In what ways is the word “work” as used i rqk0bwd/ +l:atveu:;n everyday language the same as that de0 q;ab tl rv/de+uwk::fined in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Expttp-8d3 mvl3i lain.

Can the normal force on an object ever do wowp -2e*qdvjrh5x7xtv b,o:e a p;( )mprk? Explain.

A woman swimming upstrea6k9vkz 4tjs6gm is not moving with respect to the shore. Is she doing any work? If she sjzv4stk6 69 kgtops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always neqe2r9n*w2pxs mo5(t u gative? [Hint: Consider what happens to the dishes when 2s5ux*nw( po2eq9tr m you pull a tablecloth out from under them.]

Why is it tiring to push lbd-qgjyx0inofqcw rkos-/5. -p/05q ly3i2 hard against a solid wall even though you are doing no work?nbiiql5xo- 0yd0.gw 2lkq j 5//-o c3sfpryq-

You have two springs that are identisf-h 2;ts0,glnyw5 ytcal except that spring l is stiffer than sprint5 w 0 h;n,tslfys-yg2g 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 f. ujw.z00/8ughw a q)dwg aw2aorce on a block that is free to slide on a frictionless surface (Fig.6- az)h0gdw.j qawa wu. ug28/0w30). 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 gravitational potential energy change when9sq( ggb*j7)e/ f p5oic4ef l: ha-dee you jump as high as ee5gi qdp7f)9 l( eob *s4g /:h-ejfacyou can?

In Fig. 6–31, water balloons :4lnd ccw6ccd84gas 2 are tossed from the roof of a building, all with the same speed but with cl4dgc28wa: 6sdcnc4different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is od6;tc/ dzc:b a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing th; zbctoc:d/6de largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you c6r izr 2ditw2o+p-v/xompress the spring by pressing down with your hand and then release it, can the springd2 -zpovw/irt 2ix+r 6 leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a stee8guz,.zfms uvwl q )-o64vn k2l wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall u,4mq86v onlvzuwg.)z2fsk-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 water at the top of ns y+oyx1g a;8a waterfall falls x +nao8ys;1gy to the pool below?

Describe the energy transformations when a child hops ukd r1 4-uake-z4mi,y around on a pogo stick.

Describe the energy transformations tu//l6,kmg db cer-y- uhat take place when a skier starts skiing down a hill, but after a time is brought to rest by e klmb-cguu6yd// , r-striking a snowdrift.

A child on a sled (total mass m) starts frr7c5 u:ji-f4 rssbfd-7/epjq om rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is p74iej d/-5ssfq7jur-c bf r: no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rxgs.n b82w z(rather than stepp2g8 zx(wsrb n.ing on top and jumping down on the other side. Explain.

Two identical arrows, one with twice ;xnqiz jke7,ms:k:mvp ,/9 eu q2 a4rkthe speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on theq: :az7r eikpnuj4 9ms; k2,qvxe,km/ arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of dss6u)k (wc +ba simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction intowc(kud s s6+)b account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped,y:ns cr0tq :; *u/s /b saf)jfuudn1-c can it rebound to a height greater than its original hei:sftybuf; a*-/suq:nc 0ds/1jcrn )ught? Explain.

Suppose you lift a suit osgy l5q42h ur9e18fdcase from the floor to a table. The work you do on the suit4 ryh9q 8ufo2le1sgd 5case depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the workookyjw k:aa v y9q48zd-(pv(hs.:ds * .

Why is it easier to c)f 1ioaoh;2 yplimb a mountain via a zigzag trail than to climb straight upf ;)12ayho oip?

Recall from Chapter 4,i9swbv 4p+d4vglzw) sta -a47 Example 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 fo)a4sw7pd-9 zvbl tia sv4g4w+ r this, using energy concepts.

