In what ways is the word “work” as used qut qecm8/cip(20w .bqy1b* ain everyday language the same as that defined in physics? In what ways is it differu8bap/m2w 1.( qc*i0bectq qyent? Give examples of both.

Can a centripetal force ever doj r lt4t)j7:fn/0iu/+ egkmqo work on an object? Explain.

Can the normal force on an object ever do work? Ep egrplyfum89;f5 .:o-c od q1xplain.

A woman swimming upstream is not moving with rethui w9( arz 9hi.e4a,spect to the shore. Is she doing any work? If sr(ii,.ewa 9thza u 49hhe stops swimming and merely floats, is work done on her?

Is the work done by kinetalugr3y,3;* k wx xq*wic friction forces always negative? [Hint: Consider what happens to th3 ulrk;w*xax, wqg* y3e dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall ey ol7;y s9(:ozywqrgg )bg5s+swo 8x8ven though you are doing no w; g g9w87( +qoszyswl)yo ry5 os8gxb:ork?

You have two springs that are identical except that spring l is stiffer than r,k-v r30 xfm7a )ssdqsprsmr 370fq-vr d)xs k,aing 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 horizon* z.m z3z xq.ik o-+p3sl*stxgtal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a dzzoq+kz isx*m. .stx-* g 33plistance $d$ 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 when xdw -kr9hk2/6t iv:i 6o tc*gkyou jump as high as you c c6gi/rhi: ktv o29d*w6kxkt -an?

In Fig. 6–31, water balloons are tossed from them )cypxeh6,8 y roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignorpe6x)8hm, y yce air resistance.

A pendulum is launched from a point that is a height h above its lowest point in ij4+1d)lypt*k,j ucu 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, 4,ijtp ykl ) u1j*+cudand 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 compress the/e4y)b4 m 8 gg f6rjqoo)1mv3dknios+ spring by pressing down with your hand and then release it, can thfr8oi3qjmbe mngo o4 64)1yd+kvg )s /e spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceili qye/0b/ub-,y +msfg lng by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands agbf/q,eyg/ s0 bmlu-+y ainst the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the grat v wz h3*30ws1y*pqk rg3/agkvitational potential energy when water at the top of a waterfall falls to the pool beloww*ap3gr3* k/y13 ts h0 vkqzgw?

Describe the energy trans*4uj2l0p/v v:ye s qkyformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skie(z x iia d q/(yjz2i2.16 mrg8twlo0jor starts skiing down a hill, but after a time is brought to rest by striking a sno1ld zwq xgo(0/t jmo (ji2i8a2.iy6z rwdrift.

A child on a sled (total mass m) stankzarsnfb)9;r:n d j5oh728acm * :farts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and )n:n:7 a rmraabz8 ksho;2j*9fnfcd5(b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their patxn:hxaqn).t6:; unmo h rather than stepping on top and jumping down on th;ma.ou:nx:hn6)nqt xe other side. Explain.

Two identical arrows, one with twice the speed oowh .j*0ew; rkf 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 muhwk0 .jor;ew *ch farther than the slower arrow? Explain.

Analyze the motion of a simple swingi5jdgb4*:lrk ggq 3k;fa 2hf p-ng pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a gf hp4-k;a: *glqfdkb3 j25gg rrandfather clock has to be wound up.

When a “superball” is dropped, can it rebounddtt+, lv y2vl8c j*p)l, gzws7,i7e xf to a height greater than its original height? E ig d,cvll,j 7)8txplw+ve, yzt*sf27xplain.

Suppose you lift a suitcase fr kuvm 26rtv;7su9v5g mom the floor to a table. The work you do on the suitcase depends kr2;vvm us9um6 v7gt5on 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, and (d) the weight of the suitcase?

