In what ways is the word “work” as used in evp;; wyevwgz b;a,3 qq:eryday language the same as that defined in physics? In what ways is it different;;;ebqw v pa:qwz,3 gy? Give examples of both.

Can a centripetal force e3v a o +xn l7-zxol8yjuhia4,3ver do work on an object? Explain.

Can the normal force on an object ever do work? Expewy8 3 f.km yy0bl ;9rf2uajl+lain.

A woman swimming upstream is not moving with rj3upr2go,*9m bp 7e pqespect to the shore. Is she doing any wo,eo2 p* m gqu79jb3prprk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces a5byte l q:ajhmlsz5,8k --dw6lways negative? [Hint: Consider what happens to the d5 :58,zhqkwbm-atld6- j lyesishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though yp90)oo ly. nmjou are doing no workn.mo oyj l90p)?

You have two springs that are identical except that spring l is stiffer than sph*c/qtpdnhs2udh dph,10 8r-f.kp ;vring h*d uhk ,2d;0tp.8np h -fc1prs/ hdqv2 $(k_1>k_2).$ 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 tcy2rnfo0 tu3 ;n nh12jhat is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has travele;on y rthjcn012 2u3fnd a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy chik-0n zom7 dnk6:9mpdk2k 0qtange when you jump as hight9km qki-06 nk027mdzonpd : k as you can?

In Fig. 6–31, water balloons are tossed from the z o. oyy.w6/f1v 6wtrhiqup ;7roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? yzpo6uy67/ qifo;vw whr.1t .Ignore air resistance.

A pendulum is launched from a point that is a height h abovel ;10 ,byyx mc)mtpye1 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 p)0 1l, mtxcm;yybe1y 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. It1r3 mpzaal2cw.qz 4 )f you compress the spring by pressing down with your hand and then release it, can the spri wtl )r2az4mqa z1p3.cng leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung fromjbe-h s1lc 1m95 jwjf6 the 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 avoid injury the instrucm j jwc bej15-6h9f1lstor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energyef lo1r vgtk zk77y:k6 o3h8d. when water at the top of a waterfall falls to the pool beoh6o:3.klg t 7z 7k8erfv1kydlow?

Describe the energy transformationsp7 4qinl*n*n1 e nhi*j when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skm fga( ybjn031ier starts skiing down a hill, but after a time is brought to rest by strika(j3y fmbg01ning a snowdrift.

A child on a sled (total mass m) starts:4 w 6 i;huzcpl3msmj0 from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep sm:mcilu4 36sj;p h 0zwnow)?

Seasoned hikers preferslra 9o (9uyq0 to step over a fallen log in their path rather than stepping on top an9ury l(9 0saqod jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the othe 7inr3 flfico.ck,3fvu3k *4sr, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will pe vc4l.ifu7*o 3kn,k3is3rc ffnetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pedegfr+pxm *i1dc 20( lndulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatheri gl2e(p f+ 0r1xddcm* clock has to be wound up.

When a “superball” is dropped, can it rebound to0 9d0qsho v ec9dy4ot6 a height greater than its original height? Expl e 0ycoht9dsqo60dv4 9ain.

Suppose you lift a suitcase from the floor to a table. The woszm1vye i9i.s0j 0+k.ay + samrk you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, ( .0+m1.ayj m +iszaisk09syev 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 than the work.gjp6*wo33b 7 p-q;. za*9jqnhuazo7 dalzl5d

Why is it easier to climb a mountain via a zig2,jfjhxr sp: +zag trail than to climb straight uhj, s2pf+ x:rjp?

Recall from Chapter 4, Example 4–14, that you can use a pullgzra2zo 7co)b2 n*1uwey and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised,no cwz ug*7ao r)2bz12 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 driver fz z0r. jymjn7nyqx60-p,vxj9 alls 2.znr.yxjz 7vj6-j 900,mqnxp y80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. tlf ahw) o2fw3j1lx9+ How much work is ref+xwo 9 2w3lhf1lat )jquired?    J