  How much work is done by the gravitrw* tiej:.e* s: luc0vational force when a 265-kg pile driver falls 2.80 u c:ej*irw e:ts0*lv.m?    J

  A 65.0-kg firefighter climbs a flight ofm3k(nu)u(hde stairs 20.0 m high. How much work is required?edk(3)u(mhn u    J

  A 1300-N crate rests on the floor. How much5lw(;cwfcd) u35sejn f *5ngh work is required to move it at constant speed (a) 4.0 m along the floor againstwlnf5)3wgc f ( d*nujec5s 5;h a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hor4o:e5)qgxs / ia,aogdizontally) pushing a 160-kg crate 10.3 m across a rough floor5 eio,ogg:4 ds )aax/q without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerhm ns.,nd*co 7ated by a force across a floor at a rate of for 7.0 s. Find the net work done on the box. son,n*.m h d7c  J

  Eight books, each 4.3 cm thick with mass 1.7 kg,ixiq: fqw*u ,2s lbcz nq/,u4: lie flat on a table. How much work isu nqiwiqu: x,*/,sq fl 2c4:zb required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 canoa o+:9jxr hzcg2fk 0k x6ou99;5nav v be used to liff objects we might not otherwise be able to liff. Showo9k 2kvcg ua5o69zfxxnr:vjah9o0+ ; 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 ubboy56m+nz , frkm60and is kept from accelerating by a man who is pushing back on it parallel to the inclinezumb5fnbrm ,y0+66o k (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 7k6 lf5tby (;rhgl8qean acceleration of 0.10 g upw keyrh6;l7bg f8t5ql( ard.    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 /5 .y+wxax8kod4 qiqyp k.b t*k kz80othe distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along thfofgnttp,-k j71/ia; 7wyz-o+g i pq-un lm(7e x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the 7zfiq-og ow-7 mt1 upl ,gky +7 -npia/ft(;njobject (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 particle acts god, g3(686m yrg oinrin 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 mole69cph7 fcq8 tecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed increase gkxdz/2a:. l j:..-pyihovze d? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elecin qd )w;bfj)+q/h h9qtron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 kca / 0il)zoh*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 dq* 6ndm7 s*:z4pqc- x,ijnfd exerts an average force of 110 N on the arn:dx4jn*p z7i-csqf,* 6 mdd qrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’l7+d: (bgb pdws glove backward 25 cm when the ball ib+l( bwd:7pgd s caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by kdkw qnzd +y;h-04z3x50%, by what factor will its minimum braking distance be increased, assuming all else is the0xqd nkz kh4-y+z; dw3 same? Ignore the driver’s reaction time.

  At an accident scene on a level road, 3nhci45e,*u :j hkvmpinvestigators measure a car’s skid mark to be 88 m long. The a,hm4 uvk*5 n3ei:jp chccident 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 reach p) y)gc6 ya dk1vr(8j0eebs)48lzcxhes the plate, it may have sx8)cjzcb h4g) (pe) ay 0drky68lesv1lowed 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 someonep2f gwtu(*xw7 who does 80.0 J of work ox7wgu2p(tf* w n it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically why)ai /xtv, p/od9 e.aith an acceleration by a single cable. Detx d.)/9,/yvoaptiaehermine
(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 sprin *2jpgrib57j2-vm z ong stiffness constant, k, of 440N/m How much must this spring be stretz-2pj ni7m2 j*g rbo5vched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is theae ny6kv.p.r z*3+izb change zr.nz i*3ke v y.a+6pbin potential energy?    J

  By how much does the gravitational potential ener-qbq+g(bxej (gy of a 64-kg pole vaulter change if his center of masqq bj(-e+xg(bs rises about 4.0 m during the jump?    J

