In what ways is the woh e5nm: -qxsh +z7c8bc-5zeo srd “work” as used in everyday language the same as that defined in physics? In what ways is itbesnqecs m 7:o-hx5 h8+c z5z- different? Give examples of both.

Can a centripetal force ever do work on an mwbv,1x f/ uzr qtsj ifqf-: (fn1-9p*object? Explain.

Can the normal force on an object ever do w c(ov .rn6hyy4d.l)pl ork? Explain.

A woman swimming upstream is not moving with respect to the shore. I1 q ruap-le.wr l ed83hi* h9n)w:s:krs she doing any work? If she1*elwr-:dqu: lr krs)ha p w 93hn.8ei stops swimming and merely floats, is work done on her?

Is the work done by kinetic fricxaiv.i9 huy ww9i.- 0qtion forces always negative? [Hint: Consider what happens to the dishes when you pq y ..uh9 0i9i-aivwxwull a tablecloth out from under them.]

Why is it tiring to push har1s at:fzkw;*k d against a solid wall even though you are doing no workktf: zs1*aw ;k?

You have two springs that are identical except that spring l is stiffer t e+dy s1,pv( ha,r0lwihan spri rs0lhdw,yv,a1pe (+i ng 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*lljrsfm6r 9) on a block that is free to slide on a frictio sm6r) fll*j9rnless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy chas- f6:w)/ epl.gc rpihnge when you jump as high as you c p/fhs) r.gpwe6c-il:an?

In Fig. 6–31, water balloons are tossed from tq*:p xfbn zk 1).ds*zjhe roof of a building, all with the same speed but with different launch angles. Which one b *1dq*.:jfks)xn pzz has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point in6ts. rmv3bqr5 two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the s5q.mbv 3r6t requilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spri+;6q+o(x ifc kc qzma/ z-l-rdng by pressing down with your hand and then release it, can thekql-irfzq/ cza m+ + oc;6xd-( 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 instru2b4ghfr./7 -t5axt i(ofvci vq :rnz4ctor pulls the ball back and stands against the wall with (t4ohcg/b nt qif . f4rx avrvz-7i52: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 o/4ilox(qib t si6*1wqws16ua f a waterfall falls to the416bioxwws s*iuaq/ql 61(t i pool below?

Describe the energy transformations when c ,f jdze(c 5h/t2mlg8a child hops around on a pogo stick.

Describe the energy transformations that take plact,1zixow-ix d 6 n6nlei:u a 00lm8yl(bx1 3ese when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowt6d ,:-enul1six llx0ym(6aen18x w3ozii 0bdrift.

A child on a sled (total mass m) starts from rest at the top of a hill0cocj,6s4ip n of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is p4 6ccsni0o, jicy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rav:484+ arxnobmidv m:ther than stepping on top and jumping down on the other side.oivm: b8dva4 rm4xn:+ Explain.

Two identical arrows, one with twice the speed of the other, 3xe zhu8wmzh7sf33 c 7are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther thh3z83cwuz x37 hs7 feman the slower arrow? Explain.

Analyze the motion of a simp 2(hfj de5 8*n j8ssr.ljg9gpxle swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain wjflhn8j 82ejrd s*.sx5p 9g g(hy a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than2ylzvwuhit( lpjv+.l9 3s)vhe 8 s59s its original height?l3vzvs9 vtsp9+.hjiulys)w ( 82hle5 Explain.

Suppose you lift a s-ch44w)aw 3vkt.bu *k8o2r bjq-wvdg uitcase from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, d4whj2)v.gbw84k * woq-rku3v-tc baand (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than thef c*2bkp)k4 9sjj2j iw work.

Why is it easier to climb a mountain via a 2yjjyd1y.e5 n zigzag trail than to climb straight up?5yy12 djj. yen

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to decr/ s7b, yc-hurluya zn68gb2k)ease 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? Accycb, k87yaz gu2s6h/u l )rbn-ount for this, using energy concepts.

