In what ways is the word “work” as used in everyday lanp +*gzvj;bs za (r7f.;fyvg (rguage the same as that defined in physics? In what ways is it different? Give examples of bo(grys 7;vzfj vp*+. brz fag(;th.

Can a centripetal force ev )jq f0srkjf;9wss- y2er do work on an object? Explain.

Can the normal force on an object ever do work? Explain.c izu(n) .i1,jpz4;c, zijrbu

A woman swimming upstream is not moving with respect to the bm),ah0v yn8fuf )b;f; v pob9shore. Is she doing any work? If she stopaov y 8f )bub,)b0;mhfpnvf9;s swimming and merely floats, is work done on her?

Is the work done by kinetic flsm(a yle3 6x-3gud3 xriction forces always negative? [Hint: Consider what happens to the dishes whe3gul x3xlds 63ae-y(mn you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are dz4vp;j *7q0y g(*yljhk:yglgoing no work(4v g*hgk7ll*0pz qyj yg;y :j?

You have two springs that are identical except that spring l is stiffe3a+rud*(ybsnwy x3rwn6;dvd3j jx 5 3 r than spring3nn xy3jrsda53vy6 drd;(x+ 3 wbwju* 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is frz 8gts)mz)h0xo0 )zs,cy )uaiee to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has tra o))c 0gzisaz 0uh) yzmtsx8),veled 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 energy7,kkd:9 bfus m change when you s7b:f ,d9kkmu jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with th0vy4cjv gq1k0lj 0banbc2+5h r5:o rve same speed bl5 qv 02jg1nar:4c0b5vjroc+k0 byvhut 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:hul, d.a/ s5pqt oui0 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 launch it is directedpqh,s o5i a.d0t/u:l u 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 sprb(coer5 o u0q)ing by pressing down with your hand and then release it, can the spring leave the table? qrc5(o 0u)obeExplain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33)o;ad,a ,k *zkr. The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release trka ,d;o a*z,khe ball without pushing it. Why?

What happens to the gravitational potential enyc8xg4asuj ho/; (,nmergy when water at the top of a waterfall falls to the nx4sac, (j;muoyh8 /g pool below?

Describe the energy tfg6 zaqf4, in-j8n kh5ransformations when a child hops around on a pogo stick.

Describe the energy transformations that take place wh 5/hhwm zwbv3k9 8dfk5en a skier starts skiing down a hill, but after a time is brought to rest by strikinghz m35w /kwh9v 85fbdk a snowdrift.

A child on a sled (total mass m) starts f/ gt )jh+geyz-kn,-t5 3occ rkrom rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep sny rteggkk5t)- j3,-+ zc/o nchow)?

Seasoned hikers prefer t;xljby(o0 i q/v e+5fr1pt7xao step over a fallen log in their path rather than stepping on top and jumping down on the other f j 5q+x tyi/(baerl0x vp71;oside. Explain.

Two identical arrows, one with twice the speed of the other, are firxq ph(oj3e *0brw;v:ped into a bale of hay. Assuming the hay exerts a constant frictional force on phe *3: bj0qwx po;(vrthe arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingingk pluc*7s/0d ii1j6;julov ntz0y;t( pendulum in terms of energy, (a) ignoring frico0pi0tkzd uv1;*nl j litc/7j(;u s 6ytion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater t5h 5hdt-0a gsjhan its original heig5hh-g5dta s0 jht? Explain.

Suppose you lift a suitca /1bkvr /h;uoase from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift;/uv h ako1/br it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the po e3n98 r0rt5n/k*e0qk a eproc,e3cjtwer needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb stra qplp2/nl eimb ol27huy6:w6 ts)eb08ight up?h6m0)yslb6n 8 p/lle27u 2opt: qbi ew

Recall from Chapter 4, Exambwxoh yig u;2v5u3j+:zo87v fple 4–14, that you can use a pulley and ropes to decrease the force needed to raise a hea 3x:8ojg 7oziuvv5h+bfy2w;uvy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by thwiy9k*oi(rsl 5k mi+7 a(dd,m e gravitational force when a 265-kg pile driver falls 2.8+wm ki dlo9dy5((i i7a*m,srk0 m?    J

