In what ways is the word “work” as used in everyday language the same as a+hx 6v y(-bet ;-jr kuf06i(kybghx.that defined in physics? In wha;-v yr(tj x06ukhkax bhgyfb6e.( -i+t ways is it different? Give examples of both.

Can a centripetal force ever do work on dpov10x tta5)hy/ :dlan object? Explain.

Can the normal force on an object ever do worldl0n4y wu i/)k? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she)e0nq s mon:z7uo v9+x doing any work z7u)n :sv0 9qemoo+xn? If she stops swimming and merely floats, is work done on her?

Is the work done by kinet ulbgm;n pi4lv. psv488 3z1nzul:af- ic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth ps1l-af. 4:zzumu n;8pn g4vvil 3l8bout from under them.]

Why is it tiring to push hard against a solid wall even though you are doing bfic8n7vv z 2tk+*ufi(un/ 9jno woiftnbu8n / f+v 7 jzk(*uiv2c9rk?

You have two springs that are iay+xf0eg1 :k eg+g 7endentical except that spring l is stiffer than springgg+y:eke+a f 17 0genx 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 )q v3f0nz- mt9-lwbca 1n+ pbga frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the mn1vwqpa-ctnl-zbb 3f0g + 9)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 gravita 3hey.au 91 qoy.kj 2k-m4guqfi lmo,:tional potential energy change when you jump as high as yoofha g1 ekym9m32q,4-. yuju:o.iq klu can?

In Fig. 6–31, water balloons arz+ny4ab9*s npe tossed from the roof of a building, all with the same speed but with different launch angles. Which *pn 49s nb+ayzone has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h aboi4i 5cxzfg3ys0 63.cewi jxz6ve its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s O5jiis 3zg04z3c.w6c fiy6xxe n 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 the spripm)f)ir e)bj( ng by pressing down with your hand and then release it, can the spring leave the table? Explain, )rfip(ejmb) ) using the law of conservation of energy.

A bowling ball is hung from the ceiling by a st bqlg*)w4r;xar e6sy2 eel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball agaiqba6rrw l *42)xseg;ynst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational poten 1 97htjbutwjz,f3m/k tial energy when water at the top of a waterfall falls to the pool bm 9u,j1k/3w7j tbhtzfelow?

Describe the energy transformations when a child hops around on a pob/-fz m0sv4 o4qpim gl-(+uac go stick.

Describe the energy tr9p0. zhiie*h*ih qv5p w56dvoansformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strikp d5 h0*6v*.ewiip hqivzh5 9oing a snowdrift.

A child on a sled (total mass m) starts from rest at the top oo r;i6c-tta +d)tii+sf a hill of height h and slides down. Does the velocity at the bottom depend on the angle of oc ) it++t6-;isdatir 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 a fallen 64 w/2rmbqsk /qle1 aqlog in their path rather than stepping on top and jumping qbm42eq/kr1 /saw l q6down on the other side. Explain.

Two identical arrowsqo9eecq;wh (qn) /5 ab(heu y0, one with 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 slowe(y0ewuha5/;( neqbqhq) 9co er arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms 56l 4o0bxm zjnof energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to m jb6z0 x54lnobe wound up.

When a “superball” is dropped, can it rebound to a height greater thanffqs*b., fit sfy:1d/4 rrct3 its original height? Explainyd fb3i cftr1qs /.t f*,:r4fs.

Suppose you lift a suitcase from the floor tomvj* s/(ibg v7h *t6qk a table. The work you do on the suitcase dependsmk7 jsvvg6h *(tb/i *q 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 the suitcase?

Repeat Question 22 for the p a(p9qec t;blr 7ei7z+ower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb sa *;vuf:r*iuvtraight up?v*ufi; ar:v* u

Recall from Chapter 4, Example 4–14, that you can use a pulle).6n7bbuuw ujp 9luu dx+7il-v2.xiiy 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 tn2d)7 x-v jxiuuu7i.b u6 +iulp .bwl9his, using energy concepts.