Repeat Question 22 fortwjt,a3 e,5po x21vys hlq( / d5zycb/ the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to clim:hbhyg 2 pgq u+/ ht 9:z6b,vdk,zh1knb straight up?uh: 9 gpbyk6,/n:th dh qb+1,kzg hz2v

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dec* :wn*tsei,d 4afpevn.n g6d1m1vqs)rease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load ei*)4wf* ndpe.ss,m tn1vv6:gqd a1 nis raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the opf voyb5ikl(7vx .46gravitational force when a 265-kg pile driver falls 2.87 iyk(5.4blovvxf po60 m?    J

  A 65.0-kg firefighter climbs a flight of stairsfu+u(3d 8zf9rk +n qjo 20.0 m high. How much work is reufz+o fk n(d9+r8u3qjquired?    J

  A 1300-N crate rests on the flooyhvzz3w 4b426ckdugnw r /l91r. How much work is required to move it at constant speed (a) 4.0 m along the floor az h2g1w3k4yr6 c4u ld/bzw9n vgainst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crav+wl(9 frrpqi7le 94 xte 10.3 m across a rough floorrx +7erli4wpq9fl(9v 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 apl 9-envs 2iiu3t.,lkt a rate of for 7.e -.iiklnsp 93t2lv ,u0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, li1tz u o3lr;pgb,4db/ee flat on a table. How much work is required to stack them one on topurt4/ z 13bbo,dlp g;e of another?    J

A lever such as that shown in Fig. 6-:fl6+;+zcwse vruc ou: te qdn:rf/s of-/-6 p35 can be used to liff objects we might not otherwise be able to liff. Show that the ratict6w-/f; ovs6 +qrlou ru-f s+d: :np:zfeec/ o 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 8kg*f1 6 rv)wjkxeo-fjye +kn:)us/tand is kept from accelerating by a man who is pushing back on it parallel toet +jg6 1) vrjoykun)*xew kk- f/:8fs 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 k g)+ctp4nht0 of mass M an acceleration of 0.1+ptkgh4)tn c 00 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 lita44 frj-+b: eh vu9t)lays6anear 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 x 6x59lcb/vizt; gg m:x axis, varies as shown in Fig. 6–37. Determine thelt 9g:icg5x vmx6bz;/ 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 thx 5b9ojh6 ym97 p1axdve $+x$ 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, a 2 yj9 *xo+q1pn-qxlqfn 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 arro; ai1yydg:m i9 a,u3q n1klm/tw is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to sa;9 prtd* qlbg;, mm2dw;amn5top 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 dpy gv8,hmixj:/f mit-wg 1(b 2one to 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 average force oa1heucsrx z f2,psik ;90)vpo pz79i8f 110 N on the arrow over a discu ezsri0zhk,vifo1 pa 8x97spp )9;2 tance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) )m9v-ee-zyfcv q gb8fq h) ).89ab)j,bp h bqptraveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the b8qvgbvm,jbqef p8q) p a)e-bfy9-)hzh b)c9.all on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum br t6*ii:9) uxcppszn /paking distance be increased, assuming all else is thit* )xi9np p s:p/u6zce same? Ignore the driver’s reaction time.

  At an accident scene on-c)g4wy7pq u9jg+otw /9gxau a level road, investigators measure a car’s skid mark to be 8ucgu xq wy+4 ggw9-/)po7a9tj8 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 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 reache b2h.obsys+1ac b hvwtly f n8(h0(iim/;m0) ts the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance betweec2to)(m /. iv0s8mlfhbhy(bn1is;a ythbw0 +n the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straif c v3ro (bbksk)*.nn-ght up by someone who does 80.0 J of work on it? Negle3k) r .cob-*nkn fs(bvct air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratip k5 pf5b;f86onhg*+hn c+ erzon by a single cable. Detkz eh*n;hfng r5+bpcpf6o85+ermine
(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 constan . ui yh(qvh;o(vdg4z;t, k, of 440N/m How much must this spring be stretched to store 2i;.v zvdyh (gu ;hq4o(5 J of potential energy?    m

  A 7.0-kg monkey swings from (t obhjdbh5pu79v(e8 one branch to another 1.2 m higher. What is the chanpbhe(7tjdhu9b(v o 5 8ge in potential energy?    J

  By how much does the gravitational potentialje *v3dy ,dnv9-cj u66n9wvmeaw4+bqm jj39x energy of a 64-kg pole vaulter change if his center of mass rises about 4.0e4-n6vdx+*qvvw,9 jjyjwju bamme9 33nc69d m during the jump?    J

  A 1200-kg car rolling on a horizontal su049 4ce/bap:o4tfo *vbanp pr rface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to resta :v4np0/b*cp r4aof9ptbeo 4 in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2(s c0bcx03yyckpm5cvf -w d/p 7bv88 h.20 m above the ground.( f dcy0 y-x/h88wm7cp 0pvcvb5 3kcsb What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts a -j )5iq,-altzwawyjm+e (n7yt an elevation of 1600 m and climbs to the top of a 3300-m pew -t(-zli m),j w5n7jy+aeaqyak.
(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 v+ ; tqek()qrboertically 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 to the end of the spring, where will the end of the sp (+qqb r;ekt)oring line up with the ruler marks?    cm

