In what ways is the word “work” as used in everyday langua,n du.ao q+u-bge the same as that defined in physics? In whatadon.uqbu,+- ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Expw 4yng* (,r3 tw-nfenwlain.

Can the normal force on an object evexunwsg4 jzs 0o-8x1l+ 3 mxthwk7+sd8r do work? Explain.

A woman swimming upstream is not ;k.hk lbqbwia puf+o k(6-3f9r2w+qhmoving with respect to the shore. Is she doing any work? If owk3hbu+ 2 qb(fr+; fk- lkwha 6iq.9pshe stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forj/bjyn(cr 3dfq/uxw+;v3 /azb;em 7 oces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out ca(/zjmy/ bv + dn3efx /7wb;uq3orj ;from under them.]

Why is it tiring to push hard against a solid walli2uqx8b jg r9w*iwvci549 lr rl(*ae) even though you are doing no work?a4wliqclix5 iu(9e)r bv*r2g * j r9w8

You have two springs tha2 co,abkoe*p 7t are identical except that spring l is stiffer than spring 2 * aepko2,o7bc $(k_1>k_2).$ 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 +d99aqxk :ffz7 --sbscd fg :sfree to slide on a frictionless surface (Fig.6-30). The block stafg 799+dfd --fs:b :skczaxqs rts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change bwsiw 0iru( 4qz4; 15qd wwn:lwhen you jump aswuwwqq r (isw; 4bldn5z:041i high as you can?

In Fig. 6–31, water balloons agn2* -o--ecby ty ww9kre tossed from the roof of a building, all with the sa* tw 2ywk-g-9cyoebn -me speed but 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 above. qt,3supyu,l+1 zaak its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launchtayk,up 1z.+s,qa3 lu 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. Ifwzqoe0xp 37 u tw;:i-gy4qhd0 you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law0i edowq q7 pwyt;z43gh:ux0 - of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fids3r5,9 n sg:7lr-ehzplgfm77 k-znvju 0a(t g. 6–33). The instructor pulls the ball back and stands against the wall with the ball against huvd0-7g,s:fe7 3nr7rpjl (gk m z5- ztsa9hlnis nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational po/ ft 4)bgbdbq/tential energy when water at the top of a waterfall f4bdbt /fb)/ qgalls to the pool below?

Describe the energy transformations when a child hops around on a pogo j r o:wa qkb352)sjml;stick.

Describe the energy transformations that take place when atep vd ++/c.fv+rz /ck skier starts skiing down a hill, but+/e vfpct +dr/ ck+.vz after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of /pjit / p8usqcj8l x.0a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) p c//8lquj jt i.spx80it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path 2qq cuz-z) wzozb644 drather than stepping on top and jumping down on the o 4qzc4 -z6oq)2bz wdzuther side. Explain.

Two identical arrows, one with twice the54emh rkl)p2 l 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 slower arrow? Expl 5e l2l)hrm4kpain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) igzlegk ,edzgz jko.0n8( ; (6aiw(ce6enoring friction, coe6aei,glkkn0 ( 6z 8egd.(z (;wezjand (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is d0xk5i+22 akp ni -jpucropped, can it rebound to a height greater than its originaj px+k2ic5 a-iknp02 ul height? Explain.

Suppose you lift a suit 1b,s.oo:yahs *yzy-dcase from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it y bh * os-:1o,dayzy.stakes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neer9k5oc2 j3nb (z/ ul8eh)cvtfded rather than the work.

Why is it easier to climb a mountain via a z br6m)y 7 ap7juswt6k8lu7s4m igzag trail than to climb straight uprw7bu6tmm 6ky)a8 jl7s 7up4s?

