In what ways is the word “work”)/6:p cw/mliznq ye+x as used in everyday language the same as that defined in physics? In what ways is it +y6clp:mizw/en )/x qdifferent? Give examples of both.

Can a centripetal force .0 q bh zsbf9(x3czo9zq3z vv;1tj1ud ever do work on an object? Explain.

Can the normal force on an object ever do ).e9ro5 pl1da3 gynvswork? Explain.

A woman swimming upstrvi1-1r j4liw* poa;ga *vo fo+eam is not moving with respect to the shore. Is she doing any work? If s*o*pvrl+;ia-oa1o i wj 1v4gfhe stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction f n-3zs5s rl2j*wx eaapu6 w-i(orces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth wx 2-s*lazs -j5enura3w6 (i pout from under them.]

Why is it tiring to push hard against a solid wae0fsoml;p6k 5 ll even though you are doing no work?6ksmlo fp;50e

You have two springs that are identical except that spring l is stiff 53uu m +ofql1+pox;b: gnkpee:aj341o+ jcfaer than spring ogquj +a35:1:ek f+numpf xpo+1e3o cab ;l4j2 $(k_1>k_2).$ 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 -nshesf/s9*tuk+. xx);kz sl slide on a frictionless surface (Fig.s)ss/kzlk f t.+9exn-;sx* hu6-30). 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 change wh n) 9mjgvypu7q:dv+ j(en you jump as high amd:jyn+v(v7up 9) gjqs you can?

In Fig. 6–31, water balloons are top/y39f 1x owkpssed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on i 9/1k pyxo3fwpmpact? Ignore air resistance.

A pendulum is launched from a poi r 2f.gnlh/c7b9 ;nwernt that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward alr7le 2wn9hng/f.rb ;cong the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you cvy+hbg u3(m:x ompress the spring by pressing down with your hand and then g:(m3x h +vyburelease 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 instb.h kknxgb( r e42.ow7ructor pulls the ball back and stands against the wall w.k4e go7n2 .khxb(brwith 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 potenti g j)ay;ptli,bqt +q1,al energy when water at the top of a waterp l;)1j q+t,,qaib ytgfall falls to the pool below?

Describe the energy transformationtc-b)1yl ct 8d, j.skks when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts qaj3de amm+gt92aqh yo)* 1rpu; c 6p+skiing down a hill, bud*j )oa+3q rgm au+ 2a 1c6teph9ym;qpt after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m twlgd3idy6m 8c ;-tv2oc7l 6mw/yng:) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (byvm -g62wodi6mgwll7y3 8t cnc;: /td) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path raf0dsf e9.w skl;vaa d1*3 zj0ither than stepping on top and jumping down on the other si;d*.1 90f0jwdsiaevl f3k aszde. Explain.

Two identical arrows, one with twicb ,2 n3k8r f1bn4mtm6l) jyllze the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force 81,n l y t)kf64m bll2n3jbrzmon the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a silbj33u:fx fygc03pc* ei u+2 hmple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking0ugpjh3f i:cbel3f3*c xyu2 + friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rvwrtcv:l)f 1 6.c vbpnti3l.,,w u i;7: rxxsfebound to a height greater than its originb cf.) xur.vxw6 vtrl,i:7;,tiwl: fps1vn 3c al height? Explain.

Suppose you lift a suitcase from the floor to ac1 n74ex m6dhj table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a mjn 71 ch64xmedore 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 thxg2mzt3 n)t; c/cd:h pe work.

Why is it easier to climbonr.p.76. z6ruso/7 k5i 13 :qqv ntnyhlxt my a mountain via a zigzag trail than to climb straight upyy 7itnn6:nroksvq.qm.ho 1 /rlpux7z63 t5 .?

