In what ways is the word “work” as used in everyday language the same as that dekb )j)s4t/ jurfined in physics? In what ways is it different? Give examples of bbkt/ j)ju4 )sroth.

Can a centripetal force ever do wo*/: 5kmfyc rw,zv1nzc rk on an object? Explain.

Can the normal force on azp+m 5uki-( fdn object ever do work? Explain.

A woman swimming upstreau+1jy)1tl -m 1hdijrkm is not moving with respect to the shore. Is she doing any work? If she stops liy) mu+h jkjt1d1r-1swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negativex0jf8q2qdx c-cb /x+eu6 y5es? [Hint: Consider what happens to the dishes when you pull a tablecloth out from undeqc+806c 2xe s5 x/deqj-xf buyr them.]

Why is it tiring to push hard against a solid wall even thyb9vfjgo 31 ;vuv 6zd+ 6r;qihough you are doing no w;vvh g b ;+rq936z61ujdov fiyork?

You have two springs that are identical excea/)scd:p3y dc pt that spring l is stiffer than spring y/psd:3 cdc) a2 $(k_1>k_2).$ 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 horihh+ i,. d vkie eus wyl-k2w*1-tt6sk*zontal force on a block that is free to slide on a frictionless surface (Fig.6-30). Tuhks+d2*e ivkt li*1- t6whs,e -y.wkhe block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energi. ,) +mryf 1du;g:xlqs(fiz dy change when you j ifsrqf, :dy g+iud.;)xmzl(1ump as high as you can?

In Fig. 6–31, water ball *nv, )y;xltz v0nti)k2+cgf6 r trg0loons are tossed from the roof of a building, all with the sam;ftr y nvg,rn)c 0tgz 62kxi0 vllt)*+e speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poila0z3 fmt n67/7akuq wnt 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 directed downward along the trajectory. Which launch winzu7afl 6 m0t7kw/aq3ll cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tablehlv yavh )dz.o+: /w k1;qnik(. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservavz.qi:d kn+hw ;)hvo(1yl/ kation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig 8o rgb9h1uan8. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoidnh ub8r 9g1ao8 injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the grapq:a vq-ob( bt i7f*o,vitational potential energy when water at the top of a waterfall falls to the pool vb-qta o,b*q:7op(fibelow?

Describe the energy transftrf7vx.: c2kb ormations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starr (,v 9dtwyspr1qbl7)ts skiing down a hill, but after a time is broughpyt)1rrb vldsw 79q,(t to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hilujhy6m1oqh, +7r ; fszl 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 ;1ujsr,z qf7om+ y6 hhfriction (deep snow)?

Seasoned hikers prefer to step ovu grql2mc* (mzog07z,e 2ag4+2m oer 2aqi,dver a fallen log in their path rather than stepping on top and jumping down on the otheuo2(g27 gqvlarcm,a zd4 +i0erm 2*m2,gz e qor side. Explain.

Two identical arrows, one with twiceps0rr ;)z4oya the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fastr ) yr0zo4sap;er arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of enrzj3lhk op0(0 5qe- mtergy, (a) ignoring friction, and (b) taking friction into account. Explain why a om-hpzl5krj3t0e 0q (grandfather clock has to be wound up.

When a “superball” is dropp df 69h:cta:q:efiw0bof ;8mhed, can it rebound to a height greater than its original heighe6:9ham :ht d0iqbcf:o8 ffw;t? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on tx2, yvu+wp, fang/w748 al ddnhe suitcase depends on which of the following: (a) whether you lift it straight up ora/4u8,agy+xnwwnp2d, f 7l dv 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 power needed rather than thf z5wc-0d) lwbe work.

