In what ways is the word “work” as used in everyday language k c g4q)gn4n j pisyr):;6mg:xthe same as that defined in physics? In what ways is it different? Giv:n4c:mgpi gqygk r) 4jx)n6;se examples of both.

Can a centripetal force ever do work on an opeqxnk9 r.0 ,// nsgfjbject? Explain.

Can the normal force on an object ever do work? Enypmbl yp8 3 -8 whjo97w3ysa9xplain.

A woman swimming upstream is not moving with respect to the shore. Is she doing bw eh2(-lc/lx9:w bx wany work? If she stops swiml xblh9w/b2: ce-w (wxming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? fyv4. c0ng jh87xfvf jr;;n-c[Hint: Consider what happens to the dishes when you pull a tablecloth out fromvj;hfxcc ygnf;-nv487.r jf0 under them.]

Why is it tiring to push hard againxi/,1at kxn2m7rifu51f xx io .t oy9+st a solid wall even though you are doing no work?ot1 fxko.i mx2+1tr75x i n9u,xiya/f

You have two springs that are identical except tgkish x 7qxt7;83i9xo hat spring l is stiffer than spring7io3ts; ikx 78xg hxq9 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 force on a block that is free to slide on awhmph,p . k)qn*4td4f frictionless surface (Fig.6-30). The block sh4,4pnkdm pq) .h tw*ftarts 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 gravitatiov 4/le kb:qe1nj puc:)nal potential energy change when you jum /cpn blvj4euqke)1:: p as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buin;e ,5d n oy-5lhskm,fpbixte+o,i c9--k)kzlding, all with the same speed but with different launch angles. Which one n5ho,lk oncyk- mx- 95efbt+d,), sk-ei zip;has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that ,sphil--j ika x.*,ofis a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s Onlf,shk- oix.-, ipa *j 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 zr290otj* iqvkjti1-the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the*ri ijtvj9z12otq-k0 law of conservation of energy.

A bowling ball is hungtxf;tk+z3xy flpsr2 h*sb.1u9 2i- yy from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against hiy-u2f;9pittlzsx*by rk3h.s +f1y 2x s nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potentzjfjo0o0yco ax*o w6*l ot;29ial energy when water at the top of a waterfall falls toxw jyaj *oolt o2c9*6 o;f0oz0 the pool below?

Describe the energy transformations when a chiik 3ncgux/-b ,-8akqx1hc 6gpld hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts1r4*mmh )yvzxprks lf -h/o)l (4h;vs skiing down a hill, but after a time is brought to rest by striking a snowdrifh lyssmrmv14r)h z *)h(v;xo-4k/ plft.

A child on a sled (total mass m) stckzl57m .t w/fgh/(l7)ulww4 6aiixbarts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the ag ll. /5twaki)i7/hz4m( flxc w6wu b7ngle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over au2- g.btu*j; n5qx. vj4t y popl+(h8a zpye5w fallen log in their path rather than stepping on top and jump2xqvyebzt ; aj-8+t n 5 (*w5hgpy..pjp4uuloing down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired in ysjlc9y4jz942b)rl(6 xhuh oto a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow w l6 cxojyuz2( 9hyrl)9s h4jb4ill penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum mm 1/ (.j-xs1znj7kxx;bibx gin terms of energy, (a) ignoring friction, and (b) taking fris mjxbb .gix7kn1; m/j(- x1zxction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is droppe1g,c* c / lfgx*lz*k 0ukxixf+d, can it rebound to a height greater than its original heigh f gf1gu xxx**0*izkc+lckl ,/t? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do 4dm),+pcn0n h8s-kip dd-j loon the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of t) i-d,-c4 okm+jl phs0p8d ndnhe suitcase?

