In what ways is the word “work” as used in everyday language thwg 49;vb p0 c,a+y/eoj c;qejpe same as that defined in physics? In what ways9ep;vwo , ycaeq0;+gb j/4 cpj is it different? Give examples of both.

Can a centripetal force ever do work on anaq-ea2si ui6. va8:yf object? Explain.

Can the normal force on an object ever do work? Explainc y4,rpvu4e eq -t;+mv.

A woman swimming upstream is not moving with respect to the sho 6/pu qsp+o* vtt(ht/b:yhdi( re. Is she doing any work? If she std:/+ it*t(hhbq6pv pso/( ytu ops swimming and merely floats, is work done on her?

Is the work done by kinetic frick eneey02:xmnl6o7,nv+x )y iw3 ( jxotion forces always negative? [Hint: Consider what happ3x2 yn+owv:xney6 ( 0o7jxe)kl,ine mens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doyp8 +:w2usqyq -gxji )ing no work? qg) xpys-iw8j+:u2q y

You have two springs that are identical except that spg.m mrncq+/e) ring l is stiffer than spring n.+rmc /gm)eq 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 on a block that is free to sli;54u hx/bhwmh de on a frictionless surface (Fig.6-30). The block starts from rest at þoint A,huwm/h4;5 hbx 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.3fiz7xvge.q),:w uxak5 d vp much does your gravitational potential energy change when you jump as high :zgave.wkxdp 3.xvq5 i 7,)fuas you can?

In Fig. 6–31, water balloons are tossed from the roohb oloq 4o+*sj0n a3v86h/ +cptib.gbf of a building, all with the same speed but with different launch angles. Which one has the8*o+bo tlcvpo6 /b nbh.0q3s4hjg+ ia highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heig3g )h3jq b4f5pumgbcac(l3b; ht 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 the second launch it is directed downward along the trajectory. Which launch will cause it to swing thp3 h(jfm 3bcc) ;bgqu4 3gba5le largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upv51nj6hxy8 v jright on a table. If you compress the spring by pressing down with your hand and then rev1njjhyxv 56 8lease 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 (Ftvjviw.bra pn.46jq2 d,a0 ds 2q8i*uig. 6–33). The instructor pulls the ball back and stands against the4jq08q d. jrun2av*s2v,d w ib.p6iat wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potenmto/ylf999om s,a tk(+r 4lujtial energy when water at the top of a waterfall falls to the poo+ k(stu499m/ooyarm jtfl ,9l l below?

Describe the energy transformations when a child hops around on a pogo dc h9.3 na-.lek5 beckstick.

Describe the energy transfoqn 6h-yp6fi.6 vmsw 3crmations that take place when a skier starts skiing down a hill, but after a time is brought tomy.vs chnifw- 6p3q66 rest by striking a snowdrift.

A child on a sled (total mass m) startsuec,l)c1x pf2y )u jc; 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) l),cce fj)x1ypuc 2;uit is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path ro( lbs,6kzg- ur)xi7father than stepping on top and jumping down on the other side. Explain(riu x k6-s)7lbfg ,zo.

Two identical arrows, one with te4 hw o1;hqd2zwice 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 arroz eh4d2hqw1 ;ow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingdzm7ojnfz 7 s//epx65ing pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock z fenxd6/ pm/o jsz757has to be wound up.

When a “superball” is dropped, can it rebound to a height greater tha 66b gmtv)a tur9cf+ 8njqb6d/n its original 666bbt +a )vuc8g d/rnmqt9jfheight? Explain.

Suppose you lift a suitcase from the floor to a table. The;vv3 :ia 4yx)w6; b bjhm.axfe 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, and (d) thx6a;h;fm3 .)iwv4 vyab:jeb xe weight of the suitcase?

Repeat Question 22 for the power needed rats+/zo2j7ptcwa 5: hmsher than the work.

Why is it easier to climb a mountain via a zig i6cd vdfk )nslg g7n/e5a+fs07 vag(0zag trail than to climb straight upsdfksv0/77v0 5)gfdni(gg6nca+ l ea?