Why is it easier to climb a mountain v g s)wqmvb)jc3gc70(j ia a zigzag trail than to climb straight up? 0) m7jcvsb)gj3gqw(c

Recall from Chapter 4, Example 4–14, that you can use a pulley and rop ,dy+u mv4 g9ex fji:l g;tx6y0nqqx).es to decrease the force needed to raise.e l 0 d9;:nf v4y6itgj+muq)xyg x,qx a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by 2*ivo ;7m yxyithe gravitational force when a 265-kg pile driver falls 2.80 xyyiv i7 ;mo*2m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20na6y+sf/l.a zxkyj 5 v1+)sro.0 m high. How much work is required?rn1 .f+) aysj+zys6 x/vk5 ola    J

  A 1300-N crate rests on the floor. How much work is required to movekd1oi *q*y3 r:dw z( tsofxp4boim7.igk- + 0c it at constant speed (a) 4.0 m along the floor againstkzo4 d(cit* wi:+*ig3 7ro-y0b sdqp1x . fkmo 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 crate 10.3 m gi) r4,jqju,f across a rough floor without acceleration, if the effective coefficient of frjq,g ,r4u ijf)iction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at 89pt1+;ynoc 6wiiu cba rate of for 7.0 s. Fi p+y6 1nt;c98o wuciibnd the net work done on the box.   J

  Eight books, each 4.3 cm thick with maue/we z5g s/ghn. nhntzl69/ lec -:s6ss 1.7 kg, lie flat on a table. How much work is required to stack them one on top of ano/ 9c.g/z/5n6nwe htez g :unhsl-l6 sether?    J

A lever such as that shown icy 0/2m*3r m*g zstptfn Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the szpm*/mtf 0rg2t3cy*ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acpn xql o7:3e*zq,eilg.n: -flcelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36)o:* :lnz,7le xql.p g-qf i3ne. 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 of mass M an acceleration ofad yspl)-y+vw 90c9wy 0.10 g c9ydwv 9lyp)-say0w+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 ii 9 d56swvyok)s 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 axiscdq zom 1++r4ix2fw;9rqc ur1, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a1id orqcqxrwf+4zu1 9r2+;m c) 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 acti+rl/2 rzfe0 cxd: /tqs 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 oxygen molecule, wit gq5sqnwh /-j2h 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 fylgc5g(3ab u+),yh yn actor 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 stop an electron dppng( ,*q xv2$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar tra7er(v9 wp, 2aw a4tozvveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an5s-fa jqi0vs h0*ch:i average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves ti- vq0hs 0f*chi:5jas he bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwauc4m)b (9tj4bc chz1 srd 25 cm when the ball is caught. What was the average forceh4 cjbum (ts c94z)cb1 exerted by the ball on the glove?    N

If the speed of a car is iboy r;b g9gp)558 thjdsodi)1 ncreased by 50%, by what factor will its minimum braking distancebgd)b)odro;p 8jyi 1tgh5 s 59 be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, invea;ww 0j oth1(ylir)e4stigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic 1iel;wtjor yw0a ( )4hfriction 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 4 ha(-c; lq1cysk.i jj34fjsj the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, esj3i- ljj. a4fcssj1(q hky 4;ctimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who lqpeb. q rc5zk /2qjp-84me 5zdoes 80.0 J of work on it? Neglect akl qbz.8p qzperq cm5ej2-54/ir resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accenz6cq*u g99 jaleration by a single cab*q gcj9n6 zau9le. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this sh(9as+jwyl6or7g ece5 l-(q opring be stretched to store 25 J of potential enge clj75(yr-+o aw oqhlse6(9ergy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the d8xqd9 ;;qyh*fj 1rx.x :dvly change:dv .dfqdy8 ; lhr9j*y1x x;qx in potential energy?    J

  By how much does the gr2 m8 0mf y+erajui:*0p2 veh,ilpn*rzavitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m deela,:my2+pnv2puhmjizr r 8i0 f0* *uring the jump?    J

