In what ways is the word “work” as used in everyday language the samwu5tf :wo88 ije as that defined in physics? In what wayutf 5ji:wwo8 8s is it different? Give examples of both.

Can a centripetal force ever do work on an object?d (/i-1lztt a qddg5t( Explain.

Can the normal force xpp 9c*ik l40lon an object ever do work? Explain.

A woman swimming upsthdqa 18yz7.m ij1l ngh/s qx0-ream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats,/g q0-zmdi18jxa7s.ql h h1ny is work done on her?

Is the work done by kinetic friction forces*) s.ug omv/zo4vmkc6 always negative? [Hint: Consider what happens to the vmm.4z ocs)6 g/k vuo*dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall eve1xdd:px;2q d en though you are doing no worke;qpxdd:1x 2d?

You have two springs that are identical except that spring l i .n1 d alltxoe-r()(rgs stiffer than spring 2 1o ed)r-lnxar.tlg(( $(k_1>k_2).$ 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 blocik .i*mqt4c e- ppuh:/k 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 travee -. h:uq*4pctp imk/iled 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 potentialrj4z7:gq reqt r 8/y.z energy change when y8 .r4t rgqjzy/rqze7 :ou jump as high as you can?

In Fig. 6–31, water balloons are tosse0)i 2ui 6gbziyd from the roof of a building, all with the same speed but with different launch angl by 2ui0i6ig)zes. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched :2j7tl zi:kq,9 2e h9bux*mvmtud8rw from a point that is a height h above 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 launcht:zkbdiumwjh m, 79xq*t29 vlr: e82u it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress tht-yc9 odz2fft-z k7e ;y5ia1ke spring by pressing down with your hand and then release it, can the spring leave the5i -tcy kktfa;9fy2o1e 7 -dzz table? Explain, using the law of conservation of energy.

A bowling ball is hung )ta9o8s.(aa su oka1yfrom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose.ya a(as)1 .t9u s8akoo To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at tmhm.+p 1xf( l0v8eqtghe top of a waterfall falls to tm81( etqv x.m+plghf0he pool below?

Describe the energy trang;w w lsoa)8g7sformations when a child hops around on a pogo stick.

Describe the energy transformations that take place whenx4r/+y m u) mpyggn+2l2mfp q+uvg: 6m a skier starts skiing down a hill, but after a time is brof2 lg +mmp ny)r:qp6mgvy 4+/ x2gumu+ught to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest attms8b*.womey no upji6/:u v2ty 6 /p7 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)m7 i/8.w: tvn/sbopet*p2y66 mou jyu there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than stepp dxjub /) ez1n;sn3va5ing on top and jumping down on the othe53/;)s1neunja d bx zvr side. Explain.

Two identical arrows, one with twice the speed of the other, are fired inkbm7no0 3 lj1oesk in sav x64p90s-v:to a bale of hay. Assuminso6-lm9:vo s3n ven47b 0p1 ijxskka0 g the hay exerts 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 pendulum in terms of energy, (a) 5 -osjiphz x+ylgb n(8td8me:zo-8;j ignoring friction, and (b) taking friction into account. Explain why a grandfather cloc8ob-jd(ho5;s+8gn xt8 :mlpz y-zjie k has to be wound up.

When a “superball” is dropped, can it rebound to a height greater tf9 be,tej v df:5v84xphan its original heightv xv8ffje4:d 9e5btp,? Explain.

Suppose you lift a suitcase from the floor to a table. The work tqa.j 7a1wv6 yfipl4 1you 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, and4f11qv. i7pjlta y w6a (d) the weight of the suitcase?

Repeat Question 22 for the power needed raxvi ox(),j, xe91 x o7zbn-xgather than the work.