Recall from Chapter 4, Examp c r 1e0oaq8),ocx, ,ptldj.sfle 4–14, that you can use a pulley and ropes to decrease the force needed to .1t)xcaldo0fqc je,pr,s, 8oraise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the grh0,md4:pp )c (n2 fdkqi vdvu)avitational force when a 265-kg pile driver falls 2.)(dm:dvi,2ppk d) cv0quf n4h80 m?    J

  A 65.0-kg firefighter climbs a flight of stai y*ewn(gwe 01b .s84ujtol+5d2bxj h rrs 20.0 m high. How much work is ren4bb8jj .2u(eh5l rwg w 1eyts d+o*0xquired?    J

  A 1300-N crate rests on th*eg r8 nf0a- )jzhqtzu+oow((e floor. How much work is required to move it at constant speed (a) 4.0 m along the floor agains+t08ow hr-(*n j (agzzef) uqot a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mi 2oh- 6xzxpq -ne1y2 )fs(xrqovers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coe1-p ios26qr2hy)x -fxzq (nexfficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rlgy-8 al.-2.n (lz o*rckpxqx( wvx7c ate of for 7.0 s. Find the net work x7w.x(o(x k nrcgz.* -l vy 2-lc8qlapdone on the box.   J

  Eight books, each 4.3 cm thick wityakl ex.mahyeu:(. v0j ,t7 01e+wkvfh mass 1.7 kg, lie flat on a table. How much work is required to stack them one on toj.vf t0aa w( v+.eku e l17yem:h0ykx,p of another?    J

A lever such as that shown in Fig. 6-35 q s8h-eaucp0es4 (qs ;can be used to liff objects we might not other hq;4 c- ees8apqss0(uwise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is v/he6 - a0wnauph/(bz r*kny4 kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kiney zh 6h nwr/ve*0u-b(/apnak4tic 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 kd(m tc sk-z/;of mass M an acceleration of 0.10 g upwar (m;sc-k/d ktzd.    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 ther+o xkofwpi8x.a vf b 2*7(djf ;ka:y; distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, variehlk9: 58rrcwnyke 5 (js as shown in Fig. 6–37. Determine the work d:k(5r59h l j8ynrewc kone 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 partiml* v8p(*2tthk;h zt msc9( s;qms 2rlcle acts 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 :xl gyfd8:0m,u9mw kdgcz+td4(q,ae 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 spe9zd(o aye 44oued increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required torkn 3/4tj6d xy 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 tra.m n*ujjfr8c ,knw8)60mhc gjveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exertsn+vd+v+:7zia+ m exo,cjltq0 an average force of 110 N on the arrowv tz cad: 7mo+evqn++ x,0i+jl over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm whex9c tf;)hiqc 6n the ball is caught. What was the average force exertetx ;c)qchif6 9d by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor *lopy-ji-2vo6;;3 w nad + 4osjrzd wowill its minimum braking distance be increased, -d s j;3n6ov o4zdjrypwo+;- iwal 2*oassuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigator8 kc14i*/mi rvz5xh*.6je2rooyriut9vq e e5s measure a car’s skid mark to be 88 m l8i ve1e o oe*tkrv5i9.4m2 rqji/ *5xczh6yu rong. 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 kf07 q etl4xjhg9 j)n+bg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravx0 tbnh7e g9j4j +lf)qity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by + , cjddwne; 4wti*u0mg5q3aisomeone who does 80.0 J of work on it?45m iw qj0inaddu g;te *w,3c+ Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single;ovn(,xuc62 mujg) uzx1 bot( cable. Deu;oo,bt x(2cm u1v)(j z6ugxntermine
(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 cons:z r hx0)lqw;etant, k, of 440N/m How much must this spring be stretched to store 2wrqhl:x 0)z;e5 J of potential energy?    m

  A 7.0-kg monkey swings from u u:aev4q /4fzone branch to another 1.2 m higher. What is the change in potenue q4 z4auv:/ftial energy?    J

  By how much does the gravitational potential energy of a i aoh7xxgk,,s.-yv)vk/ f ie1 64-kg pole vaulter change if his center of mass rises about 4.0 m during vx/iosk,ik ,eh .xyfav)-7 1g the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it kih7no -wbi-(abu. mr,o -nn*strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant ob*hu7 -knrob(-o. ain in ,w-mf the spring?    N/m

