In what ways is the word “work” as used iss (7*idah sv2n everyday language the same as that defined isvs (idh2s *a7n physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an obt bs qg1n5 w j)3xwjwmbu657mfc(3x,vject? Explain.

Can the normal force on an object.lc:pzs n ;faa(vevz il:/89e ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore.1it) o0- py(qjtg 9fci1f8hr c Is she doing any work? If she stops swimming and merely floats, is work done on he( 0i) f9t1h1jc q8y rof-tigcpr?

Is the work done by ki kap7 r(:,rkytnetic friction forces always negative? [Hint: Consider what happens to the di yt(ar:7,r kkpshes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though oh m*n:ujvkc7kv*(b3, j vs+ xyou are doing no wo3umxj7b, *nv +o(vh*c:k vksjrk?

You have two springs that are identical except that sprnvhdpw.5c8pp)j. qx4(.o h vying l is stiffer than springoh.wj58 c p4.qxd .ypvnh) pv( 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 fovsy8qor vb ocu4t4;u401g:au a2jh 9 rrce on a block that is free to slide on a fri1 g4r4aaq us0 ob9tr: jou;yhv4 cv2u8ctionless 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 does your gravita 0+g3c6e(ikoqff0s-kxz*lqy tional potential energy change when you jump as high as lo6 qkqfk+g0 eiyf-*s(0c 3zxyou can?

In Fig. 6–31, water balloons are tossed from the roof of a bu*rzo lh8 7vn1hilding, all with the same speed but with different launch anglesz7rno1l*8vh h. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point tha th gou9;rddaex9)b, rpt:)-ht 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 t,ogr )9 p9r:d-x taeuhd;h)b 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 angle from the equilibrium position? Explain.

A coil spring of mass m r femo3-hp4xu s:;tgm3ests upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of enspxu tgh : eom34f3-m;ergy.

A bowling ball is hung from the ceiling by a steel wiz,a 0s-gfh1 :fqv c8vk2 (qnmdre (Fig. 6–33). The instructor pulls the - , k2hd(g:8saq0qzf vmnv1cfball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitationp zmfdv+ ,0x0umz*q4fal potential energy when water at the top of a waterfall falls to the po*xq0vz dfm uz,f+ m4p0ol below?

Describe the energy transformations when a child hops a/i6k d9e 5gsrcround on a pogo stick.

Describe the energy transformations that take place when a 8o9x w6y1 nsmwnelno5* :1q dlskier starts skiing d8n 5wmnd l*o91qolxws1 y:ne6own a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts frokrsl98lx4b jocfi 99 t23qy4vm rest at the top of a hill of height h and slifc sqil2j49to9r9l3vk x 8 by4des 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 prefqz0zw.r1s7lg er to step over a fallen log in their path rather than stepping on top and jumping dowrz.0z7qw g1ls n on the other side. Explain.

Two identical arrows, one with twice the hste)p:g 8.l. fk8m:jac n sy4speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the aryt8:m8chjls:)ga..p s e4nf krows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) igno; t v(hyrvm5y gax 5,fkul;.d+l15zh fring friction, and (b) taking friction into account. Explain why a gh+rl tk1yv5v,fz;xygf(5 .au d; l5mh randfather clock has to be wound up.

When a “superball” is dropped, can it refos5vff5:/i s 6:hse:izrv3ubound to a height greater than its original heie/:h63sfszri uv f o:55s:fvight? Explain.

Suppose you lift a suitcase from the floor to a table. The wor9olbhk siv 9+ wow5--uk you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a 5bo iwow-ku s-99v+lhmore complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the worb 96ndo*7u:h h oz1j1*gbllqvk.

Why is it easier to climb a mountain vip o9,th/q5m o.px ,fd t odt14q1+rml;eepl:va a zigzag trail than to climb straight u 11t x d;o4+.ohol tfrl,/:ppqep m5qed ,9mtvp?

Recall from Chapter 4, Ex6pu unoe zd:+ kw1/.bbample 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 eunu+w k: b6eo zb.pd/1nergy concepts.

