In what ways is the word “work” as used in everyday language the s8f4x/rhe xzd0 ame as that defined in physics? In whatz xfh8rd/40e x ways is it different? Give examples of both.

Can a centripetal force ever do work c4o ,-lq hwxj*a 701ty7dp ivoon an object? Explain.

Can the normal force on v 3m909e-6+v:hoh)fdss qnep qqek;q an object ever do work? Explain.

A woman swimming upstream is not moving with n ny w/pm4w4:j llyqw,-06toerespect to the shore. Is she doing any work? If yl4, /wwy 4 ne:tmwl6p o0jn-qshe stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction f)yr0pk9o km4 worces always negative? [Hint: Consider what happens to the dishes when you pull a kkp49 )0 ryowmtablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you wy+dmlrd1z xb /bax14q3 2 3+oy1we ylare doing no woa/1m3d1wdq4x lbb +xr 3oy 1 eyw+ly2zrk?

You have two springs that are identical except that spring l is stigr*y7q 4l)nyat t mh5*ffer than springt n45ytlrqmy*g a h7*) 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 isa0d13enmf s2g f8tyt(tz/t (v free to slide on a frictionless surface (Fig.6-30). zgt0f2f (va(8t/1s y3d ntm etThe 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 7.dmh x:pmw;gmuch does your gravitational potential energy change when you jumpx:hwm;gmd 7.p as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of ac tefs23ap(j/.l iw2tte:q b q5;*vvy building, all with the same speed but with different launch an .se / tvcwvb 2ea tt2l*q;(q3:ij5pyfgles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point inddmn0su6s75o h: tvy4 two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest ang7o0tnu:symvhs 6 4 5ddle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tpc zw hwv l69g/y a.eoy22r)a-able. If you compress the spring by pressing down with y oza.e22r hwvay) lg9-cw/p6your 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 by a steel wire (Fig. 6–33). Tt+(cgz 2 zp;j 5nbj8dkhe instructor pulls the ball back and stang8zn(dpbtk5c +2zjj ;ds 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 potential energyf;c53w.mv: p cw2hvcg when water at the top of a waterfcvh2 c p35fcw:;wv. gmall falls to the pool below?

Describe the energy transformations when a child hops around on a pogz+*me)qtwa 1t o stick.

Describe the energy transformations that take place when a skier starts skdwb m31(1s-ix m(jpmiiing down a hill, but after a time is brought to rest by striking a s mj3wii1-mb1s(md (pxnowdrift.

A child on a sled (total mass m) starts from rest at the top of q ,7h7 b0 nsl-xq 9n,chfv*kdca hill of height h and slides down. Does the velocity at the bottom depend on thekhc7nslh0,bcq-fn, dv *x 9 q7 angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen, ff rei 3w60 *esq:s2 wx;:ghft/tgjc log in their path rather than stepping on top and jumping d erwsftqf2;s*x/: h tc 3:i,e06jfgw gown on the other side. Explain.

Two identical arrows, one whwg, ukis9s;i 3*u z vpjyo156ith 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 slower arrow? Ex 15z6 9,uy*;kwhgpi3 j vssuioplain.

Analyze the motion of a simple swinging)1a tyx* ytn5m pendulum in terms of energy, (a) ignoring friction, and (b) taking fricyy* a1 mt)ntx5tion into account. Explain why a grandfather clock has to be wound up.

When a “superball” is.+fl8 adta9be dropped, can it rebound to a height greater than its original height? d t.el9aab8f+Explain.

Suppose you lift a suitcas09hfj p a (.jdahy2a zsvoy/6/e from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the wei6 0a(z/a/y 2y apsj9dohhjf.vght of the suitcase?

Repeat Question 22 for the power needed r.ncfpt cat/ehaqmuy; v:5 -04ather than the work.

Why is it easier to climb a mountain via a zigzag trail than::*h qx. yv.a zseup;r to climb straight u.:x *r z.sphva q;ye:up?

Recall from Chapter 4, Example 4–14, that you can u mk9+sju1r7cu.dm2yy9su1m hkc. yt( se a pulley and ropes to decrease the force need d7 2ysm9.r9cmkmy us ( +.ukjy11thcued 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 concepts.