Recall from Chapter 4, Example 4–14, m q fj4-kfys;7us:e-jthat you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter-7jye:-fs4;ksj m ufq the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile drive d(tz6.q8z 33epmgf zer falls 2.80 mz m8ft3z(ep.ze 3gd6q ?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hs.g l00t .fjhvigh. How much work is reqsvt00 .gf.h ljuired?    J

  A 1300-N crate rests on the floor. How much work is rea,,n n1mcmeuu5q q.e5e f+s-i quired to move it at constant cu mn1qes f5.,i ae ,5qnu+m-espeed (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 ke hbvo2g6-/a pj9;t e(horizontally) pushing a 160-kg crate 10.3 m across a rough floor without accelerativ-t/ hb;9e2p eaogjk6 on, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at abhbp //c pl-bwc 29r5s1wz1ki rate of for 7.0 s. Find 21 /l 9hksbrz-bw/ 5bipccp1wthe net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How much nt*02k/ird zgyn4 .q m tvya),work is required to stac/qta )n,0.k nymgtd*z r2iyv 4k them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be use9+p: h:; *h 97eqezaf jxlaaygd to liff objects we might not otherwise be able to liff. Show tagea+*yl:z h9 p h9af:exjq7;hat the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acceleratinfc)cpxh: ynd :t5 n.h4g by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficxtn n )h.cp5:hdy f4:cient 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 atpf.:vu)*u7 t 9hpeo of 0.10 g upwarfh tvpep.)u9ou* 7at :d.    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 thamiutu12 thyly.h0 k)3t $d_{\mathrm{A}}=10.0$ 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 F.356zqqp* wrlr ibw z*ig. 6–37. Determine the work done by ri *z q*l6ww5b.3prq zthis 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 acts in txeyrlx .glh+9-235h cdu fw; zhe $+x$ 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 ma)pojwt.ta-1(/t 6wzif0 m ewp 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 fac cnuj0e)xryixi3r, (:tor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requ p6 dpb27f*h *u.xoqcwired 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 biiwr4 q9 xkd,6. sqzt3e 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 q:9 -flw:vspogjuv .cvu 000t an average force of 110 N on the arrow over a d0 uoqcs:v:l9 .-jgfvpuv0 0 wtistance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s move:)mj 4qit1ypbi5vvpr p+2uf 2s a fielder’s glove backward 25 cm whenyf+u:v2p ip)qvmbj51rt 2p i4 the ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will itsf,fif2uyy10 v minimum braking distance be increased, assuming all else is the same? Ignore the driver’s rea 1,uiv0ffy2fyction time.

  At an accident scene on a level road, investigators measu+(/-n uq)allnzb0s7 ve ea:;zy qdy t*re a car’s skid mark to be btd)e :azqns;-0n7zqe* yl a vlu(y +/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 at By the time it reachmzfy*-(vv7 zje -d ; ai5/urgk1p; arxes the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if( aarg fi-1kzzmpr;y x-;vj/7*uv 5de the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.0 xt3)cl1nbeg ,ig+v 423ngaxhJ of work on it? Nein+tc1a )ghv 3,lg2x3bx4ng e glect air resistance.    m

  A 285-kg load is lifted 22.0 m tw f/ r59z2uc/ xojo,pvertically with an acceleration by a single cabljpu/w,o x5oc9t/rfz2 e. 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, l7cfn6 03k/ gg i1iblck, of 440N/m How much must this spring be stretcheg60 knclbl/ci71 igf3 d to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higherq :2so31f qpr5wel1 wq. What is the change in potential3p 1qwr5fseq:l2 oq1w energy?    J

  By how much does the gr-x-+hqm;d 9 uvjygu z6h-mqz6avitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the9; dzmmquhy -g j-h-6qvu+x6z jump?    J

  A 1200-kg car rolling on a horizu)wl0dtmhc 5jeb :z8odo6 u8:ontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the sprin6h5u:z):88mb deujdcoot l0w g?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m tr+75pu*biux above the ground. What is the potential energy of the book relative r b+x* uut7pi5to
(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 and clvx+j rq 9uxx(9imbs to the top of a 3300-m peak. v 9jqr9( uxx+x
(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 vert rf et(9k2yc9qically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the rqc9ty(9f2ke ruler marks?    cm

