a b7you259 d (g,jgovcycle 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 kg and traveling 95km/hl( u,dd q;:j;.uwevse in opposite directions, collide head-ond judus :(;v,.;ewelq and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with(8 oprb9n ube4 a speed uneo rpb 8b(94of 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest u hmsilx 4tw:v;l8sa;-auc-: and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13f w.;wh1)ifzda,-r4n1bwth 6zs/uucen36t h .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, aby:0r,s rs/jm nd it bounces back to a height of 1.5 m. jmsr0y:s, r/b
(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 h1n:y9dkoivth,y3cs1/la d - with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for ts 3k1 hant y: o9icld-v1hdy/,he next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point s0r;p7cq9ge8rby:8qs zcjr : 1 with a speed of If the average force of friction is ec s8rqr:8j be9 7g0psrz;:yqcqual to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a k /y2q:8lwyr4zuz 2 nxsteady 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 horizonmfo /jmt: j9g2tal 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 stoppim2 9jgf/m:jto ng 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 vertwk;ltl19 .j;h i b 69i7trkjwy 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 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch oni;i9wth1brj k ljt7kwl 9t. 6; its first swing?    m

  Early test flights for the -/lw +mb9+m jrx: eaqmspace shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h f/mm e+ jm9rqxl+aw-b :rom a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story wifhb1ej gzj*4( ndow 16.0 m abovzgj* 1e4h(fjbe?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the ae kzrsy.wey2 6mg f *182tb 13lij:gdlverage force exerted on the car due to friction and airewsgk32f 8rmj1d1e gzyb 26: i yl*l.t resistance?    N

  A 1400-kg sports car accelerates from rest qsc 45bme3l8(f in7 3src(wfq to 95km/h in 7.4 s. What is the average5c w4e7ssqmr (bi( 3 nlff3qc8 power delivered by the engine?$\approx$    hp

  (a) Show that one British hora(w2 m+jq5fa4 haiqm 0sepower$ \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)t os3i4f. 6zt. bzjht 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 slow:z3j6.h wyo efs down from to 65km/h in about 6.0 s on the level when it is in neutral. Approwf:o zhe63 y.jximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor dt1;otna*lhjh2; 7ai +p7 x jkzo in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this fay2s my7(8h tmotion takes 1.5 s, what average power was devel7y2y8s (ftahm oped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.63 ,r:cgfreezp d .0ve;z/azu10 m. What output rating (watts)zz1urezr a : fv/;cg .30,edpe should the pump motor have?    W

  During a workout, the football players at State U. ov k)us4mtyw6kf+bgp;mfq . t- ,;at4ran up the stadium stairs in 66 s. The staa4 fgkk; )uybt.mt6mq+-f 4; tpw,vosirs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclistf2d iajz +hm p4v40r4j;0pntcu 5 snu z6.lr,o 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 maximum power output of 120 hp. How steepa3. ndt4;saxg a hill can it climb at a constant sp s ad;gt3a.nx4eed 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 3htwj v)p,b9. uq;sr*kz6b4 ab10-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction aqh r).4pju wst b*b zv,96k;bis 0.45?    hp

  A bicyclist coasts down vd:8dgn3:0b ecdt 3v8s t)vgp a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumc7z/vn1gyxr+k, gy d6 pers” that are designed to compress and rebound elastically without any physical damage vny 71+gk,zdgxy 6cr /at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the 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 thx2/mu3l7vzu 9h5vq yi8vt* ewe 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 of 21 cm, and an average shelf holds 25 bo x*3te8vl u v hv75z/iqw9u2myoks, 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 jumpznw 6hcmpy+ se .5n bwe75,wh, (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch po, 5e wb5+,hns 67 hypmc.nezwwint to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopemfnpewoq8/3.h ,be is( 7* aeyd track shown in Fig. 6–39 is to remain on the track mb7 ospeyah.e n*q(/,i3 ef 8wat 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 kc9r*)c+ipu2ql dx ,dfrom 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 terru c9*+qdil,k) pd2c xminal 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 hor/hon 4yije2(,ufc olg+,9drxizontal cord of length L whose other end is fixed (Fig. 6–43). y/oj2,l ixfu cg+eon9(h 4,dr
(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 mo5lnb2qkvjwik/mp3*v o 64 l 9ountain. The climb is made in 5.0 h starting at an elevation 9q oik /vmv5jl lk6*4b p3w2noof 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 920u*cg7fnax p 6;-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 claims that its lifts can move 47,000 peopljh1bz/r01age k7x9, t bz2udp wyw-*le per hour. If the average lift carries peoplezxb7zg -l12 takdhj/w0w,ur9 1 *bype about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam aq3j+1o * s-q. :eip 0m-f.bxnuu+x6xqew u dmvt the rate of 650kg/s and falls vertically 81 m before striking the turbine bla nu1wq :f-v-mub.o q+suem0x*3dpqe6 +x.ix jdes. 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 coastqtsr pj14+p zop l49r4er 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 qprt1449l+4prs jpoztimes 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 cob7-mc84.bf h qd 9sqyma-wx4culd convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he wer7b- .4mb qfx-84cqw9 hma dycse 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 anglv)cj1(gf x 9mgf/zde.e 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 compressesmk*e ;p0 zj2hc,nern 7 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the ;,nzrej k* 0 mehnc7p2scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig.8rb6gd*r s-x/y.4am77c k a :vqmwhrw 6–45). He releases the ro-7rdr abh v 7:a/.6gm8mkr4 xscw q*wype when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0vs cdpyc4:.l;ndx5; c s. What minimum p.5 ; ;cxly:vd4ns cdcpower output was used to accomplish this feat?    W

  Some electric-power companies use h1q9hn5*a8dhl ef 2phwater to store energy. Water is pumped by reversibl9h hfdpqn2h85 hl 1a*ee turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spring .h tc6 .zakxq3stiffness constant for each ofaz.k 3 qhc.t6x the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rou 9gt1-cqdrrpy-8 w,dndi ;*ndgh 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 frj1 j0wzri/m z h5ihh.(om 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 jjz 1m/ihw5rhz(.i0hfrictional losses.    s

  In a common test for cardiac function (the “stress test”u (huu jjg20dn-/l* z*tco;ta), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the/j2hc-tn*jlt(* ;uauodg u z0 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, mpi *la.*jzs; what was its velocity whepj mz**s. i;lan it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (zmve yv+gg;dzwdxlv(i :;hbqw91/3(a) If this water wheel is set up to provide electricity /yl+iv ghz d19q3w((zxew ;;vg :mvbd output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s