  How much work is done by the gravitational force when a 265-kg pile aws mjr - )pva4/.q0g.samah/driver falls 2.80 m? rjs/w). a.-4h0aa aqm/gmvps   J

  A 65.0-kg firefighter climbs su-w1 +7 b5xg*zwyqlu a flight of stairs 20.0 m high. How much work is requ1qsw*ugy xu- l+75zwbired?    J

  A 1300-N crate rests on the floor. How much work is rev57o oa9 t): :-tdkwp1ooh;q g1ho qobquired to move it at constant speed (a) 4.0 m along the floor against a friction forc1 oow7)5o;ooqo:ah-pbkq gt td19:vhe of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a o h3 3w/sxzmh5160-kg crate 10.3 m across a rough floor without ac hwoz/hxm35s3celeration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated bsw/:be o2 w*swu8aetd -l ;+gs4cc7m ky a force across a floor at a rate of for 7.0 s. Find the net work done on the box.-e7 k s/el8um;w*ob wt cs24ca+swg:d   J

  Eight books, each 4.3 cm thick with ma2cez;)po: xvass 1.7 kg, lie flat on a table. How much work is; op2x:vze)c a required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff u :xnaa-nv-4h8h )d nfobjects we might not otherwise be able to liff. Show that the ratio of output va h)au-nn:8- 4fxd hnforce, $F_{\mathrm{O}}$, 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 anb rd o k+7rclcgo, sdwksv:kxo42*k cb6y878.d is kept from accelerating by a man who is pushing back on it parallel to the i rv, rwc k .k:6cc+b47dsk2xoo*7b88l dksogyncline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helico/(w/ 9p6wxppr vvr -vzpter of mass M an acceleration of 0.10 g upwa pv9v / /6x-vpprwwzr(rd.    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 linesh6( zc9ow8195t adjnfjt +c7sfbq:tar 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 axr ije44 ry5+uuv42o yjis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to r+ j4oyi 4ej yru4u25vx = 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 theh1owixvu. /t6n n,f7q $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, wit)n/) 2 qp( :biaeaz+-93as ns9inpwhg bn* femh 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 a)9 0gymmty cfwm1sv0 ) (5ddckrrow is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electron 84lpi46jf tqj $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kgc)8c:r*w l:j tdz)m2pixmi5 r ( /l)ao,pn glxaar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force b;6 x (4iwq+fr1bfqxvof 110 N on the arrow over a distance of 78 cm. What is the speed of the bf1qxqbv;iw 6rf4 x+( arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwar y6g)6dpj4q:l4a6sha a wlif 7d 25 cm when the ball is caught. What was the average force exert 4dl7fwshgj 6 ):i46 laqyapa6ed by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its miniep2en 7k ljc*uk)*jxt . 2px)hmum braking distance be increased, assuming all else is the same? Ignore th.uk**) xt j2xh2ppcelej)k7ne driver’s reaction time.

  At an accident scene onc7q vupw a)f,9 a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinq7 wfpav, uc)9etic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time i/ qxvsun,(w4pg7; a51p to fftt reaches the plate, it mx/(wgaqontfp5 t 4 1 spvfu7,;ay have slowed by 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 go if thrown straight up by someone who does nr414u; .a+ x/cb j - lmugouni0a7khp80.0 J of work on it? Neglect air resistancu hlapk0/gau -o14u7 b;4 ij crxnmn.+e.    m

  A 285-kg load is lifted 22.0 m vert hsd6 *4lg;fvkically with an acceleration by a single cable. Dv6gfhk*;s dl4etermine
(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 springqn6x my.3y- uz stiffness constant, k, of 440N/m How much must this spring be stretched to store 25 y mn-3quxyz6. J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.fuqs ;o8rj-r;2 m higher. What is the change in potenso;u8-;r rqjftial energy?    J