Repeat Question 22 for the powemq9 sk4mqz-blm3(1bsr needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straight 8f9no7seqir .w3lox .up?9. 8ol rsno3ei.w7fxq

Recall from Chapter 4, Example 4–14, that p5ubkfogy4 5.5s 6zvym fe 73byou 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 pulledu4vfbzpy.3 7msg eo5 5y5k6f b up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fhjgkx:9 h)7tv alls 2.vtg 7k)h 9hj:x80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is r* nxrfs3h8dgaujes 4 a-e3) .zequifua-3e dzh.*e4 gnjss 8x3r)ared?    J

  A 1300-N crate rests on the floor. Hgcps*g y)rzlc ,b2 9m0caxnan.ns,; 5ow much work is required to move it at constant speed (a) 4.0 m aloncnc,0rg m *2,nzb s9l cpgasn;.xay5)g the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did thehoqe;4j5ehd6)t9vqd e+dm +w +nv1 ke1 ql/vy movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of frictiondjqm+4o96l)1;1/nhqe dvk+w vqe h+eydv te5 was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of f.hih 9((lh9hxwgybz5or 7.0 s. Find thlh(5w 9 ih.h(gb9xhyze net work done on the box.   J

  Eight books, each 4.3 9 c0f3 a vf;hz-xgdj*ekbzn26cm thick with mass 1.7 kg, lie flat on a table. How much worzh3-*60j; fdkza e 2nvfxbcg9k is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff ob rbp) 3pjt:2eenq+9khjects we might not otherwise b 9h 32eqptpke)njb +r:e 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° incline61 t,jazxi(yc+yrjz* e (ypc5 and is kept from accelerating by a man who is pushing back y 1ie+ ( rzyjtyz5c(6cpa,j *xon 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 . ol u( fev.qo7opb01hki:5zb2 g/ iye,x)uqs a helicopter of mass M an acceleration of 0.10 g upz/bqeh usk:,x o iqo ub g)0fy 2715v.p(ol.ieward.    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 distan98 bio(g tohr:54 zx 6x(yck;ygp z6kuce axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown ib -14:d,ymczifz ar, hn Fig. 6–37. Determine the work done by this force to move the object (a)zam -fd4:b1,yic rhz, 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 xrz m1 jdb2 ;u0lrvcu+ m4y--ein the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, withyv389iiv e z8n 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 n4 w9b4c*o +yog2twu:.gfi7vp1bnpais doubled, by 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 u8fd)4rb0+ugw0 ygga4( minslj b 8 0ustop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgc675jfb8+ymnhz vhq 5har traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string;g d*yqipyp9 + exerts an average force of 110 N on the arrow over a distance of 78 cm. What is thqpg *; ypy+i9de speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s (9jk*v;2 fji0l ojo asmoves a fielder’s glove backward 25 cm when the ball is caught. What wassi*9kjloa 0; vj2o (jf 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 its minimu3x0om- xhr3 ssm braking distance be increased, assuming all else is the sa-0h33sxx rmos me? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s ski+bn)gqcf .l k.d mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinb klf q+.)g.ncetic 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 kxb3aze 7 c1d5; b70w8)drydm7 krg wvmass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance durd3kmd7rk)ezrwdw0;b v51c yb g 77a8xing 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 05 ywr(3+ kobeqwt +8vxv6whk thrown straight up by someone who does 80.0 J of work h6r0+yk twbwq v5x8e+(owkv3 on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cab(4n+rbzt1k:c(/18 uyqbzvu qb1dcre le. Deterzt1qq( 1 bruu8y/ :(n d+k4ceb r1bzcvmine
(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, oo/xwuy( 3sf7 80lemo jf 440N/m How much must this spring be stretched to store 25 J of potential s7xwoojm0(yu/lf e38energy?    m

  A 7.0-kg monkey swings f( :mmbwne 4qn8rom one branch to another 1.2 m higher. What is the change in pow8(nbeq 4mmn: tential energy?    J

