In what ways is the word “work” as used in everyday:v+cop(,tbzphv1 6jd szju a);c* 7od language the same as that defined in physics? In what ways is it different, b vjjo(d*v7zupdcc) sz;t1p+a oh:6 ? Give examples of both.

Can a centripetal force evjvcm k3y) 1 7ir8w*djeer do work on an object? Explain.

Can the normal force on an object ev;l b*krjc0 n *9s.gwgoer do work? Explain.

A woman swimming upstream k5 1tg6p38l7qous7me o)nqpuh)el u; is not moving with respect to the shore. Is she doing 5 )k lmqe6es7q3uo8uphup; o)nt 1 g7lany work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hv;:q1mzp*p4u7 tszp-d*5hyv 5npn fiint: Consider whapn s 17v5ui-hfm5: yqz4t**dppznv p;t happens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you aref* h9y+n3jxq n90 qnch doing no work? 0+n9q*nnyhf qhx9c3j

You have two springs that are identical except that sp o(q-jgt2( k po/2jkl*una0l zring l is stiffer than spri(jjk ku2onpzota 0l2/(*g q-l ng 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal for-7pgx6 er(0 , icrqntzce on a block that is free to slide on a fric0gc,q z6tn7p(- rxie rtionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how 6y ozv,rt8ai8 much does your gravitational potential energy change when you jump as high as youry at8 68ozv,i can?

In Fig. 6–31, water balloons are tossed from the5-o :/-dnm.wm)m5a dlwuwfnp roof of a building, all with the same speed but with different launch angles. aof) l-/nw. :- 5 d5wumwmdnmpWhich one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above qefkvrz ,o, wp(vcja tg1; bz-*,t; 2 jgl4tc1its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the secowlr1,4gvq;afz, tc(vtjt1*- c bzjp ,;o 2egk nd 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 uprigh(*y p f)g/p1csqroh 0ct on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using)1 p(s* /pcogrfc yh0q the law of conservation of energy.

A bowling ball is hung from the ceiling by a g,e z2qky81x; mwj. qusteel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against hisz x ,m8juw.ky;q1g2qe nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a wch r0)imu dl-qx. ++efaterfall fa )0- qf.remh icd+xl+ulls to the pool below?

Describe the energy transformatkw5f39 w)aqrs4vp ix5.yqj,v v1bda2ions when a child hops around on a pogo stick.

Describe the energy transformations tn k:nzmf b8(b;0* fovd j5fqv+hat take place when a skier starts skiing down a hill, but after a time is brought to rest by st +qj*zm nk5obfdb:0v(;n ffv8riking a snowdrift.

A child on a sled (total ma; k2:p0wakdo85 rngvass m) starts 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 tkn 0g 5:a;pv8ao2dwr khe hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather etltt/6;dfiu: u u:sboq k 5f 2xo31p.than stepping on top and jumping down on the other sidepf1dbk;eiqt/ : s2o:.o6uu5x3tuft l . Explain.

Two identical arrows, one with twic8n(cx yme t9f6ial,j/e the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force o yl/,6fe 9txci8jman( n the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a)os zc*+qh ,h. o6k+hiu ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up,ohckoz *h++ ihsq6.u .

When a “superball” is dropped, can it rebound to a height greater than irn+1zx*ty :ptpmh, u.ts original height? Expny1h.z mt p*xr+, tp:ulain.

Suppose you lift a suitcase from the floor to a table. The work you do on 8k(h7g w od4g6 fuea3wthe suitcase depends on which of the following: (a) whether you lift it straight up or along a more comp 8g(6kwdgfo ea4u37 hwlicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the p/8icn )2 bh rdjbu-b8iower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb str5vbu (w j rgr85,k40wg2ohjzs aight upjrgjwv5k(wzr, 4s2o g8h05 u b?

Recall from Chapter 4, Examplq7aw.m4m h)4xy b;yfoe 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account y q.o)ym7;mw4xhb4 affor this, using energy concepts.

