In what ways is the word “wo77lnhzvx /q- vrk” as used in everyday language the same as that defined in physics? In what ways is it diffexlqhv v-7 n/7zrent? Give examples of both.

Can a centripetal forwolti+y;g:9, ayd xo -ce ever do work on an object? Explain.

Can the normal force on an object ever do wovg 28 ij4z 8v u:y7 dkeie0cii20sth/ark? Explain.

A woman swimming upstream is not moving with ro c dvwy ;2kw p*87mmj43mgn0v0a cy*respect to the shore. Is she doing any 8o y3vk 4 pcm*v0w*y0 n 2cjd;7amrgmwwork? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alway9dt;mt k05yxus negative? [Hint: Consider what happens to the dishes wheny; 9utmdt05k x you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall1l/(6r6j j c9rv54 pxsucpmz v even though you are doing no worpc 96(c vvp5rl4 zsm1/xjr6ujk?

You have two springs that are ident;ch3 ab+a,3euyx t/zb ical except that spring l is stiffer than spring 2a ceb ;3hab+, t3xzyu/ $(k_1>k_2).$ 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 / ltcm myi6+2con a frictionless surface (Fig.6-30). The block stary6m/mc+2t c ilts 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 ener) lihsfxf* lk:0q)5*pt 0:hk uaxc5svj4n1pigy change when you jump as high n1)*c0fitplqul k5j0v5k:xhsaf: ix) * 4hsp as you can?

In Fig. 6–31, water balloons are tossed j2/n 7/v3i9 ld cbozsyfrom the roof of a building, all with the same speed but with different launch angles. bio3/9dsn y7zj2/lvc Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from o6-bwtb-l* 4bkm2k0gc5x gts a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second laun tkgsbxo l-5w2-b6bk0* t4 gmcch 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 restknl( +6e u5umis upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring le k uinue+l56(mave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wirepc ux*buq8 /i.w9 g;xh (Fig. 6–33). 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 the *hx 8gbuu/pi; 9x.w cqball without pushing it. Why?

What happens to the gravitational potential energy when water at the tm(whkkqz a1no2ve.8 - op of a waterfall falls to the pool v.2 kznkow81mehaq-( below?

Describe the energy tralh.z5j)xkf myx89h: ensformations when a child hops around on a pogo stick.

Describe the energy transformations th - daznvbyjv8 zt51,;uat take place when a skier starts skiing down a hill, but after a time is brought to rest by strikinv a-jv8 1nzdzby ;5u,tg a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a 4b+wphm df25khill of height h and slides down. 5pb +w k4fh2dmDoes the velocity 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 step over a fallen log inyqp:j00 : zu lkl py8ubcxjn9:3)(wbf their path rather than stepping on tok: 3:0wplzl09qxybj ) pbf(n :juyu8cp and jumping down on the other side. Explain.

Two identical arrows,rb)ghpz 4k u8km to((7 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 ztprk hg(u7o b8m4)k(penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in termsjcl1 w*8ocgtm si;/ 8a of energy, (a) ignoring friction, and (b) taking friction into account. Explain osm1t ;/8*a gcw8l jicwhy a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a da ou5av5p5y vf /.t(qheight greater than its original height? Explaiqotyuvdfa (5p.av/5 5 n.

Suppose you lift a suitcase from the floor to a table. The wo vhnsncc,5 g))rk you do on the suitcase depends on whi )chgnvc)s5, nch 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 power needed:6e- do kkbjjomqe0bb )/ ,4 y5vq 2lsxznn,2a rather than the work.

Why is it easier to climb3n dpcbqz28fbh6 /h) ixn:e d/ a mountain via a zigzag trail than to climb straight up?bd8 ehf 6hcnz)dn/ib/ 2qx:p3

Recall from Chapter 4, Example 4–14, that yorqt6c4u 5nm) 5ode).txu r/t pu can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this,d.5 ur/ce)n u)m5r pttt 6xqo4 using energy concepts.

