In what ways is the word “work” as used in everyday langsk :6:nsivkz+3i q; qyyd p.5nuage the same as that defined in physics? In what ways is sn5y d:.i;v:q63kn yksz ip+q it different? Give examples of both.

Can a centripetal force ever do work on antk2.k.4bfma2rux q 7 b object? Explain.

Can the normal force on an object ever do work? Ex i29prs p,2upquzi6d/ w-h0v tplain.

A woman swimming upstream is no 90*:fa p. qewlvt8)*cqsh vzqt moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on h.qqf q0wevz 9ac: 8 hvs**l)pter?

Is the work done by kinetic friction forces always negative? [Hint: Consider wha+1m uicsp9r3a g;epw 9,od6k rt happens to the dishes when you pull a tablecloth out from underw;pd 69,c i3eos 1g+ura9mpk r them.]

Why is it tiring to push hard against a solidz(;afsbcie *l-4bi o . wall even though you are doing no wa eiofbb*4 cl.z;is(- ork?

You have two springs that are identical mo w6b7/kh l(o8am);yu pl5bcexcept that spring l is stiffer than sprk8 ) ap;uml6c5(lbmoo7y /hwbing 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* mt1 uwq4pjv m:w)k4 63wtj;;dlfcph force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it ha*1 tj w t4mcjpk qw:;f;4hdm3l6w upv)s 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 cu .obhuzl8skgp.jlhbp)r)-*x+k 86 r hange when you jump as higl)r z buo8hp)8h.jul g s-xrp.k6*+kbh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a 9 ;;. zuk)jsjp6 rxp+3+:psapvktkau building, all with the 6.pkuau pvpsj ;;jtrakk:3z s+)x+ p 9same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h hq:4w*e) )fdxmvu34 zb hkox /above its lowest point in two different ways (Fig. 6–32). Duri v4x/whzb:) xkf q3* h4euomd)ng both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spriu rcp,ply6uw0+bem, 9 93e psong by pressing down with your hand and then release it, can the spring leave the table? Eb996l 0,,ueory scpu+mp3p e wxplain, using the law of conservation of energy.

A bowling ball is hung f;qrbvv6tc wq ;utx5s--o 3ov0rom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instsq vw6bvoxoc ;v 5;--urtqt03ructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at tbn tr ;3pibxm7:71oskhe top of a wateoksbx3 7tm b1 pr;:in7rfall falls to the pool below?

Describe the energy transformations*.wyb ta9h 5.iz1d- u7uiwkqz when a child hops around on a pogo stick.

Describe the energy transformations that s0m- pz3nsj4h2d6wwhz( ts k,take place when a skier starts skiing down a hill, but after a time is brought to res(ssz60dz np3w,w-k2m jth4h st by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hilld /e(7fshti;q of height h and slides down. Does the velocity at th;d 7sftqi/(eh e 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 in 1+/ydpxdt w tz) sq;p0their path rather than stepping on top and jumping down on the otherd0txqzd+t/ spw;)y1 p side. Explain.

Two identical arrows, one wi)sdgk 02uhtq-.g koc:th twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrowkgdq h.2-to0cg k):su? Explain.

Analyze the motion of a e*xvb cx88 :5ar4 vbtzog.i q(m1ajf2 simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clockv(g x8ioa8tj* vr5bbca1.ez 2:4xqfm has to be wound up.

When a “superball” is drow /y.xu xd(o30p o/p6l pr;bzqpped, can it rebound to a height greater than its original height? d q (wxo/p up3lyo;pbrx/0z6. Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on d -tj8nf0o3 lbthe 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 of thd jfbo8lt n3-0e suitcase?

Repeat Question 22 for the powe(2xw is*m8tvi r needed rather than the work.

