In what ways is the word “work” as used in everyday 1a.lq q 6 nji7 *v:1m(f w)n/frhmtmgll,bsm.language the same as that defined i. (fj tn7hq*ms11/i mmn6) :l.wrmb l,lvagf qn physics? In what ways is it different? Give examples of both.

Can a centripetal force eve4rsz bp0fl0 9jr do work on an object? Explain.

Can the normal force on an objec rt +l a; twv9fhr3kvue63g2)u+q aw,mt ever do work? Explain.

A woman swimming upstream is not moving w:nk 4 g-mc6qg1bn 1jangar2(x ith respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on her? nxr:-kaa1c1nbnj4mgg ( 2gq6

Is the work done by kinetic 0pxfkbg++j-* x;tbln friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from undf+b;0+x* xjbpl-gknt er them.]

Why is it tiring to push htrkjq )sz8( ;aard against a solid wall even though you are doing no wo zq)s(atjk8 ;rrk?

You have two springs that are.e8s y3gh:k/rp bbmvw8 t,e7a identical except that spring l is stiffer than spr3 he.bga7ye pv8k/swt , b:8mring 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is frx5 w nddo:9xsu1s8g e,br,;iuee to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by tso1x :iwdrxu5,8u s9dng,; ebhe 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 doesfnwos6)o 4-httmi1 yz kw2p:( your gravitational potential energy change when you jum2mw )pozt :s1fn (tykwh -io64p as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all witp1,jk( x5y)b8axdw p.dbbl 5:d cj( rnh the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistan ldd,d1bp(xwaj(5 c np8)b5ky:xjbr .ce.

A pendulum is launched from a point that is a heh2b*rt+z-1l7o ,eiv)fgwh i night 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.tzhiwe *-fi 7hg,)obv l+1r 2n Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you .rfy) w9xke ckgu-gr-c 2u0r1compress the spring by pressing down with your hand and then cgfk.- cryu 0)u2 w -er1rxg9krelease it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by9 6dnt5 yr rn4m*z;opa a steel wire (Fig. 6–33). The instructor pulls the ball back an5ampnz ot9r n64;rd y*d stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potentialy(q9ln21 nwhc-0 arc gyq9w 6al33mk f0*ufhq energy when water at the top of a waterfall falls to the pool c9 c ak 2qrw9lq*qg-mh(6ylywnh00fu133a nf below?

Describe the energy transformations wheq.k)v v 8w/hx(e48bep h:i: oy/bvyaqn a child hops around on a pogo stick.

Describe the energy transformations that take place wii8 g3rh3i; duip-syp0g+) jykh 8 )cthen a skier starts skiing down a hill, but after a time is brought to rest ;idh)h8iyr- g ) +kip330 tp8jcsgiyuby striking a snowdrift.

A child on a sled (total mac k,tc yn yk0 s3cg 071dya)-mve*me16zm gwa/ss m) starts from 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 no friction, and (b) there is facz 10a d3vgmge/06 n mt kke) y1ccws*,y7-ymriction (deep snow)?

Seasoned hikers prefer to step over a fallen log h ; n 1ojch96hb:y+zmsin their path rather than stepping on top and jumping downh19o+hsm z:j6 ynhb;c on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fire3a.yki .y1x lrml-*dr d into a bale of hay. Assuming the hay exerts a constant frictional force on the arrowsay13l y-dri.k*rm l .x, 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, f6h9//f7w dfozob:b+es xwo6(a) ignoring friction, and (b) taking friction into account. dox6e9zo: w w6+fbfs f7h/b o/Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its orig4vg iiirog--t 5m ;e9zinal height? Expgmi;iv5ir t-zge -o49lain.

