In what ways is the mf,fvxjk) 0a0krl0s 3.f.l)icgpl /zword “work” as used in everyday language the same as that defined in physics? In what ways is it different? Give examples of)fcrljilfv.k,)0.kf0 s ml /a g3xp z0 both.

Can a centripetal force ever do work on an object? Expla n-h+2,ijqh pwci7v )e7ow/2af*xgqein.

Can the normal force on an qj+ r7)af w/tvobject ever do work? Explain.

A woman swimming upstaegu75 tnvv xne93cd kx-69y 1ream is not moving with respect to the shore. Is she doing any work?n3ke adxc9xvg yen 9u1 67t-5v If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic f4k ohatq d8*,evpa x9q:ow-x6y (x(szriction forces always negative? [Hint: Consider whatvy:oheao4q ( p8dqx xa-9w * k,tzs6(x happens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you areba8c +av)rw3c*bwq :..orv hr doing no work?)8.r ac ba:h+bvrcow*q.v3 wr

You have two springs that are identical except that spring l is stiffer thsc98 woaorv y1u7b)vt ;uio; ;-ga(x xan spring 29xty7r)uoiu ;sa w1vgbc-a8; xvo(o; $(k_1>k_2).$ 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 const4(jft,gjt.1artiz zp 363l h cant horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and byfc,rz p4j3zaltj.g(th ti36 1 the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential enereq 3azlyxbzg5z a7ni4,q( 2 2lgy change when you jump as high a7lnzgqa ,5a3z q elz24ibx 2(ys you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildin6i ffnpi10za 6m2n aj4g, all with the same speed but with different launch an6i02 mp njaz4nff6ai1gles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lr1zsmqwp.vm :e ktl.gz.e 93/owest 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 seconsv mlem/3.rpk z9. tz.:wq eg1d launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tab dy*k 4)si(j l2(ukftwle. If you compress the spring by pressing down with yoikj4ku(wf) 2ysdl( t *ur 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 g 384z(dhb8ton26ghokdjec 9instructor pulls the balkt3 9b(2 ghcd8zg4n eohjo68d l 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 top of a**m58 e.avgv cwqbk e2+y(viy waterfall falls to the poo2+m(ia **egv bqk vcw .5yy8vel below?

Describe the energy transformations when a child hops ar4a*+6u)hae j mgo h3iqound on a pogo stick.

Describe the energy transformations that take place when a s9widwdf1/*t f kier starts skiing down a hi dwtf1fi /dw9*ll, but after a time is brought to rest by striking a snowdrift.

A child on a sled (totaabk t);;xx)(3ea zbzu l mass 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 frxz(uxbz)3;kt a ;b )aeiction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step-ua b0g2e2 i1gxqlk7pfc3 utrx i 9.hjj 2*t2g over a fallen log in their path rather than stepping on top and jumping down on the other side. 02 tfi *g2i2 x91tjeg7.g ju2 bq-uph3a xlkcrExplain.

Two identical arrows, one with twice t p55il-ao*szp1,q bno scfg6 2he speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrowsp6,o5 51z 2 lgb*fqsna-scpoi, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingj,v.c:pxwv aw8) ba2ning pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. E w a2,wc.xn:p)8av bvjxplain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it k3l m(pib 041h2udry j- 4z6e 4h.bxsa ze4rokrebound to a height greater than its original auhy p(bd4 k1sh erokex0.6mz2j3irbz44 l -4 height? Explain.

Suppose you lift a suitcase frt76lzi l-1o (+jqgz 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 complicatf 7 zlogi16rj(+tzlq-ed 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 rathebeppqy9sny:t19 d l;0 r than the work.

