In what ways is the word “work” as used in everyday language the same as that z9xd+yzcw7/rs u)ww 30lh0w mdefined in physics? In what ways is it different? x9+ zsr0wmu/wzd)0c7 y3 hwlw Give examples of both.

Can a centripetal force ever do work on0 cos:qbro-:j 1eku7f an object? Explain.

Can the normal force on an object eve*a/ pc.;sclz rr do work? Explain.

A woman swimming upstream ijg,zm/5tz e voju2f+7 s not moving with respect to the shore. Is she doing any work? If she stops swimming and merel,vzg2ej7u / m z+5jtofy floats, is work done on her?

Is the work done by kineticea 2utlw fde*+:0wi0ct1g gf: friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tfcew+200:fwetg *gi: uatdl1 ablecloth out from under them.]

Why is it tiring to push hard against a solid wall evh o7y/wkd wjuv i;i;7(en though you are doing no work?77 i/yo(;v dhuk ;wjiw

You have two springs that are idetu,83uxh4zycd v p6t: ntical except that spring l is stiffer than spring 2 u8 ,d:3t c6yhxz uvt4p$(k_1>k_2).$ 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/xi-fgcn/ be* horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). //-fnb *gcxieThe 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 gravita)um;m fag,znd*-)b t8-dy1m3u hovly tional potential energy change when you z1) - 8dd-bhmu;n ual3 ,yvt momgf*)yjump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all hf.7*fueeld/fg : bg3-oms+15rr qzowith the same speed but with different launch angles. Which one has the highest speed on impact? Ignore ab7o1 5rgfs e.h+-lfq*d/ 3gmof:uzr eir resistance.

A pendulum is launched from a point that is a height h above its lowest poi0e*dvld 6v*m eyp (yz3nt 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 large edz vy6yl dpme*v0(3*st angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If yh:om ce,qd6 h(7ply4l/f dod8 ou compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using thl/ :mloc( ,e87ddfq 4hpd6ohye law of conservation of energy.

A bowling ball is hung from t4+l 3 mebhi)v oz1jn4ta-u ni2he ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To anih tuml j4nav4 z oi+123-be)void injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at thcd7yb3pzq8c,u8+y4c8n2 qwh jg :xzae top of a waterfall falls to the pool +a:jn wyqzq8dcc3x z 2p,bcygh884 u7below?

Describe the energy transformations when a child hops around on a pogo stickjg+hogp 0)6tgr. o /qk.

Describe the energy transformations that take 76i61 sa.iddio,fl6 wqpbk zoz 02oa:place when a skier starts skiing down a hid:6oq61.wod za 0af 6ii7losp,b k z2ill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hir9+-8egfdy(s 4 y8bm vf) hihcll 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 friction (deep sno e dyi+v hrmgf8-b(49shycf8) w)?

Seasoned hikers prefer to step over a fallen log in their path rather a+mr n qjlh*d2b/::xn than stepping on top and jumping down on the other sid+rb:h2*a l mn:n/ djqxe. Explain.

Two identical arrows, one ay ie5hu2 i3j )oy.clsa) h.)awith twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explaayj 2 iac.oe)3ah.iyu5l )h)sin.

Analyze the motion of a simple swinging pendulum in termurlf m ;p0):h unwn,,gs of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a u,:nmr0 wl)uhpgf, ;n grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heiq9oy xdh.a 7hl3god.g 302ge6)gs xtpght greater than its original height? Explao60 dxphe ysldha o2q.. 3g3t )7g9xggin.

Suppose you lift a suitcase from the floor to a 5-:k fj(c(d ljqrq tw,table. The work you do on the suitcase depends on which of the following:rwqkl (jf(-:5,t dqjc (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power il0k ph57ii4o) xrd,tneeded rather than the work.

Why is it easier to climb a mountaiot3 ./u8nli-ht o a3ifn via a zigzag trail than to climb straight upo.tti u3i- /hn8 o3afl?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes 8vpiqj1/hv o/t::hran rz+ a, to decrease the force needed to raise a heavy lo vnjrioa:q/8,t+hr/a ph: 1vzad (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.

