In what ways is the word “work” as used in everyday language the same as th/ p (lvuc vt:9kqqcn08 t ./mxj;) 7x-ajonqzfat definj)t(kao t; f q jcq./vmxc/9nnpz-0qv:87 luxed in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do ato5x;,6f- yqfg ao m:work on an object? Explain.

Can the normal force on an object ever do workj8mhdc ac2a0 .? Explain.

A woman swimming upstream is not moving with respect to th r43vb txk8y;3)w bshxe shore. Is she doing any work? If she stops swimming and merely fxtw hvx3b8 )ry 3k;bs4loats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider whp0y4ogq.m ;9 k prfnn5at happens to the dishes when you pull a tablecloth o 9g0ofy4 npnq mpr.;5kut from under them.]

Why is it tiring to push hard against a solid wall even though yo 8u + ik60vmtqdn15oizu are doing no wi ido8 016ku5 tvz+qnmork?

You have two springs that are identical except that spring l b65bfalaad:2ld :oz f2f5 sn5is stiffer than sprffd fs5a6n :da52: l5bbz o2laing 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 fe ohjs 68/kmi*j.gkgm,dpn xou1rw b3q9k5 1.orce on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a disk6o bo uj1jh1m gkrmkx. wnd*3i/.pqg8,e5s9 tance $d$ 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 poten7f 2l;fq* ,lsn d l3gabsyzs18tial energy change when you jump fbls7yfl3*szs82 g l1,;q dna as high as you can?

In Fig. 6–31, water balloons *u5r tp m;e4u7toscj;mbrhhx- /o t-,are tossed from the roof of a building, all with the same speed buhj r*4xt7;mtc;tuem/obu ,-r -spo5ht with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h abo2ph +)y 63h7q6 at) xxyibc2bprspzh) ve its lowest point in two different ways (Fig. 6–3hbypa676)yrb) xh+x2si t ph 2z) q3pc2). 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 the largest angle from the equilibrium position? Explain.

A coil spring of mass m res ww1zph, wht*;ri/,)cx mu6q 5/xmnxots upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of c/o;wcn r6zxi*/,uh)5 x1mwwmtp,x qh onservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33a+0 ajjc;zg(+na4oozbrrllm+ .r-p2 ). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release thoazz;j0co+r2ljr.b-g mr a+anpl 4+(e ball without pushing it. Why?

What happens to the gravitational potential energy whdx9 d0yd.)cs ten water at the top of a waterfall falls to the pool below?dxcy.t9)0d d s

Describe the energy transformations when a child hops around on a pogo sti *znjup y46oiad4)1h ock.

Describe the energy transformations that take place when a skieu tn.u3k66hz v02zg uer starts skiing down a hill, but afe 0 n6uvug2tk6h zu3z.ter a time is brought to rest by striking a snowdrift.

A child on a sled (total massp.0i/c g o n bqqv*ex+ggss:-9cdja un/+p:t5 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) it is icy and there is no friction, and (b) there is friction (deep snow)jgd /0x.c q:o si /9bp5tqcnaseugv+ p-n:+g*?

Seasoned hikers prefer to step over a fallen log in their pat6zbhs.- cgfi(h rather than stepping on top and jumping down on the other side.-f( 6 cz.gihsb Explain.

Two identical arrows, one with twice the speed of the o,l8ch* bl+qorh s.c+j)kc8wyther, are fired into a bale of hay. Assuming the hay exertsb8 c.q)k8*cl h+y jl+chrso,w a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendu a,cch 5mupx 96u39q .wfis2ydlum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather c 3u6cc,m5xudy 9.f 9h saqpw2ilock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than itw 33k fe05v1chmp:v hes original height? Explain.phmwfeh3c: 0ve kv315

Suppose you lift a suitcase from the floor to a table. zd 37v zw;:nph0 /pdbbThe 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, andpn ;h7z:03 bdpvdbwz / (d) the weight of the suitcase?

Repeat Question 22 for the power needed ratheuvko t-wweo/5 oyr5t0n/tz (2r than the work.