Why is it easier to ch, u:d9a- dwv)4dbamnlimb a mountain via a zigzag trail than to climb straight ud)4whmda vad,- n u9:bp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to xl 2htjqvd.7/niw.- fdecrease 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?xn dw27qftjl.h-. iv/ Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver f ucin;opxav10 e v5a *(c+l.zxalls l5 zx1. x(a*;opi +euan 0cvvc2.80 m?    J

  A 65.0-kg firefighter climbs a fligb* tg pv -lfgz/x1ka)wbx (.x+ht of stairs 20.0 m high. How much work is required+ bxkf(v.)*/g 1g xx-tbzplaw?    J

  A 1300-N crate rests on the floor. How much work is re0nxjr 5z9j-excca6 4v quired to move it at constantvn4jcjre-90c6x x az5 speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3 mks. c6, j+(wrrstsvpwyl+h+ 1 across a rough floor without acceleration, if the effective coeffi, s c .yr+hsww1+pl(+tsjvk6r cient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleraups. vik4ag /+ted by a force across a floor at a rate of for 7.0 s. Find the net work da4 sikvg./+puone on the box.   J

  Eight books, each 4.3 cms*arq,2t4xog 4k(xz j thick with mass 1.7 kg, lie flat on a table. How much work is required to stack soj2k * xztq axr,g(44them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obj:6avkepw 8g7 r55v, vyoh4d -7wpsfca ects we might not otherwise be able to liff. Showpgs yha a:7w , d-o56w krvev58pv4c7f 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 odlss*./ tug88luyg2e fz+ nh3e.(qwfrom accelerating by a man os8sqw(l gegh2+ .nydf3 /lu*zu 8et .who is pushing back on it parallel to the incline (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 c+9u4hx judawgu *.)smass M an acceleration of 0.10 g upward*.h uuj w)4gxusad +c9.    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 tm .n :5r+kl 5i0zriujpube.m2he 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 ax ;muaf2 6j pw(s7misp6is, varies as shown in Fig. 6–37. Determine the work done by this force to move the mfsa2sip7u ( pj ;66wmobject (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle act79 mm6y t6k8c1yp nmars 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 ma5 twalu8g- ek;ss 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 hjm: )f-p .6ih)slca kwas its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required/h)bc sy3licdj.tsc 6k4e:r * to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be48rpin74ojr / arivwf 6/i7ti done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 xukn7fqu ;12 wN on the arrow over a distx;n1wkqufu72 ance 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’spj, drbn)te.fl zp05, glove backward 25 cm when the ball is caught. What was the average force exerted by tjtpbe lf.p,,d)0nz r5 he ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum brakiiai/ gt6 2 /y9/zfnnrxng distance be increased, assuming all else is the same? Ignore th/nnty9azr 26f gi//ixe driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mah2 .mx :2xzu1ndx k4ckrk to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction 2zxn:cm.21uhkdxk 4x 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 ti*sc*fo7.midbj tf*( zme it reaches the plate, it may have slowed by 10%. Nefm s*7i jf*o(z.ct *dbglecting 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 so.14qe h .dz9lifb4t 5vol73bcpv cx0omeone who does 80.0 J ofh4.v0 tqoz3459c d elv1bl fp .obix7c work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration *i2- .bcdktfrw)* zbt8 vbzo -wsgy/9 by a single cable. bdw --fk8)b9 vcwo/z2s* zg*.b rtty iDetermine
(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 muchj1fdmxo+y n dd;z3k 1um5)d x( must this spring be stretched to store 25mf x;u1m()xd5dzy knjdo+ 1d3 J of potential energy?    m

  A 7.0-kg monkey swings from o99ux q 5e. gf88rczqerne branch to another 1.2 m higher. What is the change in potential .er9qexg8zr5 8qf u9cenergy?    J

