In what ways is the word “work” g+ :fs ijx)/erc wt86lw9z 1kjas used in everyday language the same as that defined in phx)gste 9w 6cw1+lfik zjr:/8jysics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? E),cp z1n)f,g o1r m2qq muz+pxxplain.

Can the normal force on8 h:wc -dim6mp an object ever do work? Explain.

A woman swimming upstream is rgp1zzm ek1 17pe5,y inot moving with respect to the shore. Is she doing any work? If she stops swimming and merekerz1 7e g1p,mpi5y1zly floats, is work done on her?

Is the work done by lrwl (q3.o : ,tjj.eftkinetic friction forces always negative? [Hint: Consider what happens to the ltj, q.jef 3t:.( rlowdishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wallp0s)b6 zo1nifl)zjl; even though you are doing no work? i) f)jlz0sb1o6lz ;np

You have two springs that are idedn,376vqskxb ntical except that spring l is stiffer than sprindq6k ,x vbns73g 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 free to slide oor ,pg)(0 wh)du rz8njn a frictionless surfa0dwo) 8(uhgrj p)nz,rce (Fig.6-30). The 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 potentialic c21in-41jr wt xqb n+i(z8e energy change when you jump as high as yi1(x-n41cbje q2wi8rctiz n+ ou can?

In Fig. 6–31, water balloons ax .whb2 ixb. ll(6uil/re tossed from the roof of a building, all with the same h2ib lu6l (l.x/iw.x bspeed 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 3aa9op(nf7)chi ( dar 59gmrqabove 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 directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.o3m7d 9 a rr(5)incgaq9a( fph

A coil spring of mass m rests upright on a table. If you compress the spring by n-)nc,1eot q0n2pm lf pressing down with your hand and then release it, can the spring leave the t1pf e0q n2,ntmc-o)lnable? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire ievs(zu: )na 1(Fig. 6–33). 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 the ball wvz: si n)ea(u1ithout pushing it. Why?

What happens to the gravitational potential e:x 2fhu96h jlsnergy when water at the top of a waterfall 2lx h 6ju:fhs9falls to the pool below?

Describe the energy transformations when a zndssy1 rbue3 yz :81t6va.s-child hops around on a pogo stick.

Describe the energy transformations that take place when a skier s9n5 wxkmn: ;j4v-xvga nap+x5 tarts skiing down a hill, :g 4av5jx; x wva+m -xkp5n9nnbut after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill 3/vus nc,r4y)xgnesmks0 +r e27yc;wof height h and slides down. Does the velocity at the bottom depend on the anglencv4ge/ ,w;+esxm ysk70 snr3 )c2ur y of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path r0nsas 1kwla2h-fdqk0 ;l 3vm,9aqnj 7ather than stepping on top and jumpingl7fk 0jaq2laqn ;s 9dvwh103 asn-,mk down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into al7h8gp1avxb ; bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow willxa p7vlb;h g18 penetrate how much farther than the slower arrow? Explain.

Analyze the motion of x)r;c4e+sf sta simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking fricres ;tsfxc +)4tion into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it re l-oektt, 8pv )uj7di 1hpt1w1bound to a height greater than its original he 1wji u1o,ltht7)dv te-pp81 kight? Explain.

Suppose you lift a suitcase from the floor to a table. The ig 4.wb64c mwgdn. wp.work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicag4 ic. wdw64mgn b..pwted 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 uab la 1 vptn(prptxl+qz.6l7 3:i2lj)qa5*qthan the work.

Why is it easier to climb a mountain via a zigzag trail than to climb strayze z/n)p1g;b ight u/nbg1 z; ezy)pp?

Recall from Chapter 4, Example 4–14, that yg.8p;ycn- 4azbxm :gpou can use a pulley 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? Account for this, using energy cbym ;axgz4c 8-:.gn pponcepts.