  A 1.60-m tall person lifts a 2.1yfy ppac2f:,7a mzi 5.0-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative t 75 :.mp, ypzaafi2yfco
(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 e17 fvc0: x2zogck wuu07wi/ melevation of 1600 m and climbs to the top of a 3300-m peak. f7 :g21w ekxuu7/mzv0 0iwocc
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the spring 1-ly1- a9:p un xgm h9x1bjnmbis 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 :pn9xb nh1m1 lu-g9 jb1-xyam 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 a vine hap pq w0fj-aialr-e e4+yo;)5l nging vertically from a tall tr04ya lepefpao-w+) 5rl iq-j;ee 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 down a fr+hnuz 3uhw0q 8ictionless 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 f9ijx 7rk* jkmcd56ws4rictionless 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 kk.m64y dd)d dfyk+n8netic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her ce+).dn6k8kmdkyf 4 ddy nter 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 wkbbl)gh9cp bsuvvj 1;;cfxe 7)0e 5.jith a speed of 5cxb vu h ;ekel.vpf0bc1)b7j5 ;jg9)s.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 hlquhm0aamm9 -, 3do(), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg 0-mal mq3 ,o9humha (dball 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 frictio (:xvriymnk9*n 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 what minimum height h must yrvn( :x 9mi*kit be released?    r

A block of mass m is attached to the end of a spring (spring stiffness con4npz.y66xrn p stant k), Fig. 6–40. The block is given an initial displacement 6npyr zp6xn4. $x_0$ 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. Shh t2h59yc.hwq kjd5o)e is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness const d)5y q9jkhw othhc.25ant 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 in31oq 8dnvgbz *t* 1ipnxue)s3 Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calcuq ex)p*d zi*osn18 133bntvgulate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed oy 8f4 jh;yda7wf 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 plachp v3ym,/s/ szed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a heigh y,ms/p/3szhvt 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 of the elevator and passengers.

  A cyclist intends to cycle up a q+hw m8cs.mwl0z3 b/e7.8 $^{\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 travelnb 7xn a;h/w,fz.kl0c ing 95km/h in opposite directions, colnf7nl, /;w. zxbc0ah klide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reach i,b3k g0 u(ppw9ewtzmbz:wo90y:/b e es the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in thio ee/ :t(wb0z: p 0ib9z gu3kyp9wbmw,s process?    J

  A ski starts from rest and slid o60p2mp* qdd50c,tipp4 ri kwes down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped g ws vj o,fqnes5bx nv9z(0d o9jc7)a)7k xh)7from 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 a height of 2.0 m, and it bounces back to a height of eix6p fxb5 ks 8k- jwp+, jc y+.kg,pg(vsa(r:1.5 mwxf+je+ ,- cb asrskvp :j 6(5 (x,ikk8ygp.pg.
(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 acrn/ mokt szy3n3hd p6//oss a floor with a constant horizontal force of 350 N. For the first t3 hd63sn/n km//yoz p15 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 Fig. 6–41 passes point 1 with a spy du.+nvq bl)m()e-+iqjnu - xeed of If the average force of friction is equal to one-jnmx)+ l(iv bduqeq+uy)-n -.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 upward 18.0 j. b9tfm5rg . ge,0kgx$^{\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 blockuxnzc,6r*u q ,(sews - is firmly attached to a very light horizontal spring (k=180N/m) as showns, seqnwzxu, r-(u *c6 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 is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a ved+rd wf9k fqj+p ak11q/-f1op ry light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyondk1q 1qa +f k1rdppw /o+-jf9df its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spacepu;l*er,rd o (w0:xbr.m 01elc tmv.q shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 350me0m1(dx w p0:.or evl;ct *qb.lrur,0 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 motor to lift a 315-kg piano to a sixth8ibquztcb(l 8n. l 71y nlx5h1-story window 16llxbn 7l8i hzq5nycb18(u1 t..0 m above?    s

  If a car generates 18 hp .: q1olwei:aea 91 clnwhen traveling at a steady 88km/h what must be the average force exerted on the caqeiw eaon1l:l.:9a1cr due to friction and air resistance?    N

  A 1400-kg sports car accelerates c e(eui65jxfr5j7:3 m4m7vrt kes4tn from rest to 95km/h in 7.4 s. What is the average power 354ne:ikxt rj 67etec7 jvfs(mu r5m4delivered by the engine?$\approx$    hp

  (a) Show that one British horseq94vkg 96hb2 8bhbohwpower$ \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 unit :l r4b5v5gfvks are often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg carnfz6m3 1c7afc slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a cons7m1cna6 3zffc tant 75km/h.    hp