  How much work is done by the gravitational force when iqn-xkj4 f,2aa 265-kg pile driver falls 2.80 m? ja k,x ifq-n24   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work 1n d+2;jbseik is requ 1s+ek2nd;bijired?    J

  A 1300-N crate rests on the floor. How muchv3./*3j(9gb i4wyp re iivqip work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 234ieg i /(q jpi3vpv9wib*r.y30 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1n-li;yol/ ; hb1dn1zv0.3 m across a rough floor without acceleration,;/lo1d ; znbvy-h1i nl if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fl6rjo, pb; fy4loor at a rate of for 7.0 s. Find the net work done on thpofj 6lr4 ;yb,e box.   J

  Eight books, each 4.3 cm thick with madju8r1 rd4 mslvw 7*u/ss 1.7 kg, lie flat on a table. How much work is 7 l4 ujurdvmdr8ws/1*required to stack them one on top of another?    J

A lever such as thatn hoffd4 (l9 ig ahdhdqb-p4,x0k5 b1a7t-t j, shown in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of outxhi j ntfo(bhd1t- d agk045 fla9,bdhp,4q- 7put 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 slideuzcpb4l1:e vt)4:w ch s 3.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (4c plt)wuh be1c:4:v zFig. 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 acc*+6 vyfmx2*; gjreded eleration of 0.10 g upwar eevg 2x6dmj+* fr;*ydd.    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 tikzdfm u62yp u k76a,8y2rh :lhe distance 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, pd6-s+ f u;qi15cteqz8 x:t qcvaries as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to xqx 1z tuet+68scdf5:p q -icq; = 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 partic u4gq-sg -v*ikle 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 moleculub;h;)j* ua/.pp 1w g3frvucqe, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an ar 01e.f*td4r t pdzjm0trow 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 s b,ww-+ 8v-3 kgk4x(ewsyq +s yulx.o)m.im getop 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-kgcar traveling at 1ub 8cndls4 jak (pd+f;-pyd(+05km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a ng ch 0+wi:w0ebow whose string exerts an average force of 110 N o 0gnecw h0:wi+n the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25xvdi5y9 +u8+54aot4 5 a ovd .vfttftt cm when the ball is caught. What wasyt55 ov4 tffauatd5otvi4+98xd t+v . the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50 e-d2sjj as n0ufzq1(5%, by what factor will its minimum braking dif e-au(jqjds 2z1s05nstance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investih59a skal h;sz(1ou1)kbdj f31 r7srsgators 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 on (and locked) the brakes. (Why does the car’s mass not mattkzd(s 3 )1f;hss7 5o s9ak ural1j1hrber?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches t5wdf1+ y jqc.kj l0:g;,hxbcp; wfk0ghe plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of;ywlj.kx kg5f:qh;j,1p fcb0d0cw g + 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 throwemog+dpz :. m-0. krzoysm/9h n straight up by someone who does 80.0 J of work on it? Neglect air resistance. r z m/:p+khg myo-.so9d 0m.ze   m

  A 285-kg load is liftee,qq w: g:6o+sc4 khtcd 22.0 m vertically with an acceleration by a single cable. Determi4q ,k +go: hte6cwqs:cne
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much -..*4dex tbdgwmx ,tk must this springbx . mwek-4tdd,x*.gt be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m h ulo896y doqcs 65nu:iigher. What is the change in potentiau9qy 6sl:uo o6c n5di8l energy?    J

  By how much does the g 1zh1f :)67bia/gkpklm+ aldaravitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jul7zbgi ad/1 h: a)pfk 1al+mk6mp?    J

  A 1200-kg car rolling on a horizontal surface e8fin;)fva5v) )qpk ;pvqqd 2q9q,i m has speed v = 65 km/h when it strike8)qqv9,qf5a d )qimn k;pf2qev );ip vs a horizontal 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 :rz4 g-*jubvifrom the ground so it is 2.20 m above the ground. What is the potential energyiujrb4-* z:gv 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 1mk,r0w7qf/60zhq m,o la/z vxf j e2w-600 m and climbs to the top of a 3300-m peak. ,hr/lm qzjf/ef2,6v7omk qw a0zx0 -w
(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 v:vr4rzbw6 b4-ernsy55 h i5ehangs vertically 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 to the end of the spring, where hvrybs56r i5 e4 zn:v5 er4w-bwill the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s)sfdd6c 7dl7*s -smzi* and grabs a vine hanging vertically m*l 7d z-csds*fds67ifrom 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 fro-qj 27un g8a7+b skgvym rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a fricti xpi *inh(0rl91l rov8onless 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, Fr.v)bhb mvkw/5sxn +x5an’s 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 cev5v5)sxknh+b . wx/bmnter 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 9zv4i k8 w -f;fms xh71dtih(uof a platform with a speedsf dkux 4itvh( im-;981wzfh7 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+wh+ 6k+ ef(/x/wdpu xsihn+e), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 d+/ p+ef s++6exwwh xnu( ih/km. (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 slide55/*axlp(qmc 7tgi mls without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r),ag 5/7xcp*mlqm5 i(tl from what minimum height h must it be released?    r