  How much work is done by ha5)b gwh+ .xmo9wl;j the gravitational force when a 265-kg pile driver falls 2.80)w j5;xbmwo+gh .hl a9 m?    J

  A 65.0-kg firefighter climbs yv)-j+ k /c1i2qhvtmba flight of stairs 20.0 m high. How much work is reqv/h2b ci) -tm1qvj+kyuired?    J

  A 1300-N crate rests on the fl qs-6gp vuo:wo/o+ybwj0wp, mf1l f++oor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a frip0:j fv-b+op,/w +uoy61 +s ofmlq wgwction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing */e k mroad:dehm ;*;va 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50eh/kom *m *read;; vd:?    J

  A box of mass 5.0 kg is accelera3s s k2 wvj7)udq6;t+bjjx5pzted by a force across a floor at a rate of for 7.0 s. Find the net work dx;u2vjt3b q z7 p5+)sd6k swjjone on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tablek(: 4i z- 08pa6afjx 6heufuas. How much work is required to stack them one on top -efahujf086isap(xk46a :z uof another?    J

A lever such as that shown in Fig. 6-35 can be used to lirc f86vjfx z 5kmnbm)3h.u;*kff objects we might not otherwise be able to liff. Show tham jk5 xhuf3m vr6;nfk*)8 b.zct 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 from aca(mi4o 6jlm 5ecelerating by a man who is(ma jimol 564e pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicop wne9y7ozjb /7ter of mass M an acceleration of 0.10 g upward.jy e7now 7b9/z    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 f ou n 814lg7c gq;spverq4:0jaxis 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, actir mzc*dbo5im+ ,;k-drng along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m -r*o,;m md+bd5k c izrto 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 r1wgx7mpgiqy1;: t lp t3m/ppf) j6s(in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen mo8qp)/ka *a.ec p5i mpqlecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has : h:j;w p59qtsg8zjs; tj qd;7lg8uioits 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 -.y(wncn br)lqln s 8ci 5i,p*electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-u(utpck3ot34r:h t5ngv:ns 9f /:kzpkgcar 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 of 110 Nllfb,ca /qy2 + on the arrow over a distance of 78 cm. What is the speed of thba lq /2,lf+cye arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielde0n5 ;gfdspu v.r’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball onnd5u;pf v.0sg the glove?    N

If the speed of a car i*;jkpqua :zjs /)ey5 bs increased by 50%, by what factor will its minimum braking distance be increased, ae;juasz5j*bp :)yk/q ssuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a0jf. xy( 0davzodx1y0 car’s skid mark to be 88 mo0j1adv0 0y (yx.zxdf long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the tl436p/iya quagvk2 g 7ime it reaches the plate, it maa2pka4yi/v lg6q 37guy have 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 th/)v 0 rembuoo;rown straight up by someone who does 80.0 J of work on it? Neglect air re)rv;mbo/e uo0sistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singlx3k9c 0kurwp9r5 -i mmp +xflz;dup1;e cable. Deteri9m +5kwmz;xx9ppp3u k l1 fc0ru-;drmine
(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 440 aj8np:.+c , bhl:y8mws2fz naN/m How much must this spring be stretched j8f yn.m2 b:sh8zap+a: c nwl,to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one fag.ruz (q0 mk(14irjbranch to another 1.2 m higher. What is the change in potential enm. (r kqi0 r(4fzgj1auergy?    J

