In what ways is the word “wo/lo gu 5 qy40 avcp.wb::h8wayrk” as used in everyday language the same as that defined in physics? In what ways is it different? Give exampy aa/0yhbg45l8.wqu :c:wvoples of both.

Can a centripetal force ever dojefg-r;-k6qdp0vh5 b work on an object? Explain.

Can the normal force gik.nk) 4 pw9*cj/3, d+kjasrrghc e)on an object ever do work? Explain.

A woman swimming upstream is not moving wsmpt )a0z ef3l1k5 yry+t n,h,ith respect to the shore. Is she doing any work? If she stops swimming and merely mt)eyzt lsk f5ny ,1a+3,0rhp floats, is work done on her?

Is the work done by kinetic friction forces7(vax2q)skho,xsk 3whs 0 gn3 always negative? [Hint: Consider what happens to the dishes when you pusv)k 0x,s(q n7ahxhgo3 3skw2 ll a tablecloth out from under them.]

Why is it tiring to push hard against a sp6x r;9,m ebjcolid wall even though you are doing no wor,j9r;be px6m ck?

You have two springs that are identical excepjmwcw:t0sn 03po,+ nckx) gj+a+um8z t that spring l is stiffer than springgnwz0pj ckmo :ts+3, ) u+0+cnamxjw8 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 mj9g .ns49htsslide on a frictionless surface 9s4s9.gj mhtn (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how makxv q,yx :*4xuch does your gravitational potential energy change when you jump as hyqx,x v:*k 4xaigh as you can?

In Fig. 6–31, water balloons are tossed from the 2g-mj p 6fpcb;roof of a building, all with the same speed but with different launch angles. Which one ha-c;pmj2b6 gf ps the highest speed on impact? Ignore air resistance.

A pendulum is launched fr(d; dw aw+1 /nu l1gyooc;7bilom 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 the second launch it is directed downw u cad1gy7lw1;dobw; (/loi+nard 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 comqiuv*q lbn0l .c-.q2wpress the spring by pressing down2.0*i l u-nbcqvlqqw. with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling br-i8 lj6ou7vq y a steel wire (Fig. 6–33). The instructor pulls the ball back and standvjlqi87 o-6rus 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 gravitational potet321 s6jvl xbkntial energy when water at the top of a waterfall f3b k ts6xlvj12alls to the pool below?

Describe the energy transformations when a ce2u73l+ba+4w iaou nkhild hops around on a pogo stick.

Describe the energy transformations that take plvjynusx uq,l k;3. 2v1ace when a skier starts skiing down a hill, but aft.j n,qlu1vxuvk;s y23er a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) st5l 94h(xtk 7igbkd p)pr7z9d ejct() carts from rest at the top of a hill of height h an)t7ztcbpxdgcekj 9 ih(d49) p(kr7 l5d 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 (b) there is friction (deep snow)?

Seasoned hikers prefer xqh0n:9w mv)u to step over a fallen log in their path rather than stepping on top and jumping down nu)vh9mqxw :0 on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are 1yx l6vxzi +r1fired into a bale of hay. Assuming the hay exerts a constant fr1+ i6yvlrz1 xxictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energv s .y,fk7vpl-ptaac0 m/yg8 ) vzs43qnh2k3p y, (a) ignoring frictnz4k/ q,pf)tm.yghvspvpy2kl30c87a v -a 3sion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its orig )f6)/y lewcadin e6/)wcd)lf ayal height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do 9hyfcd-1-panu aic: 5on 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) the weight of th n ccd-fp1aa5i:h-9uye suitcase?

Repeat Question 22 for the power needed rather than the work.sm7 +ez9g umr h9/nf9yn1h -wu

Why is it easier to climb a mountain via a wvs ry qi( 7nbvr*) qk508jhln8k)m9wzigzag trail than to climb straight u()wk90 m jvih8q w 8r*s l)yr7k5qbnvnp?

Recall from Chapter 4, Ex bxi mk;sx9h;;+z */ildn hoo+ample 4–14, that 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 the load is raised, how much rope must be pulled up? Account for this, using energy; oo*hb i;/i9;n+dxlkh xz+ms concepts.

