In what ways is the word “work” as used in everyday language the kt2x( vn)* khd*m9/h dkj.mdwsame as that defined in physics? In* ndv9htjm.hdxm2dk )(*kw/ k what ways is it different? Give examples of both.

Can a centripetal force ever do work on a ,:;s9t ft ttuany(6ijhpx-8qn object? Explain.

Can the normal force on an object ever do work?2+i k4ou: 4pacsaccc* Explain.

A woman swimming upstream chw(8m,tn g5 f7h (kxvis not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done ow(fth5xm,8h (gk ncv7n her?

Is the work done by kinetir+ h2oc6 n+lqic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecr6+qh l2nic+o loth out from under them.]

Why is it tiring to push hard against a solid wall even though you ar.g+ dgf dd7b6xl2 aj4zs/b 8cne doing no wg l8bb2 dsn+cgdx6 j/. 4fzad7ork?

You have two springs 9 .d 1j01xt)kjw xcyucthat are identical except that spring l is stiffer than spring 2 1j9 kcj1wxx0d y)ct. u$(k_1>k_2).$ 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/q4ffk 4x jo8y on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and 8xjfyf 4qko/4 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 ener+t a cy52i;, qqcd+aevgv,qpy + rwd4(gy change when you jump a 5g2 awqyrptdq,cc4++ q+yv, i;(ae dvs high as you can?

In Fig. 6–31, water balloons are t0xvi0 wr9l 5afossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ig5w ra 0flx09ivnore air resistance.

A pendulum is launched cfc.6vfbaqmx-ro 26 * from a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on thevxc o6.f qm2afc6 br*- 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 up:tg5 khntndal/ yj5)ndo h0 ;,right on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservationn5 t,k) ot;gdn:ha 5d0/yl jhn of energy.

A bowling ball is hung from the ceiling -qbrh 5r,.gcoby a steel wire (Fig. 6–33). The instructor pulls the ball-cqbrg,5ohr . back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitat.*qfcwx-ba m. ional potential energy when water at the top of a waterf qawbx. *.m-cfall falls to the pool below?

Describe the energy transformations when a chs;od8. vk fk6je3d5wgs gx) ()nvtlc0ild hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts 2wxs 0ra;j 7qlskiing down a hill, but after a time is brought to rest r2qlx;s0 awj7 by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of h)//4fh ahqevg w:vd9ny7b ,d height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy andg:dehh/w 7n)b hd/vavy9f, q 4 there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step ohi7 2fm+lyh )cver a fallen log in their path rather than stepping on top and jlyif mh2c7+h) umping down on the other side. Explain.

Two identical arrows, one l;vzca;)vn;if(o-ccwith twice the speed of the other, are 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 than the slowf(vvc-caon )zc; ;l ;ier arrow? Explain.

Analyze the motion of a simple swingikof xyc2,if) s-) kl,7/ z x7le(bcnhing pendulum in terms of energy, (a) ignoring friction, and (b) taking fri n(o cy7xcf)h7/fbs kl,z)ix ki-2e,lction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it re1cz s ns.eo 54eus,ygg *w0ek;bound to a height greater than its original height? Ex5s*4y gewes.,; 0o u 1snzecgkplain.

Suppose you lift a suitcase from the floor to a table.(0gn1p (2trii of;ctk qb (xb. 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, (bit (xc(2;bo1rb0.fnq pktg i () the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powe. t ),kp1kk05hbqhmmmr needed rather than the work.

Why is it easier to climb a mountain via - gad ma9x 7*ji s2v po/bg5ynjv)zj5/a zigzag trail than to climb straight u- d z*/b5pi2gym)v/jxa 5jaj9o v n7gsp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and. q6ohsg(eavfsa s3,i3 rh 8v6 ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every3 haqvi r ,sge(.hvs 6f8aos63 meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is donntq,pj9a.;gi e by the gravitational force when a 265-kg pile driver falls 2 jqga;tp. 9,ni.80 m?    J

  A 65.0-kg firefighter climbs a f:.s 1y;7kbxv.n 66flu4 qkwyzk+fkzn light of stairs 20.0 m high. How much work is re nf sb;k:v.qz6 1uz76+x yykk4fl.nk wquired?    J