Why is it easier to climb a ma 4/xm3okji;oountain via a zigzag trail than to climb straight up? i/;a3kxmj4oo

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to d rh ceq.satu64v:9 k 6a19yjsqecrease 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 tu4sq99 ake66 s1 ctyhv r.jq:ahis, using energy concepts.

  How much work is done by the gravitation0nzfunix t :7-al force when a 265-kg pile driver falls 2.80 m? 0u:tz -inn7xf   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is r-:xzspwj3t2h z n )s,uequiredx2tz3-p:, )zw jnhssu ?    J

  A 1300-N crate rests on ejipci2f63pk;mn + f)the floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 jfm;pn6 +iiec)k2fp3 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the m (*a3gz+wnr-rgp :aw f01ezp jovers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor withou:r pgwr(ea-nj p3a 1z fz+0g*wt acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of fom*w31wft 6zi dr 7.0 s. Find the net work m6it3zw fw1d *done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. s r2li ua 7t2,zgw/8ngcaqa(-How much work is required 78al zg ngra wq t(,2a2iusc/-to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 capeezro ,,io69n be used to liff objects we might not otherwise be able to liff. Show that the ratioe6z i ,9e,orop 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 txdom36ofq *;down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The efd3q x*6;mofto fective 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 mass M an d:(tnl2hq51x dsszz 8z;x7h5lx)rsv acceleration of 0.10 g upwar)rl1 v2 s(zd;5z :zdtnxxhlsxh5 8 7qsd.    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 linee :/ pq )s*vt b8f7zmob5gxx8zar 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, actingpy.wt:u -3ph 5n5zo ry along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 hp55.rno3-y:upyw zt 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 actt3 ) /r09i.dpauzfy particle 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, with mass of :,zvzrz2ouh mv:,k /.fm+gkartn 8k0$5.31\times10^{-26}$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 speed incw0jv 90t 9p(x3hj pivvreased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop anhy:jm/:/nlpgk3x pf ,np8 3 eq:ae(tn electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling, f)p qpaltb t4 (jy0u234cs6u8 tqcih at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string anabg g,0)6f;n(ob qi jwgm7(exerts an average force of 110 N on the arrow over a dist(gj;fqow, m ggn6 )7i0b(anab ance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) t:j5isr h3ys7sau*k d* raveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the av j5arh :kysi7*sud3s *erage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what 6hybcg)fmge; -snd6) factor will its minimum braking distance be increased, assuming all else is the same? Igsg) cmeb 6fh6dgyn;-)nore the driver’s reaction time.

  At an accident scene on a level road, investigators measuva* 7m+6n *0gac znumhre a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction v+ nama*7guc*n0z6hm was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the timen,n09r wxiet4 .w,dlf it reaches the plate, it may have slowed by 10%. Neglecting gravityn,nrxl fwt.9wi 40ed, , 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 thrown straight up bxm1u y)g 5lse1y someone who does 80.0 J of work oy l1xm15es )ugn it? Neglect air resistance.    m

  A 285-kg load is lifted 2bj1.o) ue -gen2.0 m vertically with an acceleration by a single cable. Determine j-nbu1e) oe.g
(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/c o8ugw /5y2vkj-* afom How much must this spring be stretch8 wocvuk *2gj/f-yo a5ed to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one br)1g cekaz3keq7lsh2cg f f:;3y q..quanch to another 1.2 m higher. What is the change in potential 3usfzag )cykg1qcq :.e.ek 2qlf7h; 3energy?    J