A block of mass m is attached to the end of a +ujw47c )gogb spring (spring stiffness constant k), Fig. 6–40. The block is given an g74gbuo+j )cwinitial 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 tiedrva( r+ ezi(e0yt* fw(o)yzd8 to a bungee cord whose unstretched length is 1*y 0)dwae8(z+ yf(rzetvio(r 2 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car //jw1(cir he aoy 1p(ishown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, ca(p 1arhy1/i(ije/wo clculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throw(2 pdryb3p g(rdstpz//o* mw)n with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at thm+mwnwn / q,0cygyp0uf y4 8:ke bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of,f:n4q n+muw p /my w0k0yg8yc the elevator and passengers.

  A cyclist intends to cycle u+j zu d1i4cza/p a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 i,9xpl0nb5e mkg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collis95e mn,0lbxp iion? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wim1b p r(*cm+x7ygc. qmth a speed of 2.2m/s How much thermal energy due to friction was generated im+(.brc*cqxm7y p gm1n this process?    J

  A ski starts from rest and sd9o .jyq tri15eyq+cqw8/lx3 6 ;*z )o kycykflides 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 dropp3)jqon+r:- d l( *(lqj n) ylmplaj-w(cpj9oded 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 bounces back tojrv 4+0y pce;c drpr/6+w 3xfd a height of 1.5 m.4w;/xd+ d 3fpc6rrprv +0ecy j
(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 re,nep 7gyr5an, *w0jfcst, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictiog7a5yce, jw0r*fnp n ,n is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point sj kd1 wj/yt)t0 cr-n81 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed willjr 8-)ydjn tw/tc1ks0 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 189z d4w59hndrv .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 pg.hs,bj*a8k (t m2tua 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 b8k bh. sgu 2,p(jt*tametween the block and the table?   

  A 280-g wood block is f:hmd30bf3j. b ss9reud kw1y/irmly attached 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 ej1e ud/yk.d:30srhbfb 3w s 9mquilibrium position will it stretch on its first swing?    m

  Early test flights for bwif07vw7 q ; frxo+. b1b8iyuthe space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 50018 b;b o0 vibwf+wyqf.iru7x 7km/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 ln vb*isz) ; (f.a+f r:ybtfru4ift a 315-kg piano to a sixth-story window 16.0 m above?u4*;ri.fa)sty(rbnz fv b+: f    s

  If a car generates 18 hp w;-yiq zs/oa1khen traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air r/iy saq;k zo1-esistance?    N

  A 1400-kg sports car accelerarvkw8 pu1; c4z. ;rhbmu;ds2ktes from rest to 95km/h in 7.4 s. What is the average power delivere4dwv .8k ;1uuhkb;2;rp mrszc d by the engine?$\approx$    hp

  (a) Show that one British hors)zxhb4h /c (fdepower$ \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 expreyf4).i6jk-g 2yc (6 uzxlq6sf -nghsd ssed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slo ph.ly6 of0zyz 8sre3n111 npbws down from to 65km/h in about 6.0 s on the level when it isynl.61 fh3ro8 sy1 1zpp0 nebz 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 s lacl umuob8o(99df2uw3oiwh 76m (5 motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shotqtf v.ebyckk;3c+y j0 m,*i:c from rest to 14m/s If this motion takes 1.5 s, what average power wabmcc,3jtk.f;c 0i y+vq:y*eks developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a z 70ytvyy 3g- ykf;8vp1 8siuhheight of 3.60 m. What output rating (watts) should the pump motor hkp3t-hs iyyv1yv88fyu z;7 g 0ave?    W