Why is it easier to climb a mountaink(pajiyaugbw0 6oq / * m*-m4q via a zigzag trail than to climb straight up?4 obm *(jp/maqau0*6kwgi yq -

Recall from Chapter 4, Example 4–14, that you can use a pulley and rop9j :-btn/n. jubx zf4yes to decrease the force needed toxuy 4n/:.z bfjt nj9b- 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 don pj 1ha9w*;,rg0epuu fe by the gravitational force when a 265-kg pile driver falls 2.*p;per0 fa ,u9u h1gwj80 m?    J

  A 65.0-kg firefighter c)c s cua1,8ctgmf7++9uameis w)m1u climbs a flight of stairs 20.0 m high. How much work is requireds1cm 1wa+uic9mu, ua 8csef c)m +)t7g?    J

  A 1300-N crate rests on the floor. How much work is required to move it at co9/zsq.npl-wfu j iwd:ela)/3nstant speed (a) 4.0 m along the floor against a frfwal)szl/u depqni -/ jw39 :.iction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a hf( g z oueabwj;)tsjfo;;8t:m c9 c79160-kg crate 10.3 m across amubjcet:)gf wz9j;;oosch79fat (8; 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 mf u3hicqc9885vvsdrw4hu .0 for 7.0 s. Find the net work done on tmwsh 4.0u95 f v8vc8iqcdru3hhe box.   J

  Eight books, each 4.3 cm thick wxc:x *r2ie. 6ne3t4swm lrjr,ith mass 1.7 kg, lie flat on a table. How much work is required to stecl6x * smtr,rre:x2.w in3j4ack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can blgm /yb9p4 8 d1qb(dys kji)x9e used to liff objects we might not otherwise be able to liff. Show that the ratio of output fo smy94iqkdx l/j8b)bpg (d 9y1rce, $F_{\mathrm{O}}$, 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° inc 7g, caq0(py ysgx 8wnvc7/5pfline and is kept from accelerating by a man cgncs7 qx0f(wa v/5p8 yy p7,gwho 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 required to give a helicopter ofd:m j4getd qk1.r4ht 4 mass M an acceleration of 0.10 t4.rdh4e41 qkmtgdj: 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 t2 gj7wj(kem1nx 0cqnhwm f *7:he distance 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/)btzlbt sa 7y13fsl4 s q3)nt along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the objectalts/n)b4 s3s7t1bz) ft3yql (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 acqcfbleh1 oa* u 8,;3flts 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 jc:x-+ ulj,/hen 1g lf*ppys: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 whd+zrgf(ii ljv/r- (na(6tly ,at factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requirv m e)8/ly;irbed 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 )n dt3w(caf -buy4ke9 /tx3rdto stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averag,qg zkj:)mq1 ze force of 110 N on the arrow over a distzgjm :qz1k) ,qance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelingqra3s2um.k o uut60 h/ 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What6s.k0hou/ qua2 murt3 was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%,hb3s s/tn+r b4yr+ y6b by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reb btr/6sh+y3 r sbyn4+action time.

  At an accident scene on a level nuxs8h9fh64u road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why doex h489u6hnsfus the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg ism0zqe9-)tmw b pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resiszm tq9wm) 0-ebtance 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 stradnib2:++u ygj ight up by someone who does 80.0 J of work on itg+: 2+jbunydi ? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 mx9e7; raubsu(z+pfht0,x7 j uc t14zu vertically with an acceleration by a single cable. Determineb(x rzts+x epjf,4uuz709tuu1a c 7; h
(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 muuryqd*8/0.dg4lnut3pkq y j 2ch must this spring bqgdt2 ky r lpunu*0d43 8yjq./e stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hw*u8(yf abfl1dj:e q9 igher. What is the chanf(1e9lfu :w8 dqjby* age in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vault(s2 sy.1 nnzq7gqet q5kj))koer change if his center of ma 12jk 5yk .nesgqqzo7)ns(t)q ss rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kwm.qkyxk0x8- mm mc(3 m/h when it strikes a h .kx w 3cx(8mm-myqkm0orizontal 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 lifts a 2.wgpv v*djyvo :s(11h::bty :y 10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy o(1yhj :*d:vgwpv: vy:oy b1stf the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600lt . m,1 bd83x y4:,h1dni8wmjjvkd ux m and climbs to the top of a 3300-mwxij l 1n8v:h13d,,dm j. yx48tmkubd 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 hag a)is8(t6 qcgp4zxm- ngs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached togqs8 a( m)zi -4tcxg6p 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 speed (5.3m/s) and grabs a vil l:0 v8jivpuv3wi hh;rz16 )kne hangingi63 rwhvu vi0j vpk81; ll)zh: vertically from a tall tree 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 downr(mpyw +388o4xqvp ur a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a friq81b2p wsbk:o ctionless 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 kineticfbw +7oj. wbz. energy is transformed into gravitational potential energy withou7fj + wbz.obw.t 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 verticb eo7sc(m al4+ally upward from the top of a platform with a sp4 7blesc(m+aoeed 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 sprin g(jm:a cq 4e8na.y(mxg stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwardnyq(m : .ej48x acga(m 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 trac*n9b: eqlpzt t;i*9*t e x,aafk shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum heiga*q *t;ifl:be ,ap9 nte*tz 9xht h must it be released?    r