  A 1200-kg car rolling zu k(g72 b a.fbc.fq /b.ptris;h9cm 8on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brough ffk;/c z 2q7 hb(.a crb9m.pgutib.8st 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 as j,5d8v -/hsisu)yvbxkd ,oh; 6kj3ibove the ground. What is yd35 6hovds)i h,k/8 ;s bjux,v- ijskthe potential 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 -nt4yi:1v fxkm and climbs to the top of a 3300-mxft:y14kn i-v peak.
(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 spt;/8phln)wai ring 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 end of the spring lin);i wath8 l/pne up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top -b0j+-zu tsk7mbmc c.x6a- vkyv8f/ k speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swin08kk + baf6-/ -b yv.c7kumvtzcjs-mxg upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictiontpa2cl j/ul4c2 qkz 2asj/m.1less 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 give8 qyycgi i7 kpln13z.bt 69/ykn 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, Fr;a w7hrlsalr9 fv4,v; an’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave s9; rwlah,4ral 7;vfv 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 the top of a p;0i pkzkws1,x1lxexigju: / .latform with a spee 11iei zpkxgx;:/ul0j.w ,sxkd 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 m nw1w+ pa2l6rsass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.s2alrpn +1 w6w30-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 friction along the looped tra4qib7wf+qj ygy+*s;c e*lnh inj10* fck shown in Fig. 6–39. If the block is to remain on the t jc4*i*lwn j71ey+0fn +h ;fqiy*bqsgrack, 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 9x0x7v5*gps,lwk so sthe end of a spring (spring stiffness constant k), Fig. 6–40. The bv w7l0opxs ss9gk,* 5xlock 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 p82e e *vtnc2c 8c+ccdtied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness const8 2ce82 cdcce+n *tcvpant 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 inxi fvp5:wb/zps(i//m Fig. 6–41 is dragged up to point 1 where it is released from r/ bp(zvp5i:ifx//sm west. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle w99umi- )k:fh 5nidvyof 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be x a x-ni6 p rk;l5)3d3a0vidkuplaced at the bottom of an elevator shaft. If the el-0al r ua dxx5i3pi)v6ndkk 3;evator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to e4u4 a(o9k4 b6ceo ymxcycle 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 9bcr-7o7z:b. tph/.u*zz7,rhlgm yy o5km/h in opposite directions, collide head-on and come to resuzb t.pzbhoh77y .clo/g -zy, m7:*rrt. 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 wiqrgp6qgj m1;9th a speed of 2.2m/s How much thermal ggqm p9r j61;qenergy due to friction was generated in this process?    J

  A ski starts from rest 66zl*as 4 br0 iulu:apand 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 from a trey;kowj ,zbjj(a; i/a/e 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of+hk8rjmkpvu003a3q7d swy3/ nm) v o n 2.0 m, and it bounces back to a height of 1.5 mkuj3pvwhn+o)3n mqk/yvm3rs 780d0 a.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a c)lps98(* v3 zwnqr byconstant 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 speed of (ycs8zlpq )v9rw3*bn the crate?    m/s

  Suppose the roller coaster in Fig. d 430hum uoif(6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will 3mudfoi4 0( uhit reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0k5p r1goflace s*; mz,y. 9m7e $^{\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 blockohgo *3 hy:9 xccdy5u 40lc)kp4 (ezep is firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40.hy(l5 ypgu: ec0)xhc4epc zo3d49* ko It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light8j7 bp i9sy7fr 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 posisy7r 9i7jpb8 ftion, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights fo)5/ qq-q wbhl kgqcjzq4s*9uk; 1yy;xr the space shuttle used a “glider” (mass of 980 kg including pilot) that was c4 qh*qq;l;u-s51 xqk )wy kgbzjqy9/launched horizontally 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 e)ag ko1 eb u-8jddc62a 315-kg piano to a sixth-story window 16.0 m aboce o u21)6dg b8jak-deve?    s

  If a car generates 18 hp when traveling at a steady 88km/h wltk v e;ivj6s;.fp6 *))kn txahat must be the average force exerted on the car due 6k*vfj.ks tvne t;)i6pa ) ;lxto friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95kmt10s2na; zghk /h in 7.4 s. What is the averagets akn;2h 1z0g power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepo -oe ptfzu;ea/vta;+m6h p. kone1n(6wer$ \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 “kilowaty,u +gfz:s b3 z;bly4gt-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.ljyq ;0njdd4t her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) islq y;.nd 04djj needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-he)g b(yov b5(orswp ,6p motor 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 If this motip:5kxvy zwm-mqw -4. fnw4kg+on takes 1.5 s, what average power was develop5.mv-:wqz - wkfxp4k+ywm 4g ned?$\approx$    W