  How much work is done by the gravitati1(1ae rolc)3+g8cu d tf* :x)u vlomklonal force when a 265-kg pile driver falls 2.80 mlcr):1(ouc1+*) fxmal8 3 klveutg o d?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much w1f ihe((vituh4r,b t:ll -g-dadm29d ork is requ-(me ld9ugb2h1d d:ai h (-vfl4t t,irired?    J

  A 1300-N crate rests on the floor. How much work is required-pr-i o9nj r24w3teqh to move it at constan3r4-not re-hjip wq29t speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally)lqz5s bf /560l7sgl bn pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coeffici6 0nfgb sblll5z7 5sq/ent of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across /vkb,s *l2vx ft3wuh jr8wm(2 a floor at a rate of for 7.0 s. Find the net works,m2 r t(vh3uw*b2l8x wjfk v/ done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flxaa xx01rjs*rfk4 f,v/du 94t at on a table. How much work is required to stack js ax9 ,f urx4v k1ta0*df/4xrthem one on top of another?    J

A lever such as that shown in Fi9xb q,xtxn1 jq)2mc1u.f*m ou 2mi6cx g. 6-35 can be used to liff objects we might not otherwise be able to liff. Show th )i6 *cmb1fo9mmxx12 nutxqqxu. j c,2at the 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° inclinekj6y4fb qn*mn.3t pz1ab+o. t 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 0.40t.n *4+bpozk 6 fmq3ayjtb n1.. 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 of z.-(w *2 xo jner,dt ,)t8fhlh0tngog0.jr 0th(n-,fodg)ht*.tzlx w8e g o2n ,10 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is lz/9 ntxtialpu-w0r*vq)v t2 ty0:0i dinear 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 s*j4av71ctr6l bm z2c.ov/f w axis, varies as shown in Fig. 6–37. Dete/v7 bj1mzt*fosr a 4 c.wl2c6vrmine the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on arx66p*(cj boqdh gi)5 particle acts 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, with mass of4gk ,vpoo,j;w +)mijf $5.31\times10^{-26}$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 atqrg2u)ca lhgf 9,ti-;v-x:3ka lnx6rrow is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elecbhc8,i0wy q zz5sf8:ftron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kg- l9;hhy7u5co8 emt05oamzw xcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a vyg)r.e fx*3 sbow whose string exerts an average force of 110 N on e xy vr*.3gfs)the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a *rxl7es s f /bkkp4(t86e)jqzfielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glove? sf 6req/*ksj4 kt( )7bezp8lx    N

If the speed of a car is increased by 50%, by what factor will its minimum brr9ld9(ck 8z;t+ i3soa zwszw.c k47riaking distance be increased, assuming all else is the same? Ignore the drilcwi9 ss7k w4 azckt z+r3(rz9;od8 .iver’s reaction time.

  At an accident scene on a level ro)1-k;yvbvb/g j2j,dam noe.lad, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the -g) o;1 ea,y.j k/j2nl vdbmbvspeed 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 pitc0cwf ii a e9yu/)hco:/hed at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distanc/)ficc:au e9 iohw0/y e between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight ue4p8umux26 bo6aejon (ky-b1 p by someone who does 80.0 J of ubbx6oje 4ko2y 6n( 1a-ue8pm work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration cc/x l e *x n8heai**5tivusqnm 3.0r4ft-go/by a single cable. Deter3x*5 0e*etsho.n q8tcvg l-/icfuri*/n x am4mine
(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,) kaogf0-6wsziiq w s5 a6-f+e of 440N/m How much must this spring be stretched to iqzfo)-wi-g +66sea50afws kstore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one b h(h(c yn(6ljqt ce61 e q2kdy2cr0yg7ranch to another 1.2 m higher. What is the changer2chtn 0y7(ye6h(6kle1( jcq2 dqg yc in potential energy?    J

  By how much does the gravitational potential energy yt96 :inf k m8ozmat2)of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump?fai6m892)t oz:tn ykm    J