  How much work is done by the gravitational force whenca*xbi(j7jhk 1id +5i a 265-kg pile driver falls 2 ji* xa 1i(jcd+ih57kb.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muchzwj*foh 8+)v2xm0m og work is re2h jo0 o8mm vf)gz*+wxquired?    J

  A 1300-N crate rests on the floor. How much work is required to movkk:x nammde.2 ( e)zr3e it at constant speed (a) 4.0 m along the floor against a friction force) em:rk2 ema3k(xznd . of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horiw.:thkl 7hvyd-:inwck/i:3t p+x uo 7zontally) pushing a 160-kg crate 10.3 m across a rough floor without a/+owh3cwkidniu-7tlkx : p h t:7.v y:cceleration, 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 of forci jaz+piq uk4r.g,;,kbj*b5i ,v qe6 7.0 s. F izjig6p +c45qkru b;qiba, ,v*j.ek,ind the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tapkq+vkb9 6i21pxw qq8 ble. How much work is required to stack them one 9xp2+w8qkv6ki 1qqpbon top of another?    J

A lever such as that show 07illn5pbt7kl/ -usnn in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ra 7nn0/bu-lltpisk7 l 5tio 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 accelerating bpv0 e;7 ia1*rn3czmvzy a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefc i;rz3eazmv n 7*1pv0ficient 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 helicopf:5bmcgej/41u)+h;oltvzgr k - 2 y dpter of mass M an acceleration of 0.10 g -;fgl yjg d4trohvpm ck)5e2+u1 bz/:upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis 5fmq, +rl1mo dis 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 indwkvmytoj ml)*3xq+i i mos.4r9; 6 8x Fig. 6–37. Determine thxt o8 mx+isyldk;3o9jm)rmvw64i .q*e work done 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 onfu ac0za xkes 3*,l )voo0 lnu/r80)bv a particle 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, with mas0du6oia uv jn7(q:/slii;3 bz s 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 arrow1 tfgg l7*vffn( e5z1n(bhc2+ mo .ajr 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 sta. jhc ck:v/s/op an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done t xk/o x(ld9ev e l5e(2c3de5czo 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 exerts an6bs xinx*4v/+roxr 5 bdmg(2 q average force of 110 N on the arrow over a distance ofn i2vxrboq(b+mgrx4d * x6 /5s 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s move tiskr fdxpje0m,8g1q 3*emw9a) z)w8s a fielder’s glove backward 25 cm when the ball is caught. What was the average force exer8 jewfq*dp r0)xmmta8s)i9 k,3ez 1w gted by the ball on the glove?    N

If the speed of a car is increas1 suc vo95ki/bed by 50%, by what factor will its minimum brakingo1buv95ksc /i distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a qqvbb maa(3x.8ljv 1-4kkb(j level road, investigators measure a car’s skid mark to be 88 m long. The accib(xvak q 8.4-amlj b3(1j qbkvdent occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches t/r0ji ap ,klnrf fp6/:he plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a /l jpr n:pfa rfk6,0/ipitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thr lr*q y/bye5 (n0rqv/bown straight up by someone who does 80.0 J of work on it? Neglectyv0 y5/ r(eq*blbqr/n air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sing)ac 5 pwq1qqm.le cable. Detercqw). 1mapq5q mine
(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 constang88iqa 52gu2xc celg +t, k, of 440N/m How much must this spring be stretched to gax ce82ui5q gl82g+cstore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hi.adac 8b)j +3c zbiz5ngher. What is the change in potential enercd )bj8ib3z+ .cnzaa 5gy?    J

  By how much does the gravitational potentip hhbt7ey *8x0al energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m durinehp0*h78ytx b g the jump?    J