  A pump is to lift 18.0 kg of water per minute the-(mz +awnn2 nrough a height of 3.60 m. What output rating (wattnn+ n(aw2ze-m s) should the pump motor have?    W

  During a workout, the football players at Stat w2wlbubip;:6 zobj5 1-sx-po9 -deiie U. ran up the stadium stairs in 66 s. The stairs are 140 m long andzb56io wx ;i--ld-1 bwup 9:jbi eps2o 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 climwyu3e1 rc-x1lb 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 hill c +diw5 qj)fp+.ofs0t can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N? qs p +i)tc.o05+d wffj   $^{\circ} $

  What minimum horsepower must a motor have fn;qr qovw*(/ to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the cov rqw(;* noq/fefficient of friction is 0.45?    hp

  A bicyclist coasts dom(p9dzv xigd.a5 / t31w vhxr5wn 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/ag9. ynpfz 0fz.;(hutic : yn.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 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, a nyy0t. zfh;ac ngip.9:z(.ufssuming 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 i2qwosjamrym 7c9:.s1 s 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous ssyw1a.m2jc:mo q7r9 one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics sfdxr z49)ncyn n08x5ejayce.7zd b7 2hows that his center of mass rose 1.1 m from launch point to the top of the arc. What m0 bjen8zyc.ynd nxr9 dc fz7ea)4x 572inimum 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 x5h)qtg yy:j*-( kh 9n. cc:5irkfwlr along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the5i-g.fh*nlqj9 yr:k )c:y ht(wk5xc r 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 frem;.nuly *4woom 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 velo*;w une4ml yo.city 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 ho f, ykea0jp+; 66ftwhwrizontal cord of length L whose other end is fixed (Fig. 6e +,ty6hfw0w pa;fjk6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 370oul;- :;vyi ef0-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. foue -l ;iy:v;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 above a huge 49gvjoh)/d 5zb7o dcaspring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 (knk7e .svfxx 8bo da2e,ne7+ move 47,000 people per hour. If the average lift carries people about 2n ax.o ev,ek(nsb +x7 2kfd7e800 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam dj9zt) un 46grem ,)xmat the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculatgm,e x9rm )j dt6uz)n4e
(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 a3nv) ,qurn8t )l zolr9f+; rqj circular vertical loop (Fig. 6–44), the difference in your3 )qn vjr9zfu+orl l;8q,) ntr 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 couhc09h ( p;ywiuh+0fv1 (zubhnzp+mc,ld convert a candy bar directly into work, how high could an 82-kg man climyi(c9up+zb;z+m01(hhu,f hcvhnp 0w b a 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 upward mv:c m -uty-lc nv5,k(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 scale compresses p7.xjlwo.bh9 0.60 mm, and it te whp.l7oxbj9. lls you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out p r p9 em9m;9obueaj i7o2b5c1.qral(over a lake (Fig. 6–45). He r2 7a ereo1m cj .;opm9pbq(rb9lau95 ieleases 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.j2b9klds718ayl;61iio s ot h0 m in 9.0 s. What miokoly j7d;6l sh bi1its91a28nimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water v2r(ywc.3bl b ck w-+wis pumped by reversible turbine pumps f3+kblb-w .ywccr2(w vrom 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 stiffnh 3e*+iulap6 1kb a2vtess constant k is cut in half. What is the spring stiffnes*ia2uhtak v 3e+1bpl6s constant for each of the two resulting springs?   k

  A 6.0-kg block is pushefe l0.y7jju n+5nnf (jd 8.0 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 canhdd3j i6e1dwyn c8+z, accelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km,z1hd idn8 j 6wy3dc+e/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the p4sp e,vh+po7p atient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at anse pp+p7 oh,v4 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 dux*2sz w ,sw6listance of 500 m, what was it swwzsx*u2 ,l6s 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 a,ldy, -agw. sot a rate of 95kg/s (a) If l gawo. -d,,ysthis water wheel is set up 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