  A 65.0-kg firefighter climbs a fl:ao;byok og;mu- 7obl8h p9q6 ight of stairs 20.0 m high. How much work is required?uokqmo9oyo;ga 7-h b8pl; :b6    J

  A 1300-N crate rests on the floor. How+s, ku fe9a7ha much work is required to move it at constant speed (a) 4.0 m along the floohk+ fe aau,9s7r against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizonzisb-tpsmh9 n .yvesk9n*aa ,; 0w65u tally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0;t s*snwi y6ue9,9a0am- 5ph kn.svzb.50?    J

  A box of mass 5.0 kg mwm)u6nps.2x6ubo pj3 g 0;unczxct,1gx+.dis accelerated by a force across a floor at a rate of for 7.0 su3mw2 cmbnutdxzpx. jxn ;6+1g g 6)cs,.0opu. Find the net work done on the box.   J

  Eight books, each 4.3 sc-k6p 07+ xhwgm95 u+jh-wiq s ;qodvcm thick with mass 1.7 kg, lie flat on a table. How much work is requireddgqhv-9-6+5i7 qhxj+c ww s0uk;m sop to stack them one on top of another?    J

A lever such as that shown in0 eh2(1cmyfkabm se2a9:5kv y Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the k( ce02592mfem 1ayvhb:s yk aratio 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° incl5 al;clzp6xv )ine and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calcu l;z)lp axv5c6late:
(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 require8he(8i *kylxdd to give a helicopter of mass M an acceleration of 0.10 g upward(h8e d*l 8ixky.    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 distan-6*0( tgr jzrz pmxhh6/-n,d4 iqr ntyce 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 x axis, varies as shown in Fig. 6–37.dy8ka*3)c ccx Determine the work done by this force to move the object (a) from x=0 m 8cc*) ac3ykxdto 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 actsz fb9n,a/x 4uf2x7a74o) isyydgr h9z 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, sgwk1/zhdm7p 8utb/ c9ix0u0 an oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its spe( e1ii)pwtpm1mz*o+k)zdk wy , uz78ned increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required ton,p/oj 9.aoa:a byicgyp e (,/ 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 ag8n9kuaw- 8-v9k kx jme/amq) 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 ahz8 tt*b3iv8 en average force of 110 N on the arrow over bti88*h e3z tva distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3w2a8+ uun ug*6cipl eqbl640qc;: oyu2m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the iguwllq ub pu86n2c+ 6o*4y:e;c0 qua glove?    N

If the speed of a car is increased by 50%,cjq54u wke71 y by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction time.w y15qejk4cu7