  How much work is done by the gra)x7gsvrb7m -rvitational force when a 265-kg pile driver falls 2.80 m? 77mx-rsvg)rb    J

  A 65.0-kg firefighter climbs ay4gpq-b,y4raz **e8knwu3kjhl* gc/ p4 z1f n flight of stairs 20.0 m high. How much work is require3y gz4fghq 4*wkayzrn 4be-n1*pcj,l */8ukpd?    J

  A 1300-N crate rests on the floor. How much work is ref7;nxgx; (z 3m2hq xxequired to move it at constant speed (a) 4.0 m along the floor against a fmz xe;x37qhxg( nf 2x;riction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 1 mx: ig89kdim)5mw)s c60-kg crate 10.3 m across a rou8)9mdc)i gks mxwm:5igh floor without acceleration, 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 a rate ofpdsw drzas((xs/4 (+n for 7.0 zxdd(rs s/+n(sw p4( as. Find the net work done on the box.   J

  Eight books, each 4.3 cu,1i i4 l)huyrh ) av jaby2yno/1 hw1fct)g97m thick with mass 1.7 kg, lie flat on a table. How much work is required to stack them ohjc1 i)y/auf ur9 7h) b aoy21ngwi,v14ty)lhne on top of another?    J

A lever such as that shown in Fig. 6-35 07 lyv 6vycbo+cioor(1iw /b* can be used to liff objects we might not otherwise be able to liff. Show that the ratio of o lrvw*+ ibvyoc(c/iy07o 1b 6output 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 oj,2s 4zc)pzka 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic f z2kj)4zos c,priction 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 cdn. 2;u cr8ima helicopter of mass M an acceleration of 0.10 .;cni8mr2 du cg 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 thge l0xt t9y07ye 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 : 2avxi,uga c1 bw)3* 0zrxeg dg:gz3jalong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to )abec,gxxv:31j2*gr gid : z u0g za3wx = 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 p.cjvye9,,; namwc5gm 9yfaz 5 *(yaagarticle 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 w* ln27j9mt9m ct3ph3eakza 0 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 incr en,q; cnod82ieased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elec vkf0vh6 31aqttron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105k hfnw4b.ausei;e )ft54vrk+* m/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose one458t bvabpu y++ m2string exerts an average force of 110 N onv 8 y2mbna+to+5e p4ub the arrow 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 whenkwm::1mr3j*aj mr( bb the ba(mw :jbrma* mj1 :bkr3ll is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 5 :9h6jxk1vqy;sjl*iwdw 9h c *0%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reacchw9hq: i9*d; 1 j*wls y6jxkvtion time.

  At an accident scene on a level road, investigators measur vn +9zvt;6le.t*y b.ci kw*jwe a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was esvj.wz9*kb +*wl in6.tvyc ;tetimated 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 pitch*c sgb:1 .5 d tgnlyo1pr0mqj*ed at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the averqby 1o 5dp:*.0r1 gt*jscgmnlage 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 someone w*8.u (pnzd gpjho does 80.0 J of work ondpgujzn 8p* (. it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically wit1f9 v-)rqjp o,eyop9mh an acceleration by a single cable. Det m -o919ejqp,ofp y)rvermine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must -o/wk rmzovo 1og)lg, mu27t/tvtu-8this spring be stretched to store 25 J of poten owg1-,)m2o7mt8 zouog/r - t luv/tkvtial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hitz,bb(3 u fi s 9tpii,8yll:be)7mk2vgher. What is the change in potentia( fy ) 9kb,l: t2 iestv,z73ii8bmupbll energy?    J

