In what ways is the word “work” as used in eveb6o mb2b*aeh -ryday language the same as that defo6eh- *a 2bmbbined in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Explaikr*a*;nnk*fg/*p :fb3rbs bk n.

Can the normal force on an wnu68+vl7hq v object ever do work? Explain.

A woman swimming upstream is not moving with respect to th* 0mg *asfrdsg4sd 0 ls g8a0t jd)-a7yvrl1:oe shore. Is she doing any work? If she stops swimming and merely floata*gmf:8gs4*7s sj lgta0l dd- oydsvr)ra001s, is work done on her?

Is the work done by kinetic friction fotlnww 8v ukaxa r5m)tr)186v)rces always negative? [Hint: Consider what happens to the dishes when you pull a tabn)k law txvut)8)m 58rw16var lecloth out from under them.]

Why is it tiring to push har3xtok.k;ao 2laz 686q cdr4kb d against a solid wall even though you are doing no work q8o.6k46rz klc 2da;kxt3oba?

You have two springs thx++p;w nw 8vqrmlh,-a at are identical except that spring l is stiffer than sprinhw+-pm 8x, ;vwlar +nqg 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 consta wbw ooghpz1w+8,j6c ,nt horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time wo8,bgowpcz j1,h+ w6 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 potent um 53*rlc r00ltjkpu1ial energy change when you jump as high as yom tkcru0pl503jul1r*u can?

In Fig. 6–31, water balloons are tossed froj4zh5 p( g/qqvj jj0d;;nir y2m the roof of a building, all with the same speed but with different launch angles. Which 4/q prg djjqv5yz(0; jh2 nji;one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point zbq6r n78 a +s,y3odd e)mgxk(jl 9*cjin two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from 7 9ygnm,d3 zoj s8 *)crbd (lqjxk+6eathe equilibrium position? Explain.

A coil spring of mass m rests upright ;/gu7x8y cqfr -rs ;yton 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 lu7/ t8;-;qxc rysrfygaw of conservation of energy.

A bowling ball is hung from up tjb, fx7z5x y25zegktt26; the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball 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 ittx5uzt f72xg6z , ek b5yj2;tp. Why?

What happens to the gravitational po acp1vrpi/bjuq+:e 8 n.i; du0tential energy when water at the top of a waterfall q8e dvup+/r pnc.u; 1ajbi0i :falls to the pool below?

Describe the energy transformations when a child hops around on a pocou-8 pbo0 ;k2sia- yago stick.

Describe the energy transformgi5*,tww7 dgb: vk3rf);x uuq ations that take place when a skier starts skiing down a hill, but after a time is brough3kur ,gt:vw*)x 5; wfqbg7uidt to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top ofnmsqx7 w9ch0 x7kv u,wkh5 vmy,f;2/p a hill of height h and slides down. Does the velocity at the bottom dvmuyk,7x5 7 /9v w0qkpwf2cs;nm,x hhepend 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 pk:d a.)juz/k:p l.qpdf d.0ifallen log in their path rather than stepping on top and jumping down on the a:j0kd f.dlup. /ikqzp:. p)d other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired intoxn5z4mse f98 vk 7t)vyshs 4g: a bale of hay. Assuming the hay exerts a constant frictionsstfy sxz7g4 vm84:95v)kehn al force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simplkpy 3wa6oitq*.f1tssx nsgnl(,)d)7e swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explaisw,.ot) )6snf(gkl tp3n*1dx sy iqa7n why a grandfather clock has to be wound up.

When a “superball” is dropf2z6 w/f7ifzlmullo /5l;x 2vped, can it rebound to a height greater than its original heightzxf2mlzo;if /5l /2ul7 6w vlf? Explain.

Suppose you lift a suitcase from the floor k0hygey /lp23c9k* xa to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, andklg*ey0 2 3hpxa9yck/ (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the worb7ib.u e*.kfqvje3-3 n4gy,yd9ifot v+b u r9k.

