In what ways is the word “work” as used in everyday language the same as a yskecld7sj bb ict+5)+; omg:x4*a0that defined in physics? In what ways is it different? Giv* je7+loy:) dks0;5 gb+aa cxctbsm4ie examples of both.

Can a centripetal force ever do work on an object? Explain)z 6cuzh7a 7rh.

Can the normal force on an object e mq0yp d/wly(j-g ,d4vver do work? Explain.

A woman swimming upsaxq:fn i3sy78l2yak2+ q)rj-y6wh3o x:biqk tream is not moving with respect to the shore. Is she doing any work? If she stops swimmi s ayf)7 : ylqk 2kqxyw qr8x3nbi6a-:ijh2+3ong and merely floats, is work done on her?

Is the work done by kinetic friction forces al0kd8;f.fknolr c9xec7x s(l3 ways negative? [Hint: Consider what happens to the dishes when yo9;r837ek(lc s 0dxx kf.of lncu pull a tablecloth out from under them.]

Why is it tiring to push hard ag jmi fwp fy6u*h/5c3*x9t b,fgainst a solid wall even though you are doing no worku fg ,3ic9j*bf/fxm t5p6hw*y?

You have two springs that are identical except that spring l3zsrt s(atj i7v9 p lz9e*;ar. is stiffer than spring ja(9s7r;as 3*rtezt zl vp9i. 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 ie wbv3, d;lm(vl-kj /kf4+dybz;xw0js free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and bydfl(+l0 ;4wbkvz ;/by, j3 jwxdvkm-e 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 gravitationnxv)l9ns* 9b pal potential energy change when you jump9bl px*9s)n vn as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buv+qe ,xaj j+)z bwbd84b ya/.mt i:yq1ilding, all with the same speed but with different launch angles. Which one has the highest speed on impact?w mejbqtdj)8 q .aia:y v/x+y4+b,b1z Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest nyup,5 -i(2 sm1atgacpoint in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward un-a t1( ,ia2 5pgymscalong 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 t- gerw(4utg +ohe spring by pressing down with your hand and then release it, can the spring leave the table? Explain, u -gwt+goe4r(u sing the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instrb ;z0p484dmav kh1k cructor pulls t41vk8b4md;h0 krc pazhe ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potentia -6ux1 ;7tms4uq zjqkrl energy when water at the top of a waterfall falls to the pk 6;x4tu zq7m-j 1sqruool below?

Describe the energy transformations whenyobw)// al w y+rp),8mt)gfxd a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier star r/mgdvgx*w(6*miw wugqw8,*ts skiing down a hill, but after a time is brought to restxwwi6wv(w*8u** qgm r,/gg md by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill ya,bsjrf;ks m8:t;k3vqn/s0o o e94 e of height h and slides down. Does the velociorskb:va;,sm4 qfn38; sejy0e /ok t 9ty at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to 3 h/dfkd a6cuboq85v:step over a fallen log in their path rather than stepping on top and jumping downhdf3d auovc6 :k/5bq 8 on the other side. Explain.

Two identical arrows, one with twice the speed of the ysxl) 9wzosjx:):p4kother, are fired into a bale of hay. Assuming the hay exerts a constant frictional force o : swpxy))sz94o:xlk jn the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) igh 6ao 4kknx+4bnoring friction, and (b) taking friction into account. Explain why a gr6o+4xk4kb h anandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater thacd* c- //:kgwy,zjmh +7sdmkbn its originad z, sm/ck-cw +jhydk*gm/b7:l height? Explain.

Suppose you lift a suitcase from tr plqm-an+vj, ,+4srihe 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 weight qnr+- j4pa+v,,ri lsmof the suitcase?

Repeat Question 22 for the power nee1g r;;h2ii-6:s aykgwwyj 2mjded rather than the work.

Why is it easier to climb bd o8p 80nlz8s)cv or1a mountain via a zigzag trail than to climb straight uzovo 8rs18cpn 8d)bl0p?

