In what ways is the word lk3,8 (db hv x36fgkic“work” as used in everyday language the same as that defined in physics? In what ways is it differevl8(3x ikf6k dbcg, 3hnt? Give examples of both.

Can a centripetal force ever do wor/ rwgpt/+e x+g5l bxv-k on an object? Explain.

Can the normal force on an object ever do work? Explain.5+8l t31;k hbcs bxoba

A woman swimming upstream is not moving with respect to the shore. Is sheof+32mm qbwn8s bw 3j7 doing any work? If she stops swimming and mere b+7nsj ow3mf8bmw 32qly floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider wha-eofx3 lrr)o + d1v8vki 6alc,t happens to the dishes when you pull a tablecloth out6l)iklc+o-3vf ,v deaxr1o8r from under them.]

Why is it tiring to push hafus7r/sav r 83rd against a solid wall even though you are doing no f7 8/rv3srsauwork?

You have two springs that are identical except that spring l is stiffer thad0fyv04go klt* i bsjd(h8+0 gn sprin+ osl0gj gbth8y *(f40divd k0g 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 horizontr 8f uh 2:/m;atddh4jlal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled ah u:8tj;d lhrdm24a/f 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 ti 6huso-4( pygravitational potential energy change when you jump as high as you cio-p 46(st yuhan?

In Fig. 6–31, water balloons are tosspkls4 7,ypax3y2k (lwo8 txx 6ed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ign(4kp t yx,sxx p76o2 yal3kwl8ore air resistance.

A pendulum is launched from a point that ix (: b1dm4hyo)uole*qs a height h above its lowest point in two different ways * )mx(heblod:oy uq14 (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 the equilibrium position? Explain.

A coil spring of mass m rests upright on a qkb4 pt.gx)9stable. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conser.sk9x )gqpt4bvation of energy.

A bowling ball is hung from the ceiling by a steel *;yg al0(5jiw rk;e dmg(a,topeuy3+ wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. Toej;d(35,+aeg ;lm*t(wia upryy0og k avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gqj8 3smt4 v72c r*zxefravitational potential energy when water at the top of a waterfall falls to the 2cv4mx*re sf8 3q7j tzpool below?

Describe the energy transformations when a ch 3,wwuzkmf iz ho:/cqdj)+b91ild hops around on a pogo stick.

Describe the energy transformations that take pl tee;51+3z qhvszj*tj ace when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrifjh* 3t1s;e z5 +tvzqejt.

A child on a sled (total mass m) +,qirzh)e q:y xrpnuyie; dl9r*i58* 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 the hill if (a) it is icy and there is no friction, and (b5 n i;qyrhezp 9)q,el *rx8+ri:uyi*d) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in fy7gh4s2 fo,t2g7zsctheir path rather than stepping on top and jumping down on the other side. Explaif,77zgtfcsoy2 s 42g hn.

Two identical arrows, one with twice the speed of the other, are fired1 yqj8+wi/zxms7 e3ijpgo,;l t em,(p into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, (p ,ee+gj/p,xq87ms3lyoj; w ti miz1the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of 7up9 ez,ja pzs3cw7mt 74v/cl a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has tolpz3sz7cvt4e7pca m9uw,7 / j be wound up.

When a “superball” is dropped, can it rebound to a height greater 8a 9awlw c(:bur;2tim+a +:s exou9mqthan its origin:btm + us aw+9(9ei;uaqrwl:8 2 maxcoal height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the 9 m6vpbe:8ih;yogr /rsuitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the timrv/mr9gb8 :epoi 6 y;he it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the nubu+cjj67q fb7 , m8dpower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb 9p/5-id3ju wybq pnmy czc)8i2)yjw/ +wbwz( straight u bj wm) )b -5 j9p/+yp3wqnyu(zw2cz dc8iywi/p?

Recall from Chapter 4, Example 4–14, th i2loj))cb/xu cg w0n4at 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 for this, using energy conce0)ibl4oj2 g/ )ncwxucpts.