Recall from Chapter 4, Example 4– zjg5inzma(eu oy5-p8a 8 d0y+14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). B5zae-nzy5p0iu 8 y +agj(8omd ut 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 gravitati.gfaz vk9;y1-die7;kz n:y xfonal force when a 265-kg pile driver falls 2.8ekgd1.v y:kyfaxiz7- 9n ;;fz 0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hig gc)bgq/: 4k8op,uzt ih. How much work is re ):g/zkbuq4pot i8,gcquired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at c *2qf,an q/p0wnw0 rrjonstant speed (a) 4.0 m along the floor against a fri0qwq2p na/ j*rr,nfw 0ction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-5qwog5 d l8-ttkg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of fri85ottgl dw-5qction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floorrn gl 5g -ihng* f7c7nrqi,:dz4- vzy1)l:uas at a rate of for 7.0 s. Find the net work done on the box. q 7nygr5d-glr*fz-svi1ah):i4,7 l z nu:cng   J

  Eight books, each 4.3 cm thick witwt*4 ,aub02dfs b 1tv lxp7sm-re 2p1xh mass 1.7 kg, lie flat on a table. How much work f atw,t0bxps2du4-p lre 1sb1vm*2 7 xis required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 cayj wba)qb1i+8 t5 o8l8jke0-mi )jcx on be used to liff objects we might not otherwise bj +c1xtyab m-)i8o8bek8lwj ioj5 )q0e able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and b7m* ;ncv,p2 ;sikm zais kept from accelerating by a man who is pushing back on it parallel to the incline;c,kp nb*mi7z am;vs2 (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 require4e t4 zaaa8s-j/l 7ty(txqdt/;meg 5xd to give a helicopter of mass M an acceleration of 0.10 g upwar4 /x(ttg t s4e-y ;7lxa8ae5dmazjt/qd.    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 distannve+o)f q /pwenz004 sce axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the nymd f/*quhuz.f0zx f e27c r-5a++ qmx axis, varies as shown in Fig. 6–37. Determiq+nhqrfxmf-euumz/+ zy. 20fa75d * cne the 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 particle acts in the8j+x w 9 ii0duspyvii(8 ,,efx $+x$ 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-vvr+ et drk4- 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 facxe.9ez -/d3nyg rxj gnu4 y:*ptor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requ+3;ebandcq- w ired to 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-kgcarvkqsvj 22b:s s)tcs 8-zycr(4 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 forcegz w. w4:e3hrs of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves thrh4s:w 3.gzwe e bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 2 )u6n* ad3 a;w/nt,ln,w *t+uaabyfer5 cm when the ball is caught. What was the average force exer,a +lwn6a ab3/ tnd*;rf ey,)*wauut nted by the ball on the glove?    N

If the speed of a car is increased by 50%, n,vdh roar+0x8n( 8 j/o0xnyf by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction tno 0+rd/fr80ao yvnj8(,xhxn ime.

  At an accident scene on a level road, investigators measure a car’s skid mark lgy,el) s645bqt+,crx2 meml to be 88 m long. The accident occurred on a rainy day, and teqg,6+ xcl t byle4r)25smm,lhe coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (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 tm8:abt5c ; hdc9xpolb3 ap)*; qs vmb,he plate, it m:dcmq9 pv laobpbsmt *h 5xb)c,;3a;8 ay have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.0 J c+ojbtn60j2in g o8+kl unh;l,z5kh* of work 8o,+;k6ngku2ih *nnlchjl+0zotb j5on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sqw:*iws q7s)vwp:e7s ingle cable. Determinew*sq vwq :ips 7):7wse
(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 consqh w ocu36;sx7tant, k, of 440N/m How much must this spring be stretched to store 25 J of6h;oc u7q xws3 potential energy?    m

  A 7.0-kg monkey swings from one branch to aup51lvi2* do jnother 1.2 m higher. What is the change in potential eniu opd15 l*jv2ergy?    J