Recall from Chapter 4, Example 4–14, that you carth+3e0tmo( hn 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 concepts.h3+hoetmt 0 r(

  How much work is done by the gravitational for 2xr m+4uw6zvdzs 1)fkce when a 265-kg pile driver falls 2.8s)6v4+f2 xzdm1zrw k u0 m?    J

  A 65.0-kg firefighter climbs a fla1 dxid ,:4jzpxfh:c0ight of stairs 20.0 m high. How much work is reqix4:x add hzp1j0f:c,uired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at consjk -vktr 1mk4t/qkc3uv2q x) 9tant speed (a) 4.0 m along the floor against a frkqu/ rm49 kx13t)kv-t 2jcvkq iction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mik/a 7m 5-agxp9-8gs *oosf ugovers do (horizontally) pushing a 160-kg crate 10.3 m across ak xu9 -75a*-om 8gf/sagg opis 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 across a fapt0did 6f46 q 5elwz32um t,mloor at a rate of for 7.0 s. Find th5 u26tp4 tqd 06a,mz3melidfw e net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mu,f5 g-vx ah5 .n73mlzy8rkhtmch work is r rk8t5,5hah3mnzl7x -v. fgymequired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objxo6, hk.;k t 6wo2v/vj2khbk qects we might not otherwise be able to liff. Show that the ratio of output forc kjv.ok2tx 6;ob /2wkv6kh, hqe, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from a bc l)uotfx j y b (;;x*oi5c)7p0hpr,ry03zfzccelerating by a man who is pushing back on it parallel to the incline (Fig.bo bzu3ryy ff;),0hor)jt p ;x5p* iz cl7(xc0 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 requiroer *2ks:qx9felu4,o isi / p8ed to give a helicopter of mass M an acceleration of 0.10 g 2eo prk s 984sq,ielf:o*xui/ upward.    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 distapfj0:8spj3v zn l*.y dnce 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 axi z/c4 0oa+ekhns, varies as shown in Fig. 6–37. Determine the work done by t4hoackn/ +0ezhis force to move the object (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 act:o8 b,0v anrta.lx*h:sc1o q is 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 molecudre8+x -n r80usdg 1lale, 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 a;n/g/;iwbhkx( sh)rs rrow is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an efapaai 6w0i w*4h t wjbe:87n2lectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 traveli 1(;8 tjl.wyhkopstf6ng at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow (,bqaf /8 vyj me9yk.awhose string exerts an average force of 110 N on the arrow over a distance of 78 cb,ay8.aeq 9jvy /f(mkm. 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 25up862r* 5,fossf flff cm when the ball is caught. What was the average force exerted by the bal2lspu8r* o6ffff5f ,s l on the glove?    N

If the speed of a car is increased by 50%dluu)x:mc 9g1;54n lbzvijz3 , by what factor will its minimum braking distance be increased, assuming all else ;z9bugij m) ll51n4c3u :zx dvis the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid marlyq:; lunvy()k 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 mat:) yylvq;(l unter?)    m/s

  A softball having a mass of 0.25 kg is pitcr:mgnsz 6s (s-hed at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, ifz( s-6:sg rmns the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown stra)wz.a (o-u.u m osfzz6ight up by someone who does 80.0 J of work omuwoa. 6so z(z.-fz)u n it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratbbcy5 (np(tjla ;u. l)h .oj(pion by a single cable. Dh (la ;b5 (pn)ptj(c.ouj.b lyetermine
(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 Ho2 p9harnh5y b1w much must this spring bh 2nabr5h9y 1pe stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2.gbza-5a);mp v yg-kb6 8fit f m higher. What is the change in pfvaa8.5g-ty6zbmf ki b )g;p-otential energy?    J

