In what ways is the word “work” as used in everyday l qkidqa, /3:bzanguage the same as that defined in physics? In what ways is b iq,: a/kzdq3it different? Give examples of both.

Can a centripetal force ever do work on 5q3 sz 2c/ d8mteqo+w9npar2m an object? Explain.

Can the normal force on an ob:s3 u t;s0cjuzy, :ytzject ever do work? Explain.

A woman swimming upstream is not moving with respect :m t.vpw, p,k.hq0d.v:amxk4qj ps n -to the shore. Is she doing any work? If she stops swimxm.wpt.k k p aj4 :h-dv. v,,qs:qnp0mming and merely floats, is work done on her?

Is the work done by kinetic friction forces56ixl 8eyadyer;k - c7 always negative? [Hint: Consider what happens to tel cy ea8-7yr x;6k5idhe dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing ng4 o2+l v)l mhr*o2uclo wlv2l)2uo h*g mr olc+4ork?

You have two springs that are identical except that spring l 2qb 9tafi zs94 2sjlyvq8h /6eis stiffer than spring 2jfseqb942ih6/2 8atlq 9vsyz $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is fu b5u-j,k4l.zl n(bvdree to slide on a frictionless surfajl4l(vu-bb ,z5 dnu.k ce (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 eneriu8jx i.sh qeb*-oz ,sj79+rmgy change when you jump as highu, qsm-7.ejoi i+s9*zx h bj8r as you can?

In Fig. 6–31, water balloons a :bkl6 kmbce0h r(:j5p-sxwlu r.d5(y re tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? I-(b5jdr. 5 kl(eyxplk rbc06m:sh:wugnore air resistance.

A pendulum is launched from a point that is a heigh d +bj4lqf vh)e:lhr4yt0 y(l.t h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed off 0 +lq(rdv. :eyl 4jbtlhy)h4 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 upright on a table. If you compress the spring bv8lkg*kl/yf. ju5sq :dj 3ka,y pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of yk/ ,38ugvj*q.skll dakf 5j: conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–3y0g+mga0. tg(8pguugx* z ,,b0vut xt 3). The instructor pulls the ball back and stands against the 8g0ta*tg,zxu gvyxtb0 ,ugmg+p (. u0wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when watz*):jynw q l)e 98twsher at the top of a waterfall falls to th) y* :9jes)wtl8 zwhnqe pool below?

Describe the energy transforma 5hsr: 7n( 64hbnfyx3 5ptgmgktions when a child hops around on a pogo stick.

Describe the energy transformatio.(frfuf wr.n +,jrh- ans that take place when a skier starts skiing down a hill, but after a time is brour-f,a fr+ nur(j. hf.wght to rest by striking a snowdrift.

A child on a sled (total mass m) sti8ww1mxf kwb1: ;ot6t arts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy at w6wk:1 m1fw8o ;tbixnd there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in5 ci)rb*: y/fr lw0syb their path rather than stepping on top and jumping down on the other sid0 by)by cl:i5rrf /ws*e. Explain.

Two identical arrows, one with twice the spee, b1vja 9tmpj*d of the other, are fired into a bale of hay. Assuming*1p9,vj jm bat 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 swingin.iztj: * snabnu6, n2vg pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why *sj 2uz6nav.nnt b,i: a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to gz u4qm6 3njwpd4x-8x a height greater than its original height? Explajm 4-xwn dup6z8g34xqin.

Suppose you lift a suitcase from the floor to a table. The work you do ontxiqj k*m laz8+ gx36y-, 9xrt the suitcase depends on wmxjxg9qtr+ ,lixay - *zt38k6hich 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 for the power needed rather z8 +epvxr1y6o than the work.

