In what ways is the word “work” as used in everyday language the same asu t x/y33pr1nz9is g/c that defined in physics?x933 pnc s/zy/ur1tg i In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Exbze * /(5it fje58,qds 3*.cwdkl ms gab0cwc-plain.

Can the normal force on an object ever do work? Explainp yc*peu+ j x, ogk7h*c4tfg(nw0q,i+.

A woman swimming upstreampr(i 8) s5 kbbf8eir6f is not moving with respect to the shore. Is she doing any work? If se56irf fb b 8srki8(p)he stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwaysfazl o6g,g1q; negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under tho1;a zgqf6 g,lem.]

Why is it tiring to push han h;zj2+nr ncp9ns(21qc ute(rd against a solid wall even though you are doing no work?(se1n2jp+ r;c 2u zc9qtnh n(n

You have two springs that are identijmfu9k 3e3:aical except that spring l is stiffer than spri:ake3jm9fu i3 ng 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free ,k6wp+z4 w nqk7x9mix to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distwp9,xk6ix4qmk+7n zw ance $d$ 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 p k gobxav7umh:5)gf7*otential energy change when you jump as high as you cang fm75b7v*h) koag: ux?

In Fig. 6–31, water balloons are tossed from the roof of lzgzraw 3khz ljl74-3y,/r.ga building, all with the same speed but with different launch angles. Which one has the highest speed on imr73l4kjghwaz/ ylr3zg.z -l, pact? Ignore air resistance.

A pendulum is launched from a pointjbti,8i bmbe8,3/ptei8ijq4 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 launch it is directed downward along the trajectory. Which launch will cause it to swing, 838iij,p4bimj ibte/bet q8 the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If yq jex6l-:dnes g)ylo(7eaw.6 ou compress the spring by pressinge-o)syq ga.(n:e667ldwjlxe down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling (.scro g*anv+3bnk w0qu5 82d zm sr+hby 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 instructor is sm+8r2 s*zduo3cn0v5 ag+ ksnwhr( b.qupposed to release the ball without pushing it. Why?

What happens to the gravitational potentie f+m af-:5z3ij ln;lwal energy when water at the top of a waterfall falls to the pool jl-mef z:w n53fali;+below?

Describe the energy transformate/c : (fh+gth+ or6gluz2lo n/ions when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier j l8sh/ )5jh*dbaod 6x-si4 asstarts skiing down a hill, but afthad sdbx46-slh)oj js i85 a/*er a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the,t7pm, mv*wa,fe ae( r top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hilfwmte,*7ae,m va,p r(l 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 their path rather g441w7jhnd(hctx fxo -d2/dwthan stepping on top and jumping down on t 1ddj dnh4gxx-w4w2c/(7ot hf he other side. Explain.

Two identical arrows, one with twice 9+kdm(hmr ydsw9pg2y g6 s8w+the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force 9 ry+dysp( d+8khwswgm2 9mg6on 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) awma 8(,e+y 5wbs ow)pignoring friction, and (b) taking f8woepwwya5s m +b)a,(riction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heightf*hdlqe+ v5d 8jj6ofx s;) h5t greater than its original height?dof)ftesqhh;+ *5lj 6j x8v5d Explain.

Suppose you lift a suitcase from the fl f1d,dfhqhn0,oor 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, an0h,1, hddn ffqd (d) the weight of the suitcase?

Repeat Question 22 for the power neee-v 72(;msptgubmk r/ded rather than the work.

Why is it easier to climb a mountain via a zigzag trsn;2-oldf28 2wz k hdyail than to climb straight up?d2sz8-fylkn h 2wo2 d;

Recall from Chapter 4, Exampqa n l*2e)1hz5a e4xejagok; 6le 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, ul *25)nzj eg1aaheqxe6oa 4; ksing energy concepts.

