In what ways is the word “work” as used in everyday language the same asemc5t:0e+: fron p;rrw . uk e;p*fz2x that defined in physu fpenk;rro*cfm:zx;p2 5: + r. e0ewtics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an ob, mvnc78kvc f s4e,k mh i1l(*ht51sozject? Explain.

Can the normal force on a a 0x j.v -bn/qh5jmemw*.tse.n8e xv1n object ever do work? Explain.

A woman swimming upstream is b o3fp q7z c-uha80e+jnot moving with respect to the shore. Is she doing any work? If she st8b370ouaq cjh+ ez-pfops swimming and merely floats, is work done on her?

Is the work done by ki9h- n(xdezez9h: n s2fnetic friction forces always negative? [Hint: Consider what happens to the dishes when ye 99hd:f2xs -nhe z(nzou pull a tablecloth out from under them.]

Why is it tiring to push hard against a s 1l3bdgb4t5zl olid wall even though you are doing no w 3bdb5l ztgl41ork?

You have two springs that are identical except that spring l is stiffer than h+f+cj,o f z7nvg8,pkspr+f7hp8,v+ zfojkg nc, ing 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 t +wu,)(t 0dqtylnzi2cbm69 sox1hr p0hat is free to slide on a frictionless surface (Fig.6-30). The block 216 ou t,+znrxq)lw0td9 bsipy0(hcm starts 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 poten8h9 rp6zjsggns.2v p /c6ez /avla)z;tial energy change when ygge8p6ar hvn ssjz9)c v/lz6 z/p.;2aou jump as high as you can?

In Fig. 6–31, water balloons are tos vo7k 8:jw,xn0z4lp ovsed from the roof of a building, all with the same speed but 4w vp k: ovo,x0l7njz8with 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 above its lowest point: j1s n-dgck.q in two different ways (Fig. 6–32). During both launches, the pendulum is given an inits:jdg.n1 qc- kial 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 compresc1r- c miz g7lr-ji oj2a7x*;bs the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law oc -iijx2 g*7 mca7lrr- bojz;1f conservation of energy.

A bowling ball is hung from the ceiling by a steel ;zh faeis7 a +3wy06nvwire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. fvn+3 wh;7a e0az siy6To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the grosh/m(,isi9za l rqp(m 5cy3. avitational potential energy when water at the top of a watr o5m/ pai(mq9sh ,cl .sy(z3ierfall falls to the pool below?

Describe the energy transformations when a child hops around on a pog14z*eg t qehm5o stick.

Describe the energy transformations that take place when a skierw v)ebef-4stof pw3 2* starts skiing down a hill, but after a time is broug4*)twbp-w 2es 3 voffeht to rest by striking a snowdrift.

A child on a sled (total mass m) starz 3f-(pr,zfd bts from rest at the top of a hill of height h and sli3 -zbf( zf,rpddes 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)?

Seasoned hikers prefer 6x,e )yk)q hm9qm:p lrto step over a fallen log in their path rather than stepp eh)l6:y, kqrp9m) mxqing on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired2ee c00guoisgyj/1 k1 into a bale of hay. Assuming the hay exerts a constant friction0oc geieks /u20g 1y1jal 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, (a)xzn1lcs*mlvz : 4jj+d ra++c* ignoring friction, and (b) taking friction into acc cx:+4*ndj cl+m j+*r lzvz1asount. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heigh7fdd kly))dw h;y7/qwt greater than its original height? Explai)qlyyhw;d dw kd)/ f77n.

Suppose you lift a suitcase fry-5v j/l)+;l(smpwy e/4zlzx1 bjqk s om the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether4pbekjlml1 )z ;/y / yszqwsj+x(5v -l you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powerlis iqw)(*xw2p /y 2rro3ejsq6 nr f;- needed rather than the work.