  By how much does the gravitational potential energy of a 64-kg pole kl8p gs*sep ,0)o9eiy vaulter change ilgek 9*spoie8)py,0 s f his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has spvl)by( n )xmf,eed 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 (, vflb)xy)mnthe spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.1o oqg .0;jhl:/fw1riw2tfx 7x0-kg book from the ground so it is 2.20 m above thef2. lt;/ 01fxi jwogwxrqh:o7 ground. What is 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 p m*gou3b3t7q)qdkm .6e vv0oand climbs to the top of a 3300-mgqmmtvk b o.vd0pu eq* )3o637 peak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the sphf +xv1ux;n4.gkq;sa ring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now athx1 f. a;xk s;gv4q+nutached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarans*4zz m70ogvak+*-tw hn x+zan, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a thzw0znaotv4 g -*+x+a *nm7s kall 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 rey -)9zhnz9zyhst, 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 up a frictionless 28x 2cwknyecg 7r+q,t-* /fe1xu.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 tuk/enpw 24al yvc/s3)ransformed 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 m and cross the bar with a/43 yaslv ue )wpkc/2n speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps 3o7ji)w,qxvavoe qyt8ckb ; 31 xaj9(vertically upward from the top of a platform with a speed of 5.0 m/s. (o kavw3qxbt , (8cq ;1)oxj7e93aiyjv$\alpha)$ 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 spkrfv +t l*ol( swd4;,myg2en 3ring stiffness constant is 950N/m is attached to a table and is comprfsrow;( e2ktd,lgvm 34ly+n*essed down 0.150 m. (a) What upward 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 loopeg*oq:g1.i fyx4 h yks4 n sihbsl,y-90d 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), f b9 fqxih 04,1*ygs gyin-so4.hsk:ly rom what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffn/e0d jx5i )3czvaahe2ess constant k), Fig. 6–40. The block isdc h/zix0evja53e) 2a given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bu ag0jzzfg1n2 pb7 k. rm/.hj(nngee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hook2.p1mgg jnn bzj7fakh0z.( /re’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 tot6dn dad)c a/ns1x hd5l7f30u point 1 where it is releau/5dnfl13d)tn7cadh0a s6 x dsed from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown( x-xlysk2- rk with a speed 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 sp8mxidi5 lolm*q24py9ddui)7 ring to be placed 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 qm uly i*985o7dlpd 4 iixd2)mrest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyclwqqbysz 606nf7; swn/e 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/h in opposite dirxpu )d 0.tbi4y4wd z/oections, collide head-on and come to rest. How much thermal energy is produced in this coll4wdib .tp0y o4)zd/x uision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and laqyn6 x,))rmq ( pjb6+ oo-km*w0eltreaches the bottom with a speed y6pq)ert( wl x mo j*mboq06l)ak+n,-of 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides8m7w7e *p 29bikhr.h jt7mxux 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 abo-2uca4kgz x:rve 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 2i zl4fp 9mk7w+-ghklhz )e;u. .0 m, and it bounces back to a height of 1.5 m. 7lg uwiz;+lmp )k.he4zfh -k9
(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 /spcmdu) 4p*6hoc e f)from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next ofcmpdps*)hc /e)46 u 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 passes9aypbx*)tma jy gx -*: point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what sp :y**xpxb-yg 9 mjta)aeed 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 steady upwardq au( hie1b6*q+cvz*a 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring ( a5:ho4.zhu eok=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, wheaoeoh 4hu :z5.n compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horiz.amr ; u rk rzhorh./5gbd7b71i.bw;s ontal 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 7griazu5o1mkb .b.h ; dw/7hb.srrr ;equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle usep 76f/hdd0xbco:mhc2 x 6jul5mh 94cz d a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a sp6jbo p c7l 9c:6md 2/0xx4 fhudm5zchheed 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 sixj -t-.p/cndxw xw0eb8th-story window 16.0 m abovexje.-0d-ncw /p t xwb8?    s

  If a car generates 18 hp when traveling at a st2o:6-ujas-,iq;abicv :j yvfow.j q1 eady 88km/h what must be the average force exerted on the car due to friction aujf byw,a:v .-6 vaioc;:qo2i-jq1j snd air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h i:e j,t p, o9mrf.is4y5ix.to qn 7.4 s. What is the average powe jfi ,,tpe 5q.i oys.otr:xm94r delivered by the engine?$\approx$    hp

  (a) Show that one British horsepow87sc um0fh:tb09ofo oer$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed 2ddp(mj t;7a8pi0r(oau-z mdin 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 in about 6.0vuw:ico1z391 d+rla y.)bol:n wpz49e n;e y u s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling i9blwyanu 9 v;w y1pe+l:14dco.o)3 : zrnuezat a constant 75km/h.    hp

  How much work can a 3.0-hp motor do inurvrg3*n f5pn / xf2s2s :+xf;. vhuxl 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot froik1 s,pashki 0-6mk,mm rest to 14m/s If this motion takes 1.5 s, what avm 1,kkp 6-si s0mh,akierage power was developed?$\approx$    W