  By how much does the gravitational potro;9)n4d+jz wzp +fzh bp31mxential energy of a 64-kg pole vaulter change if his center w1o+zrdfpn h z ;x+m4 j3)z9pbof mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a ho -yb/,q:q4avnl )fjcrrizontal surface has speed v = 65 km/h when it strikes a horizontal coyc fn :alq)rjbq/, -4viled 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 2.10-8za 30pw /j,15qwu w z)xm7f ukebetx1kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relaex0fz5kmww1e) u 1b ,tw37 xp /juzqa8tive 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 of 1600 m and cimic 4509ecdl.q sul8e ,0ipglimbs to the top of a 3300-m peak.cmu5cl.s 4,ql 8 giii00ed9 pe
(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 sprinw *jq39x a,i*abqa.v lg is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the ena 9w**li,qabq a v3xj.d of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top sph(e.wwis;sd ; e.n-d ieed (5.3m/s) and grabs a vine hanging vertdi.ehss; ;wi -n(edw .ically 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, start2qk). s3fya ihing from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionr8-hnc g3v6 yeless 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 kineticgil;0lcv (er*iz ,gb2 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 center of mass 2.10 m an2(;*egc 0lzbl vii,gr d cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from yz n/ezq 3a st*:/ibh(the top of a platform with a speed of 5.0 m/s. (:/*a/hizy3e qzsb (nt $\alpha)$ 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 (ik,lw 3** gtqftg4z8v bgnore its mass), 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 tq38k gv* w*4z,lbtgfto 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 witi, s6hyb y,x0j p db/v5x9fc-chout 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), syhdcyx v-09 6/p5,cbf, ixbjfrom what minimum height h must it be released?    r

A block of mass m is attached to the enjjn a+/zgz-m017; za ccz9 ehmd of a spring (spring stiffness constant k), Fig. 6–40. The block is z mczz1;/ c-09 7hma jejang+zgiven 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 jump v7qx ,ob)wlp(s from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calcu(px7w,oqvb )llate 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 g9a1k-i lyas( y9f/.sf7 tzmjit is rel z( akij7s99lfymy /.fs- gta1eased 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 antj j*/g7ooemvcyg-jo6i5 8n0 e be;s 6k53iva 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 nk2)n+mofm8bi,yij1m i5l s- 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 sprin,l js18biof)n5i-ymmm + in2kg 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 cg/ 15m6ol(qn/oen wdup a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in 4;gwq hrgp9mls)780m)gd bxq opposite directions, collide hgb ghg)x7qd )mlrws pq; m8094ead-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 reaches the bot8do nesc g3t (dh yk1bt.8jo42bb7o,6uks6kr tom with a speed of 2.2m/s How much thermal energy due to friction was gener3jkk(ys7debt 8b8d61tg 62ouc nos4krbh. o ,ated in this process?    J

  A ski starts from rest an.7x :u 1medwoh6f1y tvd slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped e**9lqvwyui- -) i 6zpgxm -x(zv5 czzfrom 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 ahxsiv.7jy*omq i8 ns/aw)v /1 height of 2.0 m, and it bounces back to a height of 1.5 m.s) s.*7w va/mhji8 ivqn1 x/yo
(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, starh. im1fdwh+w)j t0mi0ting from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final w)jh.m iwt00if d+hm1speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If thecd;5+ a tgn-z()kdbyv ave gn)(d ktz c;-b5y+dvarage force of friction is equal 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 stsbr crm 9 sr(ut/h,h7wop3 jmk4k 2n;,eady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is fupl/g1eh74g xom4pw*t n ,2fgirmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that t/ 2wmnt 4f,p1u4ho pg*gx7egl he 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 very light horizont 7v: kg xpbgsg4x24qy*al 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 sprg7 bxgyvsgx4 *q42 p:king 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 ap)x z ;q3a.ajr “glider” (mass of 980 kg including pilot) that was launched hoar3aq; p)xj.zrizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story hes lc b27f-2cku0 hm0window 16.0 m abovecsleh- mbhck07u0 2f2 ?    s

  If a car generates 18 hp when trav36(x .b8rj( mwrohuxieling at a steady 88km/h what must be the average force exerted6i jw(xhb3r.( umx r8o on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95kq8wbxl3ieo2+,r(hgmp ekl*4m/h in 7.4 s. What is the average power delive+qlo rim(4bx8,2kp*gel h w3ered by the engine?$\approx$    hp

  (a) Show that one British h mmc4e*e xcj /3wr59x- w3 ;npbtd4pzjorsepower$ \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-hocrtf72c:c/ 9wm6pd x hurs.”
(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 b1b4i6wx, xzess-g ) w5 htl0t65km/h in about 6.0 s on the level when it is inbtl 10wxxgt5 es6i wb )s4,-hz 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 3y1uq/r.7- 0pemjn k(av +vbfsea( z8k.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.:/fb:qr,+z trg o61bdpsy x a+3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average/d by:sot1x6rfz+b +g , :apqr power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of y:x)0sysp vfq /z5 u4c3.60 m. What output rating (watts) vy5p yzs)fx :/4cq0su should the pump motor have?    W

