In what ways is the word “work” as used in everydal e oe6d--bqp.mf6 6zpy language the same as that defined in physics? Inm -ep.bzq6-6epfldo6 what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object bjm1y0 q;zld/? Explain.

Can the normal force on an object ever do work? Explain2 xvl ptpy/7s ia9vn0 txt1igc: 7.z3j.

A woman swimming upstream is not ;725ordztp*wmp-g hq moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done o; -r*phpotm7 5qzgwd2n her?

Is the work done by kinetic friction forces alu0upk3nkt13x pqer 4k:v;0 lmways negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under them kn :x4qklv33 0r 0umpep1;ktu.]

Why is it tiring to push hard agai hfvli)o+.at7p 4 u(ytnst a solid wall even though you are doing no woi 7h.tlo +tp 4)(uyvafrk?

You have two springs that are identical ex)u ;u r,hsx0czcept that spring l is stiffer than spr) 0u, rz;xushcing 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 horizontal0u+r (ou- kkxri:7luyhnby90 force on a block that is free to slide on a fr0k+7y bu0 -lurkru:(nx h9o yiictionless surface (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 much ( pt-z u10b)gx slya2zdoes your gravitational potential energy change when you jump as high as you ca1zb t(y 0sp2la)-xug zn?

In Fig. 6–31, water balloons are tossed from the roof of a building,6 jjxmx;y9hmp i+ .t8e all with the same 8.+ij6yxm; p eh9xjmt speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that bqj.d wp-dd6/ se i*wl;v)f9yis 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 pen./v)df*wed j b 96s;y diplq-wdulum 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 angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compre6ah(pt)a w8 iess the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservationi8ht6w paa (e) of energy.

A bowling ball is hung from the ceiling by a steel wire (Fi2n+klwcf5srnew t/ 87 g. 6–33). The instructor pulls the ball back r8tk2wlfn n5ew c7s/+and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when was6wd d/ hw)y3tter at the top of a waterfall falls 3dhd ww/)ts6y to the pool below?

Describe the energy transformations when a child hops around on a pogo stn:qk4p/ lxfe/etz.z /c3.eq jick.

Describe the energy transformations thaxeqzw ,k)g c0,t take place when a skier starts skiing down a hill, but after a time is brought to rest by strez c 0x,wq),kgiking a snowdrift.

A child on a sled (total mass m) starts from rest at tow0a7.s/grba31*misg9u tzy he top of a hill of height h and slides down. D97g 0 gmb.w *suzi t1yar/3oasoes 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 to step over a fallen 27w+dt namsr. log in their path rather than stepping on top and jumping down on thet7w n 2m.dr+as other side. Explain.

Two identical arrows, one with twdc0 yl(7kid)juyo 6.agrx0f.ice 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 0o .f 7(ax.ujyky0gcilr)d 6d? Explain.

Analyze the motion of a simple swiq5 hke2 ft .xe, q)s3rp0s di+40kdnssnging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be woudd s ne.f2 iq50 ,+sh3)ktqxsp4r 0seknd up.

When a “superball” is dropped, can it rebound to a height greater than its orign/ f+otoa w(*cokb1 3q x9i/4i (6rskqx pkh,oinal height? Explah wx(1qc /ox f6i3aot*o /rk p9ko(s4knqb,+iin.

Suppose you lift a suitcase from the floor to a table. Tlqe o ak(dn97 -wni1fauf/a ,9he 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 tq7/aa ifak1eo ,nd (ln9uf- w9he table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather thjdjl( dfy lukda h/ :9,xv;77lan the work.

