In what ways is the word “work” as used in everyday langua lttfx.ttfg5,bvrnn2 .0g4lwhb n0 o(l :0:cege the same as that defined in physics? In what ways is itebolb 0t(tfn2tf 50.hg,: c lnv.l rxnw0g 4:t different? Give examples of both.

Can a centripetal force ever do work on an object? Explawymeg/(kvg7u q)4 ; plin.

Can the normal force on an object ever do work? Ex2/bituk4t8 br3 lzswrdg )7d 5plain.

A woman swimming upstream is not moving with respect +fcw030z72eo ll yylyto the shore. Is she doing any work? If she stops yclllz0y072+ fw ey3oswimming and merely floats, is work done on her?

Is the work done by kinetic friction forceg p)c-rdl wk)k/y(4iwxh 0hc6 s always negative? [Hint: Consider what happens to the d-i) r hl)wc/k4 (dxcpywkh6 g0ishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doi 4dl,;gkr5 nmk3 syos6ng no wor3,k ; rglsokmdy5 n6s4k?

You have two springs that are identical except tha/ djpe8o35xmv f0hd g/t spring l is stiffer than sprgv5 8/3pd dmojf/ex0 hing 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 for s k8ss.bj18)xt ; lg-vxj4wl0(jvva dce on a block that is free to slide on a frictionless surface (Fig.6-30). The block s( ;-bjg.tsk )lv80swvd j8l4x s1vax jtarts 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 enb+le //e6gd 0zoft 5hd+s ri)rergy change when you jump as hhelzr0)oirs 65ef/d /tbg++digh as you can?

In Fig. 6–31, water balloons are tossed from the roof gw xezwmez05ahi px /d(4) a6(of a building, all with the same speed but with different launch angles. Which one has 5waiz4x/ 0)x(dwez a (e6h mpgthe highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point iewe* l)w ;)6 .m.ziakzy n4qya+hp,db n two different ways (Fig. 6–32). During both launchesde.n l4+*pm)kay;iqybh ze , )a.6z ww, 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 spring byfl942fg wt hu5 pressing down with your hand agh9tuf25f4w lnd then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ce0 p*s x/pesb druv.h*tv/p-h 6iling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball apd.p htrps* x/*suv 0bh6 ve/-gainst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational pi rdzr0znjv70sph2x,)ah )1 lotential energy when water at the top of a waterfix2 7, ) n)10svhldjrparh0zzall falls to the pool below?

Describe the energy transformations when a child hops around on a pogo sticknxk94 k:we6 mq.

Describe the energy transformations that take place when a skier starts skii45:n0d 2z5vgjlbahme ng down a hill, but after a time is brought to rest by striking a s2z4 0dg5h:bnmja lev5 nowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of p ynfpma2*t++height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep ya+tpn+ *pf2msnow)?

Seasoned hikers prefer to step over a fallen log in the8ack:ydj b-;/ naobb* ir path rather than stepping on top and jumping down :jy*bbcno-aba;d 8 /kon the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into g 3ks6 e8+u eo3sptsq5a bale of hay. Assuming the hay exerts a constant frsog5+8se3k s t 63peuqictional force on 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, ( 9*/uohd9sz7,9 m oewvtawq+oa) ignoring friction, and (b) taking frieodsh97* omvwqto,w9 9a/z +uction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a 969h.tu;ifws0q x h:psg5iecheight greater than its original height? Excsfh;0 tx. 9qiugw:ih95ps6 e plain.

Suppose you lift a suitcase from the floor to a table. The work you do r; 9, l2wb(i g lr*v ejyoc3dzmqt:u*8on the suitcase depends on which of the following: (a) whether you lift it straight up or a:e c*y2ij;8q bzr wl(t9* ogdurm,3lv long 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 /xajk)cdu be*,b)fv + power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb strai.+t7lguur;h wgdd( xc/n 5ux+ ght uprlc7xgh xg5+d;un w/d. t+u( u?