  During a workout, the football players at2 gtm1pb4 )jd9h4gr;bhyw *gi State U. ran up the stadium stairs in 66 s. The stairs are 140 m g db4tyj*1;hp9m 2r ib4wg)hglong and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 x83a5 +j;n:q d)obwrjgl (cgu$^{\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. Howbs3:f u86d id, /ngb hsbu3zv- steep a hill can it climb at a constant speed of 75km/h if the frictional fors-zvbg8 3/ bdsbh6i3:u,u dfnces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have tosv le7 )p(1wjm-u-va.(um uha11q d1jasvm5l be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient o1umju 1l vv.e7uvwah pqda-l(-m5ss am (j 1)1f friction is 0.45?    hp

  A bicyclist coasts dowd x s/ww xx36uop1gr08n a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that ardg13kym nky7mmi r1 :1f-pk1ne 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 bk1n- y3p1i:gdm k1nfy1 m7mr ky ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library ta, 4ibx8b ft7vssgg/fphv/0-he first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 3 pagvfs4/8/g btfv07b x -his,0.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous lonrj1yw d/zy4qa8 io*r; g 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 he was traveling at 6.5m/srwo8rz4 yjy*;/d1qai at the top of the arc?   m/s

  The block of mass m slice: he5k8 d,fyding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even ede: yc5 fh8,kat 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 witv jkpsr+fd mv29mr64go6a60 ihout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilo2imjopm rk 9gv ar660fvd4+s6t’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 tz(q(d9pmz d h l97fl9 tz7div3o a horizontal cord of length L whose other end is fixed (Fig. 6–43)(q3(vzl h7i 7 9dmtzl9zpdf9d.
(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-e;d5tbgnh/ xzk i/ 6yu(f:e z3m-high mountain. The climb is made in 5.0 h start(tu/e x z5d b/;gzfk6 n:i3eyhing at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaksg t/+z7puva2s when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that2q*o bg 9;bsyi0/todr*hh sv/ its lifts can move 47,000 people per hour. If the ave2y;go/q*h i tvrhbsbs*o 90/ drage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m bev0q 15iqido,*b tyi0 pfore striking the turbine blades. Calculate q,ib i5vq*0td1yp i0o
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Ficyh *y lhueg2kofmp c/5,23.f g. 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 fric*ylmo hgy/hc,ck.e 5uf2 3p 2ftion. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how *g(iq y7m.n:aivk0hj high could an 82-kg man climb a ladder if he were fueled by one barviy (jn.i7g0 ma:q hk* (=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 8hb*uz+ ,zzas29 bsurg-fo:oan 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 inside the scale compressesc) 5 x78o))d1s-aogxkeymv fx 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 15o17)gy8 x)v axm)d-fcsxke o .0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out;db*3nxbuqd)i:iv, g over a lake (Fig. 6–45). He releases the rope w:v3)ui gnid;*bb , qdxhen 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 athlegs./2f;nlt: - l yd duu1(dpdzte climbs a vertical distance of 5.0 m in 9.0 s. What minimum pow1-duzn;yg : t(ds/2ddf .lulper output was used to accomplish this feat?    W

  Some electric-power companies use water cgb *,hai*0fmm 69t deto store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the en m *dgc6ih*fam0t,b9eergy 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 w vh rfqk7as;. g+f83mhalf. What is the spring stiffness constant for each of the two resulting springs? r.a 7vf;+h3 skqm8gwf  k

  A 6.0-kg block is pushed 8.0 f zkg;f;u)(ko 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 lo7cdiq gy2:vk -ng will it take to accelerate from 55km/h to 75km/h Assume the p ckv:yd i2q7g-ower stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”)) zu5jiyz+yyg* n 3m:f, the patient walks on an inclined treadmilgjniy 5+)yu*y: mzz f3l (Fig. 6–46). 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 distanfw./ h3vyh) zoce of 500 m, what was i w)./ yohhv3zfts 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 y.zp )l ekahabu2t44 (e-9 gqc95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximup-4zua lq.k2b)e a y4thc (9egm power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s