Suppose you lift a suitcase from the floor to a table. The work you do on )o)yr6sa*o mh 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, (cm* rah)6 o)syo) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the work.5to/z iny7j5m

Why is it easier to climb .wrn43aifm 5t a mountain via a zigzag trail than to climb straight up? nmrf.wiat4 35

Recall from Chapter 4, Exampl/jzn) z. qh8gu4m rv7( 0avrmce 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 energy concepts.).uchz( rj487q am/mrn zv0vg

  How much work is done by the gravitational force wuru89 d po,mr8 5g6,om x0yyufhen a 265-kg pile driver falls 2.80 yr,fu85 9myu6o8godpur m,0xm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m highudihx6,pu w/z +idv 57. How much work is required? /px+ , ddhwui67z5iuv   J

  A 1300-N crate rests on the floor. How much work is required to move it at con a);tj(c bjed(stant speed (a) 4.0 m along the floor against a fricti( e; jj)dbac(ton force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horih xl/o:np/ 5rhzontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effphrn5o:/l/x h ective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a flo q*mlqes 1(k8dx58jnior at a rate of for 7.0 s. Find d5 mj8s8l e1 knix*q(qthe net work done on the box.   J

  Eight books, each 4.ahcs w n(y7n;jh::yk(3 cm thick with mass 1.7 kg, lie flat on a table. How much work is reqhy (n;nh7yc( :kjsa:wuired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objectd5/ .w+dt vqims we might not otherwise be able to liff. Show that the ratio/ti m5dv +qw.d 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 accelerati0-yi4 krb yv1qng by a man who is pushing back on it parallel to th-ibv1k yyqr4 0e incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleration2s de -4,a 0gu/wbkpxe of 0.10,0-dpke buws2e a/ 4gx g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is lu m15k k1b0ceyinear 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, varis54bgz ) 7e ro3:ttzbdwi/,ties as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 i s3r,tzw5 eg4dt) : /o7zbbitm    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 actv38gw) x;a6fj:bos fps 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, 5 0o+le k;da iw,yc;oa(7fpxh 7n a4ruwith 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 increased? 4*e np: /;1e*;d 4xw*c qovmsrgonarh$ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electro0k e -k r3cdhpp4/yea,n $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-k0-pf/ ptr uynl-/n u,xgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an aveaz*bi+d-sg8 mrage force of 110 N on the arrow over a distance of 78 cm. What is +dgmi z-*8abs the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 czdo s1*q-; jk2heu*)s c ,mtrrm when the ball is caught. What was the average force exerted by the ball on t*uet-k,m*rrd;h cq1j)2o z sshe glove?    N

If the speed of a car is increased by 50%, by whal x6q04kru*l ct factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s react lcur04xq*6kl ion time.

  At an accident scene on a level road, investigators measure a car’s skid mark --lk-0;jolqx3zj)sy + 5*co lvtfybsto be 88 m lon3 -j+ kt)cy5-*lxq j;yo lbls ofzvs0-g. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is p.t4engt3*+cra/3bq1 fu ncshitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimatsc3ft /c.ura 4+t1hb eng *q3ne 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 id;( ao5tct/bx8bgnl17ig mz5f thrown straight up by someone who does 80.0 J of work on it? Neglect air resistancxtg7gna; 8 tl d5 mzi1cb(/ob5e.    m

  A 285-kg load is lifted 22.0 m vertically with4/ -blb9t i wil6ijrl:1;pkhb an acceleration by a single cable. Determine l94/blwli -j;ihp: tb16krib
(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 es*a gcipib;*l wc.*+much must this spring be stretched to ss pacc;*wi * ie.g+lb*tore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the chanasqdy 9,c0fs4ge4qf,y09sac s d in potential energy?    J