Why is it easier to climb a mountain bz udv2h77n+jti r55 oit 4z6fvia a zigzag trail than to climb straight up? i25 57fdtt4riou6hv z7 zbj+n

Recall from Chapter 4, Example 4–14, that you can use a pulley and rope7ujqw 5)d ww09mx7soes to decrease the forqo u wew 09j)wx75sm7dce needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when aik)9g:uw hqp90e qa 9)pia:ft 265-kg pile driver fallsi9 keaq: p0ihtp :u9ag)wf9q) 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 mah/z q3(m t6 up+k.md28spsx c 6ght1m high. How much work is requigpq ptm3tzxm su6(da/+ 82 khh6m.1scred?    J

  A 1300-N crate rests on the floor. How much work is rew8qrvxjf; 39jquired to move it at constant speed (a) 4.0 m along the floor against ; xfjvj893qwr a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally)f*g mj9 a.j(g87ihx, 9r hjzfouzs0l0 pushing a 160-kg crate 10.3 m across, gilz097z8x.rjg(jo0 ha u9*jmsh ff a rough floor without 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 fo.d:cyiq/* -w (avaczu r 7.ic.c adqv w(:-u*/z ya0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a(kev. cysbd2;7a y /k 93z;e7bw cpn3r0dthns table. How much work is required to stack them ocecy;7 /0 sds(n 7ntpz2wa hbv .ke;93y3bkdrne on top of another?    J

A lever such as that shown in Fig. 6-35 can byz trluul3 1j-)/;hsbe used to liff objects we might not otherwise be able to liff. Show that the ratio of output force; 3z- )ul rt/ju1hylbs, $F_{\mathrm{O}}$, 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 accelerating by*dksx;7zpo/0 s9k9 mtyt e)lr a ) zod0 7xs9e/t yms *9rtpkkl;man who is pushing 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 requirebcny*c+wf6n 1 d to give a helicopter of mass M an acceleration of 0.1wy 6bn*+n cfc10 g upward.    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 h qugcdhh s(4oql i-2l:l2f 29and 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, jrflmj*1 xav hrzfrs0km 11x-0b* x/ :acting along the x axis, varies as shown in Fig. 6–37. Determine the w01xlba 10*:rf rjx / xm*f zjhs1mrkv-ork 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 partic v,48w)d15nrqxj jfc qle 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 u 55mwa8kmu o+7kxaga7 k 1dw+oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speeg- iv9a;grv7xd increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required ** h7jwzvi+v hto stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 1kq29u qy2zqz,zfbv 0:hn;1b k05km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strielq: w90b jm5 7+d hkqo mvnp/nnz*l:7ng exerts an average force of 110 N on the arrow over a distance of 78 cm. What is thejn lmnq:b dwn0 mk z*/: 75+lvepq97oh speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a uj uo/v5-ti zm8mg33lin j38 afielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the gloveoumv3tij8i 8n-au35gl mj3z /?    N

If the speed of a car is increased by 50%, by what factor will its min+ w,;a yun3mfuimum braking distance be increased, uua my;f3+wn,assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road,za 82s /fwmt*q 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. azst8fqw2/ *mUse these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches td rk2 u)(1:x hez 9yzib44qgcuhe plate, it may have slowed by b2ru cexz(ig)kz4 4:h9uy qd1 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if0bdx wm /r8jr49l+tv t thrown straight up by someone who does 80.0 J of work on it? wdm0 9 l4r j+8tvb/xrtNeglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single qohb8 w.(i+ciz.7r adcable. Dc.(arbi7+.wh ziqd 8oetermine
(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 How much must (ads5+eg lw0jqq.m4u zl0/ryx,y7kk2 o/k okthis spring be stretched to store 25 J of pok2 kylo0, gqoq+wrm/(a4u/0j xydel 7zk.s 5k tential energy?    m

  A 7.0-kg monkey swings fromj ,o+am5(wk)c-k y+d,vnk ceq one branch to another 1.2 m higher. What is the change in potentyc,+d q(vk kj)k 5wa+n -ocm,eial energy?    J

  By how much does the gravitational potential e.4h su uvpef30nergy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m dupsu . v3he4u0fring the jump?    J