  How much work is done by the gravitational force when a 265-k+0b9 amj0f)7ebimtp;2n/tp:i az ws eg pile driver falls 2.80 ma/ bz )a+; 9ie00ps7:mniwb etj2tf pm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. vv-pse 4ix3d6 kb l-w;How much work is requirep-ds 4v6;wix3bvlke - d?    J

  A 1300-N crate rests on the flho 4p1er+.o3.zv cwfy oor. How much work is required to move it at constant speed (a) 4.0 m w+oo 1fz p.hcrv4y3 .ealong 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 108u s hjm*9hx wn:6lrux-9 ux3e.3 m across a rough fx8 exjsrlu9mw 9nu6 x h*:3-uhloor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratec y;x29npx3uxpmp j001p,s pud by a force across a floor at a rate of for 7.0 s. Fi3,s0;j9nuxp cp0px 1mp2pyxu nd the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie u)8nac2k k,+vvxlm 1 +lz b/yeflat on a table. How much work is required to stack them one +yu8v x e,nkkm vl2+al)/bc1zon top of another?    J

A lever such as that shown in Fig. 6-35 dv7hmz3avlfc e/5* mfk4ry: + can be used to liff objects we might not otherwise be able to liff. Show that the ratio of 7 +vfrc:z*5/vfdkmla 4he 3myoutput 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 8mv i* a)u6nrjfrom accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effe6u njav8)im r*ctive 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 acceleration of.tag.3*8b p9 ktja d sad) /a e9pmtc+xn2t,ur 0.10 g uu. 9t)* n.p8dmap /d xtsk92t cajbg3,+etara pward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is1s *a ;8q4vtfn1qsanv linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in 1one ,ip f0qrlf it25*and1 n4:wze0k.tvsa ;Fig. 6–37. Determine the work evt;0di0t51*fl4fia:snr kq z2, peoa1wnn.done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle ag k +qz*f fbrmb4l2;a1k4(hhdcts 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 mass :mip;2 y6e enryrzsm t,r)t68of $5.31\times10^{-26}$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 s6t s((:t qktwmpeed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required toie1gduv9 0on 4 )c6fge 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 be done to stop a 1250-kgcar traveling at 10s 4ulgqa+6x- d3yh o1v5km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts awpv9-e ylv z0*n average force of 110 N on the arrow over a distance of 78 cm. What is the spe y*v-0ez9lpw ved of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’1e.54m 3)upx ioac uygs glove backward 25 cm when the ball is caught. What was the average force exertia1y ugupm5.c )x4e 3oed by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum braki*ie/s 6e 2gppxng distance be increased, assuming all els x pege*/i2p6se is the same? Ignore the driver’s reaction time.

  At an accident scene on a level d;le.-qx(wz6u5ubojte(n w0 road, investigators measure a car’s skid mark to bee5z(-q6utl ; 0one (dwwbxju. 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 car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched*f wm p611ixik 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 distance between the pl6 pkwf1i1 i*xmate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock:ux2 ma*. pygaw; .ym s91(smqiiof5 b go if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistany( :x mm9wy.gais2*f5 ;1bi opu.mqsa ce.    m

  A 285-kg load is lifted 22.0 m vertically with an lizsy) 7s z/ z0ui1.sqacceleration by a single cab.1zs0)z/ lzysi sui q7le. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this z9)v1qlr xz k:y*xv5kspring be stretched to store 25 J of potential enerkqx y z*9vvl1z5rxk:)gy?    m

  A 7.0-kg monkey swings from one branch to another 1.cfl1 aalz )94 an)wl93z,.xyal/ibbcne :v6t2 m higher. What is the change in potential energy? nyac6)an l/f4i xa3zlz : allwvecb19, tb.9)   J

  By how much does the gravitational potential energy of a 64-kg polp .*l;olljpx 9e vaulter change if his center of mass rises abollj o*pp.l 9;xut 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has sp atn-p1 -;6b1uyzz ma5haued,uln4, c eed v = 65 km/h when it strikes a horizontal coiled spring and is brought topt 64u ;yn aa,,1cu-nzhzu 5md labe1- 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 is 2.20 m abou.ykt4r ; yw)kve the ground. What is the potential energy of the bookt.)kyk4y u w;r 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 atv8x(1o alje h1 k ac1sdh7b(qyac.0oy+)1h ck an elevation of 1600 m and climbs to the top of a 3300-m peak.k1c1)(y0yk+.a87 o xd chheqsv b la11hjcao(
(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.10zme mwvh z2gae:xd:2qf0 l next to a ruler. The end of the spring is next to the 15-cm mark on the rul0mgma02:1qfle2dz.he z w:xv er. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s)zd:qvb(a(h ;j k9 j j-0flmhrst;o;os1ug72b and grabs a vine hanging vertically from a tall tree in thv gf0 ;js;-a(b1hu:92 ;(mtjd kjooqzlr 7bshe jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a 2)i dgp:b4b+bihwdg -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 give5+.co3 hrfcx pn a shove 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 ki:9k ia; aqu7dknetic energy is transformed into gravitational potential energy without the aid of a pole. With whatku9; kad7iaq: minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform wit;w*-uw vddv g6h a sp6w*gvd du;-wveed 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 constant is*bkf857yzkvc zo 5 el; 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can 58 ecy5;7zokbvl*z fk 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 looped.*rp-bh b/gl u 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 mir/u-b*hg.p b lnimum height h must it be released?    r

