In what ways is the word “work” as used in everyday language the same as viw 1q1/hl wn6that defined in p wlw/11i6nvhqhysics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on ihe zj8qu s6:tm6,2gh an object? Explain.

Can the normal force on an object ever do work? prn f.rf4 3yl;Explain.

A woman swimming upstream is not moving w5qa d9 gx6ohc5ith respect to the shore. Is she doing any work? If she stops swimming and mq oach9 x56gd5erely floats, is work done on her?

Is the work done by kinetic friction forceh,u9. wefelk8 o1 ozy7 rv4z9gs always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out fo w.gv rkhl4y o,efzu971ez9 8rom under them.]

Why is it tiring to push hard against a solid on,hz48p2vd9 uvdt4c -gw iv )wall even though you are doing no )ogt4 2h ,d-98cpn v wizvv4udwork?

You have two springs that are identical except that spring l is stib3rlsx4j6( o bf88ccmm c 2f0mffer than sprbsm8cbmf ml6( cr j0 x32c4of8ing 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 ib9;b ;p:c4cwo-qhq qb*o:ylqs free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it :pqw-q 9q h;4oqybo bb c*lc:;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 howoy7/nb5 zzl .k5i:k(bbat r;d much does your gravitational potential energy change when you jump as kn7b;tkba 5riz.lz:5(yo/b d high as you can?

In Fig. 6–31, water balloons are tossed 5+dy2/osvoqwqs( 6zjn c 2m*efrom the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resqd+ey/n6 zo(cs*52owjm 2 vqsistance.

A pendulum is launched fro:k jq7qb6 wn7c rf9cms;4fep2m a point that is 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 On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from te scbn 6q7f;7 rk9qf24c: pjmwhe equilibrium position? Explain.

A coil spring of mass m rests upright on a table. vvzbx.5j/r tzua2 i68If you compress the spring by pressing down with youzb/rzit58.v vu6 xja2r hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire fqv a5va;2d8ib )f i2p(Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball againsa5dbqi 8a pi2fv;v2)f t his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top ofs fi.k.)cuklomo8pn 1).kt w( fr8+ds a waterfall falls to the poo s81()n.pwk+)f to k so 8.ilc.dufrmkl below?

Describe the energy transformations when a child hops aroun5 hp* tg x6wcpy4)nwc2d on a pogo stick.

Describe the energy transformations that take place when a skier star,pisq2p6 zi ,;bka co8b.ayr) ts skiing down a hill, but after a time is brought to rest by striking a snoab2,;)aycisrzp,iok b 6p8 q.wdrift.

A child on a sled (total mass m) starts from rest at the top of a hilu (6eubwl*v5sl of height h and slides down. Does the velocity at the bottom depend on the angle of the hill ib5 w(s*uvleu 6f (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 ra+zn yk- z,*-felyoy 0fther than stepping on top and - +z yyn0ofl*yf- z,kejumping down on the other side. Explain.

Two identical arrows, one witb :t(v .le35qtge e,cah twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arroet,baegct.qvl3 :( 5e w? Explain.

Analyze the motion of a simple /sqy rm7 aq3m7swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.qyq7 3/rma7ms

When a “superball” is dropped, can it rebound to a hu jk 1yt-2cu+i8lzil /weuk42eight greater than its original height? Ey+ c1 iekkluul2/jtw28 4iuz-xplain.

Suppose you lift a suitcase from the floor to a table. Thx 50 sh flay2 s4+)iwd3ye;kiie work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated patiy) h5leaf i4w0y+3 ;2xsksidh, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neededwhm7xz /csyz8 v*ddy ou00u 4- rather than the work.

Why is it easier to climb m92gw1z sj m.wa mountain via a zigzag trail than to climb straight upzsw92 1gwmm. j?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dektp+;yjkjz 3 hm e0iwt7s ss9794p6g dcrease 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 for this, using e6 myzjwsj;9pk+07ts4est3 d p i9h7g knergy concepts.

