In what ways is the word “work” as used in everydats hd6ia/ om*(y language the same as that defined inom(i 6 td/sh*a physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do w k ei*nz00thp9ork on an object? Explain.

Can the normal force onwca*4*tj ( (*pg ng 39jkwxw:nhzyd6k an object ever do work? Explain.

A woman swimming upstreikm kn ;em ks,a./efb,g g-( ba+12kvram is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done o.smra , 2;mn b kkk+eav, gig(eb-/1kfn her?

Is the work done by kinetic fri3ifleq90edia k*8n - 1z tlph/ction forces always negative? [Hint: Consider what happens to the dishes when fzp-18nt9i3l0eh*eqd a il/kyou pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even tho9.onou3zajz)u q /4p1cb du x8ugh you are doing no work c o.u13 /9bnozq xja)8puzud4?

You have two springs tha*07 3nlmderxp1d5c6 , cpglz pt are identical except that spring l is stiffer than sprin pc7 0gl3ce*zp5 md,lxd6rnp1g 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 f1mp 0rmruv1q ;orce 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 distanr 1;mu0vq1rpm ce $d$ 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 r2fc. j :r e;a( fkuzrk95y-lfchange when you jump as h29(f5 kf.r:alyr -fjceurzk;igh as you can?

In Fig. 6–31, water balloons are fs rf*c9khadm: +:yp2 tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignorpmrf9cha+:: fk*y 2dse air resistance.

A pendulum is launched from a point that is a height h above its 4 tigpwb9u jt0 ra(s0gh m)8:elowest 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 direjt hibru g:0g9 e4wm (s)8tp0acted 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 2blmuet.afbf .6 q, 0ua table. If you compress the spring by pressing down with your hand and then release it, can the .uut m,a. 20fb6febq lspring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. vuuoo 7c fg/z8g5vai b*s uly29o*c646–33). The instructor pulls the ball back and stands aga oc 9g8vzo4lyui ubv *c5* af6ou/gs72inst 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 gravitational potential j kukg d(n7ye0y. 1b 9fnb.4ok cvv4d8energy when water at the top of a waterc bkeyk1d yd ofj9vu 78gb(k n4vn.0.4fall falls to the pool below?

Describe the energy trao gf ,fizjfqy)7wdz, mr sb -;),8gge.nsformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skieza jx n.8iz8hyj: ka;7r starts skiing down a hill, but after a time is brought to rest zna8 8:7ijj zk;.xyha by striking a snowdrift.

A child on a sled (total mass m) starts from rest4w 9 am)rctd4z 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, an4r ) t9w4cadzmd (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather t xyx:ov*w2( s-4 ucllxhan stepping on top and jumping down on 4lu-olcx(*x2 xv ysw: the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired inti zk(0(uwq7eq o a bale of hay. Assuming the hay exerts a constant frictional force on the arroweik u07w (qqz(s, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a)xxih qz 8e73 5;z (ao/xzmh8fb ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be woun m/aezzxhhxf75 zo x (q;38b8id up.

When a “superball” is dropped, can it rebound to a height greatex-n 6n6wv/flnk1hts9 r than its original height? Explain t6/nn x691nflwsv hk-.

Suppose you lift a suitcase from the floor to a tablqw (n4c7q5d) is+ay mme. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) ts7mqn icwy)+q4a5m (d he weight of the suitcase?

Repeat Question 22 for the power needed rather than the worq lud-1. v1epp36,x*n xr:yi 7aw xwz3fo4tp fk.

Why is it easier to climb a mountain via a zigzag trail n4sw3c -7* z,.db)fuxehhmwd than to climb straight upb3w)h,e4*d c 7szwm .fn dux-h?

Recall from Chapter 4, Example 4–14, that you can use a pul 6;gfaao:(thjn jk 15fley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Aca k ;j6tf:ja5gno fh(1count for this, using energy concepts.