Why is it easier to climb a mountain via a zigzag trail thanw2n x xe9c.5en to climb straight unwc 2ee xn5.x9p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dec*z6-bl)m.h,if qjcm arease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load i .ij-m6qma,lfz h*b)cs raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 26a+56 a9v -o+awoacnetcf0w d35-kg pile driver falls ofad5 0tc cvew- oa++n aa6w392.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wor c*grb;4n3ljt jb0,ugk is required?0grl 4jj;bn ,bu 3gt*c    J

  A 1300-N crate rests on the floor. How much work is requirg+on p 8,)wdl e7dw6by;czio .ed to move it at constant speed (a) 4.0 m de7ylog 8)cnw i.d6b,+wzp ;o along the floor against 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 cgerkz v.n6+c7b(k 8cyrate 10.3 m across a rough floor without acceler.r86(kcv k ygb+e7 cnzation, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force ac/1hf 4aq mmof2ross a floor at a rate of for 7.0 s. Find the nq2 /1hfm4oafmet work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.:/;dpeiiiwv460r: dxd h gk n+ j6)oda7 kg, lie flat on a table. How much work is required to stack k vhwx6+:6nd)jd;a4: gi 0idri oped/ them one on top of another?    J

A lever such as that shown in.km 3 ,5o(z-qhqjwklfd6 (pac Fig. 6-35 can be used to liff objects we might not otherwiselk-(ok,qp5(qf.z3c 6ha mdj w be able 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 +ena o:j 7p(0btrx qq(and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective tb(aj (e: n+qo 0r7xqpcoefficient 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 ofei:+,7 (pjv-bwjdcl/ kf. gme poqn20 mass M an acceleration of 0.10 gbfj70ogce m vpkwi+(/j d.- nlpq,e2: 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 ax:da6tccn* k8q tr;in *pb8d1bis 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 aa eg mb c ds-k,0zs.:bx5o8w:,ca0wkpm 7nd/rs shown in Fig. 6–37. Determine the work done by this force to move the object (ab,.wnps7das / :0c x,g8 kdmaz5we0m c -kob:r) 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 in4.1.q qo )xiaeuof/ah 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, withy 7n+m8dh,osa x zw8-(p 7xbtstme+ n* 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 increasedz: mkj9r8jqm(? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to st9.z abd pkiapbq425u)yh3 btp 9)rb8mop 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 to stop a 1250-kgcar trnot1smv5el w+ szse:)0 .oo +f0oa/kraveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a b0c*yag yo xo4,vhy+,vow whose string exerts an average force of 110 N on the arrow over a distance,c+oo0y y* vxha4,gv y of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/-mnc 8tm,rupw s,e(8 ys moves a fielder’s glove backward 25 cm when the ball is caught. What was the averags pu,w8,nc-8( ymre tme force exerted by the ball on the glove?    N

If the speed of a car irc ct;fsdy-qmfja)c 0g51m3w 8 uw.0 is increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the sa3r005c1mc -ti u8fw;qmjy gw.f) dcsame? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure 6h4i 8f-+0 urnya cxuja car’s skid 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) c86xu04ni jahfy +-r uthe brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is piwr0w9 eoxp3j/,dy 5tstched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher er5w9 d0,jt3soxpw y/is about 15 m.    N

  How high will a 1.85-kg rock : xqb, 2ezgjo/go if thrown straight up by someone who does 80.0 J of work on it? Negle,ezbx: j /2ogqct air resistance.    m

  A 285-kg load is lifted 2r dnhgb94 9d qap658qsh1tb- n2.0 m vertically with an acceleration by a single cable. Deterqtgnq s5h4-91 dbh b pad986rnmine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this s2 .hsgz dhzq7:pring be stretched to store 25 J of potehz 7 :ghsd.2zqntial energy?    m

  A 7.0-kg monkey swings from one akop90tnwip q 8 un1r4,r2 1ve6oe /jvbranch to another 1.2 m higher. What is the change ornp4680 uvnei1vpj/ko2 a w,q9 t1re in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vauj v3wb 3s(ko(ix.nha2v,s f7ulter change if his center of mass rises abo,wfh u3vss a3x2 i((bj7kvno.ut 4.0 m during the jump?    J

  A 1200-kg car rolling on p4:v+yejs/ du a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiledes :vju+d/y4 p 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 hphh, :, j1smt2.10-kg book from the ground so it is 2.20 m above the ground. , hsj :phh,m1tWhat is the 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 m and climbs to the top of r3 4gu8te5 hjm/p7mqea 3300-m peakuj5qhr73 e/t8m4egm p.
(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 hdk vx1.u::p7k+eajp uangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marvpa:up7dukkj.:+ex 1 ks?    cm