  A 1200-kg car rolling 2;0b*bs-lcugwvkb8 t vi pp )3on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest ib3 g i0p-c*pbs28utvkvl;w )bn 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 above r9n6v b2 wuos27ttx4a the ground. What is the potenn9r w 62ao4ubt2xvs7t tial energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs tor0lwuv6j(8p t the top of a 3300-m p0v pt6 rwlju(8eak.
(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. T+sv0pk,g mrl /apaxnz* 5k9t0he end of the spring is next to the 15-cm mark on the ruler. If a 95am0v+zkx0s/ank r p g*,lpt2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running s*pzs: 8 cu.)idp;*flsljt +k5iki q*at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swi5p;su* )zlktqs: .c *sip+djifl 8k*i ng upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startin tzt- rh6d,5mrg 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 gnqo uao 49vr x0futxr( bt-3e9-e +ra/iven a shove 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 transformmlkos) fy8m 50ed 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 and cross the bar with aksmm) ol0f 58y speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jump + ogjm--g3 h.mev ;mc.zaoxx+s vertically upward from the top of a platform with a speed .g h3 -m gvjoxxm ;ae.zoc++m-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 spring stiffnessxw-. bz5+ dpwo constant is 950N/m is attached to a table and is compresdop xw+w-.z5b sed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withofyen g- b62fca,r+t/xut friction along the looped track shown in Fig. 6–39. If the block is to remain on bnf-,a 6e2 yf rg+/ctxthe 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 (spring stiffness cone) wb,,qj -iucl.en)cstant k), Fig. 6–40. The block is given an initial displauc,w -bqjnee)),ic.l cement $x_0$ 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 t/sqr8o z+s5on7zwvw+hi) ;dq o a bungee cord whose unstretched length is 12 m, and falls a tod8noq;)q 7ws z +i /+hvwrs5zotal of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where it is rvy qk7cdxj-m + *okj:ti2,n5k eleased :x*+vt, 5 yjn q7mk-kjcokid2 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 throwni:x7c)sbyxci z ft9 z0hr9(b)kc q )a: with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a 4yair71lxya yb8e0* m spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a hea4 r* 8ebmi0ylxay17 yight h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyclebtn, w*9an )sf 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 95km/h in opposite )kd-qk r;q kh+directions, collide head-on and come to rest. How much therdh-rk kqk+ ;q)mal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m highd,+3)r +whjw 9v( u epw,v:edf(be-a0qwriew and reaches the bottom with a speed of 2.2m/s How much thhq -r :eeb,+uawrfdewv (vi0+e)p93(,jwww dermal energy due to friction was generated in this process?    J

  A ski starts from rest and *w(3b3s mgp7 wsmfi:hslides 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 m above the g6mw1 eao. qyr6round.
(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 r-: fq4g ekw( cz5h;5fbe;u hsheight of 1.5 m. g-h k;wzef e:r hu54b s5(q;fc
(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 )b8e :b0t kj mi0+fy pynn*l:ewith a constant horizontal force of 350 N.b8 t ib0my:e:0kj+)f ylnn* ep 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 speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 withvv9m 6w* 6v.p; isqc l 8e3iaqc0j/-t6hxnlh v a speed of If the average force of frict03/a 6 ; etsq6hlpimqw6vj-x8 n9 vhiclvv.* cion 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 m+eu.bt: gbhs y.h,+zpll ww)/ w:+jareaches the foot of a steady 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 horizontal spring m0+ e*c f6x h5,rafosd5g unc:(k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretch,:f*csh5r mfxu0dane co6g5+ es 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 fi 1)pmtl5 b:lgprmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stret bp 51l)mtp:lgch on its first swing?    m

  Early test flights fktbe 8r)r:8h por the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h b8h e:)prt 8krfrom 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 tom0 u4gl 95c4( lqpqycr a sixth-story winguc5 ql mqc4ly(0 p9r4dow 16.0 m above?    s

  If a car generates 18 hp whlvs ce 2*6dy1ken traveling at a steady 88km/h what must be the average force exerecsl y*k 26d1vted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Wha-masr3j5b er5p3- bi ot is the average power delivered by the engin5br33sioj e--apbrm 5e?$\approx$    hp

  (a) Show that one British horsepowerb5mdb )gqm;:k $ \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 fo 124itzpm;v xl *4sw)wdm*wyvv: ,boprm 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 tha ,:,b*l9-hka .lkj .nsgf 7mblnbrfm. t her 1150-kg car slows down from to 65km/h in about 6.0 s on the slgn kfjlb*,m.rakh7- l..fb,:mnb 9 level when it is 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 mo4 9q+vngc 5cs-w;x:b t8sytaf tor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s Idr 8o m8myn 01tdv/ a.quj+ub2f this motion takes 1.5 s, what average power wa+1dojuv82uymm ab q8t n r.d0/s developed?$\approx$    W