  A pump is to lift 18.01jj f-qc mb,b2 kg of water per minute through a height of 3.60 m. What output rating (watts) should thbm-q, jc1jfb2e pump motor have?    W

  During a workout, the footbalftw8 uhw6p .q.l players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inc w..huwpft68qlined 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 6.0 z*k6x(tknonz5wx y 5 *$^{\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 steep a hill can it c . 9u z0*6fdpy jz.msl/qlqme0limb at a constant speed of 75km/h if the frictional forces add up to 65jqslu pd0 .*elf0/mz .9m6yzq0 N?    $^{\circ} $

  What minimum horsepower lkesooy r2(.2 must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is oerylo. s 2k(20.45?    hp

  A bicyclist coasts do l+9mjdj5xe6 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 cygzh-jbq 38 o(ars 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 like an elastic spring up to that point, what must the effective spring stiffness constant of th8(jqzoy3- bgh e 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 f0ctgq 49 qz8rtirst 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 1.584zqt rtcqg90 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympicsn6 e2osgh8quj3r/x5yvwu . k+ shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed di .y xrwsuq385eok njv6g2+/u hd 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 slidinwr s)b7y6n07 sgktga 4g without friction along the looped track shown in Fig. 6–39 is to remain on the w 6s7 0rsb)nta7k g4gytrack 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 from an aircraft without05.pai r sbbk* his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minorpb bakr0s5i*. 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 end is fixed (nsd/(gw k7i.ih 0c0kp pke3 q+Fig. 6–43)70qicgnk3pd w0+hkk. p(s ie /.
(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 mountain. The climb iskzbfe6g7*tl*z 5bv /i made in 5.0 h starting at an elevation of 2300 m. Cal7z /t b6lg5bfe z*ivk*culate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a +khkohxm-*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 r7ig x7sdr3zr o+sf)n0o(q)vCalifornia claims that its lifts can move 47,000 people per hour. If the average g 07ox) + oiqrs)rndfr73s(vz lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of am/b:6odv/tn fjwcjl+u;;q:650kg/s and falls vertically 81 m before striking the turbine /d:f;ln/; mtc6v+jqa:o ubw jblades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (4(hfnsezaew )8xre7+ 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 an7f8r eh)+ w(4xesaen zswer 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 candy bar directly he0 y 9ky,9;sfk tsjx;:wfcr/into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) fkhr ;:yt,f;sjxcw9 9e0sy/ k   m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle ofw6)q( n inhyierfd;yn ,:q 95-ydm *ix 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 compresses 0.60 mmju:; ic9z ax*w3py -nb, and it tells you your weig-i9cy ;jbzu :pax wn3*ht is 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 gp :2a/5t dmnpmrabs a rope, and swings out over a lake (Fig. 6–45). He releas td/m:25mppnaes the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in nj2,berxbsc 29:1.eq h f.q iv9.0 s. What minimum power output was userhj:se2bqqf c1 n9, vb.xei2. d to accomplish this feat?    W

  Some electric-power companies use water to store /papizvx8rjd ; p/f*6 energy. Water is pumped by reversible turbine pumps from a rj/p/z6 vpd a*px8 ;iflow 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 cuthv2n. g.yk5ad z)5v f5 .mf,pzg*omiz in half. What is the spring stiffness constant for each of the two res.)* faz g mvoz5km.nph5z.ifg5y 2dv ,ulting springs?   k

  A 6.0-kg block is pu4 yw:)4j bbwo. ji9kqr5 6bacsshed 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 from 35km/h to 23gjq0h9d xdp 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 fr9h pdj2xgqd03ictional losses.    s

  In a common test forz t u1r wb2+h8.kh(djr cardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmijr wz.hd u (rh1+k2bt8ll 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 d 8l yxv/,vk0 hd0clk2 ;32ab/xck hcrlistance of 500 m, what was its velocity xccrck,l khlv x;0l/yh38 0k/av2bd2when 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 cc 6dc- myatx78,9yll0 kpie;i:rj e*from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximce cmye l,:;6*i yr9-xp dlai 0c8tkj7um power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s