  By how much does the gravitational potential energy of a 64-kg p7ikf tjj5nh .rwm/nvy* q+9 s3ole vaulter change if his center o /*59 y+mnftvs7nhw.3r kjiqjf mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v ;r 0jzwr(tqh)sokud 7li.r 36 = 65 km/h when it strikhr(;lj 0q3ist6ukzr.w o) dr 7es a horizontal 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 l9gf6t 0:0opotnoa +huf1en;p ifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative totenf;fo t0hn0: opop9ag16 u +
(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 xcoubm ; vd6/+elevation of 1600 m and climbs to the top of a 3300-mcbvx+oum /d;6 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 vertical8 ao nzs+);adxly next to a ruler. The end of the spring is next to the 15-cm mark on the a)xd;zao8 n+ sruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spz6 o, ci+qtfd4eed (5.3m/s) and grabs a vine hanging vertically from a tall tr,ozit cdf+4q6ee in 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 frictionlesp sk *bnzol4qa60hw r8dd,y h 91.hq2gs 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 upm rylm w3-ikttw;t37 6 a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitationalbsncodnu+dg1m4.7 q(j: pq +p potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her cmpo .4+dn:d+p1(7gqjqc nub s enter 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 thlrhsri; )m8pb pn4uvajy:n6:/ p7c c5e top of a platform with mp5ni6r :c/sr:b n ;7pal8ph4)cju vya speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness.i+j+ue*fig;srddvxy w .c1, constant is 950N/m is attached i+d. g.1u dc r+e;s*x,vifjwy 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?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown l1nua 8)e 0xwlea6i0qin Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r)n uxeae1i 0al)q6l 80w, from what minimum height h must it be released?    r

A block of mass m iss 2jz*;.yj1(nzeu( abqu o xz7 attached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displj( .qn1s7*j(ouzzyze2b ; u axacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bu hnx0lw.o+rp7jw+1u2pn7 jhvsws (( x ngee cord whose unstretched length is 12 m, and falls a total of 31 mw jn(70n +jlo+w 2xphush.psw x17vr(. (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 shown in Fig. 6–41 is dragged up to point 1 pfb+p g :vvfz/nsl,0b)*g3 ku,s yg1t where it is released from res)+f:/ *0s,g pvtgup,blfz vb 3gnyk1st. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown;ybvc+rysn4, with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placedlk 6 e kr:6 cq v5+.ozdjt+*vcgg*+ztl at the bottom of an elevator shaft. If the elevator cable should break when the elevator isctt+ l.+gzj lc6+*oz 5vg 6krkvq* :de 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 cycle up a 7.ft+u yajt5a 1s,sc,9 rz5nu d68 $^{\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 trave5k-9p j6bh.j;ye;hc5 *0jt ymhsa khwling 95km/h in opposite directions, collide head-on and come to rest. How much thermal enershe*;9.j; b mk5cy60-k5 hhaytjhj pwgy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descf 7;x2.y,ht api::1*zkt f riwt6oz iiends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proczfitf: o6 1z .tii;w: ry x*,k7iapht2ess?    J

  A ski starts from rest and slides d1ttug-xd.t d;n ska )8own 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 trmi 5p; o:ublo2ee 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.lv4i56wcqg3 g /c.t:is v-rcg5 m.igvc :5q6 -cr4.sti gvclgw 3/
(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 frkpymn2hr- fl4r ((.is om rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficie4rnyp( khlsi2. rm-(fnt 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 of If 4.dyfb) p 6k(xts1pd uthe average force of friction is equal to onep)bt46y k1(f x dpu.ds-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 sterf i4xvxi,s-r /5pb ;pady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (k=s3l 2d-fi 2/ d6foz+ gce fm;mabte1.o180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kineb-ddz6m1fcoe;/2 sai 3eft.o l+gm2ftic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizon- sz6gri7( enc gvl(v9loo d72tal 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. v(von7 dl-gei9g ocrz7(l6s 2 If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 k2smzxfku)83 5 3elh4tet(p22 adaa yeg including pilot) that was la3(tz8 f)u2atadek a225m e ysxh3p4le unched 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-kg3 0msf+k qmr)b piano to a sixth-story window 16.0 m+m0k)3rq s bmf above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the .uhj ;to,rmlu js(/i-average force exerted on the car due to-;smui,jr lh(u o.t/ j friction and air resistance?    N

  A 1400-kg sports car accelerates fm9 xn5*k)*qwecjd ;vt c5 -mgsrom rest to 95km/h in 7.4 s. What is the average power dc twg cen*j5sm mk -9dq*x;5)velivered by the engine?$\approx$    hp