  How much work is done by the gravitational force when a 26f,e,/u ma 5brc5-kg pile driver falls cm,5b ef,ar/u 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of sta v co:4qko6my5d76lcxirs 20.0 m high. How much work is requirk6qdm6ov 45cox :lyc7ed?    J

  A 1300-N crate rests on the floor. How much 55.xmar bbpao6ym +*cwork is required to move it at constant speed (a) 4.0 m along the floor against a friction forc+bar5 *yp .6bcmamx 5oe 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 d(i 6-om(qephk2x tql ,ik;:a:e-jzr m across a rough floor without at q2r hkai(jlme-6:oqkd, ex;- (:izpcceleration, 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 rg *+:,n:,fs qofv dwfat a rate of forqwn,+f df *r:,vgf :so 7.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on . 8p7 ,c,jfmceoznus8a table. How much work is required to stack them onc,j8 z8np.,7 s fmuocee on top of another?    J

A lever such as that shown 98kn4j2 e pciein Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio jce4kin829ep 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 27l6vlg1; (3 wubrgbact rqb,(8° incline and is kept from accelerating by a man who is pushing b rar6tc lbvq(;w1b7l, ugg3b( ack on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an qyr8uenj 0m9qt f- 7 xo:.ovz6acceleration of 0.10 z:67nve.9y-fq oxu0moq8 rtj 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 theq fis3z );djvly5.it9ld+bwe, a3n*k:rt 3 cb distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varop/ oxs 1pi32au+s o+mies as shown in Fig. 6–37. Determine the work done by this force to move the o/io1o 3++omx 2apu spsbject (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 jwc) .yu*i6*obu-bq e $+x$ 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 m.d7p/m u3za/1 ur,ae7zgi wjd(o;e ioxygen 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 factaki)v, z; oct3 xs9e-hqh8oy 3usz** cor 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 ,7 emad;x. 3le(d,8wg n snwwa$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kgc4; 3vi13byajxdl,g kfw hto+5ar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fromtkzj whq/s6f 0a 8k+;z a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it/zjhk6 za;ks0t8+ fwq leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glov2hiro f: pp)byn.a(9gil)7wqe backward 25 cm when the ball is caught. What was the average force exerted by the ball on tp lyf: i7i(2nob9.a )gwhqrp)he glove?    N

If the speed of a car is increased by 50%, by wha bhad6k/-dqy9 t factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driverqak9 dy-bh/6 d’s reaction time.

  At an accident scene on a level road, investigators measure a car’s*5 q2cyg 2cs,kzi*wj :eb8 ssr skid mark to c sykbigqr:5 c2z*2s,*w8e sjbe 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time gcc 1l8xx 6 wd:+d6.7-okyl i4tamdubit reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is ld6.8ct xmi7u c4x ldb-y1:6k wd+oagabout 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doe;vobeu vx+ am) 8q4n5s7cj* nps 80.0 J of work on it? Neglect air resistance.8xoqpuc bm);5 a+j 4vnv*s en7    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratioci;f;; kwb8kc35t e2qqa hs/dn by a single cable.q faith;b q 8csek/k5wcd;;32 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 jv nq89 )2vwe(k u gv7xju) p4azi7la(constant, k, of 440N/m How much must this spring be stretched to store 25 J of potentiav(n7wa)qik 8jzx) 9 (g 2l vuapvu47jel energy?    m