  How much work is done by the gravitational force wh.1xl oh+n7ok71yu dzrmv 2cu 9en a 265-kg pile driver fallsuck7nm v o2.9hrxd +y17ouzl1 2.80 m?    J

  A 65.0-kg firefighter climbs z7zu7tos,eq )kjd-d 4a flight of stairs 20.0 m high. How much work is requireq ej,d-zsdtk7z u47) od?    J

  A 1300-N crate rests on the floor. How much wo ,tfmm87ahhd, rk is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 N, tm8,d ,m ahf7h   J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 16033fhmakhou.3ds :f8s6w9i oz -kg crate 10.3 m across a roug 96khfifsw: 3mh.z3ad8o 3usoh floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a f9 ywxusjyx:3r7rb6 :porce across a floor at a rate of for 7.0 s. Find the net work done onyjb u:3: sp69yrr wx7x the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lij ,n-8l3 qiq ynyileu 4y6ow0,e flat on a table. How much work is required to stack them one on top 8-nyjeyl, 3 in, q4owql0yiu6of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objeclmo /+r ;m-1bdvs5elrts we might not otherwise be able to liff. Show that; ovm -dl/s brme+lr15 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 and is kept frok gr+b4;,0iv6j(nrmjp urm8v m accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coeffnr(+6ru4i,jv ; 0v r bpkmmjg8icient 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 acnb,rjn:3 s -tjceleration of 0.10 g upward. ,nns r3j-bj:t   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 linear and tha hm08pw9f3( z 6ckaa t:sigi*ht $d_{\mathrm{A}}=10.0$ 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 Fig. 6–37.7quce fr*d)j f (uq(d8 Determine the work done by this force to move the object (a) from x=0 m todu7)ffe(cq * qd8u (jr 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 t)xc*/bqxsk3l he $+x$ 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 oxyge2j tfw 8tr2t;cn molecule, 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 arrow iklt 3d1r:6sgzs 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 szj*gu ;:mn 7lto 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 travelind6,xbx3y pm7a j3 n-pjg 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 5i8fz k2 k5kukN on the arrow over a distance of 78 cm. What is the sp kukk8i5kz25f eed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s molze f8k2j7l*z1zea3a ves a fielder’s glove backward 25 cm when the ball is cazf la7 l28jea e*z1kz3ught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by wh. 4ags3afsiduie ( u,r/2:qyw at factor will its minimum braking distance beys w2r4a:/af .,is(iqued g 3u increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measu a20it iovo7m/6k*xtbre 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. (Whymo/6bt x 7ia*v0t2k io does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time ir8chec6 +/ deut reaches the platcher/u8 +c de6e, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if tf tbccy8(/z8chrown straight up by someone who does 80.0 J of work on iczf8b/y(t c 8ct? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single3 ( de(grsv- f+z2wrgqw7a/ bq cable. Detefz+s (2vb-rqqw rd(a /w73gegrmine
(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,hq8x4jx7xjn 2 k, of 440N/m How much must this spring be stretched to store 25 J of poten2xjjx 84 7qhxntial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. an vi:78d7b0pxgq7l q What is the change in potential e0:787liqxbd gq7pv annergy?    J

  By how much does the gravitat1i t7bid0:bgm2/ nzdz:jz r 3yional potential energy of a 64-kg pole vaulter change if his center of mass rises abou jbtdr37zmd yn0i1/biz2 zg::t 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h ftvwgf)1814bq.r hqm when it strikes a ho1fmt8 bqrv4.q h )gw1frizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.1enc7z9 ,cy f10yrio 0w0-kg book from the ground so it is 2.20 m above the ground. What is the potic 1,0y0c7ewf 9ynorz ential 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 uh+f)c6em bnj8nt 6d1of 1600 m and climbs to the top of a 3300-m peak. cnnebh6u)81+ 6 djmtf
(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 ruler. The end of the spri8,,nl.gg 3 uarsei:zing is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler ma,rig 3nl8e,:.usigz arks?    cm

