In what ways is the word “work” as u 40 grit((xxuv 6dgsvtk.x9x (sed in everyday language the same as that defined in physics? In what ways is it different? 6xstxux09(ggv t.v(xr (id4kGive examples of both.

Can a centripetal force ever do work on an object? Explai3ij /.xzzt yb(u;v 1scn.

Can the normal force on an object ever do work? Expla5ir p4v89ek qlwt 5fqf59y3pxin.

A woman swimming upstream is1gqq0: tprq/y not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, 1:/ 0qgtqqpry is work done on her?

Is the work done by kinetd.4sbsrq msdgxmm.. hev61o,+gc; +s ic friction forces always negative? [Hint: Consider what happens to the dishes ,1ss.4mm o;qrdsx .mbchdev.g+6s+g when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are t3nhq70,o n gqdoing no wooqn 3thgn07,qrk?

You have two springs that are identical o/fsdmbs4v( xg*wfry 7/0je5except that spring l is stiffer than spring 2 /(e x5/o4 fsv0*bwdgfrsyj7 m $(k_1>k_2).$ 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 dj0r.jv7x. jef. a3lc7+qsiion a block that is free to slide on a frictionless surface (Fig.6-30). The blocaejq.l.vid7ixf7r jjc 0 3+ s.k 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 gravitationf4bw aj1 (0v:-bc vqzqal potential energy change when you jum jz41(qvf:v -b w0bcaqp as high as you can?

In Fig. 6–31, water balloons are tossed fromeg67ux5 v (n -u t:lkw9ynzkjoh::h0 t the roof of a building, all with the same speed but with different lauxz:h0u( :nhtoejy:v6 -5 l79nk t gwuknch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a pofe k;*(ann m2dint that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first 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? Explad en*mkn;fa2(in.

A coil spring of mass m rests upright on a table. If you cvxe7t9 f rzcx7u67-p gompress the spring by pressing down with your hand and then release it, can cpt9xe7vz-g76 7rufxthe spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a sterps9/r1tf ,yqx gln0 .el 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 t,9 .nql rpxfgs1/ytr 0o release the ball without pushing it. Why?

What happens to the gravitational s3d u-;mpk/r4z-gn alpotential energy when water at the top of a watprklus4z nm ad/-;g-3erfall falls to the pool below?

Describe the energy transformations when a child hops around onbitl 45m2os f- a pogo stick.

Describe the energy transformations that take place when a skier starts skiing nksv9wxhnf hs235aqow1 1*6n74fosjdown a hill, but after a time osjn1 34w1hf ss*9q56w 7fhnxo2vka nis brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top oh :av qxh*/ sdogt:fk19-acbv lb:-3qf 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,fcq s:3qdh bavt:xkl /g1hbv-*:o -a9 and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rathermc u8c95efcyz73. 4f 4oompu r than stepping on top and jumping down onr5ze u4f4m pucomfo9cy. 3c78 the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired iil+ y+wt9k p pww(*sn9nto a bale of hay. Akp9n(s+y*pilt 9 + wwwssuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple se3 p1 sx*qra1csoe414nlf8ugwinging pendulum in terms of energy, (a) ignoring friction, and (b) taking frictrl qe114 n4eoau31pcsxsg* 8fion into account. Explain why a grandfather clock has to be wound up.

When a “superball” is ho clh5y.noz2 v+i t;l) g,-lmg8wyt( dropped, can it rebound to a height greater than its original height? Expghn( o5lztyimh c8o)t yl; ,+l-w.2gvlain.

Suppose you lift a suitcase froy *8zn1ppxmfua. gis8omdk a3b9+l47m the floor to a table. The work you do on the suitcase ayl1inm9k. sb p4 + 7da88*mzfugx3opdepends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 forgqmab j:c z wm0 40z4fo/e*vya1a7w*z the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straie5.ab zpk7c0cx/ elz2ght uax p/.cze ke0z lc572bp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and rov52bc62xinw mpes 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 bnmw2x2c vi56 pulled up? Account for this, using energy concepts.