Why is it easier to climb a moun,edb c7n7 s553bbkbl)si2z a atain via a zigzag trail than to climb straight up?)sbs ,2z3 cda5ebi5 77ba nlkb

Recall from Chapter 4, Example 4–14, that you can use a pull(g7f-pei r 3(nnxfqz-ey and ropes to decrease the force needed to raise a heavy load ((7 -(-gn fn3eqxpif zrsee 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 force3ik8qz.m37qotbt , o zqf-m)a (+gsze when a 265-kg pile driver falls 2. g3ez( k,qt)-bm83z+ist.q oq fm7azo80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0py r khal e7 ny*czwc4x7/-/s6 m high. How much work is reqz a//4 c ewscyn6pk-7xy*7lhr uired?    J

  A 1300-N crate rests on the floor. How much work is required to:7f/jxp tj;kz (*u fvo move it at constant speed (a) 4.0 m along the flokvz7j u;f(jf/o pxt:*or against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hor*mdttu9 3qc5y,e2n0yeo tv ;z izontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50? 9ez v2;o t u53*yemdttcy ,0qn   J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate6d g.55:f+h o +x q v.s+ul0qckbqqiva of for 7.0 s. Find the net work done on the b 6b +qhs5 g +x+if.qk vco5q:q.ald0vuox.   J

  Eight books, each 4.3 cm thick with mas1ft) g +k1 )n4yyebogbs 1.7 kg, lie flat on a table. How much work is4)egb )k1yt1yg on+f b 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 not4oc7i xeeambiwx 6j/55 g 6a;n otherwx7in6m/je5w6x4 iab5goa c; eise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is a4ct+pqdk.nm nm/)y5.ikm9 k kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic f49pd/i5 m t+qn)mm.nk ackky .riction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass pv: mpfrv (d.t/,x)q bM an acceleration of 0.10 g uxp/)pdv(b . ,mqvtf r:pward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear auo- 5nq f7fe: cuu:oe/nd 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 Fig. 6–37. a)oms w ;0ah*m9qreo/Determine th *hm a o)0e/9qor;maswe 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 particle acts in thb h(i jfj(p0t*m 7gb, k-gw(qb(l cdb8e $+x$ 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 may+t61b 1mql2l:fqbskct fw23ss 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 dp5ttr. iispeb1434 zhas its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an el lg37q y4ts qkfmk6d17ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 traveling at ;ivewx8pj n:q-67hl ;rev , fa105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a b4gu( z,cw x n riy*ig,d3+yh(wow 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 as it leavesyig w4drx +(g( iy*,zhw,u3cn the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove baulhbr00bjq5 a*6 ej ;hckward 25 cm when the ball is caught. What washj5bq lr0e*u6hb0ja ; the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will itsbbr r(a g*21bm minimum braking distance be increased, assuming all else is the same? Ignore the driver’s react*1barg bbm(2r ion time.

  At an accident scene on a level road, investigators meo+-rhasj) -tpasure a car’s skid mark to be 88 m long. The accident occurred on a rainy daa-os- )tr+phj y, 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 pitched at td) osj +(5dj2ucdz e7 By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between th+z2cd su)j dte7jo(5 de plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thc7ibyrc8q aqafgpl3080/z7 of6/q4 tdz,l by rown straight up by someone who does 80.0 J of work on it? Neglect air resistanceyq bqt,7c6cf /4r8z ao0/l7iapyl fg0b3dq8z.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single y 7e)zbi:(dx gfuh; l5cable. Determine 5fd uh ;elx ib:z7(g)y
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much mussgd) 6jb.1qe1x x c ab,qj k;6u6(hmzd-fa+gdt this spring be stretched to store 25 J of potential energy? -ek1 hdfu)1js6zg+;a q xm(b6dadj. 6 xcgq,b   m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What 6mp5ycac g5d/-c . f f) dd/1bb6dhsksis the change in potential energy? k ycp sg/-5 s/fb6df.d)ca6dcdbmh15    J

  By how much does the gravitational poten*wsh4zefl16v.1cw0 ihccp7unq5 vo 9tial energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m dusv* uc1lvzo.40pfc51 iw hc6nq97he wring the jump?    J

