In what ways is the word “work” as us:eo+ -6koi p k;q ln/hbgt355yoqwc)hed in everyday language the same as that defined in physics? In what ways is it different? Give examples hql; +ooeno5 6:kcpw t )/5b3h -gkyqiof both.

Can a centripetal force ever dj xaffvr7 f amy:j2xo3x074;/i d w(bmo work on an object? Explain.

Can the normal force on an object ever do z8* vu /thm0vmj10v5;rjcl r uwork? Explain.

A woman swimming upstream is notrlk 82pqsyb65 moving with respect to the shore. Is she doing any work? If she stops swimming and meqyb65 2p rk8lsrely floats, is work done on her?

Is the work done by kinetic frict qfuc nq8f xy:tee:y/2hf0al 9)3p(v zion forces always negative? [Hint: Consider what happens to the dishes w/l02nx q8y(v ufyc fe)9e3zhq: f:pat hen you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid ;kpbzf u(a3-pnf k52z wall even though you are doing no worfbzfa 5k ;-n(k up3zp2k?

You have two springs that are identical except that spring l is stiffer than spwdu89pxpl xs al3d3 6nbr82/o ri 328ox ld3ux a8wbsp/pr 9l6dnng 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 tj: ;bro6h: tn;rjzr(zvv+ l2ahat is free to slide on a frvrhal ;jr 2rz j:6:b onvtz;+(ictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy cht 3kdop idcj- :,vz9k0ange when you jump as high as yovk,ij0o3d: zt-p9 dcku can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wiic2n z qju/(n 3tz0dj2th the same speed but with different launch angles. Which one has the highest speed on (3/nq u0jzj t d2cniz2impact? Ignore air resistance.

A pendulum is launched from a point that is a heighv9 bhl6, )a9d:kf xaqft h above its lowest point in two different ways (Fig. 6–32). During both launches, the peb6x,lfk hf):q9 vad 9andulum 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 the equilibrium position? Explain.

A coil spring of mass m rests .u6 )eu:a/kdftwdn6s upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conserva6:uf6 daw)utk .edns /tion of energy.

A bowling ball is hung from the ceiling by a stk. g5 zjdlr;s9eel 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 it. 9sd.rkz; j5glWhy?

What happens to the gravitational potential energy:q , axwvz)1m/tncs *w when water at the top of a waterfall falls to thema/:nwqtxw c1*zv ),s pool below?

Describe the energy transformations when a child h3o3gch/3(ywfrl x.3tz,vj wat 6 jxj*ops around on a pogo stick.

Describe the energy transformations that take place when a1 qbxfzy-8(ss s +,xhk skier starts skiing down a hill, but after a time is brought to 8qhxs fk(- s zbs+y,x1rest by striking a snowdrift.

A child on a sled (total mass m) sta mk7*2d xecm9jrts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on temdc *9k27mjx he angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in so4ypu9i)zc; qm;w c km8 lp++their path rather than stepping on top and jumw+pz)ys m8mco4p;+l cu iq ;k9ping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired *1+q-khft-a dt:dg-ru lb+w uinto a bale of hay. Assuming the hay exerts a constant frictional force on the a*td+ kf1ul -u-qawb:g t-+hr drrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum.8y,xnu cd+cmkf,jcq. ih .8a in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a granj f d cnc8.cqxh,.+k y.uiam,8dfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gr iuyo gx.l)v.4it:bf:eater than its original heii xiotvf u b).lg:4.y:ght? Explain.

Suppose you lift a suitcase from the floor to a tabmfh bg0)hf)4 tv -ueaw7 (zod9le. The work you do on the suitcase depends on which of the following: (a) whetb9wmuf)(4) z - fvd ohg0hea7ther 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 rath) bfn0 3dmiic(er than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb st);; b2tx6gf6ei +csfrjl p w4xraight up? w6+pstfx4 gebic;xj6 f;r2 l)

Recall from Chapter 4, Example 4–14, that you can use a pulley andbpl-vnal /q-k, la5ofv;ao -- ropes to decrease the force needed to raise a heavy load (seoan -vk--bvl5l paq;fa /-l, oe Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitativ +m+fhjfgelj9v6 -g, onal force when a 265-kg pile driver falls 2.80 m? +lg -f9vjvhfem +,6jg    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much workyn2 obb5cz.a n2zt8s q( ex1x, is requib. y5zex22qcaz,ox n(bt8 ns1red?    J