  Jane, looking for Tarqf).yvi* m, p +3wjyeczan, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swmqe+ ).*pc3yiw,fy vj ing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down ayubiz dj. * *k;yj pse1b/1fw p4xq(7p 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 frictionless 28,z*b)g d ar/is.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 g3j.ko2hbimfyi. h91v ravitational potential energy. 9yhi2of1 m3i.jbhv k without 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 ve3/jbkghfj38 :l9h.uw d ru9bq rtically upward from the top of a platform with a speed of 5.0 m/s.qdu.h 8klujr :h/ bw939j f3gb ($\alpha)$ 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 stiffne z7 gbg)x;( vi9yyzak)ss constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What uyz;i xa9y(bg g)kz7)v pward 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 then pbr2n3r0e8r6ny 4bp looped track shown in Fig. 6–39. If the block is to remain on the track, even 6y8n 2bn3r4b rner0ppat 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 l-z/ uwi/p9)byrulh/of a spring (spring stiffness constant k), Fig. 6–40. T-zlphy /wlrbu u )9//ihe block is given 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 bridgq +vam91s182*r witc lhkk(ame. She is tied to a bungee cord whose unstretched length is 12 m, and fkl(i89a1 a vh1*sqk m2mrw t+calls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car showkt7l z4.h r*crdb27.4iqmvx k n in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speedb kvr th7 lxcz.mq*4rd7k.i24 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 atvb2+um3m4se k 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 at the bottom of anrgnx 4ok 38 vrxe9g3 m)avw1(l 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 stiffmax g3rkg(wl8)xv 9 3 nre4vo1ness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a r, pi: bdpn;s17.8 $^{\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 trave(b .-z yqs) gfk.e5pojling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in thiqz).(5o - f.kjgp besys collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m t988kx bpslpr82 vici4j3 *czhigh and reaches the bottom with a speed of 2.2m/2i8r*488j9scbppt zx k3c ilvs How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides do4gn c,/a5aryg wn 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 tlf5yyc+;b ;y:h (nknabove 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, an)4sh.lcgsd, od it bounces back to a height of 1.5 m. cl4,sg. dsho)
(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/lpcmx i15y6;nphv 2 o constant horizontal force of 350 N. For the first 15 m the floor is frictionless, ihlcxv 2pm5o1p/ 6y n;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 passes point 1 wiqg 9z. ctn:.fim d: bw(4n4qicth a speed of If the averai4.zccigd. b9ftwn :q4n(q: mge force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches thes6adeo -7r 4e-7hblh*yo8wqx foot of a 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 attached to a veryv m/u7 xu/lb.z; asr4m 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 coefficient of kinetic friction between the blockvsbmx/z7luau m./; 4r and the table?   

  A 280-g wood block is firml(n +8h qt/acyey attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the s y qan+/t(8cehpring 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 thep,) px3w-xl-0pt vqsd 9j5b lt space shuttle used a “glider” (mass of 980 kg includin l --w9vt5jpb30)lpps dxtx, qg 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 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 motorjm.svk 9tlu 9 a y/drwwk3(y3( to lift a 315-kg piano to a sixth-story window 16.0 m abovej d((wlw/39s3y. muakr tyvk9?    s

  If a car generates 18 hp when travelingi1(sfg; ;lz6rj5p svw lxf);o at a steady 88km/h what must be the average force exerted on the car due to friction and air resistancef)(p;oi6fz g;1vj r;sl ls xw5?    N

  A 1400-kg sports car acceleratauhkc;q6+b .b:j vl f5es from rest to 95km/h in 7.4 s. What is the average power delivered byqk.5 :hualbv+fb j ;6c the engine?$\approx$    hp

  (a) Show that one British horsets +ko.jx x7:epower$ \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 expre ocbl/0w8boa7m0 krov)s;ab*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 1150-kg car slows down from to 65km/h ino-72d8 5fu xfzkvje8c about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) f -cf8zex2o8v5d7k ujis needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motu-:u jbb.omq +or do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this n 4np+fd;9rd9yzbt -- ew, uupci;od8motion takes 1. piducn bred+4 -;8dnz ,yt99wpo;-uf5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3srur1g:f ayhsv7.w98 4x6/ eul 0vxmo.60 m. What output rating (watts) should the pu./rmufsuvlr y 67: xa0v osh198 gewx4mp motor have?    W