  By how much does the gravitational ubc+4dbd* vlk5tzd2x,y b9iy y0.s+e( d(g lbpotential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m5izy,yd 9*2ds.ld bkcbb(tdbgev (x +4 y +u0l during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v )ml5kyl; a ou*= 65 km/h when it strikes a horizontal coiled spring and is brought to rest iu5l* )kmo;lya n 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 2sioz lg)++ x sif3++s;s6jfd ut( q;ia.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book r qs;3xiu+z(f)is6a++sdgj t;fso+ li elative 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 clv h-e yz3yz 0nl7eux4(imbs to the top of a 3300-m exenvy0l-h3 y7zz4 (upeak.
(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 rulek.1rigef7 c3npdzqz.r ( 0t5 fr. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring(tzi0 nr5 f dk.gp1f q.7ze3cr, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spenqyr* ca9 rzlp(e5 tr4 j+9n5red (5.3m/s) and grabs a vine hanging vertically from a tall tre5qr (r* rjce+rlzn atnyp5499 e 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 dow5wjmh .xrs/hw/6 t l u;;cq(oen 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 afj :tstx t9h8* cr4dr jej4c a45;d)qr 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 transgz,ovas kl45 3formed into gravitational potential energy withoazlvos4 ,5gk 3ut the aid of 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 up)*u 2anjrc2 isward from the top of a platform with a speed of 5.0c uans*jr)2 2i 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 i,v(g;yv ma.na nlg;2 fs 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it gi(nn gg;;vl2 m.ay,vafve 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 sh:(ij bmr2h)ve own in Fig. 6–39. If the block is to remain on teih (mrj 2vb):he track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness constant i3d zp91tcamd; i. i8ak), Fig. 6–40. The block is g3 iap 9 ida1imcdz;t8.iven 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 bridgk.xa6as h0h4qc8 sp1we. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assum1aapx4q.sskhwh68c 0 ing 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 j: wb(*zjta.lmbo6-sis dragged up to point 1 where it is released from rest. Assuming no fricti la*m (bbtojw6-.:sjzon, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle ofvv oa,vyjd9q d2swu 4nv+u.*/ 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an el/d+d)r)c8xf o nrklcd, 2gc/ levator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an accel)/l/crckd,o8 cf)dld2+n x greration 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 to1jb ,kjhbh y+:zc c xvv0()v;h cycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite n,sz7zj01nrp* ektd i)3s 5hh directions, collide hez r5spnzd)*it ,hjsnhek71 3 0ad-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 slidr: 3o y;wa9p r,/n6cnlqv: gfce 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due nr;qg/:y nr cvf3 ap: cl,o69wto friction was generated in this process?    J

  A ski starts from rest and slides down a m2n3kpog;r.e oi,d:k 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 1 g86;pt a 3glb2gjrht.:1tev uwj0qjiw5ks(:3.0 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 hqu 8v d+uxu*6keight of 1.5 md6 uuq8ux+v *k.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, .h3n jmltqf .s .i9j**hj6btkc6 :zpz 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 coefficient of friction is 0.30. What is the fin t 9 zbijtsfpj..6lhc j3n.kzq:h6m**al speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of zyk t3oax3.z ) If the average force of friction is equal oxyakt3)z3z .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 ste v tejofoi80.)ady 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 ven, 15hd l/0 hsopvq6aory light horizontal spring (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.0h1oovdsap /n56q lh, What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontak w7 s0/wadyfv n+5pz.l spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch 0pask/ 5f.7wdzw yvn+on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 98m+(s on,3mst m0 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) s+ mmn,m(so 3tWhat 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 m ;xgj(ow5)sbp5qmt * sixth-story window 16.0 m abotbm5jws )oxq(p ;5*gmve?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be th 8qgxa3 r8v63j/9 wu ruyrt+f9zvua35gv c6rbe average force exerted on the car due to friction anj/ru u5q 39w8gta6gbr vv6r c3av3 + zux9r8fyd air resistance?    N

  A 1400-kg sports car accelerates from re(x d2h4 +mchbfst to 95km/h in 7.4 s. What is the average power delivered by the ed2h x +4bfmc(hngine?$\approx$    hp

  (a) Show that one British hors62oh vgzp*vuk7 5s .qwo );nmjepower$ \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 exp+5 n-ox xqczwnk4q+)tmh*x1qressed 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 9w )pi g0pbev e-4oe3j to 65km/h in 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 c 390-v pgp)e4jbe owieonstant 75km/h.    hp

  How much work can a 3.0-hp movxi6euc;h) yg nu) .9ctor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shozeqoeb-y a3.q2m oy6 3xtru :)t from rest to 14m/s If this motion takes 1.5 s, what average power was dev-z :3)36teoyrqayxqumo. 2b e eloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 38*ulgjnm ms;1p q8ys3.60 m. What output rating (watts) should the pump *m31 jyq8;su s lnp8gmmotor have?    W