  How much work can a 3.0-hp motor do indczdv ca9; *,x 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s jxe *,gc:s yj)If this motion takes 1.5 s, wh y)scxj,eg:* jat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minutw 6hpp6 u2nok(e through a height of 3.60 m. What output rating (watts) should tn2op wu(k6 p6hhe pump motor have?    W

  During a workout, the footbnv4ttl tv )+9hall players at State U. ran up the stadium stairs in 6ttv vn4+ht)9 l6 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 t )oawp *ekk.j83mhuk*i7m2sa 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 czj+ s kyw :.mo avvfv);):kso2limb at a constant speed of 75km/h if the frictional fo;f:s)2kvy+o: kao)msv.z w v jrces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motwl)zqrl:e7 n* or 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.lzn7r wl:q)e* 45?    hp

  A bicyclist coasts down +j5yh ij auy:q51uo/n 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 buiv 4*zt1rzwwp-lt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If zw*z v-rw 1tp4the 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 +gn*i wu: qflb51 l py.3id8do10.0 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 required to fill all the lpdyw i1+ *iu l5 :gfq.b8dn3oshelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous ;xovvgt4+wa;2 6wkyj 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 gww kvaxt;+yo;jv 462 traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding wity1kgq ge.ye;ur0ujjh,l7(3h hout friction along the looped track shown in Fig. 6–39 is to remain on the trajl y,jhu 0.e kyhu1 gq7;g(r3eck 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 t 6tl. md1an8ud rm)t2from an aircraft without his parachute opening. He landed ad t2 t1 m.rm)n8ltd6uin 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 L whose othert8p3oidoy n dcd+xkb3)6h/c v1yzc+ ; end is fixed (Fic z 8nd+t)3cx;ob ok3ci+ yyhd p6vd1/g. 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. bh7ljb tj x8j)1o 1w4dThe climb is made in 5.0 h starting at 87l1wxtboj djhb)4 1 jan 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-kg0./c9 s2 ptacby xxgl8 elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can moq9pas1z 51m1if p xw(sve 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate tx1as (ws11 zp9f5 mpiqhe power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of p38bm8;gaevqptf fb8 1:p4w c 650kg/s and falls vertically 81 m before striking the turbine blad83ptgp;b 8f1 8wa vf bepqm4c:es. 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 loh(zt. 6cbej, td 3kle)7(hnn oop (Fig. 6–44), the difference in your apparent weight at the )n(eh bek6n 37.j t(lcozh ,dttop 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 bode od a )qg*2d8u5cgpr :m8wxq+y could convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=10gdc)xed85q qopagr:8um *+2 w00kJ)    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 alq2lee - uz ,o +6di5t4yqc aci1k4qq3t 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 bath*;xpg v omv:1kroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight ism:*gvp;kvox1 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, and swings -xg uy tj -6.oejfy+9sout over a lake (Fig. 6–45). He releases the rope when his velocity je9fu- + .gjyx-oy6t sis 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-z;,lw,rw( pif()edzzm m 02w tkg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power outfrd2 w(z0(zm,e,tw);zpml wi put was used to accomplish this feat?    W

  Some electric-power companies use water to store,*)dy9oq*hv blzw lv/ energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the enehz *b/9,lvlq)yd*v owrgy 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 spring stir 1f tdm*f37ogm*x c+z(7d hfuffness constant for each of the two resulting z1tmg3odfm7u*+7fcrfh d *(xsprings?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3wey9ysx0 fzq,5+4syl gz9( r dvu3yi*7 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h t-7zzy/1n i5jj.uv; za bc+n 6uou,skin 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fric zv57jzn n/zcbyu ;iu,61-u.kt j+ aostional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks onpyv j1l0pd1*b0e 2tyo an inclined treadmill (Fig. 6–46). Estimate jpe*yovd1p 01 lbty02the 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 rockkn/78j k-9ghm bq v4gr vertically upward a distance of 500 m, what was its velocity when it lef 7k9gmgq- br4vkn8hj/t 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 from a height of 2.0 ry co0ba o85-a6wpri/*nrvc,m at a rate of 95kg/s (a) If this water wheel is set up to provide electv-oro,i nb 8pycwa06*r c5a/ rricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s