Recall from Chapter 4, Example 4–14, that yv(yy rzuf66k9 ou can use a pulley and ropes to decrease the force needed to raise a heavy load (seufz9v6ry k(6ye Fig. 6–34). But for every meter the load is raised, how much 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 dr n-//zd cqul8viver falls 2.80 ql-n/ dcuv8z/ m?    J

  A 65.0-kg firefighter cl cla /o41,obnoimbs a flight of stairs 20.0 m high. How much work is required? n/a co41obl o,   J

  A 1300-N crate rests,r,qi ezac1ou/(+ooo+ou).0 djlhmb on the floor. How much work is required to move it at constant speed (a) 4 o+oez/hlmri 0bdo q( 1u+,ao ,)j.cuo.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did tuxhdpq:euka5 )x gcc405hu82 he movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction:kxdccap u54qh2 05ux)8 heu g was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rat/v(nh a,+ ifo/gu:an1fp9 r 5oguh2 fcf(lhq8 e of for 7.0 s. Find the net work done on the boxuaalh oqgnn r+9pg /8 ch1(:offfv(if2/uh5 ,.   J

  Eight books, each 4.3 b9l*mnllf)j-0 equl8cm thick with mass 1.7 kg, lie flat on a table. How much work isl qlbnf)*j 9mlule0 8- required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects ikci r8zc62-t we might not otherwise be able to liff. Show that the ratiztcrki i82c-6o 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 from 0ef j-o dwof:(accelerating by a man who is p-:jd feoo 0f(wushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mazby5(8mqfyqx 7 uw3(nss M an acceleration of 0.10 g upward. (x8w(7zy3 qqb fnym5u   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 h tzhsw;2q8qyg)j5 u07kls )yaei; a 5q38nsolinear 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:m6 yjy.t:5z5 f sl5lyba 4fns the x axis, varies as shown in Fig. 6–37. Determine the work done5y:46 :.bfsy5nf y zm 5ltjsla 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 iqtzq yhuk;xg,rl/9p g- e/(z3 n 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, with mastij6h ,i pkz0b(dm;ep/ vj96ys 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 sb7u + 8b 2abrki1rllr(peed 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 e(jz 7a pts4koq,f/v6clectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 at nx yj0bu b9ov1/w7u +b105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whos et0/xckbd 19vbmw1)bqjrd o)-tz- (qe string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves dxt1 ( bbr)cbmz0ekq o9-/-qwt1jd v) the bow?    m/s

  A baseball (m=140kg) traveling 32m/s move6yaq qto39f7rs a fielder’s glove backward 25 cm when the ball is caught. What was the aver96yq roqf3 at7age force exerted by the ball on the glove?    N

If the speed of a car is incrzc5ux60 vn 0oit gc5h-eased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the d65xi0 u0n gc z-och5vtriver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark 3hhuu/q 5+8t.s hbbzt 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 thehstzh 5buu/h. q+b t83se 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 ibc g-wlz+n,1:lc,jttime it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance durin: gi1b,-ctw +zc,lnljg a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.0 2 csrt. z((cco wdc21kJ of work on it? Neglect air resistanc dzc 12 w2cs.(ck(rtoce.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratio 5eu7)i 4o n,rb-qxwiqn by a single cable. D7b- oquxi5n qrie),4w 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 440N/m sdoj ) qt,m zd/jew7 ts-0;:sw How much must this spring be stretched to store 25 J ofstmd- ;dt 0j : jqe/s7)sw,zwo potential energy?    m

  A 7.0-kg monkey swings from onew,jqs gq/)a0p.gi6lgo4t / cx branch to another 1.2 m higher. What is the change in potential egt g0g,c6px4s/)ja/q o l i.qwnergy?    J