  A 1200-kg car rolling on a horizonuxe*c6e6etsj(7c n) 5w ha)dntal 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 co)*necn6 (ejw6h xs)7t5ea u cdnstant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the grounkkv ga h11:t;ia7a3 tyd so it is 2.20 m above the ground. What is the potential energy of the book g: 13yh1ati; akk7atv 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 th3hcelmu 4 5q:nem c0+re top of a 3300-mc5eqc3emhun0 rm+4: l peak.
(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 of kko;o 4ity rq2 we.+*dthe spring is next to the o.dq2 4kitwyoe+k ; *r15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed zk81s/cslk5 vxz;ji.(5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can shevs/15zj .xl8 ;kczks i 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 y e0rnpfu4hrenv4r -r u8(4 j8frictionless 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 1cgoe8 th 3ey n5gc)k3d3rdg cgx+7 t,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 kinetic energy is transformed into gravitatio k-rq)*x7 zqcnkg 3(nenal potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bark7rq-cx3ekn n) ( z*qg with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a plrz,o0m62bv h fatform with a speed of f o,6hv20mz rb5.0 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 is 950N/mb55lmn(b :0ag.y cg/0 qaejhq is attached to a table and is compressed down 0.150 m. (a)ghy bqjlqm cg: (.bean0a /055 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 with (,dvsdz.o1tb out friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whos., do(zv bd1ste 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 s k9onott1skes m 60r3wh( 8jh9pz; vr4pring (spring stiffness constant k; 89o6oekm3nkp t (whrzr49ssvt 0jh 1), Fig. 6–40. 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 whose unj tdb,0 sr++wb)m*calstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies.*mcrtsd bl0+a,)b jw + $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is d:v9pjwb di,s7ragged up to point 1 where it is released from rest. Assuming no friction, calculatd7 wvp9 jb:is,e the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throiyfp9 iba9p -4n. 9dhvwn with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom oj 4.yamo9r r/nn( *trkf 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 na rnromyr/ *.4(9tjkof 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 ufrvg n h;h( a;;+biis 1c+ll,ea) rt7gp 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 ilav zqlgahf u .;*07es7j9ho6b-) ofs kb84 yqn opposite directions, collide head-on and come to rest. How mgz 4oaah o0 l q*;j )q8b6ebsfs7lk.vfh7u9-yuch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom pnjp:3 z/ k)j22re1d pokd.kbwith a speed of 2.2m/s How much thermal energy due to fricti3d2j/1ren:kpk jp)z .d k bop2on was generated in this process?    J

  A ski starts from rest and slides down a/5ldk,f xj7o*i ltv ,q 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 4dcj/5p oyem-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 bounb55sukd y8 n,)sex.jnces back to a height of 1.5 mye5b8j)sux ds . nkn5,.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant ho6lr1) 1ovr*; l5pn otct,la*j w yrz:1kdvk(crizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m thelr;1wz tro,rant1c 1kol( jl6y:pd v*c v)*5k coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. yhgrv7 55kl( i6–41 passes point 1 with a speed of If the average force ofk 57(lhryigv5 friction 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 foot of a ;b4nau9ud t r-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 7tq 6rwgr9o6 jv r719jdqfn,ofirmly 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 bgf 6vo6rojwrtjq71d n7r9, 9qeyond 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 attached to a very light horizonj nt(w )4m7qsf7p uy0mtal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium positi mqp(4swyt0f7uj n7m)on will it stretch on its first swing?    m

  Early test flights for the space shuttle usnbi cx 68md8g4ed 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 speed of 200km/h (a) What would its landing speed hag 86bcmdix8n4 ve 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 3u;n 2 mfx: rd/w;xf-pr15-kg piano to a sixth-story wind p-2r r:;wnfxfudm/ x;ow 16.0 m above?    s

  If a car generates 18 hp when blpuy:3 /i)sk/q 15tn-id 5eqzy ns6ttraveling at a steady 88km/h what must be the average force exerted on the car due to friction and air resl-/1e) b:q t5/k6yzniq5 s3dtu psiyn istance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7sv,a :bdje7) :iafpg8 .4 s. What is the average power delivered by the engi e )vpsija8gf,a 7d::bne?$\approx$    hp

  (a) Show that one British horsepi:8lp5n o-s gdower$ \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-hhgchdd -;+qw)xi-v- p2hoey 7m9o+gw ours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65()tx 3wm vsxr1km/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 travelingsrxtv(3m1 x)w at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do iz3u0 am7 gdfp8a 5/oggn 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fromg d v pbj/m1i esqa)+*i;p/m0k rest to 14m/s If this motion takes 1.5 s, what average power was dvs*ep0 i+mpgqm b)a /dik;j 1/eveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m.rlm,.wny yvt+z3ctv *n 10 ;yp What output rating (watts) should the pump motor +,z . yy*cpr1mv 03tvytln; nwhave?    W

