In what ways is the word “work” as used in everyday language t.7u2tskt+i kr he same as that defined in physics? In what ways is it different? Give examples of7i+ 2.rttukks both.

Can a centripetal force ever d *5-.xh:x0 wsssyffn 9bbzom4o work on an object? Explain.

Can the normal force on an object ever do work? Expa 7fjk8)h;uov5,ut celain.

A woman swimming upstream is not ur+ h ru;*qu1smoving with respect to the shore. Is she doing any work? If she stops swimmin;*hu ruq1rs u+g and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Conyiz0 +13t6 vyb/:t5oql tkre dbd)fj(sider what happens to the dishes when you pull a tablecloth out from ut+b/tkdoe(di:rjf )35v6 yqtb 1 lyz0nder them.]

Why is it tiring to push hard against a s1j/m:;1js 1hy d ykpjro6js*zolid wall even though you are doing no work?jsky1mj;6 /1* y j zhsjpr1o:d

You have two springs that are identical except that spring l is stiffer thb5d / 1rxudc(aan springxudc 1ba(dr/5 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 ads xwq/x: 12w-gu amy0dp4 /sj block that is free to slide on a frictionless surface (Fig.6-30). The block4 jaxgpx1ws 2d0ym s /uw/-:qd starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy chpbx/ i aoqew68/z 2lc7;a3 umjange when you jump as hii aax/bqe8zu;p2/ ol7w3mj 6cgh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wiaw qmj++08 svtl,f-o kth the same speed but with difvtk +am l-0s,q+fw8 joferent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height xc :/b;cnsgvfk0(ne /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 /:(fcegn ;ck0bvx s/n 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 ra / icc+w.zauf bl:7q3ests upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring +iwlb/q .zc7 a cu3:faleave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–3zp9 .1gr)yzbsxajh.w:+q yb-3). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release w +z) x:19jbh.rz-a p yy.qbsgthe ball without pushing it. Why?

What happens to the gravitational potential energy when water at the.e+ogvb1s7 v2j hti jv9e -,o,ya*ncp top of a waterfall falls to +va jj *npv i1.ov-btoe ,h7sy2cg,9ethe pool below?

Describe the energy transformatiofwwfc,31 .r5;jzjv k tns when a child hops around on a pogo stick.

Describe the energy transformations that take place whi gg 5ca hlhi3c).)o5nen a skier starts skiing down a hill, bn))gic 5h5lco.3 a gihut after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts fhvay g.me0wu67t 5a8ksht0 (grom 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, wyg umak5tt h0s8.v(eg70ah6and (b) there is friction (deep snow)?

Seasoned hikers prefer to st4pim s uw*:hc*ep over a fallen log in their path rather than stepping on top and jumping down on the other**4 hum wcips: side. Explain.

Two identical arrows, one with twice the speed of the other, are fired s6 na42 wj0amy 4lz.n3, piptyinto a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fnjts0na.m li36ypw 2py4,4zaaster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of adlb4 wl(ku 6( c8l-:mi)dgw 2dmjuk4 q simple swinging pendulum in terms of energy, (a) ignoring fric:d6 8ld mwuc2 )iwqm b-(lkgj(l4dk4u tion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is drovvfr:ai/qn+2j3a uf 4-i j jo;pped, can it rebound to a height greater than its original height? Explain.jqnrijafa3+ 4/2v v;-ijo : fu

Suppose you lift a suitcatrjq9;2fu4oy *x3eyd se from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weig42r e39qo*t;xyd fyjuht of the suitcase?

Repeat Question 22 for the power needed rather than thefwz oz*a 5+wm1 fy*m2zhn1br1 work.