  A 7.0-kg monkey swin85f mjhk 8z1dxgs from one branch to another 1.2 m higher. What is the changexdm185 hjk8 zf in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg 6f 8gr9:bee)zfqa f5mpole vaulter change if his gz95ef: bf )qra 68efmcenter of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when7+g) d;b/.yc itm pmj-q5j e lqfyf*f( it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffnessjiy )5bq;m/g (+7ff.fy- mtpcledj *q constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m 88uk;s/7k9jrb.a zbyr kh rg, above the ground. What is the potential energy of the book relatarkbk; z7 sj9ru,k8/8hy.rgbive to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to thy7i:w t5(0px;bz0;x1jag xe6z ncu3x rmhg 5he top of a 3300-m peak.xx5m y06i7;zt0 c(;arg5 nebug1xpzj:hw hx3
(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 s)8(el0 z exazhangs 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 sl0(az8 ze) exspring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/p:wi ;q ms7vkf: (ale*s) and grabs a vine hanging vertically from a tall tree in the juefwamks q:l *p: 7;i(vngle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, st5*- z )xibleku u.*vdlides 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 friction.hnkihdph4- l ygo8s/c 35r x e)k-s/lless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transcl rhmul2- o(t, (9ulq)-sjuw formed into gravitational potential energy without the aid of a pole. With what minimum speed must Frau h-(omtucq)r s -9llwl2( ju,n 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 verq +91k./rpnwpc2e19 mv cppix;7 jbvetically upward from the top of a platform with a speed ofvebp;j 1.9ec / p7mpnwk+ix2cv1rp q9 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 spring e p j6d8q7)b1vro. zpbstiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when releb o) rvpz jp7bq8d16.eased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without frictio/p(v4ialuksy k)3+ xrn along the looped track shown in Fig. 6–39. If the blovxa+4s3 py(u)r/i lkkck is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a sp(i29*l,s oxq wdy6crcliih 58np4r h7ring (spring stiffness constant k), Fig. 6–40. The block is given anp x 2rods(8nh45h*l ilyrq,6icci9 w7 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 bridge. She is tied tgbs z (d0ukv1a9k2zz1o 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 bungv0kazd(zgk192zu bs1 ee 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 7ayx0 e) 4-cp.nnxp oldragged up to point 1 where it is released from rest. Assumcx7 0ax - nlnp4o.eyp)ing no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a hkh :m1db,)gxspeed 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 placed1pot 0b: gxv-i 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 acceleration of no more than 5.0 g when brought to r-iv op1g:0bxtest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to98t+xv7mze h 2 iwzq0j cycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 9 wwu0k4u;e/u (/*mdve3si j7ffu w.k l5km/h in opposite directions, collide head-on and come du3w*kukslew ui ;v/m4/ju0f.f(7 weto 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., c.xu.it7( g ww3oi.mdg9lq5 jdc/vp 5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in thi .,vxtu/dw59m w.jici3gp g7(c. oqdls process?    J

  A ski starts from rest and sl egtzc5cei.-,aq. u 2gides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is droppeds pnq5d(s .e+qwmt+l/+ ey gg- from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.su2bf38 e 315wuqs2tkgq x2h x5 m. 1sw h2qqtx b2s3f k35uu g2ex8
(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 constan wsgn 7jb*:/gkt 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 og/b:*7njgwk s f the crate?    m/s

  Suppose the roller coaster in )b).reme g .)1gqwvct 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 speed will it reach point 2? The distance tr.)tgcgvq r em )1.ebw)aveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady 5ssa)t4xx /kn*p 9qsz1bkk /sk ss9.yupward 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 very light horizontal sprinp1 b7p,0o6oyz 1ty,o hr4l uljg (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 so1 u l l0ohj,14pzt7o6rpy b,ytopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is fir;vdw ;ee ng)gkbcf- y +kufd(u 9rkx1a(9zc7(mly 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-9x en)k dvu(fbf7rk1azg(kc; cuy9w ; d+ (eg 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 spac ma2t:glqr,x 6e shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 50a,x m2: grtlq60km/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 motor to lift a 315-kg piano/v.;pr2 hb*vz8nqkb u to a sixth-story window 16.0 zh qvnu2v/*r p8 bb.;km above?    s

  If a car generates 18 hp when tra nvjsmat ul v:i9,rvri(l()2:8-fa czveling at a steady 88km/h what must be the average force exerted on the carv98i v2rl(v:ulz c(,sinr-j)af:mta 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 aver7c lc wosp3k4;age power delivered byswc p7cl4k;3o the engine?$\approx$    hp

  (a) Show that one British ho j 3:g, pqfzsv/v,b 3n*bpel1frsepower$ \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 ex:o uc7+(dk+h fasq-tvpressed 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 u wp82wp oi3w7car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and i8pwpw w3uo27hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 2 v3 lw93+ -p4sbguj-w ;titnl6rtpluv eg4f43.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg -/6 0tzmzabkg shot from rest to 14m/s If this motion takes 1.5 s, wha0m6k tzbz g-/at average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of unsss,ke6 0:y water per minute through a height of 3.60 m. What output rating (watts) shoule s6nkus y:s0,d the pump motor have?    W