  A 1300-N crate rests on the floor. How ptqc2kkb6tq54x*q y 0+d gx4s much work is required to move it at constant speed (a) 4.0 m along the floor 65xksy0qxqc4*2q +tkbd 4pg tagainst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the moo k02o0;h3bwfb tcd: ay-2vj4/ trwsd77v v tgvers do (horizontally) pushing a 160-kg crate 10.3 m acroswfwakhybd3c-vs:rd 2o0tgo0;/2 bv7jt 7 vt4s a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by yla 1+fvi+wc;n;kh+ e a force across a floor at a rate of for 7.0 s. Find the net workh;yc +nfl ak1eiw+;v+ done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fladt 799+szic/fin w 63hnqr5 ,misw-j vt on a table. How much work is required to stack wzit3 n-c6idhmq v5srsf 7/+j9iw, 9nthem one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we migh3ia:e to x+)fht not otherwise be able to liff. Show tha3 ia:+e t)oxhft 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 fziidu 8.g):v-zsr v3is kept from 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. Calculate: - isdvivzuz8f)g.3r :
(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 lrs v0618/uw)w0l hbh a. l;dzvsj fy9acceleration of 0.10vll6 sfjb/w; 0vy9hdr81 hlu.0zsa)w g 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 tgopx 2r;1l0sxz /xm j.hat $d_{\mathrm{A}}=10.0$ 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.,xfyxl :45 i 6o2xnv efk9eay6 6–37. Determine the work donel o,26any v4i exy:6ff9xe5kx 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 acts in lwqcw6js9 - 1jthe $+x$ 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 oxygen3dx-9hs y d,)fj 9ufrd;(pg er molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed inc/n18d)zs f pahnse91 oeoe,1w reased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to c,2x,5(od epv5g-g kux c1cntstop 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 bml4wdj)x6v :k1 cex /tyt: *exe 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 whotr-hu1p h)b fnd k lrl8g0)l5u4eu( o9se string exerts an average force of 110 N on the arrow over a4ld0fpuue bhlr)19l(h)kurgt- 8 5on distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) trjkzv/0p19;yun vg9g daveling 32m/s moves a fielder’s glove backward 25 cm when the ball /;90pvgg9 j ndzuky v1is 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 fa5 ju*ci6ucw4 u..b krgctor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction .*.6j iwbrck54uc guutime.

  At an accident scene on a level road, investigat3/k wlsh*kfd y+-6tcbpac ; +aors measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coek+/k3 a- habt+cl;yd6 *wpsf cfficient 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 pitc.gs9s,49xg mjr d3oqa hed at By the time it reaches the plate, it may have slowed bqsog , d 9as43gjrm.x9y 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock govxmpt xkoslj;6/y;e/0a2ln;o fg y.4 if thrown straight up by someone who does 80.0 J of work on it? Neglect v2/egy ;m .xjf;;4tnl0x6oos a p/lykair resistance.    m