A block of mass m is 53/:o: p*mjd4pqip9qpzj s ur( -wohk attached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an in-wupr 3 q:d9mk(j op 4pp z/jh*s5:oiqitial 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 buqfrz ojid7:xr3 (cm j)k e+e3pz6,(yjngee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k rep d+,7e3) jrkf(cj63y: i zxj mzoq(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 7/l+pakbv 4 4; qtevmyup to point 1 where it is released from rest. Assuming no fry7;pak +t lvbm/e4v4 qiction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ofv: ev.2dilo1q u f*s6df* ,gpq 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 at the bottom of an el9. -lllbay 2caen2z/ hs a;o 1pgk4ls5evator 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 g4y1/c -l.9hpnkz5 l2osaae; 2lslb aof the elevator and passengers.

  A cyclist intends to cycle up a 7b1ot5ny,6ssgz tf+ w..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, eacy;e nxd e/z44h4*hfs(bf+mb ah of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this /dze44(xa+fsh f 4ebb ;hyn*m collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a spee13 hgctxiyqj( g )wv10d of 2cihg y11jv 3 gxw(0tq).2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22,)g++(kmzw n7 gxkawn $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the groq3hntuce. ;x1l 2 q)hlund.
(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 ofb,1cu0 7tp wjk 1.5 mpt71 u,b0kcj w.
(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 h ryudc,rj+yl: ) m7qe:a zi6()no*enfloor with a constant horizontal force oz+i)a7l)n:e, hyqyej *(d rmcro un6:f 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 speed of the crate?    m/s

  Suppose the roller coaster in Figtko0j apmk);6. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reac t0opjmk;ka)6 h point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady up0j53vxdl-rs fward 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 r 94 nfn nry,-udmyld/:l1b/5a1iq qh to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm 1fddr:l l5qh91yqi naby4,u m-r/nn/ 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 horizontal spring, F v1(eq)n rp ki7o0z+ptn-g *beig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N cvp+bg*n)r0 eotp (qe 1ink-7 zompresses 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 shuttufq rsmq)qll ;u-9t71 le used a “glider” (mass of 980 kg including pilot) that was laun1rumf7llqs- t ) u;9qqched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the 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 m 7hzm yjp6sesnc:j28o8zm 3 ux *g4h3fotor to lift a 315-kg piano to a sixth-story window47y36 : ssuhhz8 *xznfp23 joegc8jmm 16.0 m above?    s

  If a car generates 18 hp when 5oq0( wvu8.hxul5b3mnp 7 thhtraveling at a steady 88km/h what must be the average force exerted on the car due to friction and mu (5vq. wh 0olux85hb7pt3nh air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is l9b74*e+rfrmj j ti: qthe average powebre4f j 97*tj+ mlirq:r delivered by the engine?$\approx$    hp

  (a) Show that one British horj0 fcgia634ffsepower$ \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 “kilrt) 0gospmo hj+,o)m /owatt-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 .)fqk +pz1 hy xevz8y:pg0i 7hin about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed eh y ixh vq7)08:.zppfykz 1g+to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor dv vy;qgg:0;k eo 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 take)b4))khsrlr 2 ;juxu b s6dz0ys 1.5 s, what aver kr4dsh6bly)su0ux;z2 rj))bage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute0,y ai*9 jp 2tm*l,jn/ijht ux through a height of 3.60 m. What output rating (watts) should the pump mot u/jxy*himtajl,p 9*j,0tin 2or have?    W

