In what ways is the word “workp 7qu),c h( pjfehyh-+i6wkq 3” as used in everyday language the same as that defined in physics? In what ways is it different? Gi3uihe) k hcy(p-+jpf ,qqhw6 7ve examples of both.

Can a centripetal force ever do work on an objw0d98yqbkr u j;(bf 42ia xozq.v1i+vect? Explain.

Can the normal force on an oq*wx-c : 4dnzjbject ever do work? Explain.

A woman swimming upstream is not moving with respect to th q)8s -v7f wr0yl6m xsta-zwl6e shore. Is she doing any work? If she stops swimming and merely floats, is work done ls7wv6 q t 6ya-zr) -8fm0lxwson her?

Is the work done by kinetic friction forces always negative?l3qq-4 ku4 tby [Hint: Consider what happens to the dishes when you q4qyul4b-k 3 tpull a tablecloth out from under them.]

Why is it tiring to pus //mesgsg-:qw h hard against a solid wall even though you are doing no woms/qge-/ gsw :rk?

You have two springs that are identical except that spr5ipbgt0 n j+c-ing l is stiffer than sprinn bgtj5ip c+0-g 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 to e4zv ioeccg.3o: +j .rpqbo r ):zzs,6slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and:i .eorzzro6 ,qc3 .: ez+bovjs4 gcp) 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 energy channu).5k t8 ( -rg2glhl d86wlyxgl2,ha,gctrbge when you jump as high as you canltk)cgr,5w- trb ldg ahl8 ng6g,(lh 2x8y.u2 ?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with ve + gh/3)exr,go tnlkq*h de90k,mx: the same speed but with different launch angles. Whhr+d,m0 k9/tn:hxvg,)q ke3e*g leox ich one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowes i75j7/wl4n un hrn ls7xek-u2t 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 5n- h suilre2n7u7 w7k4xj/nltrajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m resyogr1 -3 .ihwiv4i vc/z,ef3fts upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spri z1io3/ ,eviv.c-wyfi4r3 g fhng leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The ins6hfhj59ds )4ku 5v tkltructor pulls the ball back and stands against the wall with the ball against his nose. To avoiddk l hv55kts h6fu)49j injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravittugcuu5f4bn5z :s2ra1m w w ;71eu q1qational potential energy when water at the top of a waterfall falls s1rwqb tz5a e5 u1:;u2wfm7c4gn qu1u to the pool below?

Describe the energy tr8al plkt6 ;t.fansformations when a child hops around on a pogo stick.

Describe the energy transformations that ta,u q)5exclvf iqrn3m m (6inyg 4tt-79ke place when a skier starts skiing down a hill, but after a time is brought to rest by str6fc ru 5nqe)q4in3l ,7i-xt mtyg9vm (iking a snowdrift.

A child on a sled (total masar;df a8o1or7m9:v ns s m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) i;8o:d9vf1am nsraor 7t is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefe9f4ff( ) h0m5ptastm 4qwqax:r to step over a fallen log in their path rather than stepping on top attmqf5qmx( 44 :)f0h9afwpsand jumping down on the other side. Explain.

Two identical arrows, one with twice t/ob;n wuaa +nt5d +qb/he 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 slowdw5/;+ butnnbq+ o/a aer arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of eneryor2i/ewec an r,*7t8gy, (a) ignoring friction, and (b) taking friction into account. Explarinewa8te ,*o y7r2c/in why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound u,1bxgus2sg 0 to a height greater than its original height? Explain.su,bgxu1g0s2

Suppose you lift a suitcase from the floor to a table. The work you d7j0k8rp pwhx: 8dbi5mo on the suitcase depends on which of the following: (a) whether you lift it straighb:r 8h0wd 7ppjmikx 58t up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neededzcnr +7:pd:s q rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climyg b6ob3mgt;x 1mwih 65chw(a3 6g/zmb straight up?h 6 g/ gwax 5(3m;6mow3ctgyhzbbm61i