  A 1200-kg car rolling on a horizos 3rlric*f2yn z7.uq ,ntal surface 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. What yl scu37rnirz,.*f q2 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 2.20 m4n4eiyq zz y;o70i* uh .d+lho above the ground. What is the potential energy of the book re. lu ynio04;7qhied4+zz hoy*lative 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 e)s ts wq 6sx2guxsru+38n.(qkc8o :vblevation of 1600 m and climbs to the top of a 3300-m qtokv.s)ss2q u(6ws rg8x3xu:cb n8+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 vertically next to a ruler. The eckhy9j)p( i ,dnd 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, wheryh kcdi,9j(p )e will 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 vine::ljg hn y : 9rfr45;ys0hfatf hanging vertically from a tall tree in the jungle. How high can she swingr:rh4:y0ny:t jf hf s59 ;aflg upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from mmwxa *g ekg(h6pz3,)-,wa8ts9 b mer rest, 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 nsx 7a)f xtrzv0/ueez *;j m6.shove up 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 grav alyc ie-ax,mu.1; g,nitational potential energy without the aid of,. xa;uc1elgi ny-a,m a pole. With what 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 z z 2 5;mg+lzbs4g87:0w2 wsb xifjuptthe top of a platform wit 7zfsu485gb j+z2 z mt2wsilp;x:0wb gh a 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 constant is 9,bp-caziya2; 3gv 7sk 50N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30ybp; ia7s2v-3kacg ,z-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown in Fig. 6z ij222/ikmlmc7 vx r w/rj*3n–39. If the block is to remain on the track, even at the top omimwriz3jr*2v x7 /jk 2n/2lcf the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is ,:: s mib;ecqv63)9 s xat;ahu 8 gsrmy4i3dxtattached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is gii x:83 r9a,:6mst3essmxgbuh ;;a)div t 4yq cven an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She ik*x(ejdpx 3f2y ,z)mw s 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 Hooke’s law app3xxe kp,)dfj2 mwz(y* lies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragg3 x7x yno.0rhxed up to point 1 where it is released from .3yrx0 xxn7ohrest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thr;c)n(qa/ u oerown 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 placed ad9( 39g xbfhu1izmp0.js nw1k0ay5 fjt the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculataky95 bidfzw1 0jgsu9.mh(1pxj0f3 ne 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 cyclehye wb 4duiil0/) rzp )fd0 26e2zi;fb 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, eal / k: yra5rib*xpnr* jxjn6 u)o;32zsch of mass 7650 kg and traveling 95km/h in opposite directions k 6 j*xr;pbn5lujz:si)3n *ay/2orrx, collide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the botl*f.9 deo i/aju/2 vpftom with a speed of 2.2m/s How much thermal energy due to friction was generated i* o/.dp/jale92iu vffn this process?    J

  A ski starts from rest and sl6 isgyt: x)b)gides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m abov j:pg+(cje2g oe 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 heigh+.i pa(wh ,+hlyvta+ ut of 1.5 mw.uvi+h+ +l, yh at(pa.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a cons zo6ib:yfmue n:y*r:a hhpm ., -4cpp0tant horizontal force of 350 N. For the first m:ppr*yh :-n hzoaic.04u,:e6y mp bf15 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 pan zqvryf: or/.r4 5e8lsses point 1 with a speed of If the average force of frictiof5 8:q r4/.rvrnzyleon 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 stead0gm.1u q*pqma8w +o gwk57y jwy 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 sprixlrd16 ;x, eq55 vq/e wc;t4q jmw/tnqng (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What mjcx5;x,q q5 /6n1ed t weq /q;4rwvltis the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light h;)p)t(; iyc pr28mh(lsqme b yorizontal spring, Fig. 6–40. The block can slide a;ty(;pprq 8m(im )ys eb )2hcllong a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shu3 ;e13u.t ,wppd btqznttle used a “glider” (mass of 980 kg including wz1qd 3 uet,.3ppt b;npilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W mox9*0l:a h.a8sjciu 2 pktlm.v6odnr. tor to lift a 315-kg piano to a sixth-story window 16.08a.6 mlut 2v.:o* sij9xd0 lknarhp.c m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must rvi 2-f6fz9rm be the averageff r6r9vimz2 - force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from resn qh3-fp( 3sq.4uankdt qk0 0*tgwa w:t to 95km/h in 7.4 s. What is the average power delivered byd *p.tq(3 n w4wkk0f 0ahq3gn:u- taqs the engine?$\approx$    hp

  (a) Show that one British horsepvmr1 4 qimw05si7k4pyower$ \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 dj72 wueks6v) expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in drkuvg(u 2o:)about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75k:gko u2(v r)dum/h.    hp