  By how much does the gravitational potential energy of a 64-kg poled/* 9 q fe8wunsu,ls zpu2s0c, vaulter change if his centercu 0 , s*z fn82lqd/eu9ss,puw of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surf0gll dq4 *c)pyb3njs2ace has 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 y2 3* l4 cbndgjqps0l)spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg )pjmda3 t9o o05n. cf:xut6 cubook from the ground so it is 2.20 m above the ground. What is the potential energy of the book relativ o: 5nctfxao6)ucm0.uj t9dp3e 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 0vrh11v os aw0+lwbz+tcl 5-tdcdl- /elevation of 1600 m and climbs to the top of a 3300-m pewo -/01lvv bhsc-l1tw0zrt++ca dld5 ak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a rulerl7s(a ftdr.ka2z eu9/-zdex 1 gpip-1. 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,ad(d7kt lx2z.s1e/p19ef rz -uip-ag where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is l4h*pop3q3o 56cnu.us 39gep jjrqq; running at top speed (5.3m/s) and grabs a vine hanging vero64cplp; hjpuoq*q. rsqg 3n3e59uj3 tically 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 frow0 7/j..p w6potoksej m 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 fris1s c, 4acjle6ctionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic en0)wv4goz4k l- +tvt joergy is transformed into gravitational potential energy without the aid of a pole. Withvlg40to- 4jv t) wzo+k 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 speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the toe lzxp4 se*j*(fyxh 8zlp/* 0w16dz otp of a platform with a spz l*/t*0eh4 w zdxez*y(op s1p6j8 lfxeed 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 stiffnestnm 4ag9/ ahkts:0zi( s constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball whe4/zns t0it:9 a(a kmhgn 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 the6vi.s6rv +;vss lkup 0k jim.( 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), from what minimumikm 0pj+iv 6.us vslk.;s(6 rv height h must it be released?    r

A block of mass m is attached to the end of a spring (spring s6*iz4js) r caxtiffness constant k), Fig. 6–40. The block is given an inita )s6*r cxji4zial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose )vqq7;v hdhe*8w xjjjujahs0r6l 7) 9 unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, asxq)q0hjdwrhej 6u; lav 8j797vj ) s*hsuming 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 dragged11kdw y ,ms9a (ew2uyx up to point 1 where it is released from rest. Assuming no friction, calculate the speed at pointsys(we,wy 1x2adm1 k u9
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 w,1)vkrt/ g2dwx4i18ujaj j t 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 t c7dh u.*4xos:f7oz aahe 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 thatuo7f:hxad.o*s 7 za4c 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 toftk;rczr6/w44xg 5 o t cycle up 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 ognx le .o0r ru4;0wtl0awx1l+f mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collis0a0nr r t;0le.14xlwwxlu g o+ion? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches+ itz5 hz/59hqr)ttegpxl na1xi6; 0j the bottom with a speed of 2.2thrjx/zi;p t6+ilxqg5)tze 5na0h 1 9m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest xfl*-n5cd.; n; ipuyzqc2)crand slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped froxqfkq0y p)s9( m 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.,m9 dcpk1e2tg0 m, and it bounces back to a height of 1.5 m.2dmekcg 1t9,p
(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 wqmj0hy .1 e4+k9 qxrk6omp4vconstant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final sp 4.+mekh9j rmyo41wvp0xq kq 6eed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point s+zyk )8 ti3wl1 with a speed of If the aver3w8 l ktszi)+yage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwarn 3ckduc(z++xd 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 firml cn .*l-(ape*kcf9w bpsh r68dy attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before 8 b9.pcfnph*read w sk6l*c (-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 veryr)fk w+x .c9mnb,5nep 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 position will it stretc k5m xb+,.cnwp)re fn9h on its first swing?    m

  Early test flights for the space shuttle used 8r+5:nl h3 a,hzyhka7 k6 icdxa “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air rxa+6kid a y hh7cr8,5nh3l:kzesistance?$\approx$    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 w3kv5;y8r07 t f nxqytwindow 16.0 m above?v07n x tr w3ykf58qt;y    s

  If a car generates 18 hp when tw5:lig zjiu8i(u; z-nraveling at a steady 88km/h what must be the average forceg 8zl ;zwnuu iii(j-:5 exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates +s:ie.(yoqj /n avk2kfrom rest to 95km/h in 7.4 s. What is the average power delivered bsk+e /kvaoj(ny.:2 iq y the engine?$\approx$    hp

  (a) Show that one Brit-zn :wn26pi5 he+)+rw kbsxctish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form ofw/lg -+n sacv vn4hy3ajs(rgy)r570d “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/s,iism4.*tx f h in about 6.0 s on the level when it. i,*xmf iss4t 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 3b an,9ddhnqw.+55en b.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/3wy /n( n:n 12vczzlv2 y9mnars If this motion takes 1.5 s, what 2waymc nv/n3ly 1 vnn29r: z(zaverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per mfjq+ 90d8vxpc(7 dip ninute through a height of 3.60 m. What output rating (wattsd+jnp8(vxq7if p9 d0c) should the pump motor have?    W