A block of mass m is attached to the env udq) w(kjf7;d of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacemen7 uqdk; wfvj()t $x_0$ 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 bungnc:1e)jop ac4zayi* 3 8o m-peee 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 appli- n*:8ijeo3opya a)4cm 1epc zes. $\approx$    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 poin.x8k /qlne:vj t 1 where it is released from 8qjv.eknx /l: rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at axptndk)-+dh3swdcp 8z 8a:q . x9bp*zn angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottoe5 o3mmsfy-mu; z+xz i,wn2o (m of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total massm3sn yio5oemx,+mwz z2;(u - f of the elevator and passengers.

  A cyclist intends to cycle up a 7azo;o: (a/qw9 ilqm/e u-cxd+ .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, e.q*ecftn7t-r.s0b avach of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this q.nfta7cbvt * -er0s. collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bo*h8 gxgq0fl6 g- ui3alttom with a speed of 2.2m/s How much thermal energy due to friction was generated ig*g qghf-8 li0x3 a6uln this process?    J

  A ski starts from res ud(jt c7:(xbrt and slides 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 acig5z 24vhg3qrmdo(enr68tr id* q. + tree 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 ugy,mx ya h90sz),nnu;qw2w* 1.5 m. yn,9 y qxas;u20u m)gwz n,w*h
(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 from37acqc ) gzbu6 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 coefficient of friction is 0.30. What is the final speed of the crate? g ucb)z 6q73ac   m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed vs0c p8 9pdk3: unc+cz nuq;h2of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled9svnp u+8 c:z 2uc30pcqnd ;kh is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a 5lutu+v hbar 8;z;/m/mosjq/ steady 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 attj )yp3rk/ bq2uached to a very 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. What is the coefficiyb r)/u3 pj2kqent of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizonta53ke .meb nu: rtbssrv97z0 ,dl 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 rbn50t3u7kbde :v,z. esm9srspring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights fshzet)qj/ q;w 96an t4or the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in ts)jtzqw/46aeh ;q tn9he 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 l mydi r0 evp3.e*m(al8ift a 315-kg piano to a sixth-story window 16.0 r*diaem3e80(.yp vlm m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must 6,dxvm i5w*yvhq+ 7eb be the average force exerted on the hdie+6v ,mxw vbq*75ycar due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is bj0y63 4 cdpshhxfr ( 2ktwi2*the average power delivered bykw i*3 dcbrypt hsf2j(406h2x the engine?$\approx$    hp

  (a) Show that one British hoy-1 4pc nukuqn t +q7zi+.*kiorsepower$ \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 expreg3vhz,jin8rfciidk 73v.z t ,uwwm ):r2d4;o ssed 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 1114 q+ta/dppc z50-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what powe4cz1qpt+/pd a r (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*lx m1ye,om8 xacf-,p in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg sh t egh( won.q,ui s1vjla1y016ot from rest to 14m/s If this motion takes 1..nuw,t1l vqao0(1jge s1 yih65 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minuteku7./xk9l .v th2.inf nwvqo4 through a height of 3.60 m. What output rating (watts) should th/k 2utx79klf v4onhn.i. qw. ve pump motor have?    W