Why is it easier to climb a mountain via a zigzag76. m wgfosxsr)l6pmj 5o2j 9u trail than to climb straight u6. ls )p9wx jj f2mours5o76gmp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropesou 3z4 2a;eebw to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how 3az 2w euoeb;4much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fo yonw .bwxylt48 88d)2 k.vbfalls 22b4 fwobwody88. ltnky8)x v. .80 m?    J

  A 65.0-kg firefighter climbs a flight of 7wu +nfrz0s.z j9 ge 7a3,a yt8rnxj,zstairs 20.0 m high. How much work is requijr7+jr,yazf a, 0sn9ntu 3 gzwxze7.8red?    J

  A 1300-N crate rests on the floor. How much work is required xx6d i99 p (rb;jsva4cto move it at consta4i9c6jd;(b9vpa sxr xnt speed (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 th6vwr0 z6qc-1a lvq .0uo;( lyn.dtokwe movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coev tl r 61;v na(z.ulq. -kow6coq00ywdfficient of friction was 0.50?    J

  A box of mass 5.0 kg is c 3/io7nu lv0znun7y. accelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the /3noiyul. n7zu7c0nv box.   J

  Eight books, each 4.3 ch* nig 8jajo62m thick with mass 1.7 kg, lie flat on a table. How much work is rh8oji *2j 6angequired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35;9fiim, vpqs-n**i ,tl(*ngee ks-e t can be used to liff objects we might not otherwisvnf *e-,9k( l*iip;et*ins-,tgm qs ee 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°56qs+ -tk jig83tv)vi wr+e tx incline and is 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. Ca+ 5qrx3sgii+twe tj t -6kvv8)lculate:
(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 acceleratiof4th - 5b2yklnn of 0.10 g upward. nk-hl54ftb y 2   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 axis is lh qei-+ qodi 4(0prvz2w1tcln-6g ez4inear 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 as shown in+c s6z b2twwq6 Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m 62bq tz+scw 6w 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 a+1ar zais6spx+o kqz (8o /2cucts 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 molecule, wi9 x1qbj 8i.9u dof8xsfth 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 arrow is doubled, by what factor has its spee ekyeuu:+e-r3+ my1ojukcj *5d increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requ74j(1fadup scn g1p. gired 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-kgcar traveling -wtbj eu;bq+5qb: f q+at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow who,mjcyvh4 5u 9lse string exerts an average force of 110 N on the arrow over a distalu4yj, 9h vmc5nce 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, kk(bz7dqv4s fielder’s glove backward 25 cm when the ball is caught. Whaqdk,s4kv (bz7t was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum br nd 31 d.osy0oqnu+6ukkw p6)faking distancesnu0q )6u d+of yondw p1k6k3. be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, invest8mpve9/8 krtyt4,l9 :;w vpl9jq ubwnigators measure a car’s skid mark toy :9n;m8bk8lqj 4pwt w/v9 9lt,up rve 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 matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it ream ro:et bar0*8vo6s a)ches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance bebrme)o0v86ts: r*a a otween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someolvx61ak9d 1p2 up6f ymne who does 80.0 J of work on 16pma6y9v2x1upk fd lit? Neglect air resistance.    m

  A 285-kg load is lifted 22.0jb 9d;lgh2r9t m vertically with an acceleration by a single cable. D9t;d9jr hgl2b etermine
(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 41;o 0jc o5922vwv slhp+ud vlr40N/m How much must this spring be stretche+ s lp29whc5lu ;jrovv 0vo1d2d to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 ly8fo vr +v+27om1q -v/ter3-ra j pnfm higher. What is the change aov37j pr1v2fqo8r+ev/-f+- lt mnry in potential energy?    J