  How much work is done by the gravitational force when a 265-kg pile drivez *)5k5l phqp 9p6*dn imn1bwpr falls 2.80kdb59wp 1qml*pz*hpin 56pn ) m?    J

  A 65.0-kg firefighter climbs a flight of s ;.1 wun(jf*7th-a 9tnlt vtudtairs 20.0 m high. How much work is requihlvf n1 d(u- u7wj; ttt*na.9tred?    J

  A 1300-N crate rests on thee* h hlwjc.mn0fi6ay6)y8ji 8 floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 N, jhyl )6ij08n 6fih e.c8yawm*    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1d 1:8xan)jzok fihcs5qxk0k+h*o 1 b s/onx-;0.3 m across a rough floor without acceleration, i+oco1xq s)h5i n 1/8;zk-*dx: kas j0nbkhfxof the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratem0 rrzfciu3. ;d by a force across a floor at a rate of for 7.0 s. Find the net work don03cr uir ;f.zme on the box.   J

  Eight books, each 4.3 cm thic jer3t)7tv.p 5swzbf)ayrn 2 y g/t23tk with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of another?svgan tbtw 5) zr2y r3t.3y2ef7 pt)j/    J

A lever such as that shogp7v :-aby2be, 9vasgu9 /vxfwn in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of y 7vfa-v29,baus:/xev gb 9pgoutput 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 3.62glwm 8wy 1n7b m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. wbgm ywl1 287nCalculate:
(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 eyta; zsfog)w ew3041o7q au( an acceleration of 0.10 g upq1egfsa30o7;wozu ( tw4 ae y)ward.    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 axigxh g-ufnnftw5; c/k* x 1 (;uavzjt(3s 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, acy03jk 5rhcx 1rting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) frojkrrh 5c10 xy3m 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(z3e6 envw8wx on a particle 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,sczx4 xiz-9xi. 04jt c an oxygen molecule, 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 bk 8*;g0v0rczmi xik- factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requ:ld+jaf(ej++ 4)y2drlaf trj ired 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 n:ou7)ofv wax b5/ 9 dpqk(d4bdone to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force 5juc3k (a)hivof 110 N on the arrow over a distance of 78 cm) j 3c(h5viauk. 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 backward 25 cm wheqz64s5e 1e/ un e,*olygfkk *kn the ball is caught. What wak6o kn*eqfy , l*u/zgs5k4e1es the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factav0*jqjx5*bl i(o ox *or will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction v *jo*jbiqa l0*xo(x5time.

  At an accident scene on a level road, investigators 0;q6 k*) ctc(/ga b ijp,51yvjb.naidv0 uouemeasure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic frictq ./b,bukd15j aa 0occpj v*iye 6gt;0viu (n)ion was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at 7yij*jn r1+v:2q/oy9 1* drwfupuorr By the time it reaches the plate, it may have slowed bqr1+yw*1r op9j rd7 uj:*oru y f2nv/iy 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doe l0cwd*u)izu4s 80.0 J of work on it? Negllu*w4 d uz)ic0ect air resistance.    m

  A 285-kg load is lifted 22.0 m vearqa8+g o *ekmw 35,5mp1ed+tfj :j eortically with an acceleration by a single cable. Deter+j1: k,aoa5rgqf *e3t8w+epojme d5mmine
(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 co +*8hn:lpjg ayxt+e6r0g/ q binstant, k, of 440N/m How much must this spring p/he:l*tb+rg qg+x0n8yi j6abe stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the j2xj0.eiei;zeaj l5 9 change in potential energy? 5iij2.9 e;zlj 0aje ex   J

  By how much does the gravitatc*phrf z23ezw mmie.*q,(y+ cional potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jz cqp3mew*fm(czi ryhe,. 2+*ump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it striixo6-v0gaa0qat j(0tk/ nx,b kes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the sprbt 0 a(q,ig vjoa00k-a n6xx/ting?    N/m