  A 1200-kg car rolling on a horizontal a(-ef(a epj r+surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spr(+ja- eraf(eping stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m aa2d g4g)ye j3ibove the ground. What is the potential energy of d3ae ij42g gy)the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m tmzp h s ;g8,i2ra97 qbncc8y7and climbs to the top of a 3300-m pe8 gbiy 79;8rmshpzct,qn2 a7cak.
(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 verticallyd1k2 mr8l3k+e5hn1fh xmop:u next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a3: 5le 2hmur8ok+ fd1mn1hxkp 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, p npm )ahgpl*k,ev ;lgm07j9* is running at top speed (5.3m/s) and grabs a vine hanging vertically frojh*)vg9pkmel a, 7p; lnp0*mgm a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startep28 cavzi2t 8yubq2u3fx )*8lob dt+ing from rest, 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 )m0vu8- cdhm52 0lvqj-k hiuha frictionless 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 transfoavj5p(5w5bp rrmed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in or b5awpr vp(5j5der 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 a0 /pozmjtyan3., r0/6ss gpnlrtist jumps vertically upward from the top of a platform with a speed ogzjt6m .nn/a0lss0 /pp3o y,rf 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 stiffness constanlqqa:w8*x8 gi8yx- cst 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 rele 8lg-8s:*qw qa xiyc8xased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction h.xcj ldfm:; vv lku;5+p(d,malong the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimuvu+lm.kpd( clhd jmx:v;5f;, m height h must it be released?    r

A block of mass m is attaurk30xnw/e mob+pk-1 ched to the end of a spring (spring stiffness constant k), Fig-1 kr pen0mb+wko/ux3. 6–40. 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 jumps from a bridge. s;kp ue2xt6 .xShe is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate thex; exu2tksp.6 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 isot*dxwyga aw -6smc31 pi o+:. dragged up to point 1 where it is released from rest. Assuming n oa w:o+*sidtg 3y- px1.6cmawo friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown t xhtbqbf4/+. with 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 elevator shaf har75o8onp)z t. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the valor87n )5 azhopue that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle hn;rbw(3g 4:gul*m0bv+ zw m n+uosm3up 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 xtto7gl- euq5+a; u(a directions, collide head-on and come to rest. How much thermal energy is produced in this collisi tu+lxea 5;o(a g-qu7ton? $a\times10^b$ J a =    b =   

  A 21.7-kg child descenh hv49rhh7rv xp:6ql9 ds a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much therma 4h9hvh69r:xr 7vphql l energy due to friction was generated in this process?    J

  A ski starts from rest and slides d95f(dvg h9za +d4wyegown 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 drop;as4os.1skbvn d4 0 umk+5a b2nbz6 ruped 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 hei/hvjqkrdpf,un29 9a y)-d 0 owght of 2.0 m, and it bounces back to a height of 1.5 mw)j9/f yp rq9a0du2- ,ko dhvn.
(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 /*oczfsj6i u.:8v4: sltnmqq a floor with a constant horizontal force of umqj8 tcsv* :n6s4 fzq/i.o:l350 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 Fig. 6–41 passes point 1 withtii3avz q(*v: a speed of If the average force of friction is equal to one-fifth of its weight, with whavv (t3*aiqiz:t speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches ygv+)5 w.fzcithe foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a vy7+ nh07 5 ,rajwf nsb5abvty3ery light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when c+3h nbwjv5,yf nt757 a0bars yompressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sprii8)fq4fj9b 9 ggh: pxcng, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibr 4pcx)q:b 8jggffh99iium position will it stretch on its first swing?    m

  Early test flights for the space shuttle itpg8l8abb qm * :1fv.used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The gl .8a1bi:mf v8*qpt bglider 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 yg0 26l7xfwen-lu-tc lift a 315-kg piano to a sixth-story window 16.0 m abovxtfc-le0g ny6w- 7u2le?    s

  If a car generates 18 hp when traveling at a steady 88km/h what muswb3 yz gxgt31 uzvt.,y rk*:8qt be the average force exerted on thk* t:.3 b13y,xuzty 8rzg qvgwe 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 averahut s5mfmk gc 3yr2mjea934+ 8ge p k sme8gy3 cf5r3+ht42a 9umjmower delivered by the engine?$\approx$    hp

  (a) Show that one British hy6i7v ru m73h0rgt lk/orsepower$ \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 “kilowatt-houresba . 04b)2nwe loyh 3+q5xlhs.”
(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 slown6jlzxc e(c5rg b gwz:c;n1+4 s down from to 65km/h in about 6.0 s on the level when it is in 461g :g+xz wclcrjce; b(zn 5nneutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do:q.0tqj ir. b(pxbm:k in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest r bpm). fts1z,, zj4hbto 14m/s If this motion takes 1.5 s, what average powet.m, ,bz)s rbz1f4phjr was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3akn-rbm*cezy b1 vdz:-w891 vc8)kpr.60 m. What output rating (wattrda :bkn8e)1 -wr vcpyk-9 vm1 b*cz8zs) should the pump motor have?    W