  (a) Show that one British horsepowerm7 9ntzcx/ giyg* au/1$ \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 the x801l*ixnys v 2(vlxf 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 he 9vfl.n*.n bpur 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Appro*.fvl.nb9 p nuximately 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.yh5a04oyrp)8dslwsed9 l5 + v 0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If -dc; owgt0d,u this motion takes 1.5 s, what gc0-u,;odwtdaverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of ,f-y5vrbb d+rb+4fnhwater per minute through a height of 3.60 m. What output rating (watts) should the pump ybrbh45vb dnf+,f-r+ motor have?    W

  During a workout, the football players ahzxp879i- m uff-j el+t State U. ran up the stadium stairs in 66 s. The stairs are 1hxi+f9l-j muf-87p ez40 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist eme8p( u4y1enclimb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steec 6r.hfpj 0t;xv- f+il( 2o4zqo cb6czp a hill can it climb at a constant zb;cvlf24 qx0ofr +jc cpt.h- zi(6o 6speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 315;m:r av u44z )sreawe+lxmq tpg5 *7p0-kg box along a level floor at a spe*: 5 vpztuarmpa ;4mqr4gswe)xe+l75 ed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dr;d a2.bx a/zfwuy22 rown a 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 ha*;p33(uaxd(:qa: yop,vgds7/ m s f8 ugqhjcsve 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 constant of the bumper be, a(8h da7; x(qo/u:jssva*dgmp qf g,s yp33uc:ssuming 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 o l-8v, pwemw+j*,(9z ambahwwbrl+u (ff 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 flaa*w(8, r9ml+jbbu ( ew hwv+-apm, lzwt on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) 46a 2tczf:o hain the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling a4 h:zof62 ctaat 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fihbt0jpz +6 8paxkjx6.g. 6–39 is to remain on the track at all times, even at the very top of the l+.bkz06j xt6xjph8 paoop 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 aircraz stym u/h2eq1 5my4,uft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with onl5 h/qt4m1zsum euy 2y,y 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 corr yy31pren0kwj j1, u7d of length L whose other end is fixed (Fig. 6–43). 7 1ye1py3uw,rj jkr0n
(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. Td85puz4 st g71hfe 1tahe climb is made in 5.0 f5du4hsget1 t87 az1p h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a hp ke0(hwcc ft2wc:,:vuge 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 pb3q ,nl 9xzym3cq2/ zreople per hour. If the average lift carr zm zc3ryxq9n3,b/q2lies people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a da5i.zx4 rhh2awr out47 m at the rate of 650kg/s and falls vertically 81 m before strirx5htra 74uzwi4 h 2o.king 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 nx . omo8y0fqlhlng; e-42af; circular 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 ne-n4om;l2e n ; l0. 8qhfxaofygeded, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar dir9/ k(zo uomqv1 tdn33qk03drj ectly into work, how high cou t3rou vn dq31km(jko039/qdzld an 82-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 upward angle of 45.0, ;umdz 1yrx3sp tzpss-,ur4-$^{\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 c2xqgqhbgutc:nlg ,a6d:. h ,;ompresses 0.60 mm, and it tells you your weight is 71b6qn.gxa2d u:; ,hhqgc,l tg:0 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 c*kvil j6tdoas+/ 08gtn/aigtj 593w at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He rej8 giidl5 kt v/cjt* s6wg/ n03oa+ta9leases 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+-zanlq3j*b3 - hcgi70m yywf 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum0bgw*j3 ql zfam-y7i-nyhc3+ power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Watru*a6n ul 4n2aer is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW auu2*l6nn ra 4($120\times10^{6}$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 the spr 8gtsj.it3qp5ds6aj 4 ing stiffness constant fot.j83jsiat5dg sp 64qr each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 2qc r,e /+luky$^{\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 3a x-;q )3plzgt5km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power statxpalz ;g3 )q-ys the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”gh,unt uj ik,xco ki9te;wp+0p4 )4d+ ), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power pik uxk,e04 con td++ip9g,jt hu);4wrequired 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 verticallbmy)p gbk-b2; y upward a distance of 500 m, what was its velocity wheng-b y2bkp b;)m 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 amyct*fd+ /i *q rate of 95kg/s (a) If this water wheel is set uc qf*/m*ity d+p 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