Why is it easier to climb a mountain via a zigzagn)znbbgo*g21mk *z 8z trail than to climb straight up?gozz**n)k bn1mz28gb

Recall from Chapter 4, E.da (b5o 3vokxxample 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the (.kb 35dvaoxoload is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationagg f t62u4: dvecr/v3k t5tvu-cwujv36h/b4d l force when a 265-kg pile driver falls 2.80 /ujd4g6 c eug/h-dtfc32 rt 4 wb6vvku:3tvv5m?    J

  A 65.0-kg firefighter g,p rlist ;rari ,0;/fclimbs a flight of stairs 20.0 m high. How much work is requitrisg ;0/ fp iar,,lr;red?    J

  A 1300-N crate rests on the flomv2lx x1u3umxa , 55sxy*dulx,5x b/m or. How much work is required to move it at constant s5ux2m*u l5bxvsxy xmx,,u/3da xm5l1peed (a) 4.0 m along the 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 10.3 ox.qwk9 ku: 2rm across a rough floor without acceleration, if the effective coefficient of friction was 0.50?29wur:ko.x kq    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of ob(1h.,ddj 11 cromcp* ,by vs for 7.0 s. Find the net work done on ybdd(homjr 1, 11c.pv,*ocsbthe box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat a 5yk9zw5meh9on a table. How much work is required to stack them one kw55 ze9h a9myon top of another?    J

A lever such as that shown in Fig. 6-3b pbmiuk:- w,35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output for w-3uki: b,mpbce, $F_{\mathrm{O}}$, 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 ia;xzuxw o8+*l tvw-j2s kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40.+wxja* 8l tzuvoxw-2 ; 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 a.x0u8q)9pplaeft(1f q: -mrkfumr z -cceleration of 0.10 g ul0uau p.f frx (f qq:pte81mr-m9-kz )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 distance ag bzf;d rgm/5jm4n)l c5 e2zj1xis 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,phi 5( sh*;asq acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the *5 h;hs pqas(iobject (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 particle acts in tnmak h; jf04s -q+fl)if2tcm0he $+x$ 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 ol(io b/:0 v z/kaz7yc o-eg+gef $5.31\times10^{-26}$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 isy(t bxz4s3vd9 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 requk3m2b 86b3gcedw 0 vffired to stop 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-kgcat-l+e ixoe8:) lnw-omr traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whosk8 5*ex,ay o(tc9-zzz 3 kify9jum7q qe string exerts an average force of 110 N on the arrow over a distance of 78 cm. Wha 8tuo9q-kzkc7j9z3faimexzy5 , yq* (t is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) y/ m+owmfzp7lg5z bked7 s7/m6o:5nptraveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the bon7mf 7spb+ g zklm5ym o/5zd p7w/:6eall on the glove?    N

If the speed of a car is increased by 50%, by what fact)skm5e/bkn ne-h v23c8fz 6ob or will its minimum braking distance be increas/6)2nen v f83szb- c bmkkoe5hed, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a leg*okmevx i q y4g6q6ll3z3. m*vel 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 on (and locked) the brakes. (Why does the car’s mass not matte4q 6m x33l*y k.vg*ozlg e6qmir?)    m/s

  A softball having a mass of 0.25 kg7j wrk2u*b ae7 is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglek7 w rubje*a27cting 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 someone who does 80.0 ,jgwmk: 46(tpfmc s o0J of work on it? Neglect air resistancem4g f cj6s(0p,:tkmow .    m

  A 285-kg load is lifted 22.0 m verti:l- ywdli)x 88p ,gf8) ggpn)tjmuzr)s8 4uhh cally with an acceleration by a single cable. Determi pl )g 8:m l4gr)tu-iu ,f)nzyx8dswjh8)8phg ne
(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 springe wn ,o6ij5h)+kni7nbi. 2buw stiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J ow2n5 6u +bn7ib)jno ekih.iw,f potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whnz0:/d seed g)at is the change in potential 0/eng: sde)z denergy?    J

  By how much does the gravitational potential eneqi8 /falnr;b:cn87w trgy of a 64-kg pole vaulter change if his center of mass rises about 4.0 a i8l/qnwf ; 7r:bnc8tm during the jump?    J