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes s.x gsn2kcs a5) 61brokjkq)1 to decrease the force needed to raise a heavy load (see Fig. 6–34).orx j6qnk1s)ac5 ).gks1b k2s 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 gravitationaah.r pma2 *b:zl force when a 265-kg pile driver falls 2.80 m? ahbp2z .: *ram   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much woh)f/ p.hh+ i h xgvwlm c:mq(;7mm5qr-rk is re(q/ +7hvi)f qcrlh; 5pm .xhgm-m h:mwquired?    J

  A 1300-N crate rests on the floor. How much work is required too8zhx qh nnj+7 5f4r,x move it at constant speed (a) 4.0 m 5+nnf,rhx47jz xhq8 oalong the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) rw 1x6,mma qa, bt8)vfpushing a 160-kg crate 10.3 m af 1 wrmvb8a ,a)qx,m6tcross a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is a7di )z/qqe+g3ic(w1dn w2q avccelerated by a force across a floor at a rate of for 7.0 s. Find the net wora+dvn7)ce(zq wiwd 2g1q3 q/i k done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flac e* c29 h rus-f50ef,ufo9lqut on a table. How much work is required to stack them onef5r c2shfu *ceol9fe0u -qu,9 on top of another?    J

A lever such as that shownp*o)3bbd .1 jtglectquo3h*i(:nc y * in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio ofjh*3lgb1i o3* dct c)b*u.npto(eqy: 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° pgntbiu2 22 km)i 5pu:incline and is kept from accelerating by a man who is pushing back on ip2k:22tug 5mbupi)ni t 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 g1bip tq9vvz-2ive a helicopter of mass M an acceleration of 0.10 g upwarbqi9-vz 1pvt2 d.    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 anl (.;vwatoxo ktj.w;.d 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, variesa- l*j6o z0a26difwjpur*v7*yrkqv 2 as shown in Fig. 6–37. Determine tya2dlapj fu -wzvrk6*70i6ro*q2* vjhe work done 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 partihm31ea l2vm v9cle acts 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,3toelp( ,j7j wo )thv7 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 is doubled, by wh *ir(hj*zvo*oat factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop anage(z lb(+y1k9*kj tg 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 s6pb)8qftuttd r(f73p top a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 Nr ae16:+c/yia7m nu4if/zo cn on the arrow over ac : /nca yan4rzmie17f+/ o6ui distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’nxs1;s/4dlha s+zn7g -gks6 j s glove backward 25 cm when the b ss7d1xh4z jn;an6/gg+ss- klall is caught. What 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 willwwa5 n2+5u lf::a hd hos1-ifu its minimum braking distance be increasan2hu5 dffh:u5:i+wo 1-wlsaed, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roadaigb m42h*fk), investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speehb4mg 2)iak*fd 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 rq 9 7z0zseayq,.e gz/4wu;u ureaches the plate, it may have slowed by 10%. Neglecting gravity, estimate thez9 e7uezyqws;az. uu/rq ,0g4 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 i9 gptr3pm aaye28l(0 uf thrown straight up by someone who does 80.0 J of work on it?em8a93 y( pl gaupr02t Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by xb )5uv- 3anqn+ -cooqa single cable. Determinen+qb uav- c3o-nqx5 o)
(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, l0aui*qq.ov .(r :qtk2 dd/unof 440N/m How much must this spring be u.k :*alv q2/doun(iq td0qr.stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to anob pd:0u blc0vrqome,: p*3x ,sther 1.2 m higher. What is the change in potential energ:xd b0cerl0op3,:p bvu s*qm, y?    J

  By how much does the gravitational potential energy of a 64-kg pa,,t0g-fjo(hj j;sb cole vaulter change if his center of mass rises about 4.0 m during the jha jo,c jt;g, s(-0jbfump?    J