  During a workout, the football players 4p)+ah.jrct3ekld2uqifc;w z. p5,e at State U. ran up the stadium stairs in 66f khr +).e4a dt.;c,ejc5uip2qpl3zw s. The stairs are 140 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 cyclistwr fi dh3n9a j bnbl, yy):7kot4l9.7i 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 maximum power output of 1q4-iyn5s0si7s y 4 iaq20 hp. How steep a hill can it climb at a constant speed of 75km/h if the fricti qqsi-i0n47ys sy 5ia4onal forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drh qxvd7 5t(s;sg:jx 2wag a 310-kg box along a level floor at a speedx: djvsq257x;(h gtsw of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downntm.4n +uz tpny0wu c:/w1n--i,jtf y 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 have built4/a. ept8 zf ebot7v t ma:q3t(9yi3qe “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 a 4(e e:iby3q7. mqfet3a8azvpto/9 ttn 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 a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the firsimk(os 2zyv3 n(* /o-aghyl7ht shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height o23shvky-l ao ozn(g yh/7m*i(f 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 hx e5o7b;,jb*k gy)c re8fk6c’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that hi5 6e8j kfxo,b) ch7;erykcgb *s 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 at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped tr+pw bs6j+h4vxi48nc tack shown in Fig. 6–39 is to remain on hp +c +w i4x64vbtsnj8the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircrafty +mfez/99 wlasrl/7v without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate e szlf9 y9m+/r7wa/vl
(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 otherlx 6 0ra9vzws,*)mkkk end is fixed (Fig. akl6) w9rxv0*, smkzk6–43).
(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 9kvdbaa-7ep : climb is made in 5.0 h starting at an ele9k7-ev b :aadpvation 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 brend(*d*g;oyx znv -,hcaks when a 920-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 areapu9*nwag(ayra; )1 f 1hzgo ,f in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (verticnzhgupwyr9f1* faga oa;1(,) ally) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticallyh45 kh qzd,gmeklao2; e5.- zs 81 m before striking the turbine k m ga,25e zo lq-d;ekhs.hz45blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular:0t fk/4j8 g( )kqhsoujrfj4 v vertical loop (Fig. 6–44), the difference in your apparent weight at the top of th)g/r(jsvj 80:f tq k ujf4hk4oe 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 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 convyvlu )3vy, r5mert a candy bar directly into work, how high could an 82-kg man climb a m5) yrv yv3u,lladder 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+9 )c kyefieknm)lyy8 1-ps 7j angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses 0dqop9u;bof,wj0j1dy 5 */af acog;o9.60 mm, and it tells you your weight is 710 N. Now if you jumpyu;/awo9doa;q95jgf cf*od 01oj,b p 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, and swings out over a lake (+.u7 xnx/ jhmdFig. 6–45). 7xu/xm. + ndhjHe releases 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 5.c4qisr2k bvd( dmj.s. What crqdj2k.dibv(4m5 .s minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is me+ (xjsnwe,d ,bxc:xm; 2 t7m3r zp3apumped by reversible turbine pumps from a low to a high reservoiwn 2jepzme;r:xbxt 7m,dma3 s +,( x3cr. 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 conkf)(f7 ltfbb +qu5a 4kstant k is cut in half. What is the spring stiffness constant for each of the two resultingkq k 7+ubt5lfb(4 )ffa springs?   k

  A 6.0-kg block is pushed 8.0 m up a : f7px f6i* 5voecd37o ygvedvd0 ++mmrough 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 j u-s0 9seru3haccelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h A esuuj3 r-9hs0ssume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient wdejr6;ww n m((alks on an incline6w wnm(ej;d( rd treadmill (Fig. 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 upward a distanca nubr 4sk j1,ijh) e-;y3i; fbz+vcm-e of 500 m, what was its velocity when ia4s c3j ;jy1-;+vmke ihf)-b,rz bun 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 (j cu ioj 703b/jr*z8ryr4 jwy95kg/s (a) If this water wheel is set up to provide eleczio ywru7jjr b4(j3 /*0jc8yrtricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s