  A 1200-kg car rolling on a horizfva3nsl +m5b,ontal surface has speed v = 65 km/h when it strik,l nsa+bv 5mf3es 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 person18ot*.w tvx+k1ehgw j lifts a 2.10-kg book from the ground so it is 2.20 m above the groun. o 1ew*gjkwht 1+xt8vd. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the ton*vh sdiw(02reg3,m ip of a 3300-m peak.mn hv2*ws0, diir3(ge
(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 verticall4p4knyb,g a)2ff;h-w 1tt kmk y 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 4;kakk 2 1-t4)yhfpwnmftg ,b, 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 vine f-7.oe 8lv.gxad7vo 7e zupn 8*yqm4lhanging vertically from a talldpqvu7 g-a mf.l*x788voeo4nzy 7 .e l 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,ngboyx( oy.4a -gc3 *d 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 frictionless 28.0:tn xnixow.-ae9k689lusqp; $^{\circ}$ 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 m- xr ul8cgxa)xlm3/o/ n7)vopotential 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 3 mxnlo)gxl/7mo/ uxr8ac -)vand cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist 9n( hhl15mxnljumps vertically upward from the top of a platform with a speed of 5.0 m/s.5l9 lnn h1mxh( ($\alpha)$ 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 stiffness consta8du8ictu45cqq/ wa/ mnt is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwardwd8t miu8 acu5c/ q/q4 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 tracze 6jcf.s3 j9uc9/llq2e rz4sk shown in Fig. 6–39. If the block is to remain on the track, even at3rjzce2el u lfsz/94 scq.69j 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 ph,ae kj0- r:ithe end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial disph kirp,a:0je -lacement $x_0$ 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 buny4o2 n2 1tw)cazchjz/ gee cord whose unstretch yw ctahzc/zo214 j)n2ed length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car ialv t8;:em*87ausbfrrbv1 8 shown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate t8mei*7b:as lrt 1fvu b8;ra8vhe speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ry4f2.u0r(o78lo fpit+:nn lmerw3gof 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 ate hf w p5fhj1:-,sklf, 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 acceleration of ne- j lphf kwf:h,s,f51o 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 ui, qh .tlveu+6p 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 kg and traveling 95km/h in opposite direo+u* jnps0zr r7),v0qjyn 3jcze4ff +ctions, collide head-on and come to rest. How much thermal energy is produced in this colli3ze)0+ r 04yo*sc7 j+j ffnnvjqrz,u psion? $a\times10^b$ J a =    b =   

  A 21.7-kg child descendsa)n h- i(lg8c;4gija)tc r1nq 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 genera -it) ngjn h4 gl1(acci;a)qr8ted in this process?    J

  A ski starts from rest and slides down a 22e lca)y 3z9.ql $^{\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 dropp8 qf. upqn+u/ned 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, ans4 wr6i;wv *:sgvktx 7d it bounces back to a height of 1.5 m vvr*6iws4kg: 7;xsw t.
(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 floor with a constant i.:kk akznxs2a63be8 horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of fricti6.k2:binsa 3aexz 8kkon is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster i;;m 1c1*yfetdo;u8n)a*q unmqr mb v,n Fig. 6–41 passes point 1 with a speed of If the average force )me,mau;1m;*nv qnub1; c y rtqf8* odof friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady up.p0 aqx:rm v1vward 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 very light horxt -i4lfj69dqomnj )9 izontal spring (k=180N/m) as shown in it jf9o 9m l)xnjd-46qFig. 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 lis3h1.0jh)-jimn,j ;ldoh ca (fev7rbght 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 position will it stre c7bn.herjh(i)-j0 js,m3fhl va1;o dtch on its first swing?    m

  Early test flights for the space sh 7wbztn01 fvkfl.*vn(uttle 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 landingb 7l (nf.1zfwv k*tnv0 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 do1a7vmq 5mpmz s828e piano to a sixth-story window 16.0 m abo5mmo 12 8aepvm78zdsqve?    s

  If a car generates 18 hp when trr1lg67tqt)y04i d wfiv q -mu.aveling at a steady 88km/h what must be the average fo)qtdmty7uw irl0 v14gq.if- 6rce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7m30u r10/nh p 4qjma55 8r+bojqtfmzw.4 s. What is the average power delivered by th5 j4u53qnwmtf18qo0jrr b0h mm/az+pe engine?$\approx$    hp

  (a) Show that one British hors ;* w:mm q;qieay/uu-iepower$ \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 expresc+j4 qznzn4(psed 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 hnq*-pny( 8 -rejma;rher 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately wm-ny( n are8 *-qhprj;hat 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 motf aax:ocvfx 1-d9ttzsl n7x rm :67t0*or do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot -3;w1cm r0+e gkq akvjfrom rest to 14m/s If this motion takes 1.5 s, what averagejr 3mkkqv;w-g1 +ae0c power was developed?$\approx$    W