  How much work is done by the gravitat/ .4ip.je t:ovwn7nw oional force when a 265-kg pile driver falls 2 owt.4w:nj .7von i/ep.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairsljy7c9tn3gd h9hy2f -dt;7daw tu-v4 20.0 m high. How much work is reqn t d h2u7497g-9jvyyathfct-dw3l ; duired?    J

  A 1300-N crate rests on tohn c4l22*pbbhe floor. How much work is required to move it at constant speedbhlcp 42bo2n * (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 do (horizontally) pushing a 160-kg cr8i:;knhqq*r1;po-ix fn fzj:ate 10.3 m across a rough floo*q p-zi8fh:1 ;xifjnnr k:o q;r without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fdto :nhqw65 p9loor at a rate of for 7.0 s. Find the net work done on the6h:t9wq5 ndpo box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How m00gxrbgf*qe/ uch wo0 /qe *frg0bxgrk is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we might inb rs*gv:;,v6u3z xn not otherwise be able to liff. Show that the ratio of output force*u6ngnr s 3b;viz v:x,, $F_{\mathrm{O}}$, 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 ac:o rw(r0b ntkyv) zz8;celerating by a man who(zo;t ) zbvr0: kwy8rn is pushing back on it parallel to the 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 gidnd*ncfxf ,q5z4t 1 *bve a helicopter of mass M an acceleration of 0.10 g upwart*4q*d ndn c51xzfb, fd.    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, assumeg5p,o: /7qzmw(d2zle;; dcdeor hzf0 the 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 x lzfr ,2d2+p;fczq h v9ksf.(xp7uv7gcb:/ s the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x v;(q ld97 ,r/fcxp2u2gf+bkp7z.sx v: scfzh=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 9d8pp +ud-9y d9hz od(ao5buxin the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass of lc) 8/ iptol ;*x( jyttin8u*;7r gfzf$5.31\times10^{-26}$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 gc /i:nxg ve(4cl *(niits speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requirble-k6-f( g+g 8yt kueed to stop 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 travel;l1eewii4)e fp/ p ol5ing at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts av4xqc,:f -dro.r5cz9:oi ,t lkr z y.bn average force of 110 N on the arrow over a disrcr,,r5oz zxyv:..q: f d 4bi 9clkt-otance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove bacubr7k( o0 y 7:i0vytm2m* pypl0nuh h;kward 25 cm when the ball is caught. What was the average force exerted by:mk0rhyv77iuotn2(p 0*0y b h ypmu ;l the ball on the glove?    N

If the speed of a car is increased by 50%, by what fats+pu m)k*sp- ctor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s rkms)s p *-+utpeaction time.

  At an accident sceneo86u 1ei, s0hshrc -kq on a level road, investigators measure a car’s skid mark to be 88 m long. T1rks u h8c,q6h-is0o ehe 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 pitch-+gb 5sf w9osaed at By the time it reaches the plate, it may have slowed by 10%. Nefg9sao5 +w- sbglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by bcjt8c *6ea/l 8-zg m:yxijk0 someone who does 80.0 J of work on it? Neglect air resis:b/ tig0e lcj 6j ak*-zcx8m8ytance.    m

  A 285-kg load is lifted 22.0 m vertically with an 5 d( .k 8p0vjylw2ljhojxa 8b.acceleration by a single cab8b 8hx50a wjodv( yl ljj.2kp.le. Determine
(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 springtudm u(6k.ks(it wb7 5g 0vjf1 stiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of d(igtt7mbk.(u 1ku s6 vw f50jpotential energy?    m

  A 7.0-kg monkey swings from one branch to anotherime6n +gy. t b)gk,x3q 1.2 m higher. What is the change in potenti+ x6n, 3mggy tekq)i.bal energy?    J

  By how much does the gravitational potential energy of a 64-kgb8 sewq*uz4z yd +c-v5 pole vaulter change y ebqv-wz5 u*z8+ 4dscif his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizolqdi i hw lkp +:3k z0 lp6.yylcw0l*(d696coontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?zl q olk+ ic(0id6 phpk69:y yww6.o0ll* 3lcd    N/m