  During a workout, the football players at State U. ran upev7i / y11skxq the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle1q/ vskiy1x7 e 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 fa.gcj,z srt( 9ey4-7) osiju6 (pjtmclimb 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 ste c*pzsyijjo ly* 2dmbu:*zdt-)1x 9p4ep a hill can it climb at a constant speed of 75km/h :1o-*iydlmz *cbu2 *x9 zyjsdp 4j)ptif the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower m79 ig9a:iyfon ust a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is o7f:ai9nig9y 0.45?    hp

  A bicyclist coasts downztp66-*fom5-xp pmx j 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 builttxa8pa1j t3p* “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bum8tp pa 1txj*a3per 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 thk f2ql1af29*f; n kwgme 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 holds 25 books, how much wormffq;1lg2w*kkn f9a2k 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 1936 Olympics sb/l 5icy: 7twzi.bu3-x r*prvhows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum3/ b ub r7c- 5wp.ixlri*t:zyv speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without jub 8i1-i2 f sh4v,augfb27ywfriction along the looped track shown in Fig. 6–39 is to r- aw,uhiy ifu2sg48 bbjf 712vemain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping 5evkt,9a: zqalbvx5pc-c( c +geb:5v from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 9c5q:cxtk, ac(vvzgb5+apvl b -5e: em deep, but survived with only 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 of length L whosergbj0gw(c+ sm ((r ub3 other end is fixed (Fig. 6–c s0( jmb brw(r+gg(u343).
(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 + 1hm,m6t/w6sly ab gs3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Cag,yh w /1bl+a6mt6sms lculate
(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 9+v0l.rww e dc28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can m7wj-mc+2t7/yq -y 8ff6qis khrfxz t*ove 47,000 people per hour. If the average lift carries6y7w2 tsrkq7i+c 8-fzx-hf t /qmy j*f people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate ofnmhfx1m d gtx)7+u c2f)0im5y 650kg/s and falls vertically 81 m before striking the turbine blades5fmnh) 2ycfxmumi7d+ ) t1xg0. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44),uj2kfda:: o2 2, jtv:v/ytglx3fv -dr the difference in your apparent weight at the top of the circular loop and the bott dktvflv22r, axd:j g- /3::fouvyt2 jom 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.    mg

  (a) If the human body could convert a candy ba)sypxd4 .bfq av;ij.ug j()uel r 1q1l+e4ww.r directly into work, how high could an 82-kg man climbywfa uxuis; 4vdp+wjl1q.)e 4(rj )gl.qe1b. a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired go8 wo 62gn; j-xzth3tat an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bath q(ha)xfh7 ji.room scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the sj ( ix)ha.h7qfcale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over j9v3)my . vgb17uw 2e au 7xlsjqt.ie6a lake (Fig. 6–45). He releases the rope wj3 9yxqamuwv u1b 6 t .7e.l7)2vgesjihen 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 atk3k 0jc9af f0wss4h u(hlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum pocskjuhfa0f 3k ws 9(04wer output was used to accomplish this feat?    W

  Some electric-power comgxms;y b: --7 hn*t6:hcsejhfpanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW (:cthe7: -*b h;hsfmx6j syg- n$120\times10^{6}$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 jcja7y0nk ,w; k is cut in half. What is the spring stiffness constant for ejjy; 0anw c,7kach of the two resulting springs?   k

  A 6.0-kg block is punr0wulate6 mv+*-/b4lco f x5 shed 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelernj ep 2y6bv8kc j-on71ate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays t-76njbpn8yovc2e j k1he same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stressk99zq ;otpp zr:2,iy l test”), the patient walks on an ii,r: t;o qzp9lk2y9zpnclined treadmill (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 distanw9fpd-q8463rldcczljpuk8/ 9+r l p kce of 500 m, what wl f4 z -/pd3ukq pc9wrc6r+jd9lpl8k8 as its 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 ak lpyett-zc 9.ktd.j.5,a .8 knc ;n(fyyk)ly height of 2.0 m at a rate of 95kg/s (a) If this wate yakyy ct. ( d,-.n;kz.nkt5k.8 llt)c yepfj9r wheel is set 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