  By how much does the gravitag ii,rz z/)ks.tional potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump? ii) k/z.sr,zg    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whai.1i/ zk-pj den it strikes a horizo-. zipj1da k/intal coiled spring and is 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 x3cw6igb m:qfk k,cl , -/:hq5wg0ynl *kk+odbook from the ground so it is 2.20 m above the ground. What is the potential energy of the klkqd w*gx6kb+cnl:cg iw:,mhyok50-/ f , q3 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 el cy 22dz-o(p dyi0v 2c*phefb5evation of 1600 m and climbs to the top of a 3300-m p b2522 zd(fopp -cedy *yi0chveak.
(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 f0bpvj6;dzk7 8rx+ur/m hangs vertically 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 v7+;br86 dzujr pxkf0 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 spi e)qo *xrz)fm4/97.mpkjr- jdlw)npeed (5.3m/s) and grabs a vine hangingm jf p 4.okzinqrm)w9/l*rpd )e)x -7j 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 w(utfkw1)uv+,b qn + ndown 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 shovet6de k)z8b7rfc -x4w j up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into grav)lfnuckrq+ss- l -2 9zjatt9*itational potential energy without 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/skcrtlzaq+ j n2flu9)-- s9t* s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platf)e/z 7d- h lh1)iv/hvplt*ras j3za -gorm with a )rh gz)h7hv*/ai3-jdlszl -1 tva e/p speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spripuak y q58ly9 j6oe 1h6:-xvchng stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward sp1y :vk 8xho-jcua6qy9h p65el eed 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 slid t4o e28jekde3es without friction along the looped track shown in Fig. 6–39. If the block is toee4e 32 ok8tdj remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring 8l)xm fvfxc-s2*kx-b ec*; p y(spring stiffness constant k), Fig.pekc-b* 8sxmf )f-cv; yxx* 2l 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord who+iapbc2 t;l:xd hq* sj +dv7*zse unstretched length is 12 m, pt q 7a+ld*z2c:jv*;s+i bxdh and falls 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 pointog(rhk35d v* j 1 where it is released (*5kdhr ogvj3 from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of 3so7ql5 l2q :ez3 $^{\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 spriy0rb x6(slad 1ng 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 acceleration of no more than 5.0 g when brought to rest. Let M be the total 0bdsylar x(61mass of the elevator and passengers.

  A cyclist intends to cycle up a 7*wn7m a4(xzf dod dspd 09:xish)xg11.8 $^{\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 79 7yf, wm 9bjqch29qqt650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produ ft h,7qq2wmcb99j 9qyced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and b o 32tbukc2;r 7ca)v0rdq +glreaches the bottom with a speed of klc7d va3g)r2c0brobu+t2;q2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and s2eef v30c5tlzlides 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 from a tree 13.0 *qwz l9nxu7p+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 heightz y.dg7*5 qsjg m4nqru9 p9q1y of 1.5 m. 9q *9d up1.5zqgqrn y4 j7smgy
(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 constantzd2ke, x:m+5 zy-folb horizontal force of 350 N. For the fir k:fx 2-+,delzobm5zy st 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a su j-/*.p gyzrkavw4)kpeed of If the average force of friction is e- .g) *rz k/upjavwyk4qual 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 upw2ut p:a ,k, dg,kxc/wh4bf+gjard 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 light horizonr-.7 sauhyp8xtal 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 befh ua.-y8x pr7sore stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sprinp0 y cy.mmn1 oi30eo.sg, Fig. 6– pmm. e3s coni010yy.o40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inc 9.j0x wzgwtg(r4-dpbpvfhb+:xti7 8luding pilot) that was launched horizontally at 500km/h from a height of 3500 7tbx.itpgdzw4fb v r(jg9 8w - :p+xh0m. 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 n fw3rlo4a1mbei,; 7n rl83pwlift a 315-kg piano to a sixth-story window 1,;1mpfw 8n3la b3ro7ei nwr4l 6.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km ,8r jst/rh6+z,giby j.5jxdb/h what must be the average force exerted on the car due to friction and air resistance?trbjdrjz ,b, 5isx. yj68g+h/    N

  A 1400-kg sports car accelerates from rest to 95km/h in cwp.h rv4f*q 3zh mp7v gij 1z)7g(w-o7.4 s. What is the average poq*-fjw4z77prvcph(3 o imgz h.1 gw )vwer delivered by the engine?$\approx$    hp

  (a) Show that one British ;og2*-8 hb li vbo+zvvhorsepower$ \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 thex+/hm+v t ob*q: b,(t2dnrr)e; cnczmedu ) 6m 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 car slows s:1eqxouh ngi../y1*hl m,mo down from to 65km/h in about 6.0 s on the level when it i 1n:x geo/.islo* hm 1.,quymhs in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-)nxf 4 xf.,vzlhp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m5)z).is vscq w/s If this motion takes 1.5 s, what average power w. qc)w s)iszv5as developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 mz,m p5 u(c,v 3uvzg;qt(cxk5 u. What out 3zugqzv(uc; pvu(t ,m,xc5k5put rating (watts) should the pump motor have?    W