  How much work is done by the gravitatiib6 :sbxm,c9e)tub 5monal force when a 265-kg pile driver falls 2 b9x)5m uemsbb6c ,i:t.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hig1 xd qdq94rt;xh. How much work is requiredqtr x1d 9;q4xd?    J

  A 1300-N crate rests on the floor. How much wob(yqe3a d6f 8jrk is required to move it at constant speed (a) 4.0 m along the floor against a fjdqyae(683b friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do /s u(4pbvl 6ok p+b.4f se/hoj(horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wb k sp4e+4/houlpv b.6jso(/fas 0.50?    J

  A box of mass 5.0 kg is accelerat* n/2c.ky+4y hgsuk5 kxjjy+o ed by a force across a floor at a rate of for 7.0 s. Fincn j .ukkjy 4yg*y2+o 5s+/hkxd the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 k o wbel953t2yth h6-eyg, lie flat on a table. How much work is required to stack them one on top ob6 ye3l5 t-owe thy29hf another?    J

A lever such as that shown in t0j.)qus9 d hzsvmnx7l)eao -,yq, v;Fig. 6-35 can be used to liff objects we might not otherwisene-s ls ho ;m.vu)j,0avz) 9,7qtdxq y be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline dy9r* m2*w 7cazelha+and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coe7+az*9ae hy2rmw*dc lfficient 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 acceleratiok3i66 w1bz*ddcrxck1n of 0.10 g u66cxbr 1z1 dkciwkd*3 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 zi6y1yu,a08zr zis )h 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, varies i2hjgo8qc7 0x f0rtjrp8k . /has shown in Fig. 6–37. Determine the work done0op8ckg0ji . rx7h8 h tjfq2r/ by this 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 acts in th)4lx *ab u-ytse $+x$ 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 o ngktco+i84j 7c tq:k5f $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by wha31v)b* cd/ord +;nzzfhjuozo/q /u,ct 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 electr6cl *5c-l c*q.tziadre1j l k*on $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 be9 eus:*eiwh9upxb r 5(/e gsk) done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 Nx.srqw8brv;xwtm mw4s td*0n)m tp-/, ;1c ed on the arrow over a cm;x4 ebw nmx8r-),st1wd*v.r/m0tq;p t wdsdistance 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 25 cm whv/em4dv4e)gmy,p43 t f,j i zpen the ball is caug e/44j, ytz m dmvpveif3p),g4ht. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by whav q8o2w ip, 9ids 0a)w72ttsnpt factor will its minimum braking distw7isi8pt dpsn t a 2ow)v29,q0ance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigatbv++sekg cp -x0 zarha.y0t:) ors 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 nos x0vkac+. p)gbt yhzare:-0+ t matter?)    m/s

  A softball having a mass of 0.25 kgi9fo1f zipk6bxq9ci (im ae zesp6) w9314x2x is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, es11qix z6e( fsm6xci34pizkwbp2 e)x99 9 iaoftimate 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 whog lk(lrz 4 12zjkia8j8 does 80.0 J of work on it? Neglect air resisjzrg zkjl(a8 48 lk12itance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelerationfcct23q x(p0a fv 5qalmy2.2dzl*x( k by a single cable.cxxlva(23p 5f0q. lyz *2d2 mqcktfa( Determine
(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, kf o(d2x ubyk.2, of 440N/m How much must this spring be stretched2 k d.fby2uxo( to store 25 J of potential energy?    m

  A 7.0-kg monkey swing0dqs vh/fb) a;+mk +myode;4js from one branch to another 1.2 m higher. What is the change in potential energ sm )eqfo k;yb;/v+4dj+hm0ady?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chasxr j0wrs94+g :ci5-gjk+,u rk3temu nge if his centesjeix,rw r+scg3umkgj +:45 r09ku t -r of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizonthk5++ x+:sietr1l8x e wk2likal surface 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 spring stiffness constaniwthr2kx8lixes:l ++ k+5 ek1t of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m above wk)br4 7z1:lgshab 4z0hm.fb the ground. What is the potential energy of the bgw .1afszb z7 4rhhbmb:04lk)ook 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 top of a 330 8:eyo4v.t eo/dbtqau2 duoy 2kh1 b:20-m peaku2byeo4d1 k 2e.baty hodoqv: /2:u t8.
(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 rul5;3hwyuuogn w 3(gz g )hf+ o)*mw5ppper. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is hp)w hup f3g wnzmy+u*5)pogo;(5gw3now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, isig;/d k kn-ns) running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle ;nnd g/s)kik-. 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 restfztggk:nmc.n n220l i53 i:oz, 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 giveql /7iqn. j2xmsdhf(,38ns mxn a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is to0n e2ajzwtn-1j 6 y;aransformed into gravitational potential energy witho20 -1y;e zjnanoajtw6ut the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform wiyog4hafx,q;8mdn 9j yq-) ;kith a speea; kqjfhgx4 i,)-yy;m8qd9 on d 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 stiffness constant is 950N/yj1p9s5 dmz,y oi mvp w2//k*wm is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.yiwsv2k*p1 pzmjdom/w /5y9,30-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 alo o.p1/9jdrvshp/e 7uj ng 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), from what minimu pphj/sd9.j ov 17/reum height h must it be released?    r