  During a workout, the football players at State U. ran up tzpq; 9 o arnv46aog1*yhe stadium stairs in 66 s. The stairs are 140 m long and inclined at an anoa o*y4;qp 1an r69vzggle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climdqyu ,.:uirm s-ol 3i)ao-py:b a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can it.z5 o)vg oulls jkcxx h;8u3;: climb at a constant speed of 75km/h if thu;xj o)clhx;o.su8l : 3gkzv5 e frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have tbby+ ;0ya z1dno be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficieny10y; nd +abzbt of friction is 0.45?    hp

  A bicyclist coasts do 8m. tgz0kw5ngv8n,jv wn a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are designedaj.: i5((dsfh. epi c.w1e zxq 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 co(f5 : 1saedj.hxiizp q.c(e. wnstant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off tt 6mcj;kyg+v7 he ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has atjkv7y6 ;cg m+ 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 :j z9csrbs i 3o/m3clumj4b;.Olympics shows that his center of mass rose 1..jlm34/ bc 9: o;rsj smcuib3z1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m slidinrw 0v,jp 1bl1t7 y:absg without friction along the looped track shown in Fig. 6–39 is trla1 tvpb:bw701 y,s jo remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his parach tqk ijhr:lgl;9/n :f5ute openl9g;/jkt :hr:nl5iq f ing. He landed in a snowbank, 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 horizontal c 4qjqo sze;rt4co96lza3 -lk7ord of length L whose other end is fixed (Fi6l;-zjlt ooz k 4 9qq4esc37rag. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made in d)io is)ylw6uk)a a/wx1nro( erg3 6 75.0 h starting at rka6dwlxi))anr) e3s1y o/ 6(io g7u wan 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 whe myqd)cg4c-c2n a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Califyov 6:mg 7 a1q2/kki58ogwcm uornia claims that its lifts can move 47,000 people per hour. 5omq vukck1o2 7m agg:wyi8/ 6If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verti j2)e*tbeq:qy cally 81 m before striking the t q*t2 :)yjqbeeurbine 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 circular verttre;r4-k m oy*ical 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 frict r me-ry;4otk*ion. 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 conv,bh vpz ld.a8* yqze:,ert a candy bar directly into work, how high could an 82-kg man climb a lad dqa8hz:.,z*e,lbpyv der 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 iuy) k dx(p.vlkb*:yu6yd4 m :x0ej/ban upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale (8 6tcqvxgl3 qf5rm6l, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, whaf qx8ll(r tcq66 53vmgt does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, anp.u 6f j2px,lk-tj9ckf,/ v gtd swings out over a lake (Fig. 6–45). He releases the rope when his velocit/vuttf kk-,jc2g.xp, pf 9jl 6y 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 ven4u5+)a70gt cs6e izk .prw f imea+l;rtical distance of 5.0 m in 9.0 s. What minimum power output was used to acc ek0fiamp7gi.45z)s +wrat 6+ec;nlu omplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped mez-a6)3 bxeu by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW (bu63) -me zeax$120\times10^{6}$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 constuea+,wg)x;qb sxm7dnc5q- a n1n :fa)ant k is cut in half. What is the spring stiffness constant for each of the two )x5d) a1n+;m fsn7 uaan-cq e,gbq:xwresulting springs?   k

  A 6.0-kg block is pushed 8.0 m u7:5fl r7ctd uhp 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 accelerate from 35km/h to 55km/h in 3.2 s, how long will ithy 43j1 h*8bu8lrr que take to accelerate from 55km/h to 75km/h Assume the power stays th8ubqr3* h41rulj8yeh e same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patiensqh - 9z1f/ em/ds6v uegy+v,ht walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when theh/,dsfs61uvemy9 z h ve -g+/q treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vrl 9q7qhx9f u6ertically upward a distance of 500 m, what was its f69r9 l uxq7hqvelocity 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 wat i v;i (v970skm)ph.ttj h:cqrer wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to prori9jmh v hp0(qsc)t:k.7tv; i vide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s