  A 1200-kg car rolling on a horizontal surface has speer)mk m0lu-c: 268khet8e1.ep( rgf n;ebta jhd v = 65 km/h when it strikes a horizontal coiled spring and is broughtf)2(8pb;j en:et6k0 8c-hk1 e u.gm rhl rmaet 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 tp-e .g-qis 3cqhe ground so it is 2.20 m above the ground. What is thgqpe-3 cs.i- qe 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 at an elevatio oz;phl:cl+:9yijd0-iou4 : pax3lr bn of 1600 m and climbs to the top of a 3300-m peak.4u-:ya zx 9ohli30pol;j d: +cl :iprb
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically neq35rwk2or7 5m gxeb k4c6 u3okxt 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 spring line up with the rbeo k53x7uo6rm2g 3 q4crwk 5kuler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5. 2 gfi7qsbyp+5 obgl183m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high q17gi5 2y bolsgbf8+p can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from res 5jo72q ozc 3endb);uqt, 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 frictionle/ n+udazcu f0z4 t4x1wss 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 kindkjz 9c qop*.zub*54ewjmi yl (z6a:0etic energy is transformed into gravitational potential energy 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 ofiwjz5yl z*.po eak6db* q: z9(mc0j4u 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically up.vueux7 7q .hlward from the top of a platform with a speed of 5.0 m/s. e7 q7xv.lu hu.($\alpha)$ 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 stkbjw + jokcb(4 ;bbh :8,+kgg3ph6qsbiffness constant is 950N/m is attached to a table and is compressed down 0.150 cbg+;k+b 3hhwjsoqpbb8,bjk :kg4 6( 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 the looi9pm7fhb qbf b;8-*zqped track shown in Fig. 6–39. If the block is to remain on theqf9i*qbzh-; 8pf7bmb track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of ixapem68k swgo4l*73a spring (spring stiffness constant k), Fig. 6–40. The block is given an initipm i wxo3g86 7*skel4aal 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 7*yhxx3 e-pwmz .p3n ofrom a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee p3*. z-eo7h3ymwx xpn 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 point 1 whe 8.g6/vwgep ,ejom) ir;hvha. re it is released from rest. Assuming no friction, calculate t6,g)gv . we jvo/ 8;m.aheirhphe speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with xi+lnrn1v98la 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 designins6 28ev)wtx+yjsya70loof7 r g a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an)7 xtf s seyj 7a60ywor2ovl8+ 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 xj (f-nglk.aj1 0ph- ka 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, each9 v w2+ 6bbpbleedvy0ijw*i 25 of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to res6y2b9ldi v5bwpi+jbw 0 2ev*et. 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 byi o53n cmgv8q;sr1mzsw 7q1b 6gd 2/eottom with a speed of 2.2m/s How much thermal energy duec;y8eb g3qowvnsqs2m/r615dm7 i 1g z to friction was generated in this process?    J

  A ski starts from rest and slides down a cwe:c1i)y.r8ubn3libl-zd022 $^{\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* pgja-rh4 az 3xvx(a( 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 b6 - gkszr0hhs)kaxroz 7i8,m, ack to a height of 1.5 mhx6r,s 7k)izgr-o8z 0sa,khm .
(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 /x9)ojd2(iy iwcixmzec z(39 oz*cs1a floor with a constant horizonta/( ewmc (139iyico9zc2)dsxx i z*jozl 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?    m/s

  Suppose the roller coaster in vvzd ng00p9)i Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what )vvp d 0nzi0g9speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the fo0sk7men ).a ul,qcw/u ot 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 atb,;n lfx rwyp3saexa(qgn72 p- / 2x)mtached 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 anbfnx7 -wanqa3gy)x ,x;2 (p2ep rmsl/ d turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light hor2) 83w8vr zudbfyg lg at*-.krizontal spring, Fig. 6–40. The block can slide along a table where t8tr dgz2*fag lk8w y br3uv).-he 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 thzigp0 (; e pc *i/l,-yq5zuklqe 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 lzp,0zy5iieq kqcl(*l p /ug -;anding speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg j3d tz-/r wdm 8r0 c,a/h1ixrqpiano to a sixth-story window 16.0 m abov wt/i,r8-zd rrh /3cxmjd q10ae?    s

  If a car generates 18 hp when traveling at a stea fgk -sc*u.n(zdy 88km/h what must be the average force exerted on kcu* n(z fg.-sthe car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the averaq+fz4:q c*o(1ynjm3wdr g.u ;2 lf ype.hxc:gge power delivered by the engif+;gjyf. h*1.g(cu:mn3z4p :owql yx rc qed2ne?$\approx$    hp