  A pump is to lift 18.0 kg wwd/ b3r-nut2psd:a6 of water per minute through a height of 3.60 m. What output rati3/us- ad6w 2ptrbnd:wng (watts) should the pump motor have?    W

  During a workout, the football players at State U.i i xc3wfk/(1pjl0(jy ran up the stadium stairs in 66 s. The stairs are 141xjfcipiy30(/lw kj( 0 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist cl sg*2:xctr9yrv7t q ;simb 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 steev ;6n9dhnh 7-2yfur e*(gjwoep a hill can it climb at a constant speed of 75km/h if the frict f-vj(whr neu92;y6o*dgh7n eional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor hwt:6fp kg:*9goe j (mpave to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictk g:ge(f p9m: 6wjo*ption is 0.45?    hp

  A bicyclist coasts down s2p6 srs m1/ w9bgf5sq-f)vfg 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 are desi hwv/ 8vucy*5jl)g8qp ko)rzm 7d b.r)gned to compress and rebound elastical /qlurw8 m.j7b)cy5p 8 k)g zh*ov)drvly 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 wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the re6h uds ),364cb zf0j9nn pbnijmaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is ri s jb6n, c09u4 3hnnf6bpz)jdequired 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 1936 Olympics shows oc gnxti; 23j4f.l :rs(g xcq9that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need atng :g3j x;(s.t42fc o cl9xqir launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fi1dc593:dyv hge6w cla g. 6–39 is to remain on the track at all times, even at the very top oyc39avg: ed5hwlcd6 1 f 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 y. )v: khx7.1e1xjy* + fn nfx/ay tgg.zeexv7without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only g+fg*x.hayytyx 7..j e:fex1evkn v)7x n/1z minor injuries. 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 4r/9wv myph vlt,x. r8of length L whose other end is fixed (Figl,r h9yxr wvt./p4 8vm. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The cl9vt(3;gef )hbrfmx 3um1-w6hz 3 ynzlimb is made in 5.0 h starting at an elevt;-hux3zz e9m31yl6hrn( 3vfm)wg fbation 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-kv kl., qj7qd)ou fz5s8g 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 qao28obk 29lrlifts can move 47,000 people per hour. If the average lifoaoq 82bkr9l 2t 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 f+qnw/33 p fawpalls vertically 81 m before striking the turbine blades. Ca/ pfa3w3 wnqp+lculate
(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 rolle g;dzpvxq9 ;/yr 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 px;/ 9 ydvqz;gfast you go through it.    mg

  (a) If the human body could convert a candy bar dire--h(.g w1 xjsfoq0zqt6wx;gictly into work, how high could an 82-kg man climb a ladder if he we.j xg;oqsq0-z-61hfgxitw w(re 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 upward ang+ocw9mvb5ip4x1 v-c9ptvev * /bjnr 6 le 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 insida .k75htbo 8c5x9torv e the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale 5trh5o 9vbx kto.a c87from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a la-j9 k7gx ;xcd 7+vwlfzke (Fig. 6–45). He releas 7-xz9jlvg+ w;7dxcfk es the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, aiynr 6he qj,39 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was qij 9 rn3h6,yeused to accomplish this feat?    W

  Some electric-power companies use wa1yy5jdmr d r xrz1/1.lter to store energy. Water is pumped by reversiblyj51/ddmy xr1 lr z1.re turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k 3x8tg9 ltj5dsis cut in half. What is the spring stiffness constant for ed8 53jtxtsg9lach of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m /0zbds6uvkbhl,u28 ti/ . zsm 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-wzbv,urlx +n3v xq/* wt)u869 q owpj 55km/h in 3.2 s, how long will it take to accelerano-,6uztx wwvj/xw3q vp )l9b+q8u *rte from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “st47:xvhxmw7 rml+v4g 7 fivea0 ress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is slopingmlwax7:4vhe47 f0mrv 7 +vgxi 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 verthqqnn)7r80 k yically upward a distance of 500 m, what was its veloc h0nryq)8n k7qity 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 9om2kk nfo:l m1(1;4gyfkih lof 95kg/s (a) If this water wheel is sety kmi211( knl;gfoh9:lkm4 of up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s