  Jane, looking for Tarzan, is running at topu) u vol/+cf aj77ogl: speed (5.3m/s) and grabs a vine hangingo7llg)ju:7af +u/ovc vertically from a tall 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 rest, slides do;,5irp0o/vrzhfr a:m wn 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 frictitu1sq ip,ea *:onless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energav j x lfh*tnhw t;+0lmt;j6d2tg,1:ty is transformed into gravitational potential energy withoutv+t1xg*6mtt at l2:0hl jfjd;t; n wh, 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 speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from thepzxuqb *,q(u 3 top of a platform with a speed of 5.0 m/uq3pzxq*, (bus. ($\alpha)$ 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 mas. dk,uce,p4ijahrx 57s), whose spring stiffness constant is 950N/m is attached to a table and is compressed dow7u,ai hpcrd.,4 ex jk5n 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 slidespaaa.w*8 8nqck:*d ot without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the cir oca 8k*.twqapn 8d:*acle (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 sd (nbk qd+.10udy8rjbpring (spring stiffness constant k), Fig. 6–40. The block is givenk d (y .q0b8+rdudb1jn 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 jump3 ywkarxf-hsn2 v4n /8s from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring sw8-nv y 23a/fshxkn4rtiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where i ..e)c55,gxwlls)s lz58 bblqy m/tld t is released from rest. Assuming no fricy m5le,wdzx8gs/5 ) cbbls.)l l5ltq.tion, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speedbrxt e :nmjf4 g,i3th3-w z3;0tmf0o-m6hos h 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 n3n qxw0.t (dzspring 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, calculatxnw.dn(zq0 3t e the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to c h*gv1*j, s ug(pnqoi (m3k4ekycle 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 oppositwb.. b/7*f msdf4kdkj dxy5e 0e directions, collide head-on and come to rest. How much thermal energdkk.ex/ m syd *jf0d4b .b7wf5y 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 e4vdae8y,;e e the bottom with a speed of 2.2m/s How much thermal energy due to friction w eee,avd e48;yas generated in this process?    J

  A ski starts from rest anf4,bl dcn.6 eod slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is do1r7q4x qy5 baropped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a89y/ yw lvyxgt .)1ajr height of 2.0 m, and it bounces back to a height of 1.5 m. 9yxrtvl/18ygwa.) jy
(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 res.dmtppfm3vs1*ru4 s8pwr 8 ;nrrn z),t, 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 coeffrpr43rs nzwmuvsd)n fprt,m p1;8*8 .icient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a)b; la+n 38z3qalf*wjw i4aev speed of If the average force of friction is equal to one-fifth of its weight, wi*avfwwqi+e) la8n 33;z lajb4th what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachess6ftf6y3oq 7qb qk- d+ 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 firmly attached to a very 7ntq: n6pqrk 9gdfw-9r nx/z *light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What iszq wx /fr9nt6-9dk 7rpn: nq*g the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block ilv/bg v*7 ).ustklt w9s firmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of fricgt)w 7v/ut*ksl.b9vltion 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 “glideraj;arjfu (-fo 18f :qr” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventualaf(r rfajq1oj -fu :8;ly landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-storv 0banws tykml4j*0)h0:oz/by window 16.0 m above? z avwn 0 /0s tm*bkjlh0:b4yo)   s

  If a car generates 18 gc 8vu8)zew6yyz.h+u hp when traveling at a steady 88km/h what must be the average force exeu)vu c8.8hw +ez6yyg zrted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avex0 slvu 0z((ak)m8wh yrage power delivered 0lysv( 8)0wmzk(uxah by the engine?$\approx$    hp

  (a) Show that one Britisp; -t-/mwzspcx- s*fwb.2kqj w9f xc0h 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 zo4)3.tfqi3fi rtj 5tof “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 1150i* -fgh6lt5pljh6p 0w -kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately6 5 l6itgwjh p*0-hflp 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-( gk9sxctkb 07hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a-/pe k7a:5jpzbzqje* a f ((od 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was developede/d p( kfz7ja:eoq abz(p5j-*?$\approx$    W