  During a workout, the football players at State U. ran up the stqjw ;.4*e kc;.y kyosy5q1yfv adium stairs in 66 s. The stairs are 140 m lo j.yykyk f4cqwvs.qeo5;*1y;ng 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 climb42lwucl9ja3+uzx0ch z6/y a n 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)kl)7w4w uwddk- p)ioz+zt 6 r 120 hp. How steep a hill can it climb at a contw+prwlz7 ) d kzu)4w )d-6oikstant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be ;+wwdxehr7p.mval(* +h3q (z3jw v xlable to drag a 310-kg box along a level floor at a speed of 1.2m/s if t3d+xleww* 7h;ha(pwz.r q (xmlj+v v3he coefficient of friction is 0.45?    hp

  A bicyclist coasts down a rpz,ngff : j.+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/(zeq1wpk4l xt5(o1 ky8ln6k f h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical dan 1txl fp8(kk6 wk45o1qy( zelmage 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;d obedss4 u*) is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, an;4 ud)ebds *osd 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. 6–42) in the 1936 Ols;9dzn rytht 3a -s/.h,w*7ylnzql/j ympics shows that his center of mass rose 1.1 m from launch point to the top of the al.w9ayn st3 z ,r;yhls/7* zdtjnh q-/rc. 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 along the looped track sh o.2wk6olnx5 down in Fig. 6–39 is to remain on the track at all times, ex5wl.kd 62no oven 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 aircrak -1,p7snciqaft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s massik7apsn 1 ,-qc 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 Ljcxb i)xf1a+ 44omj2e whose other end is fixed (Fig. 6–) +bjmaj44fc ix 2x1oe43).
(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 made in sfhk )wp)vn36beh m.55.0 h sth kv)wmnspb.h)56e 3f arting 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 is cy,wuw2cu-2hyl;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 d99vu.xc gubo y 4xj70 yd/8ghin California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.9u/do9b4 x0 vyxcuyg8 hdj.7g$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81v:i84u;6mhiumi :huul t/r,v m before striking the u,mt6 vuli/hu;mv:iu84ihr :turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. r8lbz19qni2p 2l+zz a 8(taki6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go thrbz(9 28ti2 il1alz+qapr znk8ough it.    mg

  (a) If the human body could convert a candy bar directly into work, how+lc, :2* kdi(gyqef/r namf/b+gmw+ z high could an 82-kg man climb /(fa b2+rcemnqz g dyw+ /*+flkm,g: ia ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwardv6;uqrs:g,ee fz4ksp;uu) 1 ab )( hic angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the *: s 4g 42qb.mft jek1mij co:mj)yw0kscale 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, what doy jg:t.4mk w sm 4k0cio)q1:*jmfbej2es the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope(m od5ru a3u9lzyj: ;o( disr7m:q)ab, and swings out over a lake (Fig. 6–45). He releases the rope wh zaj dq r)3d;oo5y: a7u9( blm(:rimsuen 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 athy/iwz* ncw sehwo9 00u 26,mldlete climbs a vertical distance of 5.0 m in 9.0 s. What minimumel2c/0mw i d,hyzow wu6*n0s9 power output was used to accomplish this feat?    W

  Some electric-power v abcbiuo(/d/-p2 ,hucompanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy proc//vb aud,ih (-2pbouduced 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. W4gk 5sf megr +wvu6;3chat is the spring stiffness constant for each of the twm+ fkw;vcg5s ueg 3r46o resulting springs?   k

  A 6.0-kg block is pushed 8.oi wa,ln -ku r g03ld)b(nprep+o dxbe557)/ m0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, ho8fsskz9;7i w pw long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and;s7fz9wspi8k neglect frictional losses.    s

  In a common test for cardiac function (the “stress tnjf2oh e:6 0 pqzr(342vpskp hest”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill ishpf z240:(jpvs2okrhp 6q3 en 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 x1iax kp7akbl ,pwls 4;ja..,rock vertically upward a distance of 500 m, what was its velocity when it left thej1a lskpwpa.;,kba,xx4. i 7l 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 waq3bqfhw f5 h;g/rc*ma/ yf-( heel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide elf fh/f3*yahabr(;cqmq5 -g/ wectricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s