  Jane, looking for Tarzan, is running at tm). t-bmn w,zjop speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upj zw)n.t-mbm ,ward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides (-d20du-0xklu/3srdu sn7x u:kpzdk* zvd:n down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless 28.fj(jj.ce+ giu9hp/l-xk1 5b ) ccq2tj0$^{\circ}$ 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 kinet2 p8mrxx dfx2w7 f x-6d1m*ialic 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 of mass 2dfixx6l1 - r8m7 pxdw fax22m*.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.ldol04 8c7u46idbv u9 qk4xpky a6 cw top of a platform with a speed k4o wac dq4y6kl .xd79uc 8i4 vlubp06of 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 (ignor1 k4;- pdw2u3v yqwrn9w jr2ahe its mass), whose spring stiffness 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 when released? q-d2 kwra;v4 1r3h2jnupw9yw    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 k1rpu ru ;-,)qp+rxu etrack shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radiuerpru;uq+)p ux r,k1-s 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 stiff bu e7nxx-v b4z vz07)la+w*yjness constant k), Fig. 6–40. The block is given an initial displaw-*j7v07xn za vx4yblu+) ebzcement $x_0$ 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;fp yl+d8 c,dv a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculadcd,l; vp8yf+ te the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to pos ;aoh2:zag5n.d z8u dint 1 where it is released from rest. Assuming no friction, calculate the speed; g:an.5os zdh8zu 2ad 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 a61z fwr8z d.z4zkr)a dngle 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 the bottom of an f+ *--mglj0/u uj xe7mlwc 6ecelevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring7 *60e cmj+u-xejlu-mf wl/ cg, 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 xj98;xszr rwx)rr 88fcycle 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 95km/h in opposite directs +s1ho1e9l xjwgl6f/ ions, collide head-on and come to r6ollsg h9+fews x11j/est. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3g;co+vq9*2k ve*mxj;ne0 9i/ r;evae nzwr 9h.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy dqnn vivr k;*ee;a0z2;hcg 9xrw9ee/ 9+vo m*jue to friction was generated in this process?    J

  A ski starts from rest and slid *erj9. i5g.m4 z,ni4zosaxn ges 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 above the g)c -riupzq:w4round.
(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 22x*si ap(qpb)ybk , ,saw;p l*q4ou y1.0 m, and it bounces back to a height of 1.5 miabxk*ulqp qya;bs( 4,o yp )*p2,sw1.
(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 acroax1ah z xs/.8css a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionl8xxha.c/as z 1ess, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 5kkt*9y54s2iqnzwis 3ka9 6i3exiqu passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45k aus5eiq2t36x9z wyiikq3 i*4n s9k5.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the fo 0wt lkd(k:/cr02qxd-yj2lt2 fq2t/v( wpybjot 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 lic;+*otles- o y0e.4di gxeu3j kb .xb7ght horizontal spring (k=180N/m) as shown in Fig. 6–40. It isl3-tx+u o7y*0x eg ;ko4 sbbeicd ..ej noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a h ij 2 tf5);u1nrgj)mcvery 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 stretch on its first jm);jt)i h 2 nfgrcu51swing?    m

  Early test flights for the space shuttle used a “glider” (mass o5c0e: :lh*pgdab88 nynu5wl l f 980 kg including pilot) t 8da pncb5gyhu5*ln0l l:we8:hat 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 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 pianb3zhi,3x dd 4,0lwcn ivw3 nu5o to a sixth-story window 1lcdiuzww , 0bd,x43n3 5i h3nv6.0 m above?    s

  If a car generates 18 hp when t8yxa )heqk7+(;sp8e3;tea lqu isu+fraveling at a steady 88km/h what must be the average force exerted on the caxys( ae )q7u8tl++;8eeskf3uiqh; par due to friction and air resistance?    N

  A 1400-kg sports car acceaef1c /ip rk2w t,bx3 (a soh/-d69tajlerates from rest to 95km/h in 7.4 s. What is the average power delivestj3hx/ (e a/o1-bf aw,pc2a69iktdr red by the engine?$\approx$    hp

  (a) Show that one Brihevsny6gb6) ;tish 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 unit93mquwgn86kz;m 4 jzbv4)s nus are often 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 slo4tu i0jsg1:c+ e b4xpfm8uk7sws down from to 65km/h in about 6.0 s on the level when ittp4k87cxg+:bsuf 1si4e0umj 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 in vy) pku4 )l2zu1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If t d ,ft0.e)zeeahis motion takes 1.5 s, what average power was d0e e)eza,td.f eveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3;uijaw y4s3cib ,wtwa* 0hjc*lhig*7 2d h2,s.60 m. What output rating 2w 2 3cydti b* a,sciauhj*wh,j;ihl0 7gws*4(watts) should the pump motor have?    W