  A pump is to lift 18.0 kg of water per mij8)vb (bi*ak/bf4k1do ub 5uenute through a height of 3.60 m. What outpu buju/k()oiv1k ea8bb* 54dfbt rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stai k9 yvm99cuh40wytu+ors in 69y m940uhkc9+uvty ow 6 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 a 6.0 j ,o04lkj*k5c fs s:2qpwqjz5$^{\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 po f9deag+9mr w+m9z2lwwer output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 me2wfwz+ d9 l 9g+9ramN?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag h4xxc aq6 )wp3a 310-kg box along a level floor at a speed of 1.xqwh)x43ap 6 c2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7n2p*x upd ;3pc.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 hx3lrc5: di i,tave 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 mati :icltdx3,r5erial 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 firspwxr/6j5s-x8 w/m7i wb 0rpc6wnn sc2t shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is requ s7-r8x 6wcnrn ws5iwj0/wp bp62 cx/mired 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)/gj4o(nlxf +ve7b k)2:dkt+v /tu yse 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 he was traveling at 6.5m/s at the top of tkn)tyj/(lxst v2 + ud7v/+k fb geo4e:he arc?   m/s

  The block of mass m sly c-;qie,ehpb;dgc )+iding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the vc+cyp qi-hbee ,;;g) dery 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 jumpinghyo t0, x;p6cxwutu. 2;ve yda1 fi3-d from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilo;yu;,6od.h f xew0ca3t1- udv 2ti pyxt’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 w fo fmc95(*uwyhose other end is fixed (Fig. 6–4 (um5c ffwy9o*3).
(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 ofu l23vflea93rt zaxaea00x-e39s :xi a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calcula u23x9 e:3zaxaf-evi3l0st09 arxelate
(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 ;2rkcwuk* r;qi a+eq;hnd j n6;wlusc9g 4g /6m 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 C8-9p.vi,6galoxi-kxk m zy(nalifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the powi.l,8i zx6kg-anv koxp m y-9(er needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m beft9 9d(5kryef8f 3d uebt )0 yx4vvb)uwore striking the turbine bladef)9uvefvybded(b40t k x 85u)rtw3 y9s. 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 loopun 1wj37nk+to (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the ctnw ujnk37 +o1ircular 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 bar aj9aiih*l4 o 6directly into work, how high could an 82-k4il aoi9hj6 *ag man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwabnoo /)s0m2ee rd 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 scale compressbsvd+ b)w/(zoes 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the zsb( odbw)/ v+scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope,,t3mptf5i*t wm)tl7 +r,y2rd iqk ;i m and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. t) ,ti+2p rd3y5*7 ;ft mmi,itlmkrqw
(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-kg6; / vrae uc7*u7ztrsmw)0sy0id2xv2 om2 irv athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accompliv 70z2iu yx*t;w/ia)ru62or2cvmmd7 r0 s sevsh this feat?    W

  Some electric-power companies use wat(ivk awh3hlz05 e -tq*er to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energeq5i(w- 0alv* k3 zhthy 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 sb;fs3tphm9in 3 i-8v itiffness constant k is cut in half. What is the spring stiffnes ;sbtn83- i pi9ihmf3vs constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roughu atd5d59y55 i v5n2zrlbx+wq 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 accelerw/nz0knny y )q0rd)t(ate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate fn(q dy)r)yk0 w znn/0trom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks o(t lqv 1qffjh+qam3 2-n an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angl fv2m 3-+(aqqqt1jh fle 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 vertica6g*.a4 qjmrp ylly upward a distance of 500 m, what was its velocity when it left tq 4gj*.ry p6mahe 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 wdgo3i d4jnn,.b wafcou n 1 w99)2kiz:ater wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricityo91g.w3:zad kcwni i n j9fbn 2u4,o)d output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s