  A 1300-N crate rests on the floor. How much work is requ q -dn1x94 my1gtg:aatired to move it at constant md9q-1 n t:t1ag4gayxspeed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers dox+f/glbzhz, 2tp be7v3 e7*rw (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.5zeb7,3f*7g +hr zbx/tvepw l 20?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of forjs 7;lkhs tx ja ;g+)k0(kxsz:lq5y2c 7.0 s. Find the net wja lgxkhljx kt 2 ;sz0kc5qss:(+;y )7ork done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fla9e6yf x)ow/h6)ottts eg1 mz9t on a table. How much work is reqoo9)tf ys 6)zhtemx/t1w 96g euired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to l,f(jhipf yb/3iff objects we might not otherwise be able to liff. Show that the ratio of output force(jpb,3fh y/i f, $F_{\mathrm{O}}$, 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° inclinehmwa 4t*o;jf:nj mi)skxxl8)y g b3.4 and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36).nf3;bkjsg8hyw mio : m. ax)*)xt44lj 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 giv*qolh:+.kki +wccw e:qq0n )oe a helicopter of mass M an acceleration of 0.10 g up)wkli+.cc*qh:e n 0o k+q:woqward.    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 themb20ag+ir3r n 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 the x axis, varies as shown in Fijmpwu5om6.e 5ny;dsiv0b26h a6 fg0xg. 6–37. Determiiv; anbys 6w65f650 2.mm0phjoeu xdgne the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a payrraq-7qjj n d03 0g/eih(et2l vp4k)rticle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecu35 rkd5m3zbu5 v z)xjzle, 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 increased?mzd i* b*tevd)ak,:d9 $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elej34wof,/gll i0yun1u ctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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,c)58 ch *ep;oy ,d /dajxdqie a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firkp;h ;:2duiqqghw. zhkz ;6 :0zu 7sjaed from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow a7 : 6hsiz.gz :uazh; 2q;;kpjkdhqw0us it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves /9c,i ;bg njcmk*lxlk2m;/oizra3;r a fielder’s glove backward 25 cm when the ball is caught. What was thelimrcrn9*2ocz;g / /,b3xk lami;; jk average force exerted by the ball on the glove?    N

If the speed of a carnwl6k khrl,71 x ,c7ya is increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the san6 ckr,1 hlak, 7wyxl7me? Ignore the driver’s reaction time.

  At an accident scene on a level road, investig7u oh d.*vyiv q36cvg;ators measure a 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) the brakes. (Why does the car’s mass not yocud;.ivh vvgq*67 3matter?)    m/s

  A softball having a mass of 0z79t*z k w* uvch6jnkt5(qo3z.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resis*uw* k(q hzc75k tj39z6nvtzotance 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 straigkd8r xrg 5, *jj umu1c*hs5n*mht up by someone who does 80.0 J of work on it? Neglect air resistd5jjur8c 5 r1snumm* *h*g,kx ance.    m

  A 285-kg load is lifted 22.0 my :,my8v fjkm. vertically with an acceleration by a single cable. Determinemy .:y8m,jvkf
(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, ofy8)lb.r92q 48 d 2pi/xwjxk 7pgkgcww 440N/m How much must this spring be stretched to store 25 J of potential energ k9q8g gw wl87w2/bpxkpiyd). 2jrcx4 y?    m

  A 7.0-kg monkey swings from one branch to another 1.2 uaqe5yva3, u v99sf(pm higher. What is the change in po9v3 u,f(u5 ev9aya spqtential energy?    J