  Jane, looking for Tarzan, is running at twvgkv7fy pap 92l/*- bop speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she-l 2 g97*wayvv /kppbf 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 frictionless bv lp/pkeq 4tix /hzo.kr*83xq-h). b 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 friction7sqeysp8f+; j6icr715 j judcless 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’84*oxkps36 b0 ghdeots kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the xodg* o3pb460k he 8stbar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward f5sd2msh9+mqy rom the top of a platform with a speed of 5.0 m/s. hss5mm+y2 q d9($\alpha)$ 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 (ignorezk84hp xorg3mo 6hlxt ,0ho17 its mass), whose spring stiffness constant is 950N/m is attached to a table and is comktz 8rm0x1x 7ph6o,h43 ogohlpressed 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 withouaad8ev-firnw6(bo 60 yif o/2t friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what6byo- vwi r o 20daneai(f6f8/ minimum height h must it be released?    r

A block of mass m is attache f2r4.zq .ylold to the end of a spring (spring stiffness constant k), Fig. 6–40. The boyrfl lz. q24.lock 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 l9bmnmooc;-jvf3i 2z1p3 uoe(r,sh/ a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of t2eon3ur mhm3;/, ( o1l o i-jpzbs9cfvhe 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. 6–4 9qjyq(6ly.as1 is dragged up to point 1 where it is released from restq(ls6 ajy 9.qy. 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 spdtk:4xx .e(z 0.n8bb pq r4dnleed 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 spring to be placed at the bottom ofh .+bz.kml6ty 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 st.h+ .b y6kzmlpring 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 mcm-) +e1 nq.m r7 nxyq(yz7cqcycle 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 765d gzc5sh 1o29,lvgsa,0 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much tcs sv1lodz2ga95,gh ,hermal 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 with ac;: y:xck t5gi*tj 2yk speed of 2.2m/s How much thermal energy due to friction was generated in this c2tyg;5 kc*yt:xj:k iprocess?    J

  A ski starts from rest kt3lgpe ,-+7xfa4l 3lelmxn:and 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 34fbvtbhx3t1 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 height of 2.0 m, and it bounces back to a b25;.alobx7e zrn:tfd wvm).height of 1.5 mae:m7.2n ;v.boflbt rw xdz 5).
(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 f+ xa4;ugqxl fj : :rd:0l0tvburom rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final sped:xlv4g0x:l :afu+; 0ujrbt qed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of 7 /uhulq6ujz3ls.9jy1 6y vp+jqk7 zj If the average force of friction is3./9y juuu6zyvlq+ s jjp16k77l zhjq equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward,ocj u(znelb.x8 :1jo 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 obu+2 mm(dy(.s /va ta8f rm9i 8axts3is firmly attached to a very light horizontal 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 be/m.t88amsmo bx3v9+a2r uid ( (aytfstween the block and the table?   

  A 280-g wood block is firmly attached to a very light hor kz75375nrwehb c1tu vizontal spring, Fig. 6–40. The block can slide along a tablrw 5h5kc7ezvb3n 7ut1e where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “gl6jwn ld;wj 0 i+jmi7,fc8ztm)ider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually lcimw) jlmf7d ,+ z6w n80t;ijjanded at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to azt9d5 s fhdz93ryy k+0 sixth-story window td 9hz 9+s350ydfr yzk16.0 m above?    s

  If a car generates 18 hp zya.,hya p7fnqkh y, 95o6 f5rwhen traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air resistancr ,n9. ypqh, y6af zo5yh5kfa7e?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avfk4sle.) se a8erage power delivered by t4seaefk) s8.l he engine?$\approx$    hp

  (a) Show that one British horsepu0jz.hz* 2pyoower$ \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 “kilow/xpvl:i+*rrjo 3rpz 1 i2e8rjatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h /(*l 3twyhyk0k0n6q : gfddtkin about 6.0 s on the level when it is in neutral. Approxi3k/ (dydlqgh0 :k fy*06k ttwnmately 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 motcy+ fyw*s 86odor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7m**b)8h(ipo .kg3dlyfw p8bo .3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average powobm *lg*io8 pf(8hb.3)pd wyker was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m +j yi-y mx)3hpjfj+*p. What output rating (watts) should the pump hj-yi*p +yp jf )jm3+xmotor have?    W