  During a workout, the footbam r57xi9k5ag.2 s m)k8y wsqezll players at State U. ran up the stadium stairs in 66 s. The stairs are 1y.wzk a7i5ksxrmq)8 5ges9 m240 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 clim cp/c ncf -go/p5u2xv7b 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 h3 (ad.vl ue1pa hill can it climb pah1 dev3. (luat a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dra jyn vp.3q;7-cfvzzgd1*pu .a g a 310-kg box along a level floor at a spee7vqp.j ; *adunc 3g1y-zp fz.vd of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downkx vb0c(-2oo kbj.k+fdb6hm( c yh:*y a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) jo20i nsoai4sylo( 98a.:mzy bumpers” that are designed to compress ami. aa0ojzs9o :yy4o sin28l( nd rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and 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 jh.c /a7h/(mg0fcchy cm off the ground, and the remaining four shelves are each spaced 30.0 cm acc 0h7j (.ahym /ghf/cbove the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6– xujui2sh2)i1dyf ;1u 42) in the 1936 Olympics shows that his center of mass rose 1.1 m from 2 1 ifiuxjyu;su d)2h1launch 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 the arc?   m/s

  The block of mass m sliding without friction alo l b+.ya2w0bwwng the looped track shown in Fig. 6–39 is to remain on the track at all times, eb0a. wb2yw+w lven 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 aircraft without his iqb 1gww y8j1;parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only min;gw8wi1b1qyj or 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 h 6jgf+ljps;3 xorizontal cord of length L whose other end is fixed (Fig. 6–s l6+x;jgfpj343).
(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 37ur f4t9yu* uh 46mqtkzdq. q2000-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Ca f0q9kq2d*tur6h .yutm4u 4zqlculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge sprinm0s iy7syup)/ej; p q+g ($k=2.2\times10^{5} \mathrm{N/m}$) 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 claim5s4 hb*+z5fpu j .dfkdby13fds that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the powed z+ 53pfub y51.jbdf4ks fd*hr needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the ratek9ayggc rn/(4*9j cq v of 650kg/s and falls vertically 81 m before striking the turb/4(kcva 9 y qrggcn*9jine 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 loops dr2ss-uq pzj1 /u54b (Fig. 6–44), the difference in your apparent weight at the top of the circular lo-s/1u u qjssbzp54d r2op and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into wkj/,ye1u aet8 vn7+ubork, how high could an 82-kg man climb a ladder if 1jeenkav8+tuu/yb7, 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 upwwd.0:8 tbfw68ar ,pvd z4xuqmard 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 bawyvg,y*(xse+ uai h 23throom scale, the spring inside the scale compresses 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, wh +g2xu*aye (v3s iy,hwat 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 8kia*ab lx/4i. 6–45). He releases the rope wh/4kial ba xi*8en 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 athleter.v:vsqs wy au/ rrhfrnj( z;9r, ;g-( climbs a vertical distance of 5.0 m in 9.0 s. What minimum pow; gruf-z9rwn /( rq: hvsr.ryv(a; ,jser output was used to accomplish this feat?    W

  Some electric-power companies use water to store energd+gsk od4ea v//m1w+cs8 ,fjiy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To stords v4+8fe+,caowi/k 1 dgsjm/e 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 sti:rwnd47 dqrk6ffness constant k is cut in half. What is the spring stiffness constant for each of the two resk ddwr7 q:rn64ulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougr9j6a8 feq.oyh 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/h to 55km6h nw8r:i mtbp:5z,ya/h in 3.2 s, how long will it take to accelbpn irat5m:6zh:y, w8 erate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac b8(e5qf7 wx kkfunction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estq5(f8 wk7bxekimate 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-k0t btkv uq(k7)g rock vertically upward a distance of 500 m, what was its velocik7t 0u(k )tbvqty when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (+ib s9aaa,dfxoo9h. 6a) If this water wheel is set up to provide ele.hba6od+ia s ,a 9f9xoctricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s