  By how much does the gravitational potential energy of a 646no4uy27 +l f yey1q3z3xelix-kg pole vaulter change if his center of mass rise271yz64qlef3nuxe 3i o+ y xlys about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v =y61mv (dka:on 65 km/h when it strikes a horizontal coiled spring and is brought to rest in(ya k1:m v6dno 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 fwb8kk rd:a-exkf. ; 2b,isx;3n qm9hy rom the ground so it is 2.20 m above the ground. What is the potential energy of the book r92 xm,sxb3ik 8;rd q;kb:.-yehkafw nelative 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 tho9l4-v9cddo i e top of a 3300-m od-99v4idocl 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 ecr2m -uin9 5czb 1gzcp9i,x(a ruler. The end of the spring is next to th5zgim9-cbu cc p(9 xrn 2e1iz,e 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs ai.fp(fag5kqkm.p dujxvti-;3 t-,4sdgz . g5 vine hanging vertically from a tallg-(55 iigsvf3 .u,;.kgax zp jp-mdt4tkq.df tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionl oy /eh b/hed5k.l.:bzess 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 sh- n5c5i kic,qyove 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 transfoa ;,2ietbwc+mbp(ru ;rmed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center;tbibe2c,(umwp+ ;a r 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 from the top of a i+l63rlmlul5 5wmu0 b platform with a smlllu5m5rw 0bu+3il 6peed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore i9uz4a)jsag9ppm v5ki,m1. r mts mass), 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 re,5)4pm pija1 u9v m9ag rksmz.leased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track sho66jq7f a ju+ ;e6xsgttwn in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is t ;6te6+ 7qjag6 fsxjur), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffn h1pcbky 3j7v) 9vpyz;ess constant k), Fiy71j)b9zkv v hy3;cppg. 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 txh; r-+ kxww8 0y)-5fcpzsqx2l hpl e(o a bungee cord whose unstretched 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 l2sw5yc8eh x ;zqhlp+pkr-)( -0wxxflaw 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 point 1 where pal:dibxwo*)n 9.v i-w0+yddit is released from rest. Assuming np9a*yd-xd+bi ivw.0low d:)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 12 m/s at a vlgwx:;pwv 7+n 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 of an eleh56w logw zt )i5hon-+vator shaft. If the elevator cable should break when the elevator is at a height h ab-) zlhgtownwi 6 ho55+ove 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. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a2tcue d x+shx1-pn.+ m 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 t tzq: w 1c0n wri547sbtb1k4wpraveling 95km/h in opposite directions, collide head-on and come to rest. How much zi1qtct41n0wb5: wsp wb7r4kthermal 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 w/nu50s/mr y9j 5 ovqyeith a speed of 2.2m/s How much thermal energy due tr59/ yqvnsuy ej/m 5o0o friction was generated in this process?    J

  A ski starts from rest anxgzfq /u5l)9dymidl90 -l qh;c6 gqe+d 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 tree 13.0 m ablnc6rv8 k/vjph t+)/de7p -s wove 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 heighs+3p 0, *ju qjfs pj9 )cxkcs66s2vckxt of 2.0 m, and it bounces back to a height of 1.5 m. q26fsvxk), pjkj c6scp*csxjus9 30+
(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 pulle6ol86/y s*gr( u1vyhl j0wxaud across a floor with a constant horizontal force of 350 N 0yhlwa1 8l( juv/go *ux66rys. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 69opg vtorvu o(3+if5g.u h 9(wcloe ;.–41 passes point 1 with a speed of If the average foreg+f 539og9 po..vhtoi;(uv roucl(wce of 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 stea e7kdr-4if g -vsb0/ktskk*s1dy 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 ghgx:r +ao(k*u(lfea+tz(7 g attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction hgxf+k(g7a gl(za re*o:+ u t(between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sb ibi19g z(z+epring, Fig. 6–40. The block can slide along a table where the coefficient o b19gib( zz+ief 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 position will it stretch on its first swing?    m

  Early test flights f /cv dpekm *w8/to4be1or the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been 1p/mc*k8e 4ebw vo/t din 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 take496 k3.vdiu:y0yn lfvo s9 3;upemjw r a 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m l jv fv3udsu wp6;m9k3: 4yniy0 e9or.above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mustfek4q78y/2 wz.qj n xp q i3tk9pukb;) be the average force exerted on the car due tiw7x/2n8 ptzk.ku)3kqfey ;4 q j9p bqo friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95k*0l yiqsg:l d1m/h in 7.4 s. What is the average power delivered by the eny* :lg0qsd 1ilgine?$\approx$    hp

  (a) Show that one Britim,v)sx my;oa: sh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed1/ kkwh3h.m 0+.ep/zw-:6 veakxtwsp x: bpye 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 fromv7qbxk4/z7 f ;xgei8n9s:y w q to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the q/g84 e:bzixn; 7ys 9wkvqf7xcar traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mon aor ef1 /o:gc3xa )0idwshd 1oq7*0ktor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If7shjho odk:zlz;f- 5 0 this motion takes 1.5 sz-5hz; 7oldj0:os hf k, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kgi owir01cdsxx-df. ggx r.x .-vv.,)y of water per minute through a height of 3.60 m. What output rating (watts) should the pump mot x xgr,.. v.df-xx1.i0iw) gcysrvo- dor have?    W