  By how much does the gravitational potential a+ckno342jji energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jumpa2ko+3 ijjnc4 ?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h wd;qo w2j 1yi5xhen it strikes a horizontal coiled spriq;d2 x5 owyji1ng and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.104rdt-) in*oe jh2 -qqi-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative to - i)r2tohdjq i- eq4n*
(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 j-dh3vgdyu1c,g,4,v3abfx nof a 3300-m peak. af b xj4yhdu,cv1g g-dv3 ,,n3
(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 nex68ga9 panrzc,:4 xvlg t 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 sprx gz4 96a8,plcv:a rnging line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) /jkf8 eh +8jbmvz2f.h+gff nk-n4o ,i and grabs a vine hanging verti++iz4jjfk,mhf2fnoe /b-n v h8 g.fk8cally from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictio:dvc6 3qi8u*kxz ( wvqnless 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 shov,u:4idey x1z o ,mg,b.r y tai-nf4l2)qombw 6e 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 transformed into gravite ru3kvbgy:jrf:xw/va7 *.m 7ational 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 v*3yu7 e:bgkr7j vw x/f:ram .bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward fi ntba l/xg8 + tpzrqf0r6p**+rom the top of a platform with r6pnq ga8bf/ +l*zt*t x0 p+ria speed 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.cfg0y7e /vsye i)1pc7 /ccl yass), whose spring stiffness constant is 950N/m is attached to a tabl0gl c sf7y p1c/e)/ycy7icv e.e and is compressed 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 without friction along the looped tp , xrb, wc.g:tlhz;dz+v 4) euk-jhm:t/.kewrack shown in Fig. 6–;eje:w+l ,h.g z:wc vhd -r,p. )/tzbtk4mk ux39. If the block is to remain on the 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 sprinjsl-in 8qy ves: lv2y69 i)ue2g (spring stiffness constant k), Fig. 6–40.esyis6v9l v q 2j)2n i-:y8leu The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumpercry9j eii4rs7- , fg uc(fn)0a jumps from 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 o(9nrra e j iicsuy7,c-4g )ff0f 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 it6kj*/pt+ tpg ;l-lxmu is released from rest. Assuming no friction, calculate ;+mtlx6- jktpp*g u/ lthe speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throhi g)x .v ,+z2bbvaqa1wn 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 sprin-4mg20 m.w q owrpp9oyg to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is atpr9m4y 2wo0wm.qp go- 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 cycle up vp lwy :v*3z p2sg80waa 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 76j5 cilzikz(-inj1i0650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this colli ijn5ii0kc1izj-l (z6sion? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reayi2xpfmu g 6 yn+8t6n6ches the bottom with a speed of 2.2m/s How much thermal energy due to fricti66nfng6ix2tpy+ muy8 on was generated in this process?    J

  A ski starts from rest and skb9um,4 l0t xkr(ua.n)pkggdq0 uz j c13 b,,mlides 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 abq*bua c+b(n +led 1+5ahc l0tkove 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 afyy u 7i:x3n*uvm9n;c height of 1.5 m. nnyfu ui 79y;m xvc3:*
(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 pu*vj yoq56:x hilled 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 thjyx*o5qvh6i : e final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pz v,n/,e5la esasses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach lz, / vn5,eseapoint 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0 mmxkspc)issd,lm l x+umr ,7 m5 h*8uln7175f$^{\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 attache5wxm9ndt 4a a7d 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 between the block and the twamtnx 597 da4able?   

  A 280-g wood block is firmly attached to a l q ehjt:6skd, s9,dl7;u qf3kvery 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 ets;hqlflekd ,: s3d 7kujq96,quilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glideror ljfb a;k* y(q9:up.” (mass of 980 kg including pilot) that was launched a.u ;9yrk*(pflob jq: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 a 315-kg -cx1a gg2 ti* vzs )pfhyi 9*k:p6p9hxpiano to a sixth-story window 1fy9z*9pi h)*-aph2 1p xkgtx6 i cvsg:6.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be .bnykrdsgoi ;t ty(4)v g(l88 s.dfy(the average force exerted on the car due to friction and air resistd ydtv fg) ;(.slb. oyrigy4(s8(k 8tnance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is thet9m wa97hvgg0 average power de 0w t9mv7ah9gglivered by the engine?$\approx$    hp

  (a) Show that one British horsepf as.7tzxkw1* ower$ \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 adyow3 lsx.sar29 h 81u)k4 otmre often expressed in the form 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 that her 1150-kg car slows down from to 65km/h in about 6.0 )o8 lemq00ay*tf2s0z)cz g5hq7tf ghsq7ah00 lm z)h cg *fezs0tg2q5o ytf)8 on the 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 m)fjf 8c f72vmdb/bfxw -g/qx+otor 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 s+v 2w4vl-yda 1r q(y(slbrp: If this motion takes 1.5 s, what average power (y2pv1dl s :ry swrlbv4+-(a qwas developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What o4yqln65 m; w33i m+lbqw v6xuqe4bh*hutput rating (watts) should the pump motor4;h nhi* q 664uqqm+ 5bw3ewyxlvb3ml have?    W