  (a) Show that one British horsepow14t8n6 hgzzrr (+ jukter$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often exp(k6aik1wt tg. ressed 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 zuqgg e*/+2u u to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed t/ eug2uqg*z+ uo keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor dod7 qtu e7/vz8h3utfn3 in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from re rnc-xzy3n0,p l(7dqhst to 14m/s If this motion takes 1.5 s, what average power was-y 3h7 0r qnxc(dnlzp, developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute p1 oasy7cg td4/47abmthrough a height of 3.60 m. What output ratit/g4ymo psa4a7c 71dbng (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stairs infcg**4jxdj *h 66 s. The stairs are 140 mg4jd*c*f h *jx 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 cycl6pzih/q o.er )eqbk**:t fhw: ist 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 po +bdn/+ roxp 9x**qgvswer output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N? +sx+qg9xo/dn*v r pb*   $^{\circ} $

  What minimum horsepower must a motor have to be able to drag) p3v8ja6wp*y3;, u mk- chgxanmip.w a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fric y wwx3pkjg3v8 uiamn6)ma-;cph,. p*tion is 0.45?    hp

  A bicyclist coasts down a 7.02)rr)qz n1 4,4xcwgh nfl vh9p $^{\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 arj03rmn rob(oeyq cb: 3 h3a,,me 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 ofbr 30 o3ncreym ba (ho:jm,q,3 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 g(;0+u8db4qb)ep wfmhdfd4p the first shelf is 10.0 cm off the ground, and the remaining four shelves are e4hfged dw8df 0(q+)pbm ;u4pbach spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympezjn, 5-se ,fq*g4dukics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need a z,f4q u-dge5,nj* kset launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding q;vgx40p6yai83 dnjdac9 2trwithout friction along the looped track shown in Fig. 6–3n9q3a xrv dp28t46gj0yc dia;9 is 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 37 4jc r.upteo880 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, bu 8euto prc8j.4t 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 az74s g umc6+vq.tyc2i horizontal cord of length L whose other end is fixed (Fig. 4 c.c svgi+q672myztu 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high moafgdp no ;a f+j1f( 6ilo1za4k5; au)suntain. The climb is made in 5.0 h starting z1 ()giao;udpjkf4; n ala1 s+of65faat 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 28 m above a huge 2hb.4a l)*h:dmgfs4 nf*sd b/my op0hspring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can mov siw9u;8tluv4 e 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the p4s il w8tuv9;uower needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fallz . *dahvv,bi5 7wh3nns vertically 81 m before striking the tur3v5h. wnidnv,7 a *hbzbine 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 ci6kuz/sy/vv uh)f5f 9 wrcular 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 needed, this answer doesn’t depend on the size of the loop or how fasv/)fv6 u/z 5h9usfykwt you go through it.    mg

  (a) If the human body could convert adn; *pl j:i0o.f(cddicy: o m2 candy bar directly into work, how high could an 82-kg man climb a ladder if he were fuell;* my(j.o idopd2ccn:dif0 :ed 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 mhzw)+v,u +y4 h8wbvdy b ,3rdupward 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 scale94r 0sr1ofp-8qpfbmdsyj 9f 6, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the s o9 mr16j4frsfbpqpy0d-8 fs9cale 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 ozkbkpqzq u*9fj0rj +2:,8 itprsk pe0d0 *u(dut over a lake (Fig. 6–45). He releases the rope when jjqp f98*0,:ppk(* +2ertk z qd uu0dsz0kbr ihis velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs :;j r hzilzfjfo76-r(5x ezb4a vertical distance of 5.0 m in 9.0 s. Wzro 4e:7rl jzz bxfh6j;5 -(ifhat minimum power output was used to accomplish this feat?    W

  Some electric-power companies use w2rp.srk22a 3s; r urxyater to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store th.ur; rss322x ryakpr2e 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. What i5h/box7y fy h.s the spring stiffness constant for .yx hh5ob7yf/ each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m srx5jyc2++ly k( wka;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,j+ xwu;bn af): how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same+ubaj n: w);fx, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patieunax7xnm/6rw :uzb4tes nmy)zm5rd* +y (+h 3nt walks on an inclined t+ur6mx/4szz7ex(nntw*5 a+d b yr:3n)mhy m u readmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a clyzs9p 4en-k* hr7c2 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the vol472secn9k*zh r -c pylcano? $\approx$    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.ov-d;vp /( byhy+lct80 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power ou-(hvp v 8o;lyy/cd+ bttput?    W
(b) What is the speed of the water as it hits the wheel?    m/s