  By how much does the gravitationa u9 kkyejf9e1wz-4:ael potential energy of a 64-kg pole vaulter change if his center okeyaj 9f z:4 wkee91u-f mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling onsu*ee w3/vb2dbc9mh. a horizontal 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. v/s2m3duchew .ebb *9What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from 74dyj5nyoh w6 (xfm s 7-jzxxwrl84y 0the ground so it is 2.20 m above the sx4 jz yo05xdm746w-lwyj( h 7yx rfn8ground. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an ele 1o+r rks0mp8uvation of 1600 m and climbs to the top of a 3300-m peakr +8pmsrok0u1.
(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 ruof ct;v9 ,td)kaozc-5 ler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of t;tck9d )a f5t-ozo,vc he spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3mbo+ .ps107sjv+g / .csihz slr/s) and grabs a vine hanging vertically from a tall tre p7z0clos ..gi+s rsv1jsh/b+e in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dowqk 5yba7pk8 8xs 7hb.qn 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 giwrg ysu x dy1.mk18;2hl 0+twiven a 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 gravwm ig,7kexh/7 asp;o 2itational 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 bar with a sppo ,a2i/skg; xwe mh77eed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the t16 qax66;qazdp h3lteop of a platform with a speed of 5.0 m/s. 163aqq6 ahd 6xt;p ezl($\alpha)$ 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 masswm l1guv,en6-9pql o8gbk+- n), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when releog6pw-- 9lnmg v8nek bl1q ,u+ased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without fri6dhc1/cse)h9eb+ htb ction 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 /h ch91+ectsb )bdhe6minimum height h must it be released?    r

A block of mass m is attached to the end of a spring ejm 5n:w d6+of(spring stiffness constant k), Fig. 6–40. The block is g6 e o5:wjd+mfniven 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 w/,uxpd g9j b x-+gxfj5hose unstrejjd-+pbf/ux 9x5g,x gtched 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. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown i( v6pdbjuqk4e( /kkr1n Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, k1 b/rqdk(6 e(u kpv4jcalculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a sp0g z1xm(ib: xgeed 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 the0zkd+s- kp1g u bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest +d-0pkkzsgu 1. Let M be the total mass of the elevator and passengers.

  A cyclist intends to s ,5(rm2)e*j0pg hiitarw w1bcycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass .m7 vh;wmkgd g 6w0yx(7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collisiongh(d6mkwmy ;0xvw7g . ? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reache m;zppsg19;kos the bottom with a speed of 2.2m/s How much thermal energy due to friction was ge 9; ps;mopzg1knerated in this process?    J

  A ski starts from restpq(+vr5nb5nm and 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 a trefrw qkbrq,pci :* *x4s*-o5yce 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 fkzh/8(l( iqc of 2.0 m, and it bounces back to a height of 1.5 m. lc(8fqh(i zk/
(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 acroe9 2wvg8r5g kr 4jp+vyss 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 friction is 0.30. Wharr28vy5gkjg vpew+ 4 9t 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 thx-+ 8lt ysw::a ubrx:ye average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distancetuw:xblasy x: :8+y -r traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s re*hhlt2go 4;q:d)z qdqaches the foot 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 firmly attach9x,7gox x5mited to a very light horizontal spring (k=180N/m) as shown in Fig. mxg, xio95t7x 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 table?   

  A 280-g wood block is firmly attached t 4uwg09j/ossvq z2x d1o a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how gv4zd9o/jx 12uqws0sfar beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle uim; j;yva2n6y sed a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/v ;;2naym6yjih from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W m(2paec;fau te oy wydam*1108lp:w +v otor to lift a 315-kg piano to a sixth-story winf t v1u*pyae (2 +cw8l:meyd1owpa 0a;dow 16.0 m above?    s

  If a car generates 18 hp w:mx f537lycn/ux:2 xuit( vl when traveling at a steady 88km/h what must be the average force exe :/tulfnlyum2x7x:5x3wc(i v rted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. l itd020ga6-z06ut3f ajcuj n5 rspc6gt* o2gWhat is the average power delivered by the eng6*5 d 0p360c rat-gjtn6zacu 2u2ogigjstlf0ine?$\approx$    hp