  How much work can a 3.0-hp dx76 .usaxkco6tgs;4 motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelekpaj;2rqy0k s oy nt61,ny3,eo w7,pr rates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 t1, 0jn23r s,yew ak qonp;yk7,6pyros, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What ;jiij-vb/o6 ir d9 6axoutput rating (watts) should tho-rxja vbj9 ;/6ii6die pump motor have?    W

  During a workout, the football players at State, qq -gj 2q7aoewc8hyx,rg 29io23b gw U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined atiq, -o,ej yrqg9qw72hgw3a 8c o22bgx 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 cyclist2knp2jip 24hs++ksqo btfb p,s 7e;n0 climb 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 maxim.uvw cyfq.gp 2id+7k( um power output of 120 hp. How steep a hill can it climb at a constan..cup gwk +7f2d(yiv qt speed 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 310-kg box alwu1x*weu3g f 3ong a level floor atwwg3u ufx3 1e* a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a +as-*ql k cos37.0 $^{\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) busddul* b* sipob,f602 mpers” 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 th ib fbpo6s, *l0dsu2d*at point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the re9rxl+h.yi .w mn6jwic v3(abp)*+hq l maining fouw( c.v9jmw6 xlhiry 3ip l.b+aqh)+*nr 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 start? $\approx$    J

  A film of Jesse Owens’s fam lo69qrxle:,,r uh5sy wa p*j/ nman)lou3:s-ous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launcs w-)x nlm qrjeyl6,o:p /u hn*3o,:l5as9r uah 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 si sf2l :ggo p7 8o*2yj4n3uuwsliding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the u3g*2i4gs2 : l7ofusn8o jwypvery top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without x( 5ag1 ;t cmk36btwuzhis parachute opening. He landed in a snowbank, creating a x (t ;3uz6 bamctwg5k1crater 1.1 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 end is fixed (Fi5 fn en0chza,5w1glg7g.ce175fn5gg0 ,zla nhw 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made in62s y42 krlps2o+iqhb 5.0 h starting at an elevation of 2 rqloyhbs26p +4ks2i2300 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 92zyt;j mo1 s,p/s)) ylz-;rmit: dq rk70-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 k 3pgs q2u togibbxba u3a)m58/ks/2+people per hour. If the av2 upqibau /x3sk ats5/)o+ mkbb2g3g8erage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertny 2(z+ b txtmzibk/gt(;ft76 ically 81 m before striking the tur ibtfb2zx+7t(ky( /m6z ;tg ntbine 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 axmym/lq 2: p1y 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 looyxlq/ m2m yp:1p is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly intm; gn pw;7vomd mxx9ct8 * 42adpy61fxo work, how high could an 82-kg man climb a ladder if he were fueled by one mn 1xofx 9ap 48w7d2xmy m6*v;ctgp; dbar (=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 4** ogs1k* tprq5.0$^{\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 comph.4za0xfy - vbresses 0.60 mm, and it tells you your weight is 710 N. Now if you jumf-.x04havy z bp 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 rope, acj /s/lcqd)) vnd swings out over a lake (Fig. 6–45). He releases the rope whe l/dqjcs)/)vc n 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 yj c*je2dscw-: ,sco; 9.0 s. What minimum power output was used to accomplish this feat?- oej: jdc;s2 c*ysc,w    W

  Some electric-power companies use water to storeuli, 99m0odtb energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the en9d0u,l9i mto bergy 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 zh,)x, xy wa/nhalf. What is the spring stiffness constant for each of the two resulting springshywz)xan/x ,, ?   k

  A 6.0-kg block is pushed 8orm+*)( nsqq / pz8wup.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 z2o,rz age5 w(s, how long will it take to accelerate from 55km/h z ew2o, 5(rgazto 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patin )/hqn 0acp33on l.qgent walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 7p 03oc/gnn . 3nlqq)ha5-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 xc3g6)yf izhrlax8y)((2 kyb a distance of 500 m, what w il82hyyxx)r(y)6a zk (f b3cgas 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;-ol,m use y4a from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, e-a;4y, mlo uswhat is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s