In what ways is the word “wkm d4g x;;fw12bodh7iork” as used in everyday language the same as that defined in physics? In what ways is it different? 1h d;2m 4;iowxfgb7dk Give examples of both.

Can a centripetal force every v6 wug*6dq)wb)1 k9(3vtruvgr ijh2 do work on an object? Explain.

Can the normal force on an object ever do e ka 2xoz,f*0o9-x txhwork? Explain.

A woman swimming upstream is not moving wit*snpr2h sqw4c8;36cwwu7 sht h respect to the shore. Is she doing any work? If she stops swimmi87tc26wn* shw43ru; scqhp wsng and merely floats, is work done on her?

Is the work done by kinetic friction fkp-jd +jdk0b/orces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth +-ddkjkjp b0 /out from under them.]

Why is it tiring to push hard against a solid wall even thougib 60kcl9ura, h you are doing no wor,c6 i9 l0kurbak?

You have two springs that are identical except that spring l is stix.si2i:zv gx+x v0 zg/ffer than spring 2 g. g: xvvii0x+s2z/xz$(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slidet/*;lvd w9 az dtr,t0p on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it ht dp;a*d/wv9,0r zt tlas 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 energy change when ch4;9b: 8 4ieb44xame xf5c aqynpq- xyou :494q8c54cxne fxb-ay 4qp biae;h mxjump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a bui4 op(r0k5zr cf7yehz: lding, all with the same speed but with different launch angles. Which one has thyckro:z h57 p0(z4 refe highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its l hyru5p rlpr5rwqtc .8n8;6bnlbi1)3z- 2 qkfowest 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, alr 3l)q1ur 8nfrpk6 phynwc.-8bbt5 z ;2iq5rnd 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 a::us0gk1 + (lv3cfqfkqd+wjm rests upright on a table. If you compress the spring by pressing down with your hand and then release q1 qfj+ kg0akfu: +vsc(:d3wl 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. i7po5b rd9ev56–33). The 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 v5oebpr7d5 9iball without pushing it. Why?

What happens to the grafpzc; nc0oubn8uwn1b-0u+ssp h - e3.vitational potential energy when water at the top of a waterfall falls to the pool below?nfn b;su0zwh0- ucu8 p31eb-.ns opc+

Describe the energy transformations when a child hops around on a pogo stick.e6/jaam mc6t 3

Describe the energy transformationss13 0 ujyco:vy that take place when a skier starts skiing down a hill, but after a time is brought tou0 13scyo:y vj rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill ofi .y k**63ayj3de dbvs height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and tbiea33j ydd*s.y 6 *vkhere is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over pnrn qf8 j5ljd)e8(o)6qq bh6r0q(upa fallen log in their path rather than stepping on top nqjlq(epo8)6 ) qr uhp05b f8d6nrjq(and jumping down on the other side. Explain.

Two identical arrows,mgcj. :n4x mi- one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exem gj ix.nc:4-mrts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of en0k frq)2cw f+p h 7-i)xvy +dlz4ttfe+ergy, (a) ignoring friction, and (b) taking zc740w ++)fhvxiteffyrkqpt)2l d+- friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to xn8i3qf xfj . 2-9;yioa2t; n z.zsihia height greater than its original height? Explai2isxia;i.hy8.tf ; f zo-ixz239nqjn n.

Suppose you lift a suitcase from the floor to a table. The work you3i*qzz-ixqwbu/- owo/trsv .*;.1q arf km 3v do on the suitcase depends on which of the followingo/1v zxm z.3-.f bsw3rqiu ktqi;/ q*-wr*oav: (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 than hbt0qbvvc9h zr69 4 c+the work.