  A 1300-N crate rests on the flool/ gk1 +ke6ho ch:+gmr4q5sjor. How much work is required to move it at constant speed (a) 4.0 m along gc/r5:+jh soqk6h 4gek1lmo+ 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 crate 10. xn2esxd*,6tqbsq u 0ode;(1o3 m across a rough floor without acceleration, if the effective coefficient of fri1t*s(e;duon xdsq,bqe x62 o0ction was 0.50?    J

  A box of mass 5.0 kg is aczi w0umc1toib-e:f/7celerated by a force across a floor at a rate of for 7.0 s. Find the net work 1fweo/-0m i7bi tu c:zdone on the box.   J

  Eight books, each 4.3 cdb68b/nh yrof if: uj32b2eq7 m thick with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top ofbe ib2nf32du:/b7hr jy o q68f another?    J

A lever such as that shown in Fig. 6-35 can be used 3fvlow44p. y xq*gj d5aa ln-;to liff objects we might not otherwise be abjxw*yd v.pl;ql a4g 5o3f4-n ale 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 kept fb;dj.xr sz8 rr.f+y 6srom accelerating by a man who is pushing back on it parallel to the incline (Fig.dzbs +86 .f; rrsyjrx. 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 gi pc8fw66+(wl hawnyg5j*t c 9vve a helicopter of mass M an acceleration of 0.10 g upwc6ny8 wha5 cvt lp9+*gwjw6f(ard.    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 axi0dwdx() hw ;u0jkf j6hgj3 a1ns 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 alww,-d o0+tn fwong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move t-t nfdw,w+0o whe 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 i3y)ebvb -v)a wn 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, an2v+u 5x op-7max(vrn,ep.thh 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, b-g pf9ct)a2 f7ng pf/ly what 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 required to stop 5 3op)97kdq mizgv g.aan 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 d mghiac,fq7v6x :oa5 9one to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firedui;z ao 5wd-gz3vtg6 n,y0ek- from a bow whose string exerts an average force of 110 N on th 5-izg0vkod - nygez6w;t 3au,e arrow over a distance 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 backward 25 w dqvoag/k a0/mv-,/usa2h,j :3 ni brcm when the ball is caught. What was the bw 30 2-jimgaoq/ aksu,a,v/ dvn/h: raverage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum t+:tsghnqf*2d)/;dm zqtny5 braking distance be increased, assuming all else is the same? Ignore thyz/+st2 5*nd gftmq dtn)qh:;e driver’s reaction time.

  At an accident scene on a level road, investigat-g y3 j(zim*zjors measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic fricti(y gmzjz *j-3ion 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 uux5 a8hdiy)rb v8)e20.25 kg is pitched at By the time it reaches the plate, it may haud)hr u 8i258)bevax yve slowed by 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 someo, gq 9aq7ky3mrne who does 80.0 J of work on 39aq7gqmy, k rit? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accel/z eq))osf) ah.qs4y heration by a single cable. Determ )h/s oh4e)z).qsaq fyine
(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 must this t/sh2m)8hmbj;0s lq ospring be stretched to store 25 J of potential 8lj0tmsb ;/2ho)mhsq energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher+g ;q 1 pw5qt0mxwu v,syhu,d-. What is the change in poten-,s vt0w upwg;hq5mu ,q d1+yxtial energy?    J

  By how much does the gravitational,3w vtrl 2q33ds8/k e wvfrp+e potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m dpv,/sfqe+3l rwv2kte 3 3dw8ruring the jump?    J

  A 1200-kg car rolling on a horizy i:cuuu,j+d(0gp egmq 10e h:ontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and m0+c0gy piuqeje, g(1u:d:hu is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the gro42um9hu- vxmv1kr ot *9di 7bound so it is 2.20 m above the ground. What is the potential energy of thot2 h1dxi94 uukmb9m*-vv 7ore 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 andefm2u7tp (1sh au4w .d climbs to the top of a 3300-m4t ewuum.phf(7sa 12d 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 the sprin9x wyg i*.(,auwhln6qg 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 sprii(l.w* wyhgxaq 9,n6 ung line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vinnluo4 nh iy;v4h0t)f9f54/e wrdv 3fae hanging vertically from a tall tree in the jungle. How high can shdi/ 5f9lnvrhh4f3ty4w;eao) n 0fv4u e swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startinl9d8r,m p8dy og from rest, slides 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 bb u+2b .exh wsb0bg.-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 graviefvoru;myq , 4a 8.ba;tational potential energy.raq e;a4u fvb,m;o8y 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 bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward fej g /2wr9p2r . 72qbz7ylsbdfrom the top of a platform with a speed of 5.g7 q 2dl2s y 9rr7/bp.fwjzb2e0 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 c:o9ztu -6jv,d mei y,konstant is 950N/m is attached to a table and is compressed down 0.150 m.9ekozmu-dvt6 ,y,: ji (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 slides9plh2xxxq szls: aoac8 3l675 without 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 (whose radius is r), from what minimum height h must 3c sa2l slo:la75z6xpx98h xqit be released?    r