  During a workout, the football pl6;us l+gs ap4kayers at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and gsplu6a4sk+; inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6 )l:( txx0mmjy.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hiljdlw1aa r8 te 4aov:6 c)d ;at) 1g7fhsfvk78el can it climb at a constant speed of 75km/h if the frictional forces add up to 6)dha1 wa8ttr sv1 7f e6 k)fa;eodg4v j:78cal50 N?    $^{\circ} $

  What minimum horsepower must 1b 3ams ) b-h*ooasv;aa motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficie*a )so1mbshava- b;o3nt of friction is 0.45?    hp

  A bicyclist coasts down a 7.p:5:gv nfl f*..g . +cbsncapz0 $^{\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) bumpers” that are designed)zcmyk/ku.wi /yq up.eb lin)*c1y1 - to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness cons m-uzp1/c ykycy1w.q)i.ue n*i k b/l)tant 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 the8i2xhcmebs 73 ya q,8o first 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 of 21 cm, and an average shelf holds 25 books, h8a3287bmh, soqcixy eow 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 thsxla7iw)0kfe *h,p j: e 1936 Olympics shows that his center of mass rose 1.1i,)w0 kef l*sa7j ph:x 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 track shown in 5 dqc5:y 8uembqfu8x /j-rfw 2Fig. 6–39 is to remain on the track at all times, even at the very topj82ufbqw xd -qy um:5fe/c5 8r 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 5iy ezlp :a6*tafter jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, blpze 6t*ai :y5ut 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 ;lrgeeb. v 08xend is fixed (Fig. 6–43eg;0r.8 vexl b).
(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 ygh,mtz.9 z)r top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. gy).zh9rt, mzCalculate
(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 brvc ltru 7p78,tc-9dcqeaks 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 area in California claims thatr8igx 2km ki.oty4;; /*1 no2ygz m8d4arfjsl its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estima sy184g; o2xim k4jfytgr/.r* dml2noi8a ;zkte the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m bedjtlk h*5m0 +n /rjf1vfore strikingrh0k j/*vm+jf dn51l t the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular verti3wm*d, j3hox qpx;gi3cal loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the lg*hxd3 ji3w, opm3x ;qoop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar diid 7hd/1:ot wdrectly into work, how high could an 82-kg man climb a ladder if he were fuele:i/1d hd7d wotd 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 me/. ael tx1+wat an upward 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, theh*:,9h1 yzd;,fx vt4ns *iuulp gix /l spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale xyg ni,*zp,h/h*i4v 9td l1u f:;sxluread at its peak?    N

  A 65-kg student runs at 5m/s grabs a ruc1* i53jec;t-ux m4vcq-js lope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zxsul-*jct1m c 5 4;qv3uci-jeero.
(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 distoxba0kzhb22tsq 3rar*;qo3 , w 8 tmz/2gqc0rance of 5.0 m in 9.0 s. What minimum power outt, q;* 0oqx hk3r2o/s qz zb02a382twa rgcmbrput was used to accomplish this feat?    W

  Some electric-power companies use water to store energcaptv bz)r4l,h gi62k)ay wg72 z:b .gy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To r)bggl kzci2bw a7v,hzpt:gy6.2a4)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 de 1re4n7)ytqnm g o+bc:f61whalf. What is the spring stiffness co4mgntq1 e1o+7e6n: )dcby rw fnstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37;3zeqyhli b 5vqf;*: pwd p51b $^{\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 f:au-vv71qx x/g lmz6 will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses. f 7mg uxv1zalxq:6-/v    s

  In a common test for cardiacrc0aj1k 6 rmv8 function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power r0rcv68r 1 amkjequired 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 verticallv),o klo.ls9i*od -src w0vu7n)x1axy upward a distance of 500 m, what was its velocity when lr x,x.c o0ni7av )vu1*k-doso lws )9it 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 ofdihvku+a5s gp0 8 18gl 95kg/s (a) If this water wheel is set up to provide el gad hipv 185+80kuglsectricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s