  During a workout, the football players at State U. ran upwy2os yy0d80.jcaj4 rg. r2jv the stadium stairs in 66 s. The stairs a .ryjjrcgo. 22yj0d0vs4wy8are 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 cl2 h3r gcxpy0kx(g y5+bimb 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 can it c+mu )lid lg;o5xuk 81q:f q9qdlimb at a constqq5d mk+1)xq uf8:di ul9 log;ant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have t( g1,iz5uh0gf(ebls kpn0fw ,o be able to drag a 310-kg box along a level floor at a snf k(p0b wghseu(1i flz, 50,gpeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow4vl+cwxu3 n/b+prl y *ld:jm9 n 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/h5yhn2ps /a1 lh) 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 el51n2s pay/hlhastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground efxwq91u fiet -omk*6z u:e)+zlpe22, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf h)l2u6+: *- z2 etfqepo uew fez1kimx9olds 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 nl:(6zjl ef+rn4n4b ;j noly+jump (Fig. 6–42) in the 1936 Olympics shows that his center of masnbjj n:loz4f;yneln (6+r l+4 s 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?   m/s

  The block of mass m sl y5x q(q8ajeby2hr p lvw/(:(kiding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the lq aehwv8kxyr: j(/b 2(5(qylpoop 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 withogz -sf/)(p dv8h/l0zq5q qxi twb.o;zut his parachute opening. He landed in a snowbaxbzq qh(fzdog w)s/-. tq0z8;v pil/5nk, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s 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 horiziorbg 3*9fu9iv9o e +iontal cord of length L whose other end is fixed (Fig. 6–43).i*3i brei+fg 999ovuo
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb hf/ . 8h7vmf,ad quizigt1f/) is made in 5.0 h starting at an elevationq/imt/, .)8vf f u f7hzghdi1a 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 elevswc8k8 fs yz*cr- 5tl4ator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can movlbf2;u d5mm3 te 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power dml um b53f;2tneeded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertica, ef90 3cu3 hva*hjdtully 81 m before striking the turbine blad*9dtujafc 3 u,3heh 0ves. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fdfmr-x) gr wj+/9ruc 7ig. 6–44), the difference in your apparent weight at the top of the circular loop and thecf r g)/jm+r-w7ru x9d 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 directla5e 4lplk 9-may into work, how high could an 82-kg man climb a ladder if hel a5m4l9-pak e 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 u .rhajqxs;ay*)l6di ; pward 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 scff c z7url),ajm4jo-4 ale compresses 0.60 mm, and it tells you your weight is 71am)j47zruj4 cfflo,- 0 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, an/*;wfhtwnb w y1b+wh3 d swings out over a lake (Fig. 6–45). He rele;3tfwnh*/ bw+b1 y wwhases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m ind3 krz8/aj*gs 9.0 s. Whadjas/*kgrz 83 t minimum power output was used to accomplish this feat?    W

  Some electric-power companies usev xsy6-m8of 6j water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energ vm8xoy6f -6jsy 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 halg30. dvkz/uhvhe m6r3r37kqur vd am -g)z:a3f. What is the spring stiffness constk37. aru au:r3v/h zm3 hdd) qgev-30z6m vrgkant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rbi-wcv3lx s1;7dxx h.ough 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 acceler7m(gj6r -uqehg)le )d ate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume th er6mjgh) g(ul-)7 dqee power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “st5/hcubjxvxdhe.+o or b(71pf/cq l 18ress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an+ e uqcox/81jb5h(1flbphoxrc v7 ./d 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 ro2sy5j. )imk7o ) optfcck vertically upward a distance of 500 m, what was its velocity wheno)ifoj).y s7pt 5m 2kc 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 2.0xs05 hh15rx8x hmac,k m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power output? h,am58s kh 0xr xhx5c1    W
(b) What is the speed of the water as it hits the wheel?    m/s