Why is it easier to climb a mountain via a zigzag traxe7q5pv1k,eil (7xq i il than to climb straight up?57 q, 1 7qiik(xexlepv

Recall from Chapter 4, Example 4–1fcp9cv4 za.) j4, 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 concepts.c z9p.jvc)f4 a

  How much work is done by the gravitational qtzl vm:jpwv490+ 7r7gi5jmb force when a 265-kg pile driver falls 7 wbv+90vq l5tpg 4mjzrmj:i7 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairp;2 glszx.q /wdhwd -5s 20.0 m high. How much work is requgx5 w w2/ddqz-s l.;hpired?    J

  A 1300-N crate rests on the floor. How much work isjk)v 5oyr7p6(k3 sgle required to move it at constant speed (a) 4.0 m along the floor againok) jy5g73 p6rs(elk vst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1 zh9oe2e iyx,*i4c-tu0.3 m across a rough floor without acceleration, if the effective coeff42-,x*o iizehcte y9uicient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at ae d5w0 yswr38ri*v:ug rate of for 7.0 s. Find the net work done on the boxe*5udri:w80gws3 yvr.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat onma c:y32 wx:t erupcc ..e*lp)) hngu- a table. How much work is required to stack them one on top of anot*-).cclyp w:p)u exna3c urh.t :2mg eher?    J

A lever such as that shown in Fig. 6-35 cag 4+.) sf/g1s vxvfvrun be used to liff objects we might not otherwise be ab)vu/f+srg 1.x4s vg fvle 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 kept from accelemcb--iit r w(b9tm,4f rating by a man who is pushin rct9iwm t4m(b-- bi,fg back on it parallel to the incline (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 helicopter of mass M an acu olw,l )(c58y pmpavu 4fkucp2.k.l7celeration of 0.1lkm8lv ,c7l4k fpc )o2 upy(pu. .u5aw0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axium 2, mzu1,wa l (ykjvg,6xiuua:j,w( s 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, varies as shown in Fig. 6–37vye 6 hu, kq1g69itdmz4jzz4*. Determine the work dhdt6g9 v 1 qy6kzeu*z,m4ji4zone 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 8ur- p,8gax hdparticle 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 molecule, wit+c fa 26nqyqfg: 1n;lah 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 ilnn e97hxm94 bo;ptr+ ncreased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stou2 60esmi2l0 (encqmrp 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 1tk38 ).tybntldy ub2ki 7awk)imu*9 done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string e6xmn8s y,dwo) xerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as i8x 6,w)osn ymdt leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward pq t yah*a390si3-tb ys0n rc,25 cm when the ball is caught. What was the average forc0bq ntyt3 ,0i9*ars-apy chs 3e exerted by the ball on the glove?    N

If the speed of a car is incr n1,vddg rsly:a :yi/q 4x7-zueased by 50%, by what factor will its minimum braking distance be increased, assumin: /7au1r dgy-q, n:i ysxlvd4zg all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s sk6/m:gy2* mxe uogn5naid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’5* 2 gu/amgexmo:y6nns mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at xeb(vpeb 57 +l By the time it reaches the plate, it may have slo7pe+x le v5(bbwed 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 sf-a b5(. km0a,gs*kw pxzi y.80.0 J of work on i (xz mwa.ksi0pfb*y,ks-5ga.t? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cag.f 6 sin 6v6ash88kbs7ei,ahble. Det6s8 g.ibh8vk ,is667aae n sfhermine
(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, r 9hd e zxr;pyx09bfc04l7.ao k, of 440N/m How much must this spring be stretched to store 25 J of pox0dby;.p rxzo r99ela0hf c47 tential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thb- qpc( u5skt*h p:tn7e change5ucs(btqp*h n ktp7-: in potential energy?    J