A block of mass m is attached to the end of a sprinn8u)/hu;r8ukli 2 ehhwab ff.8i +-lf3a +eddg (spring stiffness constant k), Fig. 6–4a3; nd8 8dh/e l-hffrfiai+ku w.b+u)elu8h20. 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 cordbfks m iy m6 6:gc;j qq-vx.2v7ce.u5c whose unstretched length is 12 m, and falls a toxm vcqy7j:i.vk;qb.sc6eug - 52fcm 6tal of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to poipha52ip yshl tnc xq;79s8h- 3nt 1 where it is released from rest. Assumingh;lhia9 28sq3c 57htsx-py pn no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of :(mn md:k i7rp12 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 8,-dnpuq2t nl 9b4qbjbottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of tbq8 -nt2jbun4 l,p9d qhe spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 oeh(1zu 5so o.u0u(o m)v7l7 y* zsdjy$^{\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 ii-h6+ nl6 qttj5igmui,9k md p233hjof mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal e ,pih j-d 6tl m kui56hgijtm3in2q+39nergy 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 withz6(gmgvgo87/si kf3vv+8p3 ;u2urdl1td kjv a speed of 2.2m/s How much thermal energy due to fri g3jvi8 fuv8 tsv32/7d(;pd mklu v6og+rzg 1kction was generated in this process?    J

  A ski starts from rest andx 7u zd( ;olq.5+xoa02y 4of:o gwvska slides 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 n qf5-blsg+.xa 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,m gb+/wb5w m k nj;n):c8 a(snzaoy-;s and it bounces back to a height of 1.5 m. -ck:wnnbj mba/5s)8az owgy( + m;;n s
(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 yxyu6 34rxt 5swith a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 1ut43y5xy rx 6s5 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If tfk dzbx,v24((t0d 0pvb2d ab6vzvhq*aq gz 5-he average force of friction is equal to one-fifth of its weight, with what speed will-qa24pz5gv0b6bk,v ( (b vxfz * dvtd2qzdh0a it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwaz:o*zm, ytne6tb8wo.m./i nard 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light hor*s.+ ;; yw3gmn zdtgmqizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the tasn+ y*g;;3mqgm. dzwtble?   

  A 280-g wood block is firmly attached to a verv2n0r)b us wp8jy0a, oy light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30p002 8r)usvynwj,ob a. A force 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 space shutwjzri ,.evikhrg3 5 13tle 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 speed of 200km/h (a) What wouldg3 5rzeiik.3jrv 1 ,hw 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 f pmp7 a3ufx,(b: keov*x4er,lift a 315-kg piano to a sixth-story win av:4, xmf xb3r7eppku*(eo f,dow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h whjuqmwg5 g7+idtl o47 l0h 9,gmat must be the average force exerted on the car due to friction + 4ggl t 9ougqmi,57whld0m7 jand air resistance?    N

  A 1400-kg sports car6pxha+ ilrg/fsw,o6-y 8fr7u accelerates from rest to 95km/h in 7.4 s. What is the average power deliverhx8,- r a7oglr 6+py/6fufiwsed by the engine?$\approx$    hp

  (a) Show that one Brxtb0vyfw 1 ./ mxwt6a,zm(wi8itish 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 oft y gjf-+53)hid dlk;rxs5 ;msoen expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows dok vw;7ykvn+b4 wn from to 65km/h in about 6.0 s on the level when it is in neutra7kw vb nv4y;k+l. 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 laa;0lih, 0pqveq ((p motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7gxd4xun(yc u nc4-nm2h+c5j6.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power wan45x-g+n uc cu2xh64mjncdy (s developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height8+3ldqmvaxgst k;3 l 0 of 3.60 m. What output rating (watts) shoasvx3l+g8m3 0l;dq ktuld the pump motor have?    W