A block of mass m is attached to the en /pm,d rwzcg00bn/4scd of a spring (spring stiffness constant k), Fig. 0/z/ grcn4swb, cpd0 m6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whxjc:n6 9w*wddj z+po g,0:aq uose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cordcdadzquwgpj w: 6j, +*xo0:n9, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up tb f.jafnr(;k )o point 1 where it is released from rest. Assuming no friction,r;nf( j k.baf) calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown wiqfp ksrlxalq/a+8pl;n/(6)l ;sptb7u8nd0 gth 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 springri).ulszjrv1y4h7v+- ycz q: to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at :r.)+vqzcyy- 7sz 1hrv l4ujia 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 the elevator and passengers.

  A cyclist intends to cycle up a 7. ja /+ e*6;3h+)tv4typmc-lwk i kvvvz8 $^{\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 makvxgk*az 1 2;dss 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produ2;d1v*ga kx kzced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high a mqvpbs(j d0/uq/u e*x ;7u0xl)j9pfvg;gx m1nd reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generateds9mmj )pxp l v gubjqx/x0fu;ve u (;g/7*10dq in this process?    J

  A ski starts from rest ag;)q kg+ e9qh gaoho97f,zyy;l; ln0jnd 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 from a tree oe,jiz :rk;)ot4 boy6:zmm* v d* jbt/13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height ofr5idxf+kifa 7ms- q2. 1.5 m. kqrd5m+.fxa2 -f7 si i
(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, 9)+rg .*b(t ej5ua 9 mjmcwjd xx-.cpwis 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 mwxwe)j dja*(95c 9-x mp mjt+r ..gcbu the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–4g/jczx8eh-o / 1 passes point 1 with a speed of If the average force of friction is equal to one-fifth of jeg// zcxh-o8its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s9iiz9 v kyc(+u reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal13tpz3kur 4xw 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 equilibriurt k3wp 43ux1zm 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 light horizontal spring,n:j+ gw 2 087kf-n(hw9oknqqjc frrm, 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 sprin wf+7ko (2hr c:-jmw g9nf8qr,kn j0nqg is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used bv :jzswcr-w : s2wb74a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h fromwjs:cw :2bzw-rs b74 v a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-ato2j2cy:w,9 mvz -d ckzci6 q0,yv4u story window 16.0 m acuktvqczm :z yjw,4-yvd,62 a io9c02bove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the aj+7h9hkg o gy8t /(gorverage force exerted on the car due to fr9o g/g8(oyj+7gth kh riction and air resistance?    N

  A 1400-kg sports carb o*zru,425 :,g4 iepkzamr basysr0. accelerates from rest to 95km/h in 7.4 s. What is the average power delivered by the s 4 e by,r.zz:u*s2oarrkaig504b, mp engine?$\approx$    hp

  (a) Show that one British horr bgj-u-16dk/f cfr 0bsepower$ \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 oft- m eh/pjm2kek5m/ w0cen expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows dfcf3 c/,8)8np foenmc own from to 65km/h in about 6.0 s on the8cffnm 8con ) f/,e3pc level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a c /7::rqfxlz:(,h9 4o mlpxfts nh+ jj3.0-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 dt ni4fbqo-zfmy1h sa a/2 5iav9n72*14m/s If this motion takes 1.5 s, what average powerqnf 4v 1d fzh-ya5 m9/tonisi 7b22aa* was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.m)-tq*2qsqidi ndu m3(rug)a4 s ,h*r60 m. What outpq)*,r qiu-gqisdm )(d2ar s3m u*nht 4ut rating (watts) should the pump motor have?    W