  During a workout, the fooa 67m t,xztj+i 9jk1hdtball players at State U. ran up the stadium stairs in 66 s. The stair1 h9kd6z +ia7x tjjmt,s 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 cycli6otgm0avd,l z (+b 6rmst climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 12-j1qe / :b ,f4jcu9teo xz7 cxn5xvz+z0 hp. How steep a hill can it climb at a constant speed of 75km/hzc1jq/t: z z79+fcu, xv-xjoxb 4ne5e if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dr,183 k /r fhu7jpliwwaag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fricti w7kw 3j r,uphlaif/81on is 0.45?    hp

  A bicyclist coasts down a x5z:xm2 w;uzgo c1xx*o:m is77.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bum271v*k r qpywfi 5g,vvpers” 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 tesfv, 5ip 2vv7*rq gk1ywted by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is * ok(fmpd,)o arpufgv 1qc; -010.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above ouvcfk1fda m(q*p)o-rp , g ;0the 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 q.b47xc 7i9cuyhdg2k famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch y7bcxq2 9gdi7k4cu h.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 frictej;4i vu+xbgu8xy56eion along the looped track shown in Fig. 6–39 is to remain on the track at all times, ev8 ;g6ub xv5yue4ex i+jen at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft wfc d8m6 sx1;kay wxt zcu780o-ithout 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 veloc0 y 8-7;f1 ua6k mx8wszotcxdcity 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 (m:ai( wl zygilr1wo6 gi 34i*length L whose other end is fixed (Fig. 6–43)4 3i6:z1a*o(lglirgy miwi( w.
(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-hvh64 ,1onlo iq ni/d -5rk;u 2eap0vnkigh mountain. The climb is made in 5.0 h u2vno0vk-;d,pkl r 1 oq4ine/a6 hi5nstarting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28:ivrt a 7aa96x m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47, y* 6s 3g*o5nefvgml4l000 people per hour. fgg3*l6 e 5nm loyvs4*If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s anpwpz8 /7f dvw,d falls vertically 81 m before striking the tur d8,wpwz p7f/vbine 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 coasteg+hdd q;);(28qn3mqn uhcdigr 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 needed, this answer doesn’t depend on the size of the loop or how fast yn(32u dqh8g q g d;+dhinmq;c)ou go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how high cod4jqp/;bh gfcf8: /twuld an 82-kg man climb a ladder if he were fueled by one bar (=10fd / hq8g:j4t/b wcpf;00kJ)    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 upwa:,cep(e s ,cpau.s 7aqrd angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the sx,(qslo03gtbw2q o: g1b ygg :8ve.wr cale 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 mvos3x.w1(qw: bq: grl20oeg,8y tb gg , what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6–4vnsv r 2h,k ou0e3m4n.el64ry 5). He releases the rope 4lnservk rn m.u3h,o 2yv0 e64when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 943w9 drbzg 2*z9zyers.0 s.3r92eg wyz*zsb4 dz r9 What minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pu phhk(1 hp* a/o4l0zddmped by reversible turbine pumps from a low to a high k* hd /hda(ph4pl0 1ozreservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is(jnq blqnhrt. /q-4)p the spring stiffness constant for each of the two resulting plht. q4(q)nrjn/-qb springs?   k

  A 6.0-kg block is pushed 8.0 m up akbkbga88+v0au) q 4g y rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long wir..f y)j5o pt;4cdgdhll it take to accelerate frdco5d. 4.j ygtrp)h;fom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patientq,y 2t wjuiv+4 walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 vqw 24+,tjuy i$^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a dis/8* a hlm2pfb6:2fmd g2hy9)y isaxlstance of 500 m, what was its velocity whendx* hg2y m/b2hpfsam9l2 i l6sf8:a )y it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a w xk+g 0(.bpb .w2fbgzpater wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheelkbp (+2.gbp xw0zgb f. is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s