  By how much does the gravitational potentialns8,/vn18xm25t7fpkze adjm1 do ;yp energy of a 64-kg pole vaulter change if his center of mass /8f1 8mnvmd7sn;jkey ptzp d,1ax5 o2 rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizrxtm zo-qc;.ps3e j2bo3q5a1 ontal surface has speed v = 65 km/h when it strikes a horiz 3pt1;3-rq ms5qeo. jza x2bcoontal 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 book from the ground so it is 2.20 m amlbbh e2 / qc96exeum, +e+ei8bove the ground. What is the potential energy of the book relative t xbcmeu+e,mlee+ /h i86b9qe 2o
(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 ac38ucij8a/- n coue k:nd climbs to the top of a 3300-m peak. o unc88c jieca:k3/u-
(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 ruleo q.q1r v7umr7r. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached t.u rrom1vqq77o the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed jic* 0sn a4b+5g2 )5wxcljl ed,h9nj y(5.3m/s) and grabs a vine hanging vertically from a *j j +9ae 0l2ln)cjcghnx,y45dsib 5w 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 down a frictir.8kce ffoj 73onless 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 fricti-:xdhk p1s,i ;v fyk*:,phlv lonless 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 enerd ln s-(a- p:sh1,2 uerkhpfiq6t :6fagy is transformed into gravitational potential energy,rnf2 :6ks- hu(1hap astpd6 : qef-li 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/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from t/n(8 nle ckmk3he top of a platform with a speed of 5knc3(8l m e/kn.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 spring stiffness constant is 950Nb5vlvr5o j. (q3nlp m)/m is attached to a table and is compressed down 0.150 m. (a) What urlo.vpj5( 5bvm)n3 q lpward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without fricsbo y zhz jg7k9u whd+9u(ua 203-4xkktion 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 7 +b9 y kgkxdau9w ush0jz3-24ou(hzkr), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a sprintr k 8zyt5ky6gj t)1r*wqr0*pg (spring stiffness constant k), Fpw**1kqjg8 0ykr yzt )trr65tig. 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 ti *uyqfz jn,w(1ed to a bungee cord whose unstretched lengwu (1qy,j*zn fth is 12 m, 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 *fmqt18w a7y+vxs jc2Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no frictiyv+tm712q wfsx*ca8j on, 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/slv;tq vch);m(5g0cb(chd k 7b 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 designingu6wk uta-4 m kd+r 7:y;ec0orl a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have aory;wm rl7k0+e-d cuu 4:k6tso 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 cycl6c6 /wturrki 30srys09fq 3bje up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95 gn/bw+-apas9i zg,z479m gb06s vlrlkm/h in opposite directions, collide he ng+lizav 9bgagm4ps,0z-bw76r l9s/ad-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 bottom wif d-q*j fd/3py ;bk-mvth a speed of d-f k vj* y;3d-qfpm/b2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slid;(2lvxqh xenr3x). ices 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 drok/ rdbt7.o8wgw n45jmpped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a hwx7+sb0 g b27oxw*k oa46ds hceight of 2.0 m, and it bounces back to a height of 1.5 m. d*w+xb go072ah76xw4 ksbsco
(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 floor2o sbwj1whi77 (dz.vp with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for shob7jdv .wpzi(21w7 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 p7m v hg:-9diyyasses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.-h:y7vi9d my g0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a stt8ww4twttco(up dy.u9u.3 w. 4(bvcjeady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light ho8ji3sp1ak g +l yrr7,lrizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block ajsyprilk+8l 1,73rg a nd the table?   

  A 280-g wood block is firmly attached to a very l-5h -6w r68ho8r/h q u0quhwcmkjq2qzight 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 beyond its equilibrium82 q jh /qu -wkwm6hcrhzu6qo058 hrq- position will it stretch on its first swing?    m

  Early test flights for the space smgkin q):mrn +ymsbk+6amm-,,e8 ( xphuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 35ms(-, :kx rinam m+ bmp8)ekm+yqgn6,00 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-; jdh8n+/ (ra-tlybua W motor to lift a 315-kg piano to a sixth-story windobuan+ ;tl h-r y(8dj/aw 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the a xa0r5 w)b3 a0fjwae/gverage force exerted on the car due to friction and air resistance? x jrwa )bag005/3f wae   N

  A 1400-kg sports car accelerates fkvk3rslsr5dcon ,1,3k cz46lrom rest to 95km/h in 7.4 s. What is the average power delivered by rsls,v4zornc6k 3ldc k5k ,1 3the engine?$\approx$    hp

  (a) Show that one Bri5uk2 is.h :kostish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hour9 t-e:b g:zlq-- dvyjos.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about v2z3- u*(vhi,mtkyvl6.0 s on the level when it i(ym z3vhk vl,t-*u i2vs 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-hp motohu(u56j h hczzd+ 2a1xr do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-k1hx2 cw.,hod wg shot from rest to 14m/s If this motion takes 1.5 s, wha. h1hc,xodw 2wt average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of dv.eqls 3g 6s/3.60 m. What output rating (watts) should the pump motorvsd.3eq/6g l s have?    W