  A 1200-kg car rolling on a horizontal surface has speedcg f3wxned 2is64p ;(o v = 65 km/h when it strikes a horizontal coiled siwn x6dfc2 p;(ego3s4 pring 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 2.10-kg book from the ground so it is 2.v6oa.2a8 daqkut9 /ob 20 m above the gro.u6 t2 kaqaa89do/bov und. What is the 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 of 1600 m and climbs to o+gdy/ t/g 3 4 vst0syxfpp(j2the top of a 3300-m peak. (p/x4/fy2v sd3yjg+ops0 tt g
(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 /hec;okknl+ovv/ :w, yr; eq/the spring is next to the 15-cm mark on the wk;/eo +h/v ck/ly;: rqe ov,nruler. 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, ishuokg;):n+0yn mr n twd38fi5 running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwardt;: muiogn n0)nf rh53y dkw8+?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from restq* 0ttta l4qq(, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove u:qbyx5l/f: 0azug ,dip a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic ivqb m er)8-of 7,fj;denergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the g-)e ,o rqfdf m7;ijb8vround in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform w,v kjq5q+y n2fxnt99sith a speed of 5.0 mkt9q 5n x,yqjnvsf+92 /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 stiff. /.9xvypuesfness constant is 950N/m is attached to a table and is comprx..yuv9es/ pfessed 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 slides without friction aloa s576sykiyk ofi,2:(ns qwx,ng the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whosei syx7s,k k5iyfaw,2s6nq (:o radius is r), from what minimum height h must it be released?    r

A block of mass m iswot+*v ygg kqvn-eq k56 o2i/4j)j (ts attached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is giy2t wvo/g+jk( q jt4)snek q -6*5ovigven 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 frvl9ask(v r-4lq*2y drom a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. ( sy49ra2v d l-qv(lrk*a) Calculate 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 sho1cjm 6pkr q+d:w n1xi4ufz81w wn in Fig. 6–41 is dragged up to point 1 where it is released from rer c61fd w:k 1n1+4zj8wupqxmi st. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ot/9qi ptq 5l6sf 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 qf)2 ibwscg02spring to be placed at the bottom of an elevator shaft. If the elevator cablf2bgi2)qsw c0 e 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 passengers.

  A cyclist intends to cmg:yra 7 0azm*g(izm2ycle 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 ;v mhh2pg5t,mw-; mxlnq0u d0kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much t-hvn05;mm lqutxmwh,g ;0d 2phermal 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 reaches the bh i 98f .,e9.utxgye jjg)g,em1di7reottom with a speed of 2.2m/s How much thermal energy due to frictionfyxr.e 7ue .md,e), gj9 t9ih 8gje1gi was generated in this process?    J

  A ski starts from rest and slides down a 22 wi/f0y0a)e dg$^{\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 13.0qsi.nk te4ddj )(qy9w+ ako-**.jj sx m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces(k5gdrndt6 k 0xe-t g8 back to a height of 1.5 m.xrdd5geg860 kn-t (tk
(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, staro oa 5m(po y1 :mo8q8stdjrq2)sf.wb*ting from rest, is pulled across a floor with a constant hori(of )jqo*85q.ds rb1a8tpm y: om2swozontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pa8 ,3m8 gndtoiez/i5o osses point 1 with a speed of If the ave3ti8mn/gi ooz8e d5o ,rage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwa c 6fmzh2lh(gd3eyw2pr2 qq;lq*4sr (rd 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring c:(-,xmzhs fb7-w8 r1ewsgzw (k=180N/m) as shown in Fig. 6–40. It is noted that the blockw:m-r( - 1scew bhsgf, 87zzxw–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 jzzf.k8(f2 fp 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 released from this position, how far beyond its equilibrium position will itj2f. 8kfzz(p f stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 9 f3ah9z.vm.to bg6h n*80 kg including pilot) that was launched horbzvn.h o9 6h*g am.ft3izontally 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 piano to a sixth-story wmr238esxmev a00*md h indow 16.0 m abov ax*0e 3 m0d8rm2shemve?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be t6-zfdeqry.e du3.h2 b 2rt;mmhe average force .t 6dqyr2med;f .e 3mrbu-z 2hexerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the averawmb(wdqy49/ von3wo2i 5u.0 8ids ewhge power delivered by e (4w 0.5s3vmhwoniudyo2b9w8di q/ wthe engine?$\approx$    hp

  (a) Show that one Britis cn, sbi+xlkol/z.98oh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in tgcd 5zv9,);d1eimsuzv bo p1oz g ,7b(he 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 in about 6.0k4c,9cd98;oc: suq ak kve -vx s on the level when it is in neutral. Approximately what power (watts and hp) is needed tod :4uoc8kxe cv-9q,k ;ckvas9 keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor d apjko(5,3zd3j gr) m8 henwb4o in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7 crcs g 5gs1m;p e-h,r(lcxu74.3-kg shot from rest to 14m/s If this motion takes 1.5gxl1rs(-;r shg5peu, 47cm cc s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water ph7,i9naty ( tger minute through a height of 3.60 m. What output rating (watts) should the pump motor have? y9 ig,( 7tahtn   W