  A pump is to lift 18 q ;k0+kbdlsoxd0qz 6m2+y4l w.0 kg of water per minute through a height of 3.60 m. What output rating (watts) shouldqld q+2wb0o+6 4slzk;m0 kxdy the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stairso(ktor mm;640ro lb3j9mz w(d in 66 s. The stairs are 140 m long and omrb4( o d69kltm mjw0( r3zo;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 clhqpn r-c2wl-ijl f1/1hyu7+)oss u k7imb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a ),nw9xi; p)vk f-cfy 40jtw b 9fe*dluhill can it climb at a constant speed of 75km/h if the frictional forces add upnv;ky0 x* bcff e)),diwf t-9lu9pj4w to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag aawx zjpp5 r4i e7 (c*hv)i*j6/kpeag 5 310-kg box along a level floor at a speed of 1.2a/)6e pe5wi pxacr4*ij z(7hvkj gp*5m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts do lc4 *bijz.g +w/jp:xxwn 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) bumpers” that are designed tos) kv3 c1jjq57n ehmw9 compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming intojnmhs kqc17v9 w3)je5 a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the groundotv5ab+9wjxu(2 qpo6, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.qa5 ow +outj6p(x v2b95 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 lh .dk*o 7qug;(bl nb8p .ytjz;ong jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s(7zgt* k;8 pl dnquo.hbjb; .y at the top of the arc?   m/s

  The block of mass m slidi, -vp9ndt3e, ti;sx3 r/lzgvtng without friction along the looped track shown in Fig. 6–39 is to remain on the 3v, ;vg/- ,znd3 testxi9rltptrack at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft withbx )gkx7m)f t.a86bbr out 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 velocitykfxb tg)7) xa.m8br6b 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 y gs gm02)zs)aL whose other end is fixed (Fig. 6–4gs s0y2gza)m )3).
(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(pba*wb0i z;xua*s-m-high mountain. The climb is made in 5.0 h starting at an elevatiowb(a *0biu;zp*m; axs n 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 abo u )zqpa2ugjpb:85bi2ve 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 n*1wfebbjb )ve 6v9 9pj0p-xz in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higpx0evn9fjw6ze vj *-)9bb1pb her, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vejq)rkygy5( vs ,6gv r5rtically 81 m before striking theqsjv,rg 56yky(g)r5v 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 coasq h+x:3dclo1v ter with a circular vertical loop (Fig. 6–44), the difference in yourv:cd lx1hqo3+ 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 through it.    mg

  (a) If the human body could convert a candy bar directly into work, oo0zr, kzn28- y:rpup how high could an 82-kg man climb a o0p-zunzkyrr:p 28,oladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward anglcu6gzy 46vfwg9(q rh+e 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 sv mho778kqbwz11 tj u2cale, 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, what mq1zb7thk8o21w 7u vjdoes the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings oue *qy hkkk:d47t over a lake (Fig. 6–45). He releases the rope when his velocekk y khq*4:d7ity 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 verticalccl bd4 q2cyx lhq7 1 rvc7ev;7+q*zk5 distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish thibvk cq7q;rc 74clh vq52c* e+1z ydxl7s feat?    W

  Some electric-power companies use water to store energ86cxqa1hp-*xfy 4hrh y. Water is pumped by reversible turbine pumps from a low to a high ph61 fcx rx- qh4a8y*hreservoir. 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 cut in half. What is the sprimr +va8ka+8vpbw b+d *sh;)qhu9 6wv7h y va(kng stiffness cons v69 mkh8+7 hav d;ba +(sy)a+uhv8vw *pqrwkbtant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roug *b+gz0p .o6sa y/3u9tsvt+axovz w8ch 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 ;ltn) jx9z i5haccelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the pzl tjh;5n x9i)ower stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient wauv72 0exmu9rr lks on an inclined treu7rx ue 2rv09madmill (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 upward a distance 7pdh31cb;bd iof 500 m, what was i1bpbd3h7c ; dits 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 height of 2.0 m atj20l 3zm: lt5h rh2qyc a rate of 95kg/s (a) If this water wheel is set uphm25cr2y3q0: z ljlth to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s