  A 1.60-m tall person lifts a 2rpm3 -aa4f5/f-c w;eq 9fdq6 ativhx g9gf6b 9.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energ /q3f6fda5vi9q6 - - g4p99 cxf; gwtbafaemhry 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 a 33 )0mcnw +w9 sio)se:cu00-m poc ws:imn )0 e+9uc)sweak.
(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 vert*a gx x3o ctnpk+3(ku0ically 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 thcx03n *(aku g+3kto xpe ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vv: *hmg0i4bihine hanging vertically from a tall tr*0ibi 4hhmg:vee 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 frictionless 35rr7163*ew gf;kb, (jkzxd*d;tkg yv 7uzgm.x.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 aa y(2 deo0i codbb86a- shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s k: kfnjjs//a wni1sx: +2s( mqqinetic 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 ofq(m xsi2 ks njnas/ ::f+w1qj/ mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertic4 kifk0b )-0rvq wfg h,xyx/6fally upward from the top of a platform witkxyirfk)hq 00fgvxf , -w4/ 6bh a 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 mass), whose spring stiffness constant f3 ndw 0 bx0cl)cx4ud*qvo45jis 950N/m is attached to a table andq 4lbjx4xwc0 d3f0oucn5v*d) 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 tra,u-mlvp.fy. s6n 9f ywck shown in Fig. 6–39. If the block is to remain on the track, even a ,flvy.-m p usy69.wnft 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 t:+lcsp;n7y c0l-r x1bkn/g tco the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given anbg y+-1ck: r nc;7/t0p nlcslx 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 whose unco/k 7 wi8tnzf7x++nyv + hj,gstretched length is 12 m, a/z+8nw 7o+xjtigfny,7 c+ vk hnd falls 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 Figx 0zi8o-h0fp* l ugejhl;(/w j4r-t if. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at*8e4 jfuhzipxgjh0- lirwo- 0fl;t/ ( points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed :q ,xhwaytsmv-;;8y z 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 designivo /cn, ,x./ 2ljaj(cre*xwowng a spring to be placed at 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 whrox,/xale, *wwnjc.v( 2 /j ocen brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cwv2i*j/p r,h//5wuxwia. suqycle 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 765tvl) 8(pcun7o w5 jm;i0 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermaot)v j(p5u w;m78licnl 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 a;a . zi9l5emjreaches the bottom with a speed of 2.2m/s How much thermal energy due to fria 95.m;eiazl jction was generated in this process?    J

  A ski starts from rest and slide b/) sf;tbiuzrs;c, -iu)ani, s down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the06;m bgsmi f*6rmnl2whg zs 56 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 heightek13t bth) io0 m4ru(e of 1.5 m.()e bir u0h k3eto14mt
(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 fromm5gv9dl7 kgnkg25is / rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floo/ dlgimg2k s575nvk g9r 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 coez9q ew0d4rt1 9vl7b taster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 mqtbvetl97 r zd10e w94. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.et(ltgo: :tz(pm9ps, gs7 *tl ; bsbm(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 v8tojy .e w s je tbvg+1*()gbwh)o6-v l1ued*yery 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 8-o.e6o)sljtyet1+(vv gbwe dw 1j b*u )*gy hof kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached tojuq -,dm.g)3z bdd/eb 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 thezb,./dd )-qg ed j3mbu 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 “glidj28gj3y +l whx;s tr*ser” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) Whatw +8jyh jl2gsts*;3rx 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 sitrva7g2r cpy ,/ q,4zexth-story window 16.0 m aboveg qpvr,tc247 rz/ya, e?    s

  If a car generates 18 hp when traveling atglmc7tt-1ekuc. a,/t a steady 88km/h what must be the average force exerted on the car d1-tkclu ttcm/a,e7. gue to friction and air resistance?    N

  A 1400-kg sports car accele+g8 )g3u(yyj ewjtu7 mrates from rest to 95km/h in 7.4 s. What is the average power deliveredg 7)yjyt8gw jmue(u 3+ by the engine?$\approx$    hp

  (a) Show that one Britishf + ju9g g1p5x-7d0yjcig,r rb horsepower$ \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 expressp z9r6seg0 7)aukyvym,e 5va:ed 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 115p7i+(ar o yxx70-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 travelinoya7x ( +px7irg at a constant 75km/h.    hp