  During a workout, the football players at State U. ran up the stadium stairs in 47)i6szutqjo e:hicn :f v6+w 66 s. The stairs are 140 m long and incqhu j64:+is t7z6nv):ec iwoflined 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.m(7 d;1urs u lnu66nxw0 $^{\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 ik52 ,v+ch -mopg-sl9 el6ywcg t climb at a constant spg,s-vk5ye2-o c +ch69pgml lweed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be afk;x ,eark;ao+o2zutwr9 ) p8ble to drag a 310-kg box along a level floor at a speed of 1.2rz2wokot+;f ; a p,u8 )rxeak9m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.07y c)q2p j4cpr:3pejd $^{\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 carw+f,d t*gb+ zwt1z-*yja(pi v s have 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 material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by rammt +(wgjzw1y-*zdp+a f i,vt*b ing into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm(p tdzuayp :-c dh72h8cg) wv) off the ground, and the remaining four shelves are each spaced 30.0 cm above the pdw)a:cg7uvp h)p8d h-zy(c 2trevious 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 start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6/8n 0y,zpqnuwn ;a.l;rgq3af –42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch poiz;puawaqy8/l0gnnr.f q; n3,nt 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 sliding without friction a8 j1kvofdd *+mew8yw/ f, (psrlong the looped track shown in Fig. 6–39 is to remain on the track at al8f/s8+dm(f ,ejkp v1d*or ww yl 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 parachuk v10ss 1jfz0x 6jpgl-te 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 his terminal velocity wasj kgjl 1s61p0vzf0-sx 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 oth fux.lx758fr v 6o9q6xzkx y( h,e;diter end is fixed (Fig8;fq z6t,d7e uy.vxxxix9o(r6f h5k l. 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-highk:l0x7nh ;al e mountain. The climb is made in 5.0 h starting at anl0 eahln;xk7: 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 920-kg elevator.os njt 3,by+ j;4fhok 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 lifts can move 47,000 pe2l5qg l 3p7oraople per hour. If the average lift carries people about 202ol 7pga r3lq50 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 81 m before z;75hl -xsdip fs40d,ez-ekgstriking td z5 0zsipl --edgf,x;e7h4ks he turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coastereo ia,uwkr(-j, f-fy* with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show als ajw oyi(k *,-f-r,ufeo 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 contvnpe,1qwu *dr7 3 me9vert a candy bar directly into work, how high could an 82-kg man 1e*etqrp9 ,dw7nm3 uv 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 nwvn*dik rb.kktd.1 uc6x4 5l.j h-d0 at 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, the spring insi;go n+ ndvq j-n 5ole2wg/pi0gne.(:c de the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump gon. /:(2q+ oi n-; d leegpgwnc5jnv0on 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 .zp8n0igy2bj qprw .zud p ;.i(ake:)a rope, and swings out over a lake (Fig. 6–45). He releases nzp0d8uw.q. i pkp;.(:gi bea2y)zj rthe rope when his 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 vertical distance of 5.0 m a9dren3 ( b bl/of/(gcin 9.0 s. What minimum power output was used to accomplish thisg9fo/(rdb3 /lebc (na feat?    W

  Some electric-power companies use water to store energy. Water is pumped by reve7o23ilmq + v54mmlajwrsible turbine pumps from a lv57j2w +o34a llmmqimow to 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 stiffness constant k is cut in haxi6ukvhavucj.0l s,* *p ;2ayp u.d .elf. What is the spring stiffness consta 2.6ld*.i ;c*skvuu, e. hpu j0yaxpvant for each of the two resulting springs?   k

  A 6.0-kg block is pushed a,448ouuq vll8.0 m 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 accelerate from 35km/h to 55km/h in 3.2 s, how lonu 4 jpm8:nx-weg will it take to accelerate from 55km/h uxw:4n jm-e8p to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (t/g3d3 ct 4znbrhe “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle33d zn r4tc/bg 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 vertically upward a distance of */xh e1 f9q*6x*ahfmfcvfge+ 500 m, what was its velocity when it left the volcamgqe xh1h*a cvx*9ff f/*f6e+no? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a) .d,k-b zx)yawtsya09gv7hm+If this water wheel is set bv7+d.mz0ayt y,khxs a)g-9w up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s