  At an accident scene on a level road, investigators measure a car’s skid mar69ad krjrj.o )k 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 dj9k.jao 6r rd)river 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 im3ii:hd6toa-r1tr. the plate, it may have slowed by 10%. Neglecting gravity, estimate .doih6r :1 i3armi tt-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 n,c8fmnz4l1gqzdj 4 4 who does 80.0 J of woqz 48ncj441gl ,nzmfd rk on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single ca9:dkq5j4q y *q6b6 w 2fabv+sij0 ttgnble. Determine 6t2 +4q tqg6i0akd5vjy:jwf b9sqn * b
(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 4404k:49g vcx:0l y xg c2zio7uyfN/m How much must this spring be stretched to stoxv 2gg0k74l : 4:y9iczyucfx ore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highemj:ug(xsw7gj-cx 4bdq(n(6xe1 u( grr. What is the change g ucx((-m4ue(xsng7wj1gd6j qx: rb( in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chwc,u c nr33sx0hf4 tk an,,mt+ange ifnux340wk,fnc, ts rh mc+,t3a his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65)j5l0eprhkl+hwloj 2y*,x g ; km/h when it strikes a horizontal coiled l; j *ol,5 hyxjehk0g)p2w+rl 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 2.10-kg book from the ground0jz6 fyxzlb)) z t*0dpp(r ff5 so it is 2.20 m above the ground. What is the potential energy of the book relatfzyr6t)xz(b*) f pz0 l 0df5jpive 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 4-bwdd2xe2/p sr+pig/ l lk7 wahu;q0at an elevation of 1600 m and climbs to the top of a 3300-m pe2+;lqldpuxdwhb g prek/0wsi2-a4 /7ak.
(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 = 5341vmbjp1 v;w aN/m hangs 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 to the end of the spring, where will the end of the spj m1a wb4v;1vpring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine hang.j90y2qz b +h tsymyx(ing vertically from a tall tree in the jungle. How high can she sw.(+z ybxsh0m92tyyq jing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from resth za 4/v0nt-zz, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frickf(r8xg+ )x .-ssvs ytz90hzk u+vl n/tionless 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 s nw7 o1qphd-5whd/h2-qxf9 q kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum spee o5-7dfxh/ qq19-qw2d nshhwp d must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from thep; b2.s -.og( 2:ea6sp ik +u(o-qebfwrhrkmd top of a platform with a soa -m -(+eb6p;o.uisksr.b2grepwq(fh :2dk peed 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 sprinvq:zr.n rg,r ,qu:yt rd:na2 /g stiffness constant is 950N/m is attached to rn:,v g:ry:q r./,znqt2arud a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along tq ss58kgaaw5y ;j20zb he looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the qj y2kb58 s;s05gzawacircle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to theqy.6 u;: d:s29ww,miugnq civ end of a spring (spring stiffness constant k), Fig. 6–40. 2q;uwiv yi:.9m cwu6dgns,: q The 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 2x)*61i. dhexvdx zec(8qid hjumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calcue x(. 8)2iiezd dhhx* 6dcqv1xlate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to pv9u -fuznk,: .lfabt4oint 1 where it is released from rest. Assuming no friction, calculate the speed at points zfu9 ,at. kb4v-uln:f
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown wi-e ,zyj lbf10, s)*jtxfmvb1 hth a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an eleyayoy 2ear6 :8vator 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 paay oa:rey 2y86ssengers 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 up1jh h (5krh,j .k:sd7deux md; 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 direct3dg b )izoj4)isk ogjc * zbtn)x5--5iions, collide head-on and)4-*x-gcb55)io jk otjn izz)3gsi bd come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a,w)rr9w 3hw khu qi6olc +fb95a2u f2m speed of 2.2m/s w3u29cwrm hkql r5w 9u,+ o2i)f6 hbafHow much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides :db,qnr o* hmeu(3r af.m:w; cdown 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.*62/r mpcvspwu pp 6.b9 1qtwe0 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 boun8aj dfvdep9 dxlk. ar7)uvw 7: h.:xg0ces back to a height of 1.5 mf. u7a hpg.:rded)kv08 xld:ajv 9w7x.
(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 conh*ufgd4d - e7ustant 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 craf *ug7 de-hud4te?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poin:;k m-h:nbge z6feb2nt 1 with a speed of If the average force of friction is equal to one-fifth of its weigh- efg ::z 6bnm;b2nhket, 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 (r6jkumm*m9* 0pxolm h5mz b8a 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 ixl6wdkmf ov r1 2k2.v/s firmly attached 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 coefficienm6/v od2 2x. klvkrw1ft of kinetic friction between the block and the table?   

  A 280-g wood block is firmly a) i1tt:uv2t5 zcspj4ettached to a very light horizontal spring, Fig. 6–40. The block c sciv5t1tzjetp: u2)4an 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 on its first swing?    m

  Early test flights for the space shuttle used nbvuemvh/rq2m :k,u0 ;,; 81dn d rasja “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 the abkn1v,/dm :r 0 bn2ueuravjq,d8;ms;hsence 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 l99hd hhafoeo49e)c .lift a 315-kg piano to a sixth-story window9ehca9h4.)o9l h odfe 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h whatu a+ah bh;9wb uo:t1.f must be the average force exerted on the car due to ho1+abh;ua tfuw. :b9friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avevohja jm9)n3-n-gwb xq5z-c1rage power d3on- )5hacznj1wmj- qvbg x-9elivered by the engine?$\approx$    hp