  How much work can a 3.0-ay,f.p)w/g5 r ua lq lqi23,myhp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motio8 ukih+*jjy,8ctl qo;n takes 1.5 s, what averyt j+oj,l*8k q;8hcuiage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height ofwmy s9esm0 4y- 3.60 m. What output rating (watts) shousmyy ms4we90 -ld the pump motor have?    W

  During a workout, the football players at State U. ranln)bl z8ubg 1* fn bjog825;jo up the stadium stairs in 66 s. Thezl lbb* gjj8o15n 82gf;bou )n 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 cycli e+ttg b7+)j6iamccg qy4q;,rst 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 maxi c1 hs/j/z/s.ll bb)benvt 4e,mum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forc. cnl/1)svlt/b4,eehz /js bbes add up to 650 N?    $^{\circ} $

  What minimum horsepowe)o- si 9ql.ng pted8,lm1q *xsr must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s-q*g1lo. sndm8sei,) l p 9txq if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0a,dkk pjn 9pwf4/d);g lor6q-vzpt +7 $^{\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” thazul1u-jh sm z*/ze3:q/ izp670s nyvs(vo)w at are designed to compress and rebound elav/ave)suz -yo hz06/pl zs :uz7q3*(wm1isnjstically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cmj k)q4, 6fhqy8avvsd , off the ground, 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 holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flj8ha6vv qf s)k,dy4 q,at on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympis6-e h4zi:-r;c efy yhcs shows that his center of mass rose 1.1 :f-ri-y ehc6se4;y zhm 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 slidingkc. ol h;ti7rnq i*/,g without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very t/,7iqnot i r*g; h.lckop of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft / ,zqdjw rd d:ql43ae0without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’:zq /w30dej ,ad4dqr ls 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 fixed (Fb - 20yh6yit hqrpfp1s hu (1x8xon0p;ir ih8h0(px-t n6s0;phq2ob 1f yyux1p g. 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 to56 .1pgt*cmxnf7im dkd ny7m . the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation okx7d*dcy 7m . mngfpmi16.t5nf 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 p.h*(6jf psti) jqe5xa 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 clai 5cbdth07 k+uzms that its lifts can move 47,000 people per hour. If the average lift carries people aboh5tuk+0bc7z d ut 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the l8n h t)r0cbb*rate of 650kg/s and falls vertically 81 m before striking the)h0* rcb8tlnb 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 a ci dxiv+c 3ct pisvzs)t+p l.o3p/w:f0+rcular 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 ipticdvi+w v+c .st3p :fx0s/)3+olzp s 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 2zw)kq/ vd6 zaj j sh6ss:,;kjcould convert a candy bar directly into work, how high could an 82-kg man climb a ladde)zzahvjj:/,; j2sqs6 wkd6k sr if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upw/ gv72n,c vloeard 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 0.60c cw2in 1c+y05ya fpc-6/yxlx mm, and it tells you yo0cy/ y wcl1 2 xcy-56xcapfin+ur weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a l n7 t9x3ryik6bake (Fig. 6–45). He releases the rope when his velocity is ze39riyk 6t7xn bro.
(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 0v c(t 0mphl -ol2n,dd72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to a0 ,m0l (vd-pohtdn2lc ccomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by rev n:xu p/3,* lh *jjw*7cxldzzfersible turbine pumps from a low to a high reservoir. To store the energy produced in 1.plu l*/7zh* , xjcwn z:3fdxj*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 -ha(k6s t(r1 xgf n9jvk is cut in half. What is the spring stiffness constant for each of the two resulting s6f nrg ts(h-9ka vx(j1prings?   k

  A 6.0-kg block is pushed 8.0 m up a rouvrnr e) 9d8j +xgp1r;5zvj +kjgh 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 acceleratn9bc2q a2m* mae 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 9 2mb*qnac2 amthe same, and neglect frictional losses.    s

  In a common test for cardiac+ddbcwh+jo//fsjo 2/ 6qma +*9wjy wpo sb0l8 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 treobjs6ajfj/l hdw wo8p +9+/oqyds 20+ c*bm/wadmill 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 500vd,9zbo (o4be-kg rock vertically upward a distance of 500 m, what was its veb49vbo(d ,eoz locity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a) Ia/b0um+rt / sa8 v)hoqf this watmq+)/0u 8/ ra tabovhser 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