  A 285-kg load is lifted 22.0 m vertically wittbh()4 j1oibqh an acceleration by a single cabl tqj(ib1 b)o4he. 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, ofr4ycnc48 *i wk i7(uew 440N/m How much must this springrk ce 8c(*y4uiw i7w4n be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branc) vf ozy,c rlj-g+ss1,h4g x5rh to another 1.2 m higher. What is the changeg+o l fy)sz5,rgjx,- crvhs1 4 in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg poles( nysbrr7 7;rwgar** vaulter change if his center of mass rises about 4.0 m duria7 *r 7*s r(;wrgbysnrng the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed vmkvsqzkm58u)d t9 l(8w- m 5ic = 65 km/h when it strikes a horizontal coiled spring and is ukmc zd5)l (q8wk9svm8mt- i5 brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m 2wu7*o : qk4,ro gjptxx 9dj8uabove the ground. What is the potential energy t8,79qjgduo:w k4xopxu j2*r of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation dqi3;.atv5qqqe 3nqq1 6:/k i)frcy yof 1600 m and climbs to the top of a 3300-m peakf qi i5 :kqqa61 .qy/yq)r;q t3ve3ndc.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. ezha)s m hbm46 (rh2-ex3+w wgThe end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg m)eha w(mg bs-r3mzx4 2h6 whe+ass 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) and grabs e 4)oof:nh bo9a vine hanging vertically from a tall tree in the jungle. How high can she swing upwa foe nbo9:4ho)rd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless. en.;isd+bp7 (g xayn 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 frz +/ xo8thy;+ji+ia caictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is t2yvz5jn*mu(wtd iy qc2aa 55 :ransformed into gravitational potential energy without the aid of a polet:(azv5*n2du5 icj5 qa y2mw y. 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 the top of a platform witxu.uovrj c 09:h a speed of 5.0u oxvu 0rc.:9j 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-*bg *we)dq hzb2qz x/ spring stiffness constant is 950N/m is att *q*qeh)wb2g bxdz/z -ached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides n(k 3 slmti(/y +qko/ewithout 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 circle (whose radius is r), from whati nl3o+tm y//kkqe( s( minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stinqd.5 vhlj3g ) sn.k/vffness constant k), Fig. 6–40. The block ..3v)knvn g qh d/5jlsis given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord w *xm*2au2wadhhose unstretched length is 12 m, and *u a2 h*awxd2mfalls a total of 31 m. (a) Calculate the spring stiffness 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 it is jxrklad,9lqmcf) 7b 4pd+k62 released from rest. Assuming no friction, calculate tkmra) clx,6 qld749pd2f+bkjhe speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throw0e vg)d1 q,n.i7l lqyin with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designingm/ 5 ut:vypusw h* pyy+fh,q)1 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 spring stiffness constant k should have so that passengers undergo an ay1 w5+ qsvtp)uyh hyu p*m/,:fcceleration 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 cycle up a 7 rm(173u+8m at3fdoz+wk xswn.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 travel+stlxq9 m.i;s 5/z rsuing 95km/h in opposite directions, collide head-on and come to rest. How much trxs9u5s. zsi +tmql/ ;hermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends ak, kl+to i 4g d12xoqitt4zk/ 3ezs8(s slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due tkqtg(3x ilo, te8+zks1i/dz s42kt4o o friction was generated in this process?    J

  A ski starts from rest and slides down a qc7b4sm1/s o g22 $^{\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 fdj.g oh3 a9n2t:,bjt:2 kve q13.0 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 b:y9m0x5zyze q ack to a height of 1.5 m. zy z:0yxq59me
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constanthwc* z s1v ;2e/*vgnhu horizontal force of 350 N. For the first 15 m the floor is frictionl/cghe v1*;nv*huzw s2ess, 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 cq( 5rovf8klf53h wasf8t 2z8foaster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is e5rh(8 5f ls 23fqzt8vfao 8fwkqual to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady ea ptt) 2rm-4lsbck:1 f8oxd55 aquj 9upward 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 - +yrop07l sri6eb:;rn s6yjwlight 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 eo6i;:y 6lp 0s w7rrrs nyb+-jturning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block i(v) c:r o(xxgm( .;8pfmeppxzs firmly attached to a very light horizontal spring, Fig. 6–40. The block can slide r g;xovzxpefx)(pc.(m(pm:8along 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 twts8-y-zgi*h a9v1 b-ylr./js2 rsi b he space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air j z-wih-gs/ t-i y2.sbsavyrr89l1 b*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 tew)n 9n* zsp2so lift a 315-kg piano to a sixth-story window 16.0 m above* s9nz)esw2np?    s

  If a car generates 18 hp when traveling at npfx(e7zb -rd;g-n1 zw 588mxdr j9 mua steady 88km/h what must be the averag7menu 5pwxn z8j -z;rgbxfd9m -1d r8(e force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car acx xsrg9b;- ,p,mebb x;0ii+a icelerates from rest to 95km/h in 7.4 s. What is the average power delivered by the,beb-pa; 0, +xiir;9ibgs xx m engine?$\approx$    hp

  (a) Show that one British hota ns:jxdu*bv7 i+;:w rsepower$ \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-4fikk ,fu7z /vhours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.x /c gp 5iwkhp0p by:r885ltqpyg( o.90 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a const:8 hcpp0gg9rkq .5 y5oypw8tilp/bx( ant 75km/h.    hp

  How much work can a 3.0-hp 5c 1;e7n ;hxqtfmrdi/motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelera 7u x8ixvma f2+sj9 q4hulr8-etes a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what xs+ 9xrv qe uf-27ml4hji8 8uaaverage power was developed?$\approx$    W