  By how much does the gravitational potentia ;iywj fc:9h/tl energy of a 64-kg pole vaulter change if his center of mi/c:h9f y;jtwass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal f6poz)l bk,l b2c( ;hmsurface has speed v = 65 km/h when it strikes a horizontal coiled spkh)l( , bcbp; lf6ozm2ring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book fyw4 xq)fwr 83ece04 z/ w8tqqerom the ground so it is 2.20 m above the ground. What is the potential energy oy0xc/qz43e 8qer4 8w)wtweq ff 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 cl;(1jz bp 6c,tg5jzx zb+pqht;imbs to the top of a 3300-m peak.zzqp;65xttzg , b jj+c;h1p b(
(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 ri j,.ot(stu px95xj,.zz chzf p3/+wbuler. The end of the spring is next to the 15-cm mark on the ruler. zxpo,tf3jip.,c .b+9t zj5(sh uz/x w 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 marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) a u wj fp ;u2w-h/(ew+xh4dih3pnd grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwa4hfeppxui hjdh 2u+w3 (ww/-;rd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides do6l3m9y .lq 90 rtvafqjwn a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a( vq/ am53 bnhqe:*cil 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 + ko9q*ntiwr92u fsp(+5mvootransformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in ordr2+qifnsw pk*v9(uto+ 59oomer 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 platform z+kp ho 1qqnmx(9 2a:qwith 1pa+h: k qmz 9q(oxnq2a 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 v mp(3*8vdsyd mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwar*dvms v83y(dp d 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 track s 9gco vuxu-+q7:4 gcddhown in Fig. 6–39. If the block is to remain on the track, even cx7d:ggu uo-+ 4v9cdqat the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (srj y*,su(rkxpn+7- kopring stiffness constant k), Fig. ,pyuk+s- o*nr 7( krxj6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord who gue+3 6 fsyq9b9cgai:y* bmg0se unstretched length is 12 m, and ib9cmy* 3 9ugag:+q6f gsb y0efalls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to po( ,merejqgh: 6int 1 where it is released from rest. A e:(rhq em,6gjssuming 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 g e 5m+(nfd jn-c98 +mtnt1xrsspeed 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 z;l)ccr (2kzmnz 5p.k the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mas5zk2( ) lzp;c.mcknrz s of the elevator and passengers.

  A cyclist intends to g7:9*vjttj +.gfr6pa o h b4hew1 r;gkcycle 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 bnxs of .h1b h+q1e 5yr8rmw)u-i8r2hmass 7650 kg and traveling 95km/h in opposite directions, collide head-on 1fe2.qs8mrir1r -o b8h xw5 hun)+yhband come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descewq(+sd9y,vcy m69u iz nds a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energuw6+i(9ydc, sy m 9vqzy due to friction was generated in this process?    J

  A ski starts from rest and slidrwc: r:14rhd.xya(m nes 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.j6w zijp 6:1hi0 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 height of n+oz1du+nhz6n1tj9u 1.5 mh d91+n znoz1uu tn+j6.
(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 q7(4mt5m:kmmt g :7ibhz9ezerest, is pulled across a floor with a constant horizontal force of 350 N. For4t g m:7mh ze(:t5q e7mk9mizb the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of ;byztg wg49. moml 55i If the average force of friction is equal to one-figt .wogmi5 9mb;y54 zlfth 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 o6 hvrfc3y-xs 0f a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring 8vur i6* 1;fh)rwl-zbvopqq5 (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5v -ol 1 6 wqf8qvihuprbz5)*r;.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 attachein4a: ds1)pyby z s:+sd to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses t+ a1y pbsy)ss4dz:n:ihe 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 shr. m/m jnosyivks./dy .e;;d8uttle used a “glider” (mass of 980 kg including pilot) that was launched hony ;; iov/e /.ymr s.8dk.dsjmrizontally 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 piano to a six o8dzf9i2f4vepyw ,5:xwf)dv th-story window 16.0 m ab54wzv,w vfpxo)i9 8dy2: edffove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be0r- h- u0f/)fkgz jntlzt d5t+ the average force exerted on the car due to friction and ai lz d)-jturgtkf h0z0n5/f+t-r resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avera kvb7bijz wky7(an0q+k,f65 nd/: tkd pzj1;bge power delive5b:kbw0p+dnn,a tj iky76 z q(fz7bj/kv d1;kred by the engine?$\approx$    hp

  (a) Show that one British horsepowef(mzw0 g/us (e80 bvp+r0x ypar$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hours-sb rauyl+69vz;az/ 3cz) d 7x )5rw-atpsh gz.”
(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 11p.kbq.yr 3mx1 50-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) is needed to keep the car traveling atrkpb ..qy1m3x a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h?gcatnal w-.o*+u2o l4 $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion talf k:w/hkj7+w kes 1.5 s, what average polw+7 f/khjk: wwer was developed?$\approx$    W