  A 1.60-m tall person lifts a 2.10-kg vti;u:7ft e:lbook from the ground so it is 2.20 m above the ground. What is the potential energy of the book retvi:f;l e:u t7lative 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 (csc36sg6mou-rj / szgbm 3v/ l;jka7tu8t7r an elevation of 1600 m and climbs to the top of a 3300-m peak. vo/-s7 mcz s/gg(t ;j kubs3l86jc7r3ur6m at
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end o8b(;+h jayo imf 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;a hm(yio8 bj+ the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine ha2kb )6j wwyhl7nging vertically from a tall tree in the jungle. How highby) h7kj2 wl6w can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, sl82pios6tibynw t* e,q28ij 6oides down 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 frictionlesy c9u f:fi ric 1.a-u4-8hfyhts 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 transfq i9q;7 a rpbydh(:/s-rom5t5:x wimformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10bw tq /h (-:xm5qim:yprrda5s7 9i of; m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertix5h yla czr:-kkrk1l02i4m.jcally upward from the top of a platform with 5kl 2.jrxr-:ak iyckm 4l0z1ha 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), whosebe) q yxr;/r7fsh+jl8 spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) Wh +e;8yj)sxr r bhq/fl7at 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 alo ub7im7k n4)reng the looped track shown in Fig. 6–39. If the block is to remain on the track, 7imekr u4b 7n)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 attacjul meg.w*,0 uhed to the end of a spring (spring stiffness constant k), Fig. 6–40.,.wl0*jueum g 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 ,: mfahu)s3z eo(tun*is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate thue,s n :)m3 z(hu*taofe 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 point8bob0 gcpu4 .h 1 where it is released from rest. Assuming no friction, calculate the speu8.0b4hob cp ged at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of xbnwn+) ql) v/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 .(*/6 n93wl. ouz pxezmlgqzv4ekf u( 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 tlw9o((unf z36p/4qzmv xee*.g k.zluop 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 updiodwbt-jx1y(wd6 g) 2tw , /jgoi2 ;d a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in ksi)s 2i6u:bi opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision? 6)i:ikbu2s s i$a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with hlivd(* dp h1+s fs94ha speed of 2.2m/s How much thermal energy due to friction was genhlpvh91(ds 4i+* f dhserated in this process?    J

  A ski starts from rest and slides b*g hkgngd*u 1-r-cy+ 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+ )bng2/t0/6 foy wpi nx0guknl /0uxd a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bc4wo boxv 72le )n zr5d tdp.fd)ag64*ounces back to a height of 1.5 m 4dtacbowr) l 7zv 6x 4fn)podd*g.e52.
(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 fry5o hfui;yyr b77-;tz om rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictionzo;yt;u fb7r yy 5-7hi is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 withaygt6 ep99qat ad5 3,k a speed of If the average force of friction3 pgakat9t5e,dy96qa is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the mpn(l2d4( ai(4d trg kfoot of 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 firmc0 +2mmhr lgj k)c*:sc yogbe.59.ujwly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the blo.).csugmhgr o0lk : w9cec+5b2j*y mj ck and the table?   

  A 280-g wood block is firmly fetg+gmx(m f m+5;o. gfiz+9u attached 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 forf m gz5 ++f iemg9oxg(t.u;fm+ce of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the 9rvm j5de.s q2 07igffspace shuttle used a “glider” (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 sp7rsqd9v 2me giff5.0jeed 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 14gul(dm9tur, 9yoll a sixth-story window 16rd1u llg94tml9(y uo ,.0 m above?    s

  If a car generates 18 hp when traveling atz ,b,9er1h,mt2m2gq yl 5x k*6qcz fzn a steady 88km/h what must be the average formg1eh2*5 y,bl 92 ,znkqtzc, f xzmq6rce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h ir lo.v8 yz9o 8fqj.3mxn 7.4 s. What is the average 8fo8l93q j v..mxyzor power delivered by the engine?$\approx$    hp

  (a) Show that one Britr0pg+qgj ;)f uish 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 expressed in the form of “kilowattlir8k.ps;rt (-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 *qq)assgi . k*j i)fl-car slows down from to 65km/h in about 6.0 s on tss))qk la i-iq*fg. *jhe 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 motor do in 1.0 h? ,xeus ;g)z2io+.q xzld :fe;n $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 141sschn4so 9 mi r/ za 2,9ebh+dgio,;tk az2(ym/s If this motion takes 1.5 s, what average powek1iai9 9oh4hr ,etmz/2n 2oz+,ys b;(csgasdr was developed?$\approx$    W