  By how much does the gravitational potential energy of a 64-kg pole8nfqw4+nsh4k1 sejzr 8i98 jq vaulter change if his center szh qq4419 ke8rnsj8 jwin+f8 of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfhqkj38:obo1 mace 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. Whamkojhbo 3q8: 1t is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground pncfm . :czsbk, *4q*iso it is 2.20 m above the ground. What is the potential energy of the book relative tkb* if .*m:cpnq,4z sco
(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 to 5c,(igaqfd- ep of a 3300-m q(c ,fi5agde -peak.
(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 vertlak6k8/o0b znra)2t: -c bsap ically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where willla0ra )b-tpz6k cbnoa 2/ k8s: the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a um r9 nrpy :hoo1hdj6 4.n28wavine hanging vertically from a tall tree in p8h4 ndy1mw uh oajr2n9 6:ro.the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frib 6j2 7nwh)io ut(wdjh1a)b9 wctionless 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 ahtwfc0y3 +* p p-4)cfiu,xalovibf11 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 enerfh:nh i6ywfr7 j2, h:lgy is transformed into gravitational potential energy without the aid of a pole. With whji hyr7 h :hn,fl6f2:wat 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 to ;c7gykw 66uqzp of a platform with a speed of 5.0 m/s. (w6 zcuk;yg6 7q$\alpha)$ 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), whukxrycb a3dh2.g(w)7t6 yn, zose spring stiffness constant is 950N/m is attached to a table and is compressedz2whyu,3d n . grat6x7c)bky( down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m sl hj:ud gy1.0zyides without friction along the looped track shown in Fig. 6–39. If t y ugy01:jdh.zhe block is to remain on the track, even 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 stiffness constant ez y0g yc3dv*dy8t3i7 k), Fig. 6–40. The block is given an initial displaceme*y3y7y gc8dt3 edvz0i nt $x_0$ 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 brit;xbx w0ze u40na 94iudge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming 04t;xe4 n0 ibzaw9uxu Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown i us*zv 2j3rqr:ntd,m/*c top 3-ohpb-n Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no ft*tn vhb*sdq3 /ro zm jup-,c3po:-2rriction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of)l bmtkn1sj/z*ux px:g5pl8 - 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an eledkbdkh ho6.06 vator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengd.6dho 0 bhkk6ers.

  A cyclist intends to cycla /3uhzr9 -3jly5cdh.;c cz bje 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 9t4 ftkm*0:j8yr. /o cetka 8qb5km/h in opposite directions, collide head-on and come to rest. How much thermal energy is pro8 r*ab0ttt4y ef:ck.ojqk8m/ duced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a spet: 1pf;/zy5e* k+oyrulks+o o ed of 2.2m/s How much thermal energy due to *1:+lt kpzy;/yoo5 sr+ ukoef friction was generated in this process?    J

  A ski starts from rest and slides djf4:iw8+43(mrmz iy gt zl;w 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)xf0 s+z8 owja 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 bounceskm1art)5b8 ,m,o7 :pah vicpg back to a height of 1.5 m.tv mr5:mp 8i7g,aohc,b1pa) k
(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 e 9vwet5y)(dwfrlz20cp +( ya rest, is pulled across a floor with a constant horizontal force of 350 N. For the)fa +2 9pl ryw0yvt(wz5 (edce first 15 m the floor is frictionless, 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 passes point 1 with a speed o 1ih5nvz:ptw7n)/ st of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The ditw:5nh /1sp7i t nozv)stance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwaa1.b-k(jc.; 1fwb cys su: ayvrd 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 56-wq5x yz-rk+ u:rrkb*fe l,ziq ry5 very light horizontal spring (k=180N/5xyr r-k,5fuk bzyr:l5*w-qiezq +r6m) 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 is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly atojb+k 2w,6 s7htv tege48/bdd tached to a very 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 released62 tt7obdkdswejgv 8b ,+h4e/ from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spakl/qh9tqb)0 q9t3 c1im-c zua ce shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speq1mtuqcl a99khbtc-/ 0 qz3i)ed 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 nlm/ij 17 o*i8cq a6u9a hxdhg3d+a1kmotor to lift a 315-kg piano to a sixth-story window 16.0 m a1dm/ji*+ hlaqo8d cgk an 3u 17hia96xbove?    s

  If a car generates 18 hp when traveling at a steady 88km/h :. eog-pk 9azmwhat must be the average force exerted on the car due to frictiong9o:k.mpz-a e and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h iv8rd b/0 jdy3bn 7.4 s. What is the average power delivered bd0 jd/y3bv8 rby the engine?$\approx$    hp

  (a) Show that one British hooe 53t x(ee-qruto:xjf l)y+( rsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often exs b y mjf ;3qlt z4k18ri65ns+4pdc3hgpressed 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 down from to 65km/h ig 7 jt mxbq9/7l:bqyl3n about 6.0 s on the q:ytl lmb gb9 j3q77x/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 3.0-hp motor do in 1 t0nh;ri/iqu ,.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot f71e8pyfsig q,-d vl j5rom rest to 14m/s If this motion takes 1.5 s, wd-p1i 7 8ey 5lsqgfvj,hat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water peradtj9n9hv -:v;v q0a u minute through a height of 3.60 m. What output rating (watts) shoud0a vat;nu 9v9qvj-:hld the pump motor have?    W