Why is it easier to climb a mountain via a zigzag trail th( 1luodnyn./ .l95 9teunxz 2prmx*kt an to climb straight up*1ondp9(/x .u nz2mklxtn5 l.t ye u9r?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes 98.zlm3ldpft us r-y ,to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how yul9,t3f zmp-rld8 s.much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265v :/ik n/p:abx2l yfgx:9-tus9wt jh3-kg pile driver falls 2.80 mb:ntfx2u9hw:gx/lpy3j9 tav: i-/s k?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muchep2rwt9i- h)j work is required?)pw h9i2 -tjer    J

  A 1300-N crate rests on the floor. How much work is required to move it asa;h5ydpw6- 1mm.o*++xp plu iic pw/t constant speed (p-pyw.a1h;xm6 si p+c wi/l dp+m*o u5a) 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 g/ o-it8na1n4s -hcne10.3 m across a rough floor without acceleration, if the effective coefficient of frictich8eo a14g/nitn -s n-on was 0.50?    J

  A box of mass 5.0 kg is accelerated+iz .i+7bh .(n5hatjb4up t:ksnfmv 8 by a force across a floor at a rate of for 7.0 s. Find the net work done (58n:skthp 4m7vb. ajhib.+ +zfniut on the box.   J

  Eight books, each 4.3 cm t1/ hwxl slmfmtxf- mqa+ ngdxo1+(/12hick with mass 1.7 kg, lie flat on a table. How much work is required to stm hm/1gwmf(x qt /d1asl1fo+ x2n+xl-ack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be usenw07pj w .0oywd to liff objects we might not otherwise be able to liff. Show that the ratio of outpuwywo07 w0p. jnt 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 fr1 islo12x4 q-aehpi5rom accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Cai o5- q1sxeai4lh1rp2lculate:
(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 r1chc 6ezf /4y 0(mzmean acceleration of 0.10 g yh16(e 0merzmzc/fc4 upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear and thsyaw.ta*jz*x, 7nv6i c 2ykh:. qx2ep at $d_{\mathrm{A}}=10.0$ 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 Fig. 6–3/ti/r 4xfwjm.7p czo*7. Determine the work done by this force to move the object (a) from x=0 frmzo4pxtc/i*.j /w 7m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts iso5may uarks1q3 u5++n 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 oxbuxuh ,y)1kl2ygen 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 i*ca;)yzy, fg gl8d4g ots speed 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 e( o) szmjk8 xng*q00xmlectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar +ib.y ov/i 2bs;b ots0c: aq1itraveling 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 3ny7+3z/6ynpp pxknau* xy7 fforce of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrowxzny p3y7 *uxpnyp3 76f+a /nk as it leaves the bow?    m/s

  A baseball (m=140kg) trav46dpwzv; d;vyx,uqa -eling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average forvp4zd,; v wx d;y6qau-ce exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum brggk46p( pn 1eyg*6aqrp.an. zaking distance be increased,n*pprga g4 pgkz.y6. n6q1a(e assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid fe vqck.ov 5; wn3 ftql0,7wt p3p7zy7mark 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 spew v.w357vo7ypnlq f 3zck;tepqf , 7t0ed 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 0.2l /u6v0tx:)mnf0kg9bx a s/r a5 kg 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, i09 ) al /bvxxkmg6fa ntr/:u0sf the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straig1l; r:mym9c(k,)q-ofkpcg l t ht up by someone who does 80.0 J of work on it? Neglect air resistancc;( lmmygk:k t1f-pq,cor)9 le.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sin(9d bya4tm9r lgle cable. Determineb lm(r9ay9td4
(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 muchs/ otly5yg( d4 must this spring be stretched to store 25 /yty osld4 (5gJ of potential energy?    m

  A 7.0-kg monkey swings from one branch to nvozf .spdih+1*d0 qlf838 gv4 cgnx.another 1.2 m higher. What is the change in potential ene0dh+fvq nn 1cgxi*l dso3vf.8z. 48gp rgy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chf:-/nw pwo vu8a )zx*uucjw46ange if his center of mass rises about 4.0 m during the jump )axuj pu: 6 wc8*z-ww4vonuf/?    J