  By how much does the gravitational potent on gs7;dt0q)mial energy of a 64-kg pole vaulter change if his cenns 0o ;d7mgtq)ter of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h x f+,8vf kblf/5n 5ipuwhen it strikes a horizontal coiled spring and is broughvkfpilf8,5 /fxnu+ 5 bt to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the groaxyc . s/j;pfj 5ar;2vund so it is 2.20 m above the ground. What is the 2aj; / j;fapv.y5rcxs 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 n;ka2 kb,-huy of 1600 m and climbs to the top of a 3300-m peak. hkb-n2u ay,k;
(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 t+ ft 1zs ij:ny*1ksmksqs:.k.3m rpp*o a ruler. The end of the spring is nemj *f*.sk :sks mr3.pni 11yz+pq :tksxt to the 15-cm mark on the ruler. If a 2.5-kg mass is now 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, is running at top speed ( 5aa99qzd ak7+ b6vtho5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she 57db69 q avkh+zo9aat swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless b4kfi0cdn+ x: lt+v6q35.0$^{\circ}$ 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 ,gmi a+y,:ury- i sya v;vb*w9a 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, Franjtz 0+a d;-qj4v9ib hb s;h,ro’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center adh j;bvbjhi;9 +-,zrqto 0 4sof mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertii5;cenlxgpcr-b6+cb5d d0q : u bu50 ncally upward from the top of a platform with a speed of0gub5d : c d6b +l0cn5cbixq5-unrpe; 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 constantau-)gb h2* zhv is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it2-zhu* )gbah v 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 track shown in Fig. 65pkhht:f+;/ bh yof)r–39. If the block is to remain on the track, ev;h :y+tfok 5/hbfhpr)en at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring st eo6t g7y.oc4d:tq3 a9e1hksf j6fd,ddi1u*siffness constant k), Fig. 6–40. The bgsosd t*:q6h4o .71y dj9,iaed kffe tc1ud 63lock 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 whose un3zz/i p)+ mtsostretched 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 applie3s oitzz/) p+ms. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig.f 8zn6x sf: )m*3t.luv:drctd 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, carnf :*sd:tlvm8x6zc3) du.ft lculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle omw/ic l1 afs h6x4vzr(y+(zm-f 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of a fl:dps.vf t* 2)ko1b+slo:xzn elevator shaft. If the elevator cable should break when the elevator is at a height h above t*fflzx :k. d )+1lvps2tosb:o he 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 cyclsug;vyxt897a tkm 29 le 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 of mass 7650 kg and traveling u8)t z3g*k4y bcotll.95km/h in opposite directions, collide head-on and come to rest. How muchclzk)8o lb3t g *4yt.u thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and 7rp2 um+emjqkh(m+8( jy6cs sqvt, f:reaches the bottom with a speed of 2.2m/s How much ther pmjj(q 8, (r+6susm7y:m+fet2cvqkhmal energy due to friction was generated in this process?    J

  A ski starts from rest ah f6w; bbf2h5.exnd k;nd 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 13.0 m abov;ik4ux7p d8zm9r.k 18dpwsv ie 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 he: np,o8vr.7mbr jdg-;b,enc zight of 1.5 m. e-7 z,n .p8gcjrbrd:n,;m bvo
(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 flugoe7(r ;zv-joor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictiooe ;z-7j(urgvn is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If h7 3xh.w+yu(fx)pn h1e2- klzpx 0zwathe average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveledyxh+l.01pzwxek zuw7 )(axh-2hnfp 3 is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a q d.)g5xro 1b/+s1slicc gy* bsteady 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 lttw6ky e7 3tp)a/*w.f9jt r rxight horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What )9fyxr.a3t6t pwtjr/we* 7k tis the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizoz.-og) 58wxwb5z9l j+ fmzf mpntal spring, Fig. 6–40. The blwml5zw5fb j go.pzfz x98m-+)ock 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 stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 t 0km bbg(k6k-kg including pilot) that was launched horizontally 0kktb6b- kg(m at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg pia o38f -tnac4 tv0*ovch, 7dflono to a sixth-story window 16.0 m abo,f d-o cnv7h4laoc 38vt o0ft*ve?    s

  If a car generates 18 h8hy* uv75txiy p when traveling at a steady 88km/h what must be the average force exerted on the car due8ux 7yt *iy5hv to friction and air resistance?    N

  A 1400-kg sports car a +8,a3g5 ki xrkpyw7mbccelerates from rest to 95km/h in 7.4 s. What is the average power delivered by the en 5pa+gx8b3r ,kymk7iwgine?$\approx$    hp

  (a) Show that one British horsepowena(x8 helt ma b0nf,*,r$ \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 ofter b kmfh*b7f5:n 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 :beoa s/qa symt7wp n:o5+,9l slows down from to 65km/h in about 6.0 s on the levo:es5a+w9: olm, n bsq/ayt7pel when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do 4ea rn ag/uz g2tbiwu3 .2r9;yvr(ks-in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shlevib a+,2)8+gq .lwl 4wlm ypot from rest to 14m/s If this motion takes 1.5 s, what average power was deq8pely)g 2,m.will wv+ +a 4blveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute t u.rjc6wv*q8 zlp0.bj1f oc6through a height of 3.60 m. What out qrcpwvu1l*6.80cjo j. zftb6put rating (watts) should the pump motor have?    W