  A pump is to lift 189 mpxn mncyfa- nr-(:bn6o6)b .0 kg of water per minute through a height of 3.60 m. What output rating (watts) should the pump my)6nnn cmb-om r 96n :(xafpb-otor have?    W

  During a workout, the footballs8nn/i:bg 9dww do -f+ players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at89+ gns od-nw/wd:i bf 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 cliv;sh(yck2 vjuc5f. k,mb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can it c 1+e. z4tmkchwl(t+wnlimm1+kn cwt 4e(l+.wzh tb at a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a mo63p.x5q z*fmljbkz 9utor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coef 9z*bflukp.35jqzx m6ficient of friction is 0.45?    hp

  A bicyclist coasts down yroi)5 ie;mbef)vb5 f*ek1:ba 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 b2*-gv(b 65) 07cx etixz6bxh zemqy uruilt “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 e*2c xh)-bi7gzz y 0 (6tb5uxveq6mrxkg 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 thh(5y hzhgq7/be 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,qg7/5hz h b(hy how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s f ,gyg)5z(i ax;b vjcs+z-yii6amous long jump (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 he was traveling at 6.5m/s at the top of th-yc b5,ii+(sja6 zz;giv)xg ye arc?   m/s

  The block of mass m sliding without friction along the looped trackqrzw-x1 uxz9b1k 41p k shown in Fig. 6–39 is to remain on the track 1 kbuz- rpk14qw1xz9x 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 aircraf/no6-,ir h+gkys 1 x hy,jxzy8t without his parachute opening. He landed in a snowbank, creating a crater 1.1 m-x gi nzo6y/+yxj sh,r18h,yk 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 L whose otheu58 t9r :6ls+lmgvfemr end is fixed (Figefg6strlm+l: 5m u8v 9. 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 climb is maob;zqyaq*8 ) wc5dlex-a 0u4gde in 5.0 h8-xaw b agl5eq0 )o;yc*4zd qu starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator m9w+ m9vm*tdi is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can mov;.e*zgf t m 4gc:iucw;e 47,000 people per hour. If the average lift carries people about 2izwg m;u* 4.g e:fcct;00 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 m befaoh beg s0j2// )r.dknore striking the turo daj0k./ebsr2g )h/n bine 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 l 9j2cr2uczrr8oop (Fig. 6–44), the difference in your apparent weight ccjr 2z92u rr8at 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 bodc2c qus 06(us-:-fqt67)qvo n yxhe jwy could convert a candy bar directly into work, how high could an 82-kg man climb a uq7qu(ns q:fj 6csxv2c ey t)-oh6w -0ladder 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 ofrl*6x2:qhbx xthfzl ,b*1s v- 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses 0.60 mmk/w7 n:tqu, h8 r)envu .,dcgf, and it tells you your weight is 710 N. Now it h,qu ,/v)ngcu.e8kw7 fd:nrf 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, and swings out over a lake (Fig. 6–40+(6( 5mpuc, taxt) xru-xxn2bqp9wg* x b rme5). He releases the rope 5x ae t9xtxu c6,m0 xpgb((u2)r+x q*rn-mwp bwhen 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 ko+gdi4b 4cx815yt zlclimbs a vertical distance of 5.0 m in 9.0 s. What minimum power outpo4l8x 4tz5cy+ d1igkb ut was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped l x /0x-j8 ilw)s2vvrbby reversible turbine pumps from a 2vl-x)rbvx8l i j0/s wlow to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring sic22 -qlc8 3vbsic/ yutiffness constant k is cut in half. What is the spring stiffness constant fs ccc byq/2i li-2v3u8or each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a ry 7h)se9t7+fsnhl u /oough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/vnjo piy9v 99x93-y9gmcu cqddh8;e8 h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume thdn u- e8vxiyy dv893 m9ph 99cq;cojg9e power stays the same, and neglect frictional losses.    s

  In a common test for cardiac funct+i)dv2 ujbj.rion (the “stress test”), the patient walks on an inclined treadmill (Figdj+)j bu.r 2vi. 6–46). 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 500-kg rock vertically upward a dix) az1 e2pxany)o7d,s stance of 500 m, what was its velocity when it left the 2)azo)7exxs 1dan y,pvolcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height o9 frk(qcv y(/vf 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 powekv q cy9r/((fvr output?    W
(b) What is the speed of the water as it hits the wheel?    m/s