  During a workout, the football players at State U. ran up theclvol i30x0yn-)+h ut stadium stairs in 66 s. The stairs are 140 m long and inclined at anl0)hluoc 3nx vi0 t+y- 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 fmw2l/g )lz, zxk7 r0e6.0 $^{\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 osdbown3ra4 3gw4 9nfrw:ty* + qa/m (qf 120 hp. How steep a hill can it climb 3gywtdqmr qw:9 3*r(n4+4/a b wf nsaoat a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor ha4pkm)/ no+d pnve to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s in+pm on4)/dpkf the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a :o( t0*picrxx n f;.vjko7cv: 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars *;x5o remd:nio,kv) y2l d 6gbhave 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 must the effective spring stiffness constald o6xov;ir2,) nk eb:yg5md*nt 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 aa)7-avtya mpegj c;a+-r*o/first shelf is 10.0 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 avp7/g)vay aam-oja*-crt;ea + erage 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 (Fig. 6–42) in the 19t-abhjkh4y 2+ok,atf ymc5q9/ uog,x:33gis36 Olympics shows that his center of mass rotjqxo2y/,s5+ k9g:ch 3g4f- oiyb ,hm ukt3aase 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 frictiob2ehay2j+zih/0y-n7e +hw i 7ozo m50lof7ze n along the looped track shown in Fig. 6–39 is to remain on the track at all ti++hm2wbzl e iize y0o/f5 7 7e h-ay02njozh7omes, 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 felly 85dji/ :2gt2l7 bs 7.anacv0r ezaud 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, r.gy 5da0utbn7 e 87za:sv2icjl da2/ but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is 3p0 k g6ypp4egfixed (Fig. 6–4gk063pypge4 p 3).
(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 climb is made ing1gs vky:1cd. 5.0 h starting at an elevation ofysgvd :1. cgk1 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge spring,+ ns0y mgwv: i-(nwj z55jg6ghzh2hh ($k=2.2\times10^{5} \mathrm{N/m}$) 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 du ( nzfasi//ft 3qemghpx6v*hr;4+, its lifts can move 47,000 people per hour. If the average lift carries peo*+ir6me/v z;(fh4pntf/ax 3d g ,qhsuple about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate o 1 e5kp;gh8f fu/napf-po9 .jqf 650kg/s and falls vertically 81 m before strikqpk/;f9fj 8na5 hp1-f.p goe uing the turbine 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 c qbut ,mjmj(4)n -g3lqircular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum neede mt)34bl,gjmnu- q(jqd, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body c vpxhc sda+90o(r6) 1rr)sizkn9;tt6 at 0wqsould convert a candy bar directly into work, how high could an 82-kg man climb ap zt;waso )khncxrd6 ri ra+0v q9)69s1t(ts0 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 upwarsm 7x*;guytkw 9+ow f2d 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 the scale compr :/qehl44ge swesses 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 awe l:q4e4s/g ht its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over ag vnf9.;f2vqb xmbp15 lake (Fig. 6–45). He releases the rope when his velocity is zero. b1bvnvg;m259q fp xf.
(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 athleb ry*2j z4c.pjte climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to ac.jp jb* z2rcy4complish this feat?    W

  Some electric-power companies use water to store energy. Wa52csy4q8 y )uude . t6gomsxe+ter is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy prm+yts 6x 5oy.g)uscq8d 2u 4eeoduced 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 stiffneyt 6hus70nip; r1oig: ss constant k is cut in half. What is the spring stiffness constant for each of the two resulting spgs 60o1r7 ipiuh:;tynrings?   k

  A 6.0-kg block is pushed 8.0 m up a ry9x6/(i -n a.rsm axcxough 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 ka9c)z) /oxf paccelerate from 35km/h to 55km/h in 3.2 s, how long will it take /z 9cpa ok))fxto accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress tesoje.ex8 l8dg2t”), the patient walks on an inclined treadmill (Fig. 6–l 8d j8gx.oe2e46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 m, what voz 5alzu4(4kl0b /xn was its velocity when i( o0l4z/vunx a4kb5lzt 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 rz l-t*ga 6qc)bi,l-pc ate of 95kg/s (a) If this water wcg *p l-cqz ,la-6)tibheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s