  During a workout, the footballb l:t;yip /tm+ players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m l;:mpt t+i yb/long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.bo4 ,b 66arveu z5awy/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 cub-dn+k0qx * steep a hill can it climb at a constant speed of 75km/hb xc+qk*-du0n if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have cc(q vzfd cgm41d5e6 ;to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefd cq4 d1f (z65ccgevm;ficient of friction is 0.45?    hp

  A bicyclist coasts down n28ne7( :w, wlnncu k23v2u tq/ksrsxa 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 hla5fv x r( ;yeixtb,)-ave built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the mav if-bxt ;)5la, re(xyterial 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 cm off the ground, and the remaink;uco d,8gn 56zjb+oc k:l1 dfobr2c. ing 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 sh5 r+ 8go 2,d:oc1.6 lc jf;kdnzkbcbouelf 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 Olympicsodk6)mkpe /:zla0 *jf3 4reld 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 iedj)3r/m 6kpo4 ezafk0 *ll d:f 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 3q 6t: 5s1uiay reae:vshown in Fig. 6–39 is to remain on t6ae yai s13:urvq :te5he 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 wjrm))x-x 5v6j4:lvi 2hy lpqtw/,edhis parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. A25,i-tvwe vhjy x:/rql4wjxpl )m 6 )dssuming 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 horizontalo -jyj,hq4 a7:nf8opz cord of length L whose other end is fixed (Fig. 6oz jn4 h a:8q-jofy7p,–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 thep;w89spjf, qgce*m( r ru1h0p top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an mw,8 fsrqc;0p *9u( p gp1jrehelevation 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 or* d5r qg2ra*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 California claims that its liftsaw+:7dlc;op p,*oybv t q; 5lj can move 47,000 people per hour. If the bwl :pt;jl; y qp, +acv7do5*oaverage 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 vertically l(1h itdti,( synq. x:81 m before striking the turbine blades. Calcul y,q(t s(n.i1ilxdth:ate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical m.- z9.ubthtrk -kxi.,u sbu. loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and ukumzb xskt-ir.u h..,b9-t. 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 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 directly into work, how h3mr cam-fl y) /t8u6bhigh could an 82-kg man climb a ladder if he were fueled by on/u8abytc6mf h)rl-3me 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 ajqv7/ p;6x(t0c +qpnbwc/rce n 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, the spring insne2 n+,pis ph0kceek7 40t m.fide 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, what does the scal2pk.tn s kh0i f+ec4 pne,7m0ee read at its peak?    N

  A 65-kg student runs at 5 h9fg3 .uqp( jc 1el;g6pzm2ihm/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his v plcz.j3h 26mg i1pehf9 uq;g(elocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0a--w0ppt2t 6 sae3jk r m in 9.0 s. Wh -6sw-ppar ae230jttkat minimum power output was used to accomplish this feat?    W

  Some electric-power companies users8wf8jza t: ;2acghw5x:j*5cgwtw. water to store energy. Water is pumped by reversible turbine pumps from a low t xzc :.*twhgt2;jgscfwr :8w8a 55wajo a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stifr8ihkjp+ 7qe01 tn6 skfness constant k is cut in half. What is the spring stiffness constant fo7eqsrn8 h10ik6t kj +pr each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up kfr5j0 )h+ 3ek+qvv nta 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 frokkcnp*+0ho . w-mui;x m 35km/h to 55km/h in 3.2 s, how long will it t m0ho nxk cui-w*k+.;pake to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (thezb h5i:,i1hl .ab5yb p “stress test”), the patient walks on an inclined treadmill (Fig. 6–46hi:lbh5iay b1bz ,.p 5). Estimate the power required 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-kg rock vernn48 50dp :fzag8f 0et moate*tically upward a distance of 500 m, what was aetnzf a4 m:5od8g0ft0e n8 *pits velocity 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 ratey6:9yy9 phbn ext ws6( of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum:(tb9yx6npew69 hs yy power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s