  A pump is to lift 18.0 kg of wat-(e(gjep 3bgf y38 1wh jd8daeer per minute through a height of 3.60 m. What output r(j8 epjde3y13ggh-waf(b 8d e ating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up vl6 oze; sx.xxbh8sao)4o :b/ the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle8sbo6s b)4.:o o l;xzahvxx /e 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 cyclis(8lp,s+ tpk mxf 2gcq/t 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 1wkcnm2 ,b*mb+zm(bra-4+om f 20 hp. How steep a hill can it climb at a constant spee (a,mmrb* nw+obk4cm- +m zf2bd of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepobb-qe24i bap 1rl,.o d t59rkrwer must a motor have to be able to drag a 310-kg box along a level floor d,q-2 ibp15rbt4.blrroa k9 e at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down aecias y 3 c-0z*/b+itu 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bum jy5rv2p7sgwt*z7og5wfp ,6 dpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kgd6 5,f7 gszgp7rtwv5jpyw*2 o 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/ z- 2rpalf3xp cm 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 kg2 lfpa/zr-x3p 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)rrnrr rza7 (5. in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch 7rnrrrz(.r a5 if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shm0.1fhq 3ymraw(br( v own in Fig. 6–39 is to remain on the track at all tiv0qfmrb(ahy(.13 rwm mes, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his kl(axwx q7s5. parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with wal(x7.qk sx 5only 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 horizontal cord of l( ne6v38tehp n4 a-tput1i9 skength L whose other end is fixed (Fig. 6–s46k(t9e- p1v t38h inp utean43).
(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. Theuvr08wl6/c r evx-1r u climb is made in 5.0 h starting at an elevatu8el rrxcw0v/u 1r-6vion 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 tneifb/+ts0e5pz3 q.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 areabl7duvi lk(7e; 9vts5 in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) hile7vdli5 (us 79 ;vktbgher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of ni02e9riu16ualy n 9h650kg/s and falls vertically 81 m before striking th 6yi9l2iaren 0h1 unu9e 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 wp.w tr++eo-*n 8zrfzcoaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — o 8znf+ .rewzpr*-t+w 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 direc(j:00chs bu;x kb) lrntly into work, how high could an 82-kg man0bj ukr:sb 0(h ;)xcln climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward glxgvf 4rz140qz if:/ lhghyt(5 5e1mangle 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 sca23kutd9 n8m bmle compresses 0.60 mm, and it tells k9 mutd 3nb82myou your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out ovgljb ;w6 faexm5m7b7t-9mp1 per a lake (Fig. 6–45). He releases the rope when his veloem;ja5mbt7f-bg9mw p px7 l61city 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 verti 89k/hrxgn(twkl :w;lcal distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish tht;:rl g x(w l98k/hnkwis feat?    W

  Some electric-power companies use water to store energy. Water is pumped by e;8mtwh o-sxk8k+fe fe/ehx0(06d ec reversible turbine pumps from a low to a high reservoir. To sto 8ok-06cf eefeh/ sw exx(mtde+k8h;0re the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in hvojr, dtu :v2(alf. What is the spring stiffness constant for each of the two resultinvd,r2jtou:( v g springs?   k

  A 6.0-kg block is pushed 8.0 m up a rohcjm 049;t-bjpj m qac* 28hfuugh 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 accelerate from 35kmcp bfkm51g ,bncl75a le .3*j7ahgnuo ;gi2e7/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays7e5n5oa2b1guejhpl 3gc *ackm 7 ,b ni;7.lfg the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the fr.jlli1+ apo pl( 5z4patient walks on an inclined treadmill (Fig. 6–46). Estimate the power reqol f 1izj+5lpp(ar 4.luired from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kgy u/q8n)nuk:yr vjh.7 rock vertically upward a distance of 500 m, what was its velocity when it left the vy)yu ./rq7 n8jnvuk h:olcano? $\approx$    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 95kga snt9y.2)odugy d; *o/s (a) If thisgo)2 *ty noa.dsu;dy9 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