  During a workout, the football players at State U. ran up th7*z-ve pob i0u0gl 2noe stadium stairs in 66 s. ob*gnv-iz 0u7el 2po0 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 clossoz5hl5x 2 fhn 5x7v43ud.wimb 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 hg6o br qujk,96p. How steep a hill can it climb at a constant rk 9g o,q6u6bjspeed 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-kg2yxf8u,,cwx ; pbce-q box along a level floor at a speed of 1.2m/s if the coefficient of friction is x2,wcye;-qu 8b, cfpx0.45?    hp

  A bicyclist coasts dowjkrsad(3-0f .rdsz4zgnl ( 7rn 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 6lrpt0 r-a9 ppn 7j:soare 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, assuming-o n0 r6 pp97tslrj:pa 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 thud,fm*.:cky( q0o q carmsr 6-e ground, and the remaining four shelves aror(0qmyu6:ca.-d rfmkc ,sq* e each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, 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 tu*8 y 1j g-:chbkaed,dfn8p4i/z- tsq he 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 at the top of the arc? e cd-atj,:nfy/z du* i q8ph4b-g81 ks  m/s

  The block of mass m sliding without friction alo)43wt(vb*xgga ju 9egng the looped track shown in Fig9ag(wuvgxjtb*e )g 43 . 6–39 is to remain on the track 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 ru7+z 0ppc: ki-liq6gjumping 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. Assuqk6 r-7zpl:g ip0 +uicming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is ih:n n5pn;4-yk/*w asqcvlp ynpb+): fixed (Fi bi p)c/-np5nyklyh :p vn*q;4an w:+sg. 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 of a 3700-m-high mountain. The cfj, a57ik qgystwl,,)limb is made in 5.0 h starg iqy5a) ,jsfwl,tk,7ting 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 f (td5)a)jhvu28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can mov s 4vm7zl* 5gk i7d(njyp):gjfe 47,000 people pekg4dn*7ivmy (fz7 )splg jj:5r hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/sif)0v2 q4(4 hz)rrp3 d 3stkp8iyjxfh and falls vertically 81 m before sqrv)ipsxf)43p( zh3d2 fkyith8 4jr0triking the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with e6, nye 1w f u/ad,m,jbe(mzz7:7qz ija circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast aj/ fyz7eeu ,i7,:qe jzm(wdnb,zm 61you go through it.    mg

  (a) If the human body could convert a candy bar directl, cuf9znel ,* 4zql(tc1oj+k k1cm ,vzy into work, how high could an 82-kg man climb a ladder t,em4nlz z*j fv1q(c kcl,cuk,oz9+1if 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 a5 +34 fdu weif6lk,qkct an 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 the scale compresses 0.60 mdp 1 6)75kvlw-p p2jhm.lalkrm, and it tells you your weight is 710 N. Now if you jump on the scale lpw m hk-a d7)6lrl.vkj25pp1from 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 a lay0zzhld6y+fag .c 29rjj8 (ycke (Fig. 6–45). He relea 6ycyj+08lf (. 9 jgzcazhry2dses 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 climaa5 y5ty0 *2* sl)mibiizi0zkyp6m p 4bs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat? 62b ii *az5yp0i)l*myy4k s mt0pia5z    W

  Some electric-power compana+nm -q)k ye9ries use water to store energy. Water is pumped by reversible turbine pumps)n9y -q+kream 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 cut in half. What fc+bm u9 9is(tis the spring stiffness constant for each of the two resulting spm +9utfs( cib9rings?   k

  A 6.0-kg block is pushrr;12 e;*mj w6ljrkxted 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 can accelerdeuie. cue+t0 ):tz t4ate 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 power stays the same, and neglect frictional losses. t+ :edtu)0.zucti4 e e   s

  In a common test for cardiac function (the “stress test”), thez xhc3tcw1d 64 patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when1c 4zh6wtx cd3 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 dm1; g*hn;o,z, pto .zswbnv,pistance of 500 m, what was its velocity b;,pg*1swnooh;n,,zv .p mzt 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 wheelw-g+yl(n m ovh:ia7e2 from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, + iha:ymv 2-l( e7nogwwhat is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s