  During a workout, the football players at St4n +u nang v/id4lxok/o7z4m2 ate U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclinug4nn24dvox i7 lmko/n+a4 z/ed 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 q d/ygz;u(z7-.6e -ziqwj6od i+ff,ecpw - gr climb 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 outpuqme bh0 -pp4z4t of 120 hp. How steep a hill can it climb at a constant speed0p4eq bz4hpm - of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowerqb.68zyi a 85rbf kzr+ must a motor have to be able to drag a 310-kg box along 6 8qrr5yzbz.i8+fak ba level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7q 3aw5 kmo7k qfrjz;:s8j1g/w.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 cq3f+d0cp 8-wq ;k/ by9loqkum d 9kgk.ars have built “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 mu9 ;ld qkp-ukcyd3wbkq 0qo8mg+ .9fk/ st 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 o5yzocv et/ 6gw7*eex/f / 6xo10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all la6f/cxzev oet/go* 7 xyo/w 5e6ying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Figc i,d5 bet8(oo. 6–42) in the 1936 Olympics shows ioo cbd(,8te5 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/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fig5 k::w9 ,oupnji(c5x .bobzog(nw* q a. 6–39 is to remain on the tracw,nzj b:5xnouoa5:bo(w .*pi9(gqk ck 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 from an aircraft without his pard rh,8 +2gbtcjq9k/x*qyeb6h4rp h.bachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was yrqb2 j8qxct6 9dg, *h p4k/ehbrh+.b78 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 horizont) e4 y*xx0e)bwp tvc+ -yfv9 0rxnx,kual cord of length L whose other end is fixed (Fig.v0n9c)ybu) x4,pf+e kx 0*vx x-eywtr 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 ,2 n8 0iwynpcd, 3avfsmountain. The climb is made in 5.0 h starting at an ecn,d vp y,iansw83 2f0levation 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 90.z4j.tgl6 q .nb fcbs20-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 Ca j 1exg;s.6y:ka 4zciylifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.yjes ak;.gxiz1:cy 46$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s i;ef hw8eyun*7 qh t n-g*,2jjand falls vertically 81 m before striking the turbie f*;ytnhgw7e j2q-j,* ihun8 ne blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), the dixa4yx+1; c fr8*jge3)l ukjdqfference in your apparent weight at the top of the circula3 )xde* +1juxr al4g8qyfkj ;cr loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert +(m icgrq prqtkd6*3egu6d 8q:f49x pa candy bar directly into work, how high could an 82-kg kd4gq8m +c9d qpf g3xi e:rt (qr6*6puman climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angl / ijz 6tlyeej9hx97lmy456pwx2 bsk:e 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 u blzsza82z,* inside the scale compresses 0.60 mm, and it tez2lzzas 8u,b*lls you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runsh j5 kj3t4ff6b at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his vet5kf b4j h36jflocity 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 athlete climbs a vertical distan0,k l y7iicp)nf ww1e;ce of 5.0 m in 9.0 s. Whap w1;in ckl,ifey07)w t minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energyez zx1f0cug-+ . Water is pumped by reversible turbine pumps from a low to a high res-egzu0 +1 czxfervoir. 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 constf v4f0qcmtqx(i :o g*ycf+l6+ant k is cut in half. What is the spring stiffness constant for each of the two flvfy(0 cg xqo6m* 4f++ti:cq resulting springs?   k

  A 6.0-kg block is pushed 8.0 m bh.fu n r4) zm+/k7epwnpf6;y+u a;fm 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 3rgp ij5c0h,a xgn.*2 gi: 1sqp.2 s, how long will it take to accelerate from 55km/hpa 0.c g:2n1i jgg5rs,pq xi*h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac funk b:ubm s 0b2h)-tum;o:w/nziction (the “stress test”), the patient walks on an inclined treadmill (Fig.z -:n/wut2k ho ):bbsmmi0ub; 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 u:pu5w esl f*8fpward a distance of 500 m, what was its velocity when it left tspew8* lfu5f: he 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 0p8g/ hprsu1eat a rate of 95kg/s (a) If this water wheel is s/g hpp0r8eus 1et 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