  How much work is done by the gravitational force whio hl (6hfvvny ,.1mo2en a 265-kg pile driver falls 2.80lvv.i2o,1ny m6h( h of m?    J

  A 65.0-kg firefighterx(ntf o/g(*j5+ibw9kqbp ;qr8l,k, 0bth lp h climbs a flight of stairs 20.0 m high. How much work is req bjkw ni+t0x8lql;5b kgqh(prt(p/ hof,,* 9 buired?    J

  A 1300-N crate rests on the floor;mppox (56edi. How much work is required to move it at constant speed (a) 4.0 m along thep5x(ime ;dpo6 floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1zgc/ 0 k z bhr7kuv-qr8t(g5/u0.3 m across qt87/ 5uk(g h urvcz kz-/gr0ba rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acrosmw9 (cn*)ao trw:v4 tss a floor at a rate of for 7.0 s. Find the net work dtc:m *9vn)ts4(waow r one on the box.   J

  Eight books, each 4.3 cm thick o3y sdbu83(wy with mass 1.7 kg, lie flat on a table. How much work is required to stack them one3d(s y 8owbuy3 on top of another?    J

A lever such as that shov +syjrlc+qx;1d j :b97cr5 urwn in Fig. 6-35 can be used to liff objects we might not otherwise be d7ru;+jlr19c5 +j: yrxbsvqc 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° i(l 6u4r+gnl s odf(6pf6wjmi0 ncline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fmsl6ji6po+ g l6d fn(rf4u(w0 ig. 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 helicopter of mass M an aqt :7kd4opbcbjl8:yxwu7d. /cceleration of 0.10 g upward. y.pcqdk 4bj:wdo/ u87t7xbl:    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 dis9xq / wel/lc0htance 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, var-)4(ffc 0qafjbjiga. c ro okky4+ ;v4ies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 m + 40y4.fv(afka)jb-ocjfqgc ok ;4ri    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts in thlmlf p8s/y*6d+mau2 he $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass of+mt n- g2:4:lq d0 fg0selwdwv $5.31\times10^{-26}$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 whatj- ges2s0lo /*dr*kbj0hufc1t0foz, 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 2q a 7(qs4cbeu,0p ssp)e z8rzv;c j,eelectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 12smwxawf *(d+8d;s1ih 50-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from aq x5u6xnw v zk(h+nn25 bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of thev(5z uqhk+ 2xwnn6x5 n arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm;b1gpb-mp ev:.h+t .z yoz 1gx when the ball is caught. What pzmop1.yz;eb :-.bvx h +1gg twas the average force exerted by the ball on the glove?    N

If the speed of a car is increased bvd83*tswzib oh( v v:(bt424 ne.5a/ht xckqxy 50%, by what factor will its minimum braking distance be increased, asv d*245ne.oxvv3at4 h(xq8ikstcw t (:/z bhbsuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a7ube*vfs nylf ,+sn2( level road, investigators measure a car’s skid mark 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 ofvbfl+u2 *nsse,(7 y nn (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 a5rc /r-bbcd i-+*l cjidv /ci4t By the time it reaches the plate, it may have rcivl- /r-5ddcb4i+* ci/bjc slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by sd tipz. z9 )lgeu,4+yzomeone who does 80.0 J of work +zli4. )9,gtdep uyz zon it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a si;wn v/t2k0k4 ozudm(h ngle cable. Determinet4o /;2(zdk nkw mh0vu
(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 constanta2 d*o8 leg ) mjgr,ap8;e6off, k, of 440N/m How much must this spring be stretched to store 2ef8l8orm )6degapg 2ja, f;*o5 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. x6h.fpax:mo :k )9tvihlec /5 What is the chan5/e9ithxlx .::6acvo k hm)pf ge in potential energy?    J

  By how much does the gravitational potential energy of a 64-m9mlzdmzq7y (t96 y :b *)ekhjkg pole vaulter change if his center of mass rises about 4.0 m dur 6():y7hmm9mbe 9kqty zlj*dz ing the jump?    J