  How much work is done by the gravitational force whent llte0pli *b(7hd li+ aw)s)4 u8xl6n a 265-kg pile driver falls 2.8li8tl0px+ni a( 4*t6l7sdh ))uellwb0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high.e hxj37q9lfhwoy 81c 0f2ea9e How much work is reqex 79f89johae y2lh0 wqc f31euired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at cq cytfwm 02,4wonstant speed (a) 4.0 m along the flooc0, ft4y wq2mwr against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hori mp(,phr49uao zontally) pushing a 160-kg crate 10.3 m across a rough floo9 ho(ppmuar,4r without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of ft df.g g51 5muk u6+:sopayjt7:xh/ukor 7.0 s. Find/mtkydgjk u+t:5ufx:5 ug67.1 haso p the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie )i pmual cm+,9flat on a table. How much wor ul,mm9) cai+pk is required to stack them one on top of another?    J

A lever such as that shown in +r yi/z9m7yvf Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output +fz7y9m yr/iv 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 kep(e 6cvo f:i3h u(qz5lyo:*t rrt from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36 y q ol 5(i:h3*rvo(zr:ceuft6). 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 helicopter of mass M an accelel xz e- udys vc,qaj8ap,2bp7/s6he(4ration of 0.10 g u(4qss,e dpja-bzc uael p2x8 vy6/7h,pward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distanc bh 8+d pw*v.87mmxqefe 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 axir(/hna 5hzf23 y/rw was, varies as shown in Fig. 6–37. Determine the work done by this force to move the objecnw 5y 3(/haarw/hr zf2t (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 p0 9gz-yl-ctrnarticle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, withxwb u-:a) ff4p,l4sig 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 ar jj.eo+gxiqd(( gc v2ozw2h6+row is 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 stop an/oqha quq5a;5em;pp l2 j0e 9x 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-kgcar traveling atukhozci77ip.qy ;9y 6 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bx/w o w*r c abj/qabk6pej6en3b(mpg2b( j(;6ow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow a66ja3*cbp(qen w(b 2mbwag /r/j ;e6( kjobpxs it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwardmnf)gr+/ay 6 f 25 cm when the ball is caug /6r+m fyfn)aght. What was the average force exerted by the ball on the glove?    N

If the speed of a car .lr18u/tg6g1biknxf is increased by 50%, by what factor will its minimum braking dist/6r 1ug8nb1l xkitfg.ance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid maenp4,uo+8f 2 az xsu(gegd5n6rk to be 88 m 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 + udgu4 ape2(zng56n oex8fs,’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg ise vdm9l5q 4ehb eerl6/:r)8lw pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance betwr9l:)dm rvelhlq/ e845 b6ewe een the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someoud x z 5w,1u)z1wbfnh;ne who does 80.0 J of wx1u) nfz;, 5udb wzwh1ork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration bairld9 fbpu*b3s-) 0 by a single cable. Determ bpr*-lds90 f3ub )abiine
(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 0k bv;n0mle9r much must this spring be stretched to store 25 J of poten;kmbn vl 900retial energy?    m

  A 7.0-kg monkey swings from one branch to m(bz a6(ffn- l gz)csv-uxs*5another 1.2 m higher. What is the change in potential energys5 (*af-mvbs gz(cnfx)z6l -u?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter 9hs(r p.3d6k:cazass change if his center of masds rsh3a(.zp :ac9 k6ss rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 6cky )y8i6b 1vsv.t7 xy5 km/h when it strikes a hkv)i.s8byy txv7yc 6 1orizontal coiled spring and 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 ground so it is cidhd 6duee,n.z+9i.3whznex /g- :z2.20 m above the ground. What is the potenzexi3czie dh- dzn+9,d.: .ugw6ne /h tial 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 elevation of 160clth9fq/ ik:p*cu4*;-em xqz0 m and climbs to the top of a 3300-m peak. u:/4thc9zep;* il xq -*fmk qc
(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. Tn9+ ,s .qy2cnverq e2nunj, 4whe end of the spring is next to the 15- nu29e4wnvq en+,j2.ysc,rqn 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 a vinya7 - q,6mbqd/cg7r che hanging vertically from a tall tree in the jungle. How y, cbh c/d7ag7-r6 qmqhigh 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 f t rxlw( b.n90mz.ofs(rictionless 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 ar0y eb09b-s n/q( yozg 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 gravitational y t ,402ur5tfslkv(c4jdb--twkxp4n potential energy without the aid of a pole. With what-5kvkw44d4u2p yrj, btsn f (x-tl0ct 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 from the top of 1x :yue9o:ynn a platform with 9o n1yu:e x:nya speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whosoljxrslm4 i 4()7lorb(m1+ sfe spring stiffness constant is 950N/m is attached to a table and is compb4)o(slsjfmlrxo lir 4m (7+1ressed down 0.150 m. (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 slides without friction along the looped track shi 4c9l2 /lx3td)t; dn avputs(own in Fig. 62/sndu x9v )a(idlt3 tt4;clp–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 it be released?    r