  During a workout, the football player67odfo, haz 3t)aey4z s at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long a7 3eh4fd yoaotza z),6nd 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 luf3jljovr55 21yu:n ov1h(u ftjs. 4climb 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 gao256wu4lf l b)bs d):d3ulvpower output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictionall wfv6:u4bs) go)5udl2 l b3da forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor qki(a 51r9;cvygv(dz )r4 zwjhave to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the cgd5i(rzyjwq;9 )z(1 4kc varvoefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.ydjb3 s49w* nv0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” tg1 a.3c (sjnj1gdzf0uhat 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 el a03gfn1ud(j c.zs jg1astic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the 5av n. dgwuyyh5w0d5;/p5 dzg65b t/whm1zqr 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 5zwwgdmy d/5z5a1/hurn qwg y5v60tpb.d;h 5 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 q,zd4ew5htz. famous long jump (Fig. 6–42) in the 1936 Olympics shows that his ceqh.wt z,d z54enter 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 8 ya-6a0jdndj along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of rad ddana8-jyj 06ius 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 frompb +-v-s4 b2fjlgp3 ku(3gufm an aircraft without 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 was 78 kg and his terminal velocity w2 -ju g kfg43lbfpmps+u(-vb3as 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 Lzb1;mg01 is.zyw g 1ld whose other end is fixed (Fig. 6–43). z;wsl1z1yg0 bdg1. im
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climgob: xfu cr:3fz(pj4bo 1b- q4b is made in 5.0 h starting at an elevation of 2300 m. urc1z b:ofqp3-j4 fbxb(:g4 o Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huv1qty r0mdzlf: bf 190ge 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 move 47,000 peopleygjfz7 m m8w.+j)dkp1 per hour. If tj)+ md1w.zf yp7jkmg 8he average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam atx7lh w gc),8bf the rate of 650kg/s and falls vertically 81 m before striking the turbine bladh f7bcgwx)8l, es. 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), the3 pru+f/v6xbd difference in your apparent weight at the top of the circular loop and the bot6vxup+ r/bf3dtom 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 conw*va.hn ;1.bo*gsym1+i bbv exg5j.gvert a candy bar directly into work, how high could an 82-kg man climb a ladder ii .je1gg+vyhgxb*a* 5;b1 .ms vbw. onf 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 af iw/j8odx 8nsu,*u4 tn upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside teiincl kw1 u73bn3c .o **e-trhe scale compresses 0.60 mm, and it tells you your weight is 710 N. Now clt* *r ckbee3ou.ni 3n wi1-7if 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 runs at 5m/s grabs a ropeujra/orpt, nck1ck-hf )a4)- , and swings out over a lake (Fig. 6–45). He ot-cju n ),r/- 1krf4ah)kacpreleases 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 vfb+ +d3o.jwvathlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum3j ow .b+dvv+f power output was used to accomplish this feat?    W

  Some electric-power companies use water to store enu.:ab3duk ou* k5boxc8sc 9: tergy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the k.bauuc9tb38o 5x dou ks *:c: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 sg3mz .u 9hjd8*k:kjkhtiffness constant k is cut in half. What is the spring stiffness constant for em hu8hkkjdk .9g :jz3*ach of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 8b /gbrkx + cd+/d0sjkm up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long wilexr-m -f0an6:hb 6 exyl it take to accelerate from 55km/h to 75km/h Assume the power stays the same, anr-bey0xm6e:f ah n x6-d neglect frictional losses.    s

  In a common test for cardiac / pvnx -sx*4icfunction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required fcx sin/*-4vxp rom 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 distance of 500 m, hj mdejza je,0kx)9*2what was its veloj j02e axjk*z )h,d9emcity 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 wheelc.:(:4n8hvoo g7to skf ( rhtg from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power output (gn7rk:vgcott f hh.8o( o4s:?    W
(b) What is the speed of the water as it hits the wheel?    m/s