  A 1200-kg car rolling on a horizontal surface ea* gi5:nyg(tm ;y5rbhas speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of 5grt (;: i ebgy*ay5mnthe spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.2 ek;(xd(bt0 li0 m above the ground. What is the potential e(kd0b;(txil e nergy 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*(qpotd ,ld dq1/yle:;va t f+ of 1600 m and climbs to the top of a 3300-madodlq 1lef pq vtyd(;/t*+,: 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,8z6z0i /7mz scan pdl next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached toda/plcn67m 80 ,z zzis 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 sptvczkodfe 4+u81:) infgg j4( eed (5.3m/s) and grabs a vine hanging vertok4 8)gcf1djv : 4(ugn+fietzically from a tall 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 frictionles )tph9(;8/lk2hc,c-uxy vwpe r c6 ebos 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictio ccz4;psuao 13nless 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’no6m *g k mbvumxz2 g3s-u)/wf/yll;3s kinetic energy is transformed 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 of mass 2.10 m and cross the bar with a splnb x;g3/sm2l v wofgz-kuu6/3ym) m*eed of 0.7m/s.    m/s

  A 65-kg trampoline artm (ofk)7slwbg tt1g r07m 2j ytt7o4z+ist jumps vertically upward from the top of a platform with a speed 7lt(ogty ft mstorjm720) kg7w1b+z4 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), whose spring stiffne w:g*gtm-w:cx:mioc 3e f15;k o/ cnvlss constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speedfo-eg;mmcwnw l : i5xc1/: g3*ktocv: 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 2 liwyd4xsr f4r zu1;p50s3x)ww (r7y7xcifj the looped track shown in Fig. 6–39. 7j71 532c y; w rrdu xp4yi4)(srz 0lwsxfxwifIf 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 the end of a spring (spring stiffne1xr8 3qe eiqfwm.m4qcb +z(6 iss constant k), Fig. 6–40. The block is give be 1 .+wz8mqqe4fcq6ix(im3 rn 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 bungeebmxfm a vb0sl0-676iot5k;as cord whose unstretched length is 12 m,lvbkt06a-mmf b ;ios7a 5sx06 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 in Fig. 6–41 is d+2np m) pkx c72ls4bdgragged up to point 1 where it is released from r7pk pb2 lg2+ cxnd4)msest. 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 speed of 12 m/s at ae*ogjp- j:,wcn 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 elevatxy;1 (q pgii.mor shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, ca;g (x1i .ipyqmlculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a vmg0 -bdk1ll /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, eaco/i n23+ m sqijtn:k0u;9rbdhh of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal e nobd;:ijr nu9/s3thiqk0m 2 +nergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descenkja2;(lmz vfuo qpzj 8y4x 64)ds a slide 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 proce fz84xpua6q; jz42jmlvy) ko(ss?    J

  A ski starts from rest and slidesjcn5-a ; pyr9x 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 droppedsl 0eyk9t 8qrdfu0x /d3:wh23con3oc from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounk)p a; 83upwbzces back to a height of 1.5 mub3p p)azkw; 8.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a g-mcch,iwfw,(kc j 6 1floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next1fg(-,, cwc m6 wjichk 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 speu/va8) tw e-i flsh/mh(/5gb ded of If the average force of frict h/ut)/-va bm sl/f5w(gdhe8 iion 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 steady upward whd pixb)uq/zi/4 tf 84jqp+4fr c2-f 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 fi/ axija*8-dgtrmly 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 release/iajxa8 -*dt gd, 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 attace88jou xj qdyo1 z(8n:hed to 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 far beyond its equilibrium p:x 88ouoej18q(yjd nzosition will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inclu+ m-hequ )7cccding pilot) that was launc meucqc7)+-h ched 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 absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story a/iko ewpek 8x ciura91i)9/;window 16.0 m abw8i;1 e)a9xce/i/k9kuroa ip ove?    s

  If a car generates 18 hp when traveling at a steadt 58lwcx76z .vbeb- hyy 88km/h what must be the average force exerted on the car duehbwlczv6 x5. b8t7-e y to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 sz.1e(e, +eael c)t gce. What is the average power deliveredezee.a )cl(ee t1c ,g+ by the engine?$\approx$    hp