A block of mass m is attached to me5( 3grdcko:the end of a spring (spring stiffness constant k), Fig. 6–40. The block iedc :(r5ko3gm s given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord e qrb+p.x/99x lpf (edwhose 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 law applfd9( +q9rpeex b/xp.lies. $\approx$    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 tils b*ep)v1 m416b6n dfph5x do point 1 where it is released frovsm1h54b pd 1 lni6x)b6 p*fedm rest. Assuming 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 sp(zehi/l- yv r, r;yivo *7s2a4 atam*oeed 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 pnl rfyzp;m8+3e7ghe3 laced at the 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 accelerat; 3f37yn+ze 8plhm egrion 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 7nfwpj qdfl *f3d-a+3t*: (pvm.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 9y vtr:ouqvfcvr;q0 x: /rs7.1 5km/h in opposite directions, collide head-on and c.vqv ry:7;/0vr1sofx utq:rcome to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slideey9cicudfz+t p a69- ( 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this pry6( pid9 zeu9tfa +c-cocess?    J

  A ski starts from rest and 0*v3te -npbm fci m)6nslides 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 treew*gm um0 bqq+0ug6p vl4t: t. -zh6 ygx;m)amx 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a heightl :iz+gah2wyrso48+ ,ebnde ;9ozww: of 1.5 mg:a94zi:ehn2b+yz, l+rd ww8s ;ewo o.
(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 res m *k.+izfpgmh,iqvi1t+4hg 6t, is pulled across a floor with a constant horik.iz+1,igimp 6*t4 +ghv mh qfzontal 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. 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 sc:3a hi*yev+u w.s7e If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? Tys .*ch3 is7avuew +:ehe distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s rea jhut.4(u b:xpches 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 attached to a very2d.uk m h19iph light horizontal spring (k=180N/m) as shown in.9phd u1hkmi 2 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 table?   

  A 280-g wood block is firmly attached to a very lighv9+;d/jh8 jqd /ll ij(hqzd/ct horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of +l v/ l8d(dd /9qqjji/j z;chhfriction 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 for the space shu6ajw+0l nh0ic/wv (fvttle 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 in the absva0fvnj0/w hi6lw(+ cence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg pianbi-g 2rbpbv3) o to a sixth-story window 16.0 i)p gbbb3-r2vm above?    s

  If a car generates 18 hp when traveling at a steady 88km 8xsk: 1ua *5pwoy;kar/h what must be the average force exerted on the car due to fricti5*w8k ua:ksyxr op1;a on and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What t.+;oze 5dabe is the average power delivere5dtbe.;ao z+ed by the engine?$\approx$    hp

  (a) Show that one Briw j*d1wfg+kag4.9gsph 0 uv .qtish 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 expressed64trgf l23/*b,v sqsl x) fgju 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 aboutz5rv h7qe4j-c 6.0 s on the level when it i5r4vz cq7hje-s in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor d0y+ 9(cu1jealo aov*g53w1oz) dlnh eo in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates mcwnp9gu(c ;7od 8we, a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power wauo,mp(dg7ew9 n;wcc 8 s developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute througdqg***1 5q3t+v-c rsmnxdi ojh a height of 3.60 m. What output rating (watts+* qn5g1d s icvdt m-**r3ojxq) should the pump motor have?    W