  During a workout, the football players at State U. ran up tpsfag6q 0lz3 sh19ev1- ch ul+he stadium stairs in 66 s. The stairs are 140 m long andshu196 -qsf10 ehgc+v apl3z l 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 cycli5ykllq96/t9a i5y7rs y-v lyf st 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 120 hpn4g l:wqjtq1j,vdel 8iu q : rb.g*p9(. How steep a hill can it climb at a constant sgqu.p4 e, ::q1*d8(i lgq vjlw b9tjnrpeed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must ay6qqr:+ r0 c8wr d rfn*53s(wo caw7to motor have to be able to drag a 310-kg box along a level floor at a sp7rw frr6(rdq :a0n5q 3y cwt8*cow+so eed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow ibv(g mx4l9,80lsi qb/hzpl9n 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 carsfz,q;, g ibc hqgy+:4q have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8y+q4gcfh :z;qq,g bi ,km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 1i+aynd1jf3 e ys;o+-p0.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. I+;i+f-odjyp1 aey 3s nf 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 famous long jump (Fig. 6–42) in t5b3 d iohj: y6h8az if5- j)dj2j7tkmehe 1936 Olympics shows that his center of mass rose 1.1 5d:khjfo853-2i jj 7d6yet jh mzbai)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 without9xemi0d+c z:k (7lnl mv+,aws friction along the looped track shown in Fig. 6–39 il9de0,:a7in + vsmxw(l+mzck s to remain on the 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 afcyv 8(veoi i+9kj0bt auo+, :w iq.6sn aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived withw0bqvc6a:ji8ti vo.f 9ieuko s( , y++ 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 h*r l bs;r9 +*cmpozug8nq*tca3j-wb3 orizontal cord of length L whose other end is fixed (Fig.**bag c8qoblj t3m; zru3pw-n*cr+ s9 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 o0jzr9euk 7v1 fqt e:emb t28o1f a 3700-m-high mountain. The climb is made in z1218bktq0 veo 9ert7efjm:u 5.0 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 29k61szwjl m5pescl/ 88 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 canu3qe pw /u6*qj move 47,000 people per hour. If the averagejeq/6 upqu3 *w 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/s ;oz tnbtcq,v j.vv5(hyw ++ falls vertically 81 m before striking the turbine blades. Cn t5ov,+./wty v(vbc +z;qshjalculate
(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 vertical loop (Fig. 6m pwtug;lfqye (+1.pe-toh1:–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular ufg(qewpl; +. m1pty1eo: th-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 convert a candy bar diredyb*p il,)x8/ovn .uvctly into work, how high could an 82-kg man climb a l )/x8ovv,pylb*d .inuadder 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 wdwx cry0xy2:m 688 vz45.0$^{\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 insideeqp ye j79z, g3kn+djnkc kmp.4-(kz) the scale compresses 0.60 mm, and it tells you your weight is 7ypeqp+dk4.j ezkg,7n( kkm)zj n -93c10 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lak8 bf /7pir7uv-d f-eide (Fig. 6–45). He releases the rope when his velocf8 / i7r upfedd--ivb7ity 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 climo-+chqatn( t+bs a vertical distance of 5.0 m in 9.0 s. What minico(ah q tt-n++mum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by8i8o +2gbawzt reversible turbine pumps from a low to t+8iwzag 28oba high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. W hzi6wiz*( zo7hat is the spring stiffness constant7z(wz 6 iohi*z for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 dh/ vgnuk1tq1u,sw8 .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 s, how long will mxj e ;fbg33j2it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional lossej32em; 3 fbxgjs.    s

  In a common test for cardiac function (the “hqz 2bq8 5it1nstress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate2z btniq5q8h1 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 upward8p 5n8 5z2sdd8nl8/g jh yhj ugmc/;try/s(gr a distance of 500 m, what was its velocity when it left the volc8djm 2/;5g gc5hysry/ /ntz(8 ju dlpg8s8hr nano? $\approx$    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 r8qt *;c tt6m5 i yci:q)1njyukate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum pow:j8i)y;m5ikyt6q *1tqt u cnc er output?    W
(b) What is the speed of the water as it hits the wheel?    m/s