  During a workout, the fooq io6 ie2 no5(gd.w(j20vo6bt t0 cojxtball players at State U. ran up the stadium stairs in 66 s. The o ei0ob to2(qxod j.c 66iv0wtgn (25jstairs 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 cyclist climbu nsnh7f2(ar7)fmwq2 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 -)uhu qfsq -/n120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional uqhfn-) u/-q sforces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310- :0d/aaon 9xm.rb k0khyq1f+ lkg box along a level floor at a ob1h a90f rk d/lym 0.x:nqk+aspeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a yhd,v2cb eq91p l io15apz89l 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s car.aih or3dtcisll+n .sew.(6n :v4. n os have built “5mi/h(8km/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 ram 4nl6ieclawhns.:os r.n.o it(3+d .vming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and 2heeytcu:7nju 6 i83t 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,86euy ju:27nt ei3c ht 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 Oj1w p,i( flpi )yx6:wqlympics shows that his center of mass rose 1.1 m from launch point to the top of the apj6iw: )wf l1i,(qp yxrc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track showmp th b8;:h-(ds.yq kfos..oon in Fig. 6–39 is to remain on the trac( ts.:yhso 8ko;o. p-m.hb dqfk at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from anab( h 11)7k.e fhxbzsi1iwkr ) aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only bkhkf1 )b ziwx)1s7(rh ea. i1minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horpd+b0wd27x iuhv 4ujp 84bx5lizontal cord of length L whose other end is fixed (Fig. 6–43).vxb2x80wlpp ud b74+5u4ijhd
(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 mcv2j+v*zfmwmj l.s029+lw (vp:enjfni 0 d.a 3700-m-high mountain. The climb is made in 5.*jnvcw: fsmwm92+(n vl.mjl2 0fv 0 eid+pj.z0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-k)*dk4yaq+n+,jot ;uc myvu;jrts ;r 1g 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 claimmx:f clazzk*+v*; gfojj3i5/1 1ahy ts that its lifts can move 47,000 people per hour. If the average lifta 11;goc yj*z+x*hktmfl : /fzivja35 carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the*ki mxm; eq fhuu9ups24s(0h0 zb41hr rate of 650kg/s and falls vertically 81 m before striking the turbru4049sze 02mihxqk(h*u u;1mbph fsine 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 w3l 5-rhagsnx+ 7mlh c vj.b4l 61qvtq.ith 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 asql74h nx63.+lh .ra qjm1 s-bg5v tvcl long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body caj)jsv,w)xn92an,w5atit gahs d 0;0ould convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ),gw aa 2 v ,5nts ;0ws9anta)0xjjdhi)    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 ymcbz/ g7vf *n06vxm5angle 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 scalrht2beiq9ljpo u )6o16u:hr /e compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale frorh9 h)r ebptoiuuol 662q/: j1m a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6–xq8/dd :) ercbdr4kwfj vb2+,45). He releases 4dbdebkv :rj2w8q+cr ) ,xfd/the rope 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, a 72-kg athlete climbs a vertical distance of s.o,qn19:z cbpsfts+ 5.0 m in 9.0 s. W+cs9z 1qbst,pf sn.:ohat minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumpd +f-jmc1 zz9ued by reversible turbi -md czf+zu9j1ne pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spring dl92m:6ctos1q 7 kdjjl:rn3vstiffness constant for each of the s1 ln9j63o mkj 7:qd rvd:ct2ltwo resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a af8hmsg0zu0fcm - s97rough 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 wivolhzgj2e24q 5q;4e*-wj.st * wggfl ll it takg*w;5oeslg4jj.*2gq 2hq4z-w ve lft e to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (thm3it6wh-:mu er9n: hs1xhut y1j (q1f e “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is h: :9emi(uxm qr-1y1h1ns 3hfwu t6tjsloping 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 speaf)f ); i4c85nkcbe sfws a 500-kg rock vertically upward a distance of 500 m, what was its veksn5e )f8iacf;4b f )clocity when 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 waterbxno:6nde6 k:7ipp 70e se+d c wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheelckeenxd0p pn6o::d77i+b6 se 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