  During a workout, the football players at State U. ran up th7wg37s:owd 3q2 xylfv e stadium stairs in 66 s. The stairs are 140 mdwyfos3v7x l3q7: 2wg 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 climtg:ibiw i) 30higq,6*hqj ub(b a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can it co8 gb94* ct 0e:udv6c1(tcv7rlzv exslimb at a constant speed of 75km/h if the frictional forces add up to 650 N?s90o 6*tcevzt8vr4ug led c17 : xvc(b    $^{\circ} $

  What minimum horsepower must a motor have to be abln3 saotl 1xc)z +21b*:wy ggjme to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.42t xwb lcj)z:g*yas1m +o13 ng5?    hp

  A bicyclist coasts down a 7 343)xxb s2jx*ujfwnb .0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) g9*2y lvv vq7* mp1vfebumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the g *7*fp mv2vqvvle91y 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 r8*2svfe v3 it7dif p9yrrd15w )jm ;kzemaining 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 hoi 9fy1vt;3fmp7zdj irk2r5)*wsde 8vlds 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 Owens0 q4/mn8 max9 yp,tfqc’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if h qt/c4 qna mp8x,m9y0fe was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the yh3;4 a w(g bg8pbpk ch9*rhj*looped track shown in Fig. 6–39 is to remain on the h yb(g**3j9r wbpahhkp ;48cg 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, /aik,)tz tqg7rd *fl from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor igfal,,rz*q )it/dtk7 njuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed (F/gyiqxm.d 5 ,cig. 6–43). qgidxm,y/c5 .
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. T- boe x+ni5q1 gyke0g(he climb is made in 5.0 h starting aek+xg- b10n( 5qyoeigt 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 9208/mye jo :qcu 18kf9yvo1kj n,-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 lifts can mov m; e52jvad/ yxvfb1)be 47,000 people per hour. If the average lift carries px;5fmedb 2y/ja1vb )veople about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dqdtq t-j.ef(-am at the rate of 650kg/s and falls vertically 81 m before striking the turbine blad-qt jd (f-eqt.es. 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 vertih1) fw2vvm4uccal 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. Sho h2)cu41vvfm ww 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, ho(s z( d3 44pm 3.nyidglegyqq7w high could an 82-kg man climb 74qgysd3zqy.gd(n4 e lp3mi(a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an ph u3oay 8ojw1q/y2 m10j pl9jupward 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 inside the scale compresses 0.60 c3df 8*zi* tvlmm, 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 scale idtcvf3 *8*lz read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings ouihh gn t ( 4d2h-hi,ygtf*xg;8t over a lake (Fig. 6–45). He releases the rope when his velocity is ze*8 h thhx4in;i(ty -hf,g2g dgro.
(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 distancpq, 22das2z vs.7z hmre of 5.0 m in 9.0 s. What minimum power output was2s,qamhzdv27p s. r2z used to accomplish this feat?    W

  Some electric-power companies use water to store enevn* g ; daoscb621.wjkzfc(4ap70 m girgy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in swd6kcpz41afi na*c .2gv0(g jbo;7 m1.0 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 co7 9(ok roo5fygnstant k is cut in half. What is the spring stiffness constant for each of th5 r7g(ooo yk9fe two resulting springs?   k

  A 6.0-kg block is pushed 8wwmik7 9:eh 2 0kv yor -s2pcz4cfuz7).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/hw7kz )2e1eqi t in 3.2 s, how long will it take to accelerate from 55km/h to 75km/z2)we k1t ei7qh Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stresya;5o9 jrnu/epp r y03s test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when t9 ouryj0/;aypr n3p 5ehe 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 veul+9ye bty*t 9rtically upward a distance of 500 m, what was its velocity when it l9be utyt9l+y *eft 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 w: qi0.bh mdw wciq8du9lb5h )+heel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricityhb 0cdqq+.wh:)lub iiw8 d95 m output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s