  During a workout, the football k8xztg(t. /2 ncxs;wyz7/aea players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long ankg;2n/w.(ezt a8taz x xsc 7y/d 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 6h2 *eg xl8x4pk.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 wvndj7lzych1yo bd sd/p8i528(crcs :xy9 0/ maximum power output of 120 hp. How steep a hill can it climb at a constant speed ozj/c08wnpcs o5 cyd/7 x9i:81bydl2yhdsr(vf 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to--cdekr2 oe j7 l84 9y/gnjb1ers9xec be able to drag a 310-kg box along a level floor at a speed of 1. ck9 yeeer4-esj1/r 78xj- 2ncd bglo92m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7bre9x 9)6 h dvf+gq,g6ht.mw x.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bu 6 f9j)jb.mlvlmpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a6bl)j l9 .fmjv solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0pb4ica- xityht:787b cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to s74x8itbyit 7h-:ab cptart? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympicsu8qfuoulp 16ywa)gm6/ */asnn j+ f-f shows that his center of mass rose 1.1 -+ffu mw 6/1guq8 jnp)snaf/*ulyao 6m 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 frickqa :pjv2p(x1tion 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 lo(j vp1 a2:xkqpop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without -b i6k-fa4d cnhis parachute opening. He landed in a snowbank, creating a crater 1.d- ck4bnai6 -f1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other endun nrjpaa:p ) .c)q;p* is fixed (Fig. a))rp;q:cn *nup.jp a6–43).
(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 zs9z+al0 d s aayxx 6o05,3jibof a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calaaj,s3 y6+idsz5 aozxlb0 9x0culate
(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 sc (3m-g7v m5p;rya mbkpring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 pcds lm)*/j f/keople per hour. If the average lift carries people about 200 m (vertically) higher, jk/clf/ s* md)estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s at 7 14wkdbou0q-,n./v;hjah jpuo 3cgnd falls vertically 81 m before striking the turbine blades. Calculat o,k1oa j3vnwc;4h-d.bujqg7 h0p/ ute
(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 vertvj81z ch0( k z3aj rzsim0d.(nical 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 weightz(103j0s(z8hnm dkc aij .rvz . 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 rc na)vjo ba-)8kp.2lo6vw2na candy bar directly into work, how high could an 8 n.82-o2 paravvbn )o c6)lwjk2-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an l2* b jfa :v9bj)n(xpjupward 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 3u wg06fpsn6eo* nnv-, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 71* -6sonfpn 3w6g venu00 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a dqt/f rp9yk;+h/. am.;df.c rojt:jarope, and swings out over a lake (Fig. 6–45). He releases;/mcqt a d .f;t. p:r.o9ay /fkrdjj+h 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 m in 9.0 u0:xhd2x.*ndsjq4o es. What minjx d4u.h dn e2os0xq*:imum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by re(;x;xdc ql bz-versil -xzbc ;xqd;(ble turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is tx ebuws/, 493 zylbhesn;3c8i he spring stiffness constant for,ne3lb9b y4; xuze/h3w8csis each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 2ie /xcvs1z / 6wxbxh937 $^{\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 in5+e .v+b.mgq 4 si4umjqc b-qo 3.2 s, how long will it take to accelerasb+bq mjv eq5cim-qgo4 +..4u te 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 tes dhu gcg0t4eqb(zw81 kli0o7 3f5,tuvt”), the patient walks on an inclined treadmill (Fql50kv 8g 1hcb 40tegfi,7ow(u3 zdtuig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upwa14bq+j lr9zym: u uib*/cd2ikrd a distance of 500 m, what uyz 4 m iir1*/buc:9l j+kb2dqwas 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 95kg/s (a)(s;wh g4vzuf 9 If this water wheel is set up to provide electricity output, what is sw;94(h ugvf zits maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s