  (a) Show that one British horsnsqdhm zae- a/p+0b 1*epower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowazsjnxh+l//r j1 4(c putt-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-kg94u ysz u4/0c9cnvw 5w6m naick*. tr 5h7tvlp car slows down from to 65km/h in about 6.0 s on the leven l5u9 ts9r5ym u6wvzc*/anp4 ht0 c.7 vic4wkl when it is 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 do in 1.0 nyct33z)q1rb a 8t 5xeh? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest i4r yf m5vx1+d7d:nb zc)sx3xto 14m/s If this motion takes 1.5 s, what average power was develobfv +15xmn r xzs7cd43:di )xyped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What wa3zm)fa, mc+ w8t9tqve5b / eoutp e ea8b9,5mcf+tm/z vt3)aqw wut rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ra0wo b3t62brw en up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of beto3rwbw6 2032 $^{\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 clixm6i;q pc jw3h /o/8ykmb 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 outputt t3 3p-pqpp ez+6/ypw of 120 hp. How steep a hill can it climb at a constant spee36p3tpz -+ ytppq p/wed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a mo 0eans+f8kwm+e*g;ja7 jhrv* tor have to be able to drag a 310-kg box along a level floor at a speed of 1wehn*7j0 gam* f8ek srj+;av+ .2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0yq5+ 2ruco5x q $^{\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) bumperrbd ut)/5v cv0do4,vos” 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 ramming into a solid wdut54vrd0o)o b/ vcv ,all? $a\times10^b$ N/m a =    b =   

  In a certain library the first she nlgg3 ;f( evc5::rvnglf 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 ho:rgl gg5nn: cve3fv(;lds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 193p x+6h+rw- qit3vlhu+ 6 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 traveling at 6.5+ wlqi+rv-hx+ pu 6t3hm/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped trajq sw);6lj62xki pvd*ck shown in Fig. 6–39 is to remain on the track at all times, even at the vedkwjsl xqp i2)v66*j;ry 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 fr+hnax8-3go ijd :q4bn/pyvz0gtjm //om an aircraft without his parachute 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 veln ghj q0mb/8ox/t4 -d:+yjan/g 3v zpiocity 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 lengtti5levp+ye-cs 5p*g;h L whose other end is fixed (Fig. 6–43). ely-+ ppv5c* etgs;5i
(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 o fwjc. gc,bu(cz( q:kdt7 k7;t:ew/usf a 3700-m-high mountain. The climb is made in 5.0 h starting at an gcu .:wjc 7(/ stt;keu:kf7(qcd zwb,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 is 28 m above a huge sh h. 8py mlaoshnogrw6*h6:fgeh8 0; 2pring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 ji :nj)s xpa45move 47,000 people pejxn4 5)isaj: pr hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate offdd 25l89mdjs 650kg/s and falls vertically 81 m before striking the turbinedm lf5 s82d9jd 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 rolle7 ;t1aqksys: vr coaster 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 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.;: ytsa7q1k vs    mg

  (a) If the human body could convert a cands. )a ikrj:a:9 p0zyjby bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) aj)s .0 ::k rzypbija9    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 upward angle obbivr9bhuy93vl. va np 9 1()ff 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. u,(kw/p6tsrqv lt*p4pqe(z scale compresses 0.60 mm, q/lp.6 p(zt 4 t,vkrq(se*wupand 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 read at its peak?    N

  A 65-kg student runs at 5m49uk6xmy 0 fnujep 1d//s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zerjkfmey/u9u6n41 x p0do.
(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 athletfiunuj 5e2m4m(wv7 lj 7sk 97w g8i-dqe climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used t uw 47ug l-9wsem5k7fjji2m 87d (vqnio accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumpedcs.8nx4gw k/t, frfj; by reversible turbine pumps from a low to a high reserf4/wn8jxgts .ckf ,r ;voir. 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 half. What is thf:u,-y +;q 4*etbtdv,ht rvppe spring stiffness constant for each of tv4tutb + d;r vp,q,e*y:hf p-the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roug70r* o7w/pciqo( t2qj, nlaew-sf) agh 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 lki)fawn 4t-df(;jem 5 ong will it take to accelerate from 55km/h to 75km/h Assume t jte);5-fwa dkmfni(4he power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient wawn4 em -nrl n:gwget (lt;o:;*lks on an inclined treadmill (Fig. 6–46) ;ml:n;e* wtglwnn- gr4te (:o. Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a disdt0 )yq 7hktn+rx 5se,tance of 500 m, what was its5x + srq)khne,tytd70 velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (897 (foturc r wptm-9lt(bv5va:(v gt a) If this water wheel is set up twtvm(7 v9rgt(l vtp o9r8f5(c:tu-ba o 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