  A 1200-kg car rolling on a horizontal surface has q) p dn qxsb ljp87buft*06a;0speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to fjpqnp0l bba*ts6qd0 8);x7u rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall personsx;b;nr)v b co)4 asv+ lifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative )c v4 xa);+orvnbs b;sto
(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 a.-yo3qor az.ieiw 2w-t an elevation of 1600 m and climbs to the top of a 3300-m 2e ri-o.y- zi.awq wo3peak.
(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 c7u,kkie(lq 3to 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 q(k,c 3kule i7attached 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 (l p mq(wh+la6yct0+2)d h4 zpnehnp6top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upm+ ) lc24pnzh 0hydw6+ahnel (qt6(ppward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slidest,ag ;2fzsyofe(/ a )z 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 28n1ul)(+ yrld pgc:ft 6.0$^{\circ}$ 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 e2 gw+ij3 qlgpw6b7f 3pnergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the grf6lqwpwg g7i 3b+32jpound 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 verticalug f(ghl.i6 +zly upward from the top of a platform with a shl( uz.ig6 +fgpeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness cjp+kdf5 ib8+ bou+q8l(khtn,onstant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwarf(b++ j8+o,i 5ntdplhk u8kbqd 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 alofbimgkb.7rg3nmzj h 84. id:5ng the looped track shown in Fig. 6:fk .b8hrn 3igj5g 7 bd.m4zmi–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 h must it be released?    r

A block of mass m is attached to the end of a spring (spr cerz5u 6,qlxmf uk 184jlzsjjt1 w.2;ing stiffness constant k), Fig.. r8 2em,s c6 fzxut5jjwl 1zqkj1u;4l 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied ut;un1m e oy4;e bb:q(to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness con;;m obbe et (:yn41uqustant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 whe(wwdw-k*x7i+.( 1lz 8yxb rwgpcf 1 nhre it is released from rest. Assuming no friction(wbdn w 1wywh.rg x-8f7*ipx +(1lzkc, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an anq8j xe 3x6m(eyxu-l 7ngle 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 el;fdh4bg. i 8o ;gjvv *ygx(ce*t j-/a spring 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 vf(vbgj* gjecxh*-./;i ogy8dl;et 4spring 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 cycledwf;+-gxt-ucrb+/bs le nd - 3 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 travelin o+*r l/(mtqaqg 95km/h in opposite directions, collide head-on and come to rest. Horq (la*qmot+/ w 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 ba f5w5wjai o:k;i6 )ahottom with a speed of 2.2m/s How much 5w;i hji kfoa6w:a a)5thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 6je1hm;pf,m+ 3 k,zqp8kujq k 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 om3p n+s+z6e u13.0 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 a height -gpsipr2 a )k1g9 e2iqof 1.5 m. 922 r1gap gi-peisq k)
(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,e2i .uj9:l(gjjd+)ih : zsj qq 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 15 m the coefficient of friction is 0.30. What is the final : g)liqje+h:jjsuj .dz( 2 9qispeed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 wv)1hy4cety dpq( b z yt1475suith 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 traveled u5pz y714y4cte q 1)hsdybt (vis 45.0 m. $\approx$    m/s

  A skier traveling 12m/s r2xbuis )g 0(ic0bjzd;eaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is fj 2a),dcv -k3/lfxmwt irmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It it-v)jc23k d xa l/,mfws 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 coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very lige4rw,3/2zgwvig 0 s gxht horizontal spring, Fig. 6–4zx2gw3re/, 4iv0gswg0. 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 on its first swing?    m

  Early test flights for the space shuttle used a “glidxoc3tz7t ;jfy+f)hs.q+ oei.; i4r wner” (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 itswxzs3it .7f;+4he ;.qrnjtfy oi + c)o 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 toymgy(d 2h,u;wi:d -ml lift a 315-kg piano to a sixth-story window ;ud-m iwy(y: dh,m2lg16.0 m above?    s

  If a car generates 18 hp when traveling atec,b6,xx wcr3 a steady 88km/h what must be the average force exerted on the car dbexc ,,x36wc rue to friction and air resistance?    N

  A 1400-kg sports car accelerates fb1 5a9eojhrska;a iayt/n)/ :rom rest to 95km/h in 7.4 s. What is the average power delivered by the engine1a/h a o5sna/aejktriy:;)b9?$\approx$    hp

  (a) Show that one Britiek/ qcq nh;zh75tgz.4sh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-houra 6x lbybzv*:a* z4s64vqt5phos c k-/s.”
(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 abo- zx;ptp ldws0; j8ol2ut 6.0 s on the level when it is in 8;sp tdj -2p;l0xowlzneutral. Approximately 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 mukwp.8 20 c5-vcwivy motor do 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 motion tu es,dms gs+hoe;7j:; akes 1.5 s, what average power was develo e;u;seh7 mg:s d,j+soped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height ofi e 5qrqo4x(/w 3.60 m. What output rating (watts)/q oer(4x5iwq should the pump motor have?    W