  During a workout, the football pvjiiwx hd8h 01csk06oye,)j1layers at State U. ran up the stadium stairs in 660 i68djxo1kws hj)vi hec01y, s. The stairs 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 cyclist climb+o lza +/pa*jx 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 powenlr0hwoo5(a e9a -;scr output of 120 hp. How steep a hill can it climb at a constant as5ao9-ln;ewh ocr(0 speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepoe /uzfdbi 6,x;wer 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 0.45 6,fxei; dub/z?    hp

  A bicyclist coasts dowglr;6a( .m f) txhh1cdn 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) bumpers” that are desig2 ov+mdsn ,dct:4vg5tned to compress and rebound elastically without any physical damt45onmtd s,gvv:d 2 +cage 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 the first shelf is 10.0 cm off the ground, and the yovevt70bub ;z5 p i*k-lq7(aremaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on theblz5ktub ye-p7i*q7(;v av 0o floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics shopf.xl(:z7i t j 1 nw7;fev wg2wn(xpg5ws 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 7z5x w gp(2(e 7tnxnf l1wgw;fi p.:vjlaunch 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 looped track showkc0 f/inf ocyo+soun . 6x4.s4n in Fig. 6–39 is to remaink0ui cso+nc / yo.4nfs4fo6x. on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an z9u mvx *bkmwq, vm.*+aircraft without his parachute opening. He landex9* k*mmvqbv .z+mu w,d in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/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 o:jt8 v;.pl pwL whose other end is fixed (Fig 8;oj pv.plt:w. 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 tojs.n * k.) md xfw.e:kmi mu:2cy6:eut the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Cdu:t6cm 2i*meekunk:xf.j:s) .m y . walculate
(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 abyf smh;7jb (1up,; bpsove 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 claimxy fsy; 6 1jvu7npwx,a.y (j:is that its lifts can move 47,000 people per hour. If the average lift carries people aboutxufy7s,yv6j(; .1wj n xp ayi: 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 ms +60:lk7 ok6gx:mzdoe qeow7 before striking the tue07go:z6qwks +o:xmle 6ko d7rbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6qy8 zgx:bax/fh0yma 27ms- +lf q30yc–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t -ay8x0m 30s y2:qzf+ lmh7cfq/xy abg depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert aap ayb,rm;*o gjvh;b 7d. immw: ;k.7m candy bar directly into work, how high could an 82-kg man climb a lmrk;m:j;ambv*hi.p g.;admb o7 y,w7 adder 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 fire2-da-wq)- ssp lyott b p(7/fid at an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scapt69 w2qeh 3vwkxk c 7/h0o.fdgu y9,lle compresses 0.60 mm.gf dwtk7lc xp, q/hhyke2v0o6w99 3 u, 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 scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope,zrywubp)ev;qo863m3s6)f b g*qsy i, and swings out over a lake (Fig. 6–45). He releases the rope wh bufys3 ;,sz mi3w)q6y8 p6)qgeorvb* en 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 verticaljwui1 x5hy99ghe cm). distance of 5.0 m in 9.0 s. What minimum power output was used to1yh)jc 5hewgu 99.m xi accomplish this feat?    W

  Some electric-power companies 7fwh4v2d jpk 1use water to store energy. Water is pumped by reversible turbine pumps from a low to a pfw2d 4j 1vk7hhigh 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 springx l+j/1co d m*vu8btn2 stiffness constant for each of the two resulting springsml +* /2 tj1vbu8oncdx?   k

  A 6.0-kg block is pushed ;4d*w* nzuo)xhxf d1/ci/kvr 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 35kd0, 0ot,th:mthayw um+3qz (x m/h to 55km/h in 3.2 s, how long will it take to ac+0t hxt,o w3q amd:,0mhzt(yucelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac functio. io wm9kwewxl8 xepwx 7:)*v9n (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–4*w)x9 oi.8xke7wvp e w mx:9lw6). Estimate the 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 cqk5s5 u.zeg5 i )n7nwvl-8x 62yj bxg500-kg rock vertically upward a distance of 500 m, what was its veloc.g5 6) szx8y5uq5licewn xk2-j7vnbg ity when 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 etj93fb(d o*cynd,6 nin-jg6from 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 maximum power outputnj39yngodc(6* bj- ft i ,end6?    W
(b) What is the speed of the water as it hits the wheel?    m/s