  During a workout, the football players at State U.m +cfb*9lxkx q ut0g/6p1cy-g ran up the stadium stairs in 66 s. The stai/lp x6* cgx +ufq9m0b-y1cktgrs are 140 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 climb a 69n*g6frmy/d c .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 steep k(8sd2c uh4sba hill can it climb at a constant speed of 75km/h if the frbdks48( chs2uictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able t ;akp7*sihd;0z uyaq)o drag a 310-kg box along a level floor at a sph is ;k7uad*;ay0p q)zeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 obbn(;w3xp.ltf9uoo hs05 - 5hjm2iopf: y/s $^{\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 b3dy.3ezx3(ccgvu l) “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 cc)3ly(. zx3 e3uvbdg 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 fik,2ia (gsaj 3jrst shelf is 10.0 cm off the ground, and the remaining four shelves arega2 s( aj,ji3k 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 laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump )-k 2x.h;q kwinz:dz 5rf+9srk 6jhs w(Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum shr5 w w-kr+26zk:xsk9 jfzshn;) q.dipeed 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 frictixmys 5i(9h( uhvj ncuod28)f-on along the looped track shown in Fig. 6–39 is to remain on the track5cy j( fivxn9o)ds uhm-(uh8 2 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 witvd ms( f 2gyq./jha2u,hout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass wa /f qyh .d,ugs(mv22jas 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 whose other end is fix(ybl..p + ( 2jutuu:u trauppc*egt5-pz z9 )ded (Fig. le(cp.-)z5u 2+ jpb:(updyu z.gtutt r 9aup* 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 mountain9 b kv,8-g(w .haaubfz. The climb is made in 5.0 h starting at an elevation of 2300 m. Calc-(9 kzbah8abf. wgv,uulate
(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 wh-a(,c*gy urnd en a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its4q ijjt8,/ hij lifts can move 47,000 people per hour. If the average lift carries people about 200 h, j8 qii/4jtjm (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the raon h:tm/f1 bh8te of 650kg/s and falls vertically 81 m before striking the tuhf: h bn8om/1trbine 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 wi-3v+7ofubrg 93ye56 dhrws trth a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottre 5r 6 +g 3y7db-wutorfv3sh9om 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 /ce*ur kw/ wy0bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) *wuwe0/ ry /ck    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 an9n zt9gi1x)b tgle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside tfhrhab-/yu5 t9*ycqcsf4 0v *he 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 scale read a hs ucfr0h qfy/95*cvab4 *t-yt its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6knnfse0yd /vve8 0i pxx lp/3.d*uc4/–45). He /4fddnulkx3 vve/0 /0 8in.psepcxy*releases 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, a 72-kg athlete climbs a vertical distance of 5.0 w30uo+ ehpbk8xs,7 oum in 9.0 s. What minimum power output was uob0wku 78osu3, exhp+ sed to accomplish this feat?    W

  Some electric-power companiesswvq)+6 zn q eav36p2w 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-M 26+q wqavw)zvs6epn3W ($120\times10^{6}$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 ozplr.:xm 9q0*+v)r z cdrp prs3e2(rk is cut in half. What is the spring stiffness constant for each of the two resultin sc: ).0qoezp* 3l+2rrd(p9 zr xmprrvg springs?   k

  A 6.0-kg block is pushed 8.0 m zj q7 2yorykl2 ii1-j/6kwg/j 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 froj;h71hamh.m x.o -q fu.g +afsm 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 the samhum.xh+o;. jh-.7fa1m qsagf e, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walpvkhn8 ya-vt w:( r1;hks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angleh w(kt pravn1:;-yv8h 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 5i fkhk)mz+ :l-00-kg rock vertically upward a distance of 500 m, whatf h ikk-):zml+ was 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 a height of 2.0 m at a rate of// e:hl 10hmmufjgf. s 95kg/s (a) If this water wheel is set upgum:/ s/1hf.flme 0jh 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