  During a workout, the football plz.u;r4i ag 0uwayers at State U. ran up the stadium stairs in ;.a uwz0r4giu 66 s. The stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 m(cu9tml+bqpv )w) 3b$^{\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 hil o t,jyj*8br fv;jd d)x ) 5a,4)jahvwv,jjzb1l can it climbj afj;dvo4 vh5w8vj)zjabdy r1x j ,,t,*bj)) at 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 drag a 310-kg bgyp nfec6z86uxahz2dz 1 88t0ox along a level floor at a speed of 1.2m/6 8y cz1th8 6p z8gndu0fzae2xs if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d,r3jr am k/e qa)px).iown 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 havenft:hd j- 3na1 built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently def:han1 3j fndt-orms 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 cm off the ground, and tioy-x+ f 9(rz(la 9xsehe remaining four shelves are each spaced 30.0 cm above the previous on -aryie((+x9l9ofsxz e. 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) w rb(xt ,vo(;pjxrdg0 i0bv) famous 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 tra (p0ox(0)bjgv;trv,w i)xrdb veling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction alo1da*)* au ngiznpn x52ng the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top on5 *2u a*pg1 )ndzaxnif 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 jumpi s.h i-bi::skong from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s ests- :.b i:ohskiimate
(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 other end ,e8w baim18bt oeqdi :/a *0by;y*k bmis fixed (Figw8m tbe/:k,iq aayb *m; b1*dybo8ie0 . 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 ofw* zb c ai 5g0 /)fx +tor3ajpr)rlc8+gksnp42 a 3700-m-high mountain. The climb is made in 5.0 h r 0z)rc/s2pra3++gbg kx5nlw ajo *cf4pti8 ) starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above8kh+m4or+pu+ c n(u ia 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 move 47,000 peo/-rn undb:;xb0 lj;+rkt19 bed ne+ arple per hour. If the average lift carries people about 200 m bexlr e+tn jn n9a rrb0-d; d/1k+:ub;(vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertit* 4e,.uwyypvok4ol -cally 81 m before striking the turbine blades. Calculae ok* ytyo,4l-up.4vw te
(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. 6–44), the difpp-ost7um. g5,dj+ oeference 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 tujpet7-5m,d +o g.opshrough it.    mg

  (a) If the human body could coybmzy1d7w p:n:u;c(p sdh ,;m nvert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=10cyzb; smd:;( hy7mpd wn: p1u,00kJ)    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 st (o-r 3tzuvo0/jz2 dq* vj4uan 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 bathroom scale, the spring inside th wbo;m:lfle9 jh1n *x+e scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scaleem1l j+;b nxflo*9h:w from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over ml/b )hg j7pme zst/)-a lake (Fig. 6–45). Hhm /tb7)s jg/zml-)e pe releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 ciow71l 0cc.m s. Whl7i o1mc .cw0cat minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store em+p gu6o2hqjrz+-.zk nergy. Water is pumped by reversible turbin2ohzgr+ zu k6 -.qp+jme pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is czl(xtzrojuv y 01kyaj2(r 6 *:ut in half. What is the spring stiffness conyto( :ar(*lz6zrx1yvk 0 j u2jstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up j9 qvddujgq7 9ha,i01a 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 fromzi9vs6z rag4w nh1 nvqq dzu19l1 e;emz9-w41 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power sta q4v h1er;z4-qwz 69z9ve iuwna1ms11l zdgn9ys the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient waf:jn9wglo.j a 0ek3: : w)yiznlks on an inclined tr.9k)n:0j fz ow i: yal3wenjg:eadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically yy,caz,: v1leupward a distance of 500 m, what wyz:y ace,l,v 1as its velocity 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 j)vgio c0 .a-y;s zr 7 jv9/3gkrp-qxuheight of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electri g ;gjc/yo.jz)9pxri-v 3ksu0r -7vqacity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s