  (a) Show that one British -h va.4b1k klhtgqb 62horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilbag rzih +qal-p 5an*+ ,ym0s+owatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about9dha oc-t mi bua.9,z9.hiyt6 6.0 s on the level when it is in neutral. Approximately what power (watts and hpt.hocubz6i9 9am9,. hi-dyta) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp moto7x t8wa. )hlbzr do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg 2zysk(*h7xts5ue h4u u;ti9ishot from rest to 14m/s If this motion takes 1.5 s, what9e ihhutxsk5z;s*i 4(2y u 7tu average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute thjria56iw7g t* rough a height of 3.60 m. What output rating (watts) should thitw*rag 67i 5je pump motor have?    W

  During a workout, the football players at State U. ran up the a .gqma, f5spt;bmr *d9sbz. 4stadium stairs in .,dbf. 4rs 9m;q*mas 5pzg tab66 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 cyclim-tsry 0m 5cvo2ag7 k:q+wy6nst 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 power7rqq6vg zty w(r25uxhyb76 4m output of 120 hp. How steep a hill can it climb at a constant speed ofrvuw2t 5 ymb7q66zx q(r4y h7g 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a ms1bfql;ax7sodpvc eh6 68. +xotor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.s leoq vb6dcx8 1.fx6a+sh7p;45?    hp

  A bicyclist coasts down a 7.0 y5e 7ug+ e2)y0c)nl .cct lcar$^{\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(8kgp1gzj h78k( cm/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid w8hz(kjpg 7g1call? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 v.7zkopkz2j(y -r u v0tl;ok4cm 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, how much work izyvo-(r7kl04u pz 2o vktj;.ks 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 the 1936 Olympics showsvs l)r c20rvzwknury lb*21)/ that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of thuk1w vrl2r rz nsl/b2 0v*)cy)e arc?   m/s

  The block of mass m sliding without friction along the looped track shown i jqv7), dv(8 hic5rfaxn Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radqv c r 5,(vjxfih7a8)dius 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 aircn*y6 -9u qo)mel e: a/f0btuecraft 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 estimf/ lu eeyo:at qe m)60cun-*9bate
(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 )7a16k u bfl njcc3d u0wk)dp1whose other end is fixed (Fig. f0du b7 ck1j pl6uwk)a) cdn316–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made 33. ,: g;)lypcf fihwxm 54otd/poijnin 5.0 h starting at an elevation:p id moicn.twg, jhl34of;xy 5/p)f 3 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 wh0)jloa5j w/ mlen 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 tha l,zdvok04do1t its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (verticallyl,ov1 d4kd zo0) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically fesmy(nh 7p8 (81 m before striking the turbinee 7hsmn(ypf(8 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 coavvnub3,ux*5pv/n6vsr ur5k) zm . c6 yster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum ne3 ,vsv mu5zybv)c punr6/nu.vk6r5x*eded, 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 conve-c67agyxy no8lo8mj/rt a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=10 mc8 ao6ojnl/8 -7ygyx00kJ)    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 oo )re. )sw++0jntsjsjf 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 scis4n/feem3:j) zky g +ale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the3 4ze g+m/sky )jifn:e 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 ooa ie8k:zfs1 5ver a lake (Fig. 6–45). He releases the rkso:a 8zef 1i5ope 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, ak)dnt96s cto7hv dh0 ) 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimods7d)h)t v nc 60th9kum power output was used to accomplish this feat?    W

  Some electric-power companies use water to storgrvox7r d :ja78xc3tt*8 c),wm e saj5e energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energt*,v jc5g8exdx )8s77tw a:r j roa3cmy 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 bgy 8wh6yn2 h2fawy-:,wmt :whgh)(m stiffness constant k is cut in half. What is the spring stiffness constant for each of the two resulhb(2ty8 )m6y n:gh,hww-m fhww:ayg 2ting springs?   k

  A 6.0-kg block is pushed 8.0 m up at;54sk a+hre5ajps d; 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 accelerato-2e;a hcfsq- e from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 7q oc;2ha- -esf5km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stj795 , kkebljez7-tmpress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75meej-t9 pz7l5kkj7b, -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 spew82kh ths3z w0v-uwb gn20u(uz s a 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the 00bn2t-s zuw3 2khuh8z(vwg uvolcano? $\approx$    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 1 lua7pksv6ctl/nl24m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity ok6u7pcl4lvs al21/n tutput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s