  A pump is to lift 18.0 kg o y(jz1qm0cntv): 5def-a snd :f water per minute through a height of 3.60 m. What outpn:q1v) smaj:cfz5dtn (d-y e0ut rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadi. w)oh gl3np:eum stairs in 66 s. The stairs are 14gpe3n lho )w.:0 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 cycl 8akvy avstn2y,8d ,0tist climb 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. Hq9 bep(n ;s:ul i,dy;xow steep a hill can it climb at a constant speed of 75km/h if the frictione ypiu(:qx,sd; l b;9nal forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able soibq8t uleu -1xd;gf l ): (8amt3n1wpv52eoto drag a 310-kg box along a level floor at a speed of 1.2m/11qf 5ubt8d32x;)ln :vmoe-s(teiupw ag 8o ls if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dc(jwrl8njeps 7* 7ij /.exbp3 own 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 bu .pb.:6idjnw r/mt1: vjzbiu;ilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective sprinpn.ru i ./1d:bt ;vzi jm6wj:bg 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 cmxf7,yo duuvz/r.2c ru og81*q off the ground, and the remaining four shelves are 8uqo /ou.,cz *r72f y1gvdxru 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 the 1936 Olympics shows nml(u*36: -ea9jeiv uzsj.cu that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed didm*vs 9 : e6(iuj.zclaenj -u3u 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 frictio97 i+gomyuuv;k q3n1g3ls/ b wn 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 loop of rv3 g9l;ynk/+um3g1u q w si7boadius 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 370wkns9x- 2t8m 3:rrnd.tm( uie m after jumping from an aircraft without his parachute opening. He landed in a snowbank-t8: .3m(rn2ri t eu9kwsxmdn , 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 horiz*rab+ ju4l)3m tml hb*ontal cord of length L whose other end is fixed (Fig. 6–43hl* 3 )mmbjr+utl b*a4).
(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 clijvs:1x6g ghk )uc3 eo9mb is made in 5.0 h starting atjvkghu9s6e )x3 og1c: an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge spring (v4r kv*k* e hpx+()ww86rw gcq$k=2.2\times10^{5} \mathrm{N/m}$) 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 icvl r-t91kxkloi334 claims that its lifts can move 47,000 people per hour. If the a9i3x31iovlr klk-t4 c verage 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/s and falls vertica4 y+rz c:xlhf,lly 81 m before striking the turbine blad:czhrxl4 fy,+ es. 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 (Fig. 6–44), thef9vzz/ dd::3zcw(8ma yyboe+ difference in your apparent weight at the top of the circular loop and the bottom of the circular loop i+ cwmf:3v8 ez y:ddyoa/( zb9zs 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 bodyu)qtmn 2qe7jp7wu o4( could convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bu(7qoum2) j7 4pwnqtear (=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 angl*. : nd(hd(fhg,kk2xde54o+o kq lfvce 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 compressesijxfw1 hfk3 w -n)bi(4 0.60 mm, anfki 3jx)4wbiwh (f-1nd it tells 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 gran emoztl+);swjk7r( w 44z1t cbs a rope, and swings out over a lake (Fig. 6–45). H sw l1+tnk;(4 recz)4tmwjoz7e releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs 5 4z kb.ne8/z2jihokha vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat?ezoi42n8z .jhbk/kh 5    W

  Some electric-power companies use wate2 6 zsbzq3 dz*s+ gt1v*xfzc0ilp6n/wc00he rr to store energy. Water is pumped by reversible turbine pumps from a low to a high reserv*r/+gz0 xpz3dsvi zef 2 tb* whz60ccs6 01lqnoir. 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 sh3 g9b)j ;b6 ram)holstiffness constant k is cut in half. What is the spring stiffness constant fo)boh9s;agbr jhlm6) 3r each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.4 8qw2rd*ehgjcd 9/xz 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 acceler4+*zve9,vkii9 kcrjc3bmpeod *- 8ebate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h iek,+*bvoejrcv8iz3mp c-be 4d9 * k9 to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac6mlp;(z6gq9 dx 6go rp function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is ;6g gp 9moldp(rzq66x 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 verticallxo(3qn1w0j yc i8ku 3ny upward a distance of 500 m, what was its velocity wheno8n(0cy 3ik3q1nx jwu 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 ab kxy(h(r/rk) height of 2.0 m at a rate of 95kg/s (a) If this rxyk( k hr(/b)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