  During a workout, the football players at State U. y7 21mkic fe7mran up the stadium stairs in 66 s. The stairs k7cfmiy 2em7 1are 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 clr ) ek )sdbi)jc0w7 )qj-wsx;bimb 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 .k l2 oe3racwy;pj 2/rpower output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to2oj/ rlkaw e.2;ycr3p 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to ;gpdbt0jhq:p s. z2q: drag a 310-kg box along a level floor at a speed of 1.2m/s itzgp hq2d:0p;: js.bqf the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a +ztsiz z c x uaor6-n,f0hr4(;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 h s bq8buxw7 a f0(5a9:*nhfhvmave 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 the bumper be, assuming the car has a mass of 1300 kg and(sa :f0 bb7maw5hhv 8*x fqnu9 is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf cgix db/mjfc tf-d9b ,+ij:v0o.8,o ais 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 books, how m-j./ i0o,ftd x8i ca9ojvmc+fdb :g,buch 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 ju-(w*gy(n t ddump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if h-d(nwygt du(* e was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along t2ckndzi; g9,eb ;dft7he looped track shown in Fig. 6–39 is to remain on the track at all times, even at 9ekd,if; 72gt ;dcbznthe 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 ao,*ov9vq:. 7 p eho .g6kyjalxircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocokx*v9eoy:.6jho g q7 .ap,vlity 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 eeb-gxl q3 s)/sw3*ufwnd is fixed (Fig.wugl ) es-s wxqbf*/33 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 mountain. The c/n7p31za0pgsq fjsqxs 6d a/dw8. nh be/h31e limb is made in 5.0 h starting at an elevation of 2300 m. Calculate 1nhsswn jxp1pqad /. e/06bzg/a7edh3 8s3qf
(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 wheukwavhrcw- qrk1)370n a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its liftpu*ne y.k ,ec3s can move 47,000 people per hour. If the average lift carries ck *p3een.,yupeople about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the ratzy3 fwimbv : hbi+jlu x6+6b3+e of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculate6 +jmbfiil:w6uy3+h3bx z+b v
(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 c-dkgw8fs 8,c3guk,(l :maklxircular vertical loop (Fig. 6–44), the difference in your apparent wei- km8alg8d wk lku:3xcsf( ,g,ght at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bah691w c+qc(sln 5flfnr directly into work, how high could an 82-kg man climb afq+chc5wnls6 lf (n91 ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45.3r7a+ osb*x6akfm0 nqzd(x i: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 comufush 3vlk z7l i1u2(1presses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on ti1u 2lzu1ks7 uh3v(l fhe 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. 6–4; mwn s0uvfh :xev++w29mfxh /5)h ;fwv xwv0u+hm2x /: sn+fm9e. He releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5 kl iiifdz;b477dp. ob;p on//.0 m in 9.0 s. What minimum power output was uskdib./p477iblon/zp; oi d;f ed to accomplish this feat?    W

  Some electric-power companies use water to stgguek eaumi( 4()b8ty;0dff9ore energy. Water is pumped by reversible turbine pumps from a low to a high reservoir.b9fui m08fk ;yeeg)at (udg 4( 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 dfw8 rcduta.+n4 (2 adspring stiffness constant for each of the two resulting springs?aw.ud4+ a8rddt(f c n2   k

  A 6.0-kg block is pushed 8.0 m up a namg-s 3zinbj5lak;kp6gpf. h5m*)) 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 a 7nlz x;,l le0etamk1/fkzl:5ccelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75knk x m0tal1f:le zk5l;zl,7e/ m/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”)* o-y3nacsbm.hv2h2z , the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is slop.ya o nh-cshv3b22zm* ing 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 vertgfqpr 2l tj/;9q3ma*d+bl7 fd ically upward a distance of 500 m, what was its velocity when it left tfjt3g/faq* pbr+7d;ll qd29mhe 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 whee;d3w 7xuwcp 5rl 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 maximudu53rwpc7 ; xwm power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s