  (a) Show that one British horsepo ww4og 2vsi;4n 63 s5plablfe5wer$ \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 exprel0)iq + )d+hd vkfkwo(ssed 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 down from to 65km/h in about 6xl; ps, f6ttq gdm03c:.0 s on the level when it is in neutral. Approximately what power (watts and hp) is cpsq: ;x3 ld,f6t mg0tneeded to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor yi3wb *;t tfh+ ;)vfy;rul:qa do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates rth-7qv7.iqr a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what aih rq.t7-rv7qverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heigh9ylcipqpe3ah: o 04s ,t of 3.60 m. What output rating (watts) shoul9p4hl,e oyacip :0sq3d the pump motor have?    W

  During a workout, the football players at St;(h xaa9yyi 3a4e(eamu7 ks g/ate U. ran up the stadium stairs in 66 s. Tamak(;/hi sag eaux y74y(e93 he stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cycli:hes.lilx t7am3 +e4sw6lb4 a)nv et: st 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 outpjd2 rsbw ).j ;msy2cy;mn 08daut of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional fo;02mnr by mdjws ;y)cj.8ds2a rces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a mq+d 9ltpag2g8 otor have to be able to drag a 310-kg box along a level floor at a lagq2p+8g 9 tdspeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 cqzu/ *2sduh0 $^{\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 designed tne0q *wo fn7n6 zw*l1xo 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 rq7lo0* 16ww nnn*z xefemains 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 fi1 rdtg haq*tm8+ a+5a0x w0givrst shelf is 10.0 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 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 hqmrv x dw8 +aagi00att+g15*start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) icnwc3g 1 u-j77lwv yr0n 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 if he was travelinyn gr0wcu71j l73wv -cg at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without fricjvw, yv1dy 99r j: 1,db, mz)oxi*dslttion along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the lo9) 1o1dy9 yz,bi:jw,d tsr vld*xm,vjop 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 pa j2;q ehbubf7(rachute opening. 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 hisfu7;be 2qbj h( terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed ;9ay73zjkd lmt/d y)up(. 5- ekphc fh(Fig. 6–.;d9kup5 a-(3d h7h y t)mpfjkelz/yc 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 h0z3db1j ltf/bpxs4mt d//2vthe top of a 3700-m-high mountain. The climb is made in 5.0 h st/vs x1/3z p bd0 htm2/ldjf4btarting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a/i an :i-up:8*o* nv qbgpkvf+ 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 Califoit7nxi(u467 qt wa vt:rnia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertic 7t4q7:utx6i(avt inwally) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam atrh0tu;zl+uj1 the rate of 650kg/s and falls vertically 81 m before striking the turbine bladeu1jth+ 0u zl;rs. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop q1w1+ievk q*n (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn1*q1 w+ iqkvne’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could conv1h-a o,w:sa4;: 4ufy clv hyruert a candy bar directly into work, how high could an 82-r 1vuyfua ,hwoy;4a:: hslc -4kg man 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 aranyl;mpwmr(4+ 2 xw.t an 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, theuqzdk:ottbu zs kcv14u(+8- , spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you q4c(d tutsb,uov18 z-zuk +k: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 k*jce7 hv* un;h4r.gj swings out over a lake (Fig. 6–45). He releases the rope when hisrkcu *g.h4*h n7ev;jj velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a verk, am0 jpr,pyd5 i42ovtical distance of 5.0 m in 9.0 s. What mv a yo k2dip,5mp0,rj4inimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to stock/.uus(h)xo0, gj xare energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced isau o)x k/0gc,x.j hu(n 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 half. What iw ap;att73)sas the spring stiffness constant for each of the two ; p)sa37twat aresulting springs?   k

  A 6.0-kg block is pushed 8.0 zyi +-ayo lx(0 tf(u2xeb+;mam up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accele)u(w.urav i u2ufai3 -rate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the 2ar a3(iuuu.i- u)w fvpower stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (tyc*f sjpid(e gr29,v(he “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power requi f*jy esic2g(9(d,v prred 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 500v blvmag+f-fpg: ; 08e-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcava-b; +e8f:lgp fv0 gmno? $\approx$    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 w ;saxgj,n 7mz0orim),ater wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity gns ar;7,zj0mom) ,ixoutput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s