In what ways is the word “work” as used in everyday language the nz + i-pyllfq7l5*0jc same as that defi5i7l0yj+qllf n c z*-pned in physics? In what ways is it different? Give examples of both.

Can a centripetal force everu. t zkg,zi4-;sw,rbz gqj-8r do work on an object? Explain.

Can the normal force on an object ever do work? Explhadcn :x2t09co 5l e 4,latsb+s7yam; ain.

A woman swimming upstream is not moving with respect to the shore+37zoz9v ;f lcbka(jv . Is she doing an7+b9ovk;(cfzl3z v j ay work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [H e g z/(-idw-boc(vpikk996d jint: Consider what happens to the dishes when e-kp6dogkd wv (/i9i (-c9bzj you pull a tablecloth out from under them.]

Why is it tiring to push hardn 9qtst5 rs/6v against a solid wall even though you are doing no /vst56q9t sn rwork?

You have two springs that are identical except that sprinfwwfk- rukp8, i.z3 *vg l is stiffer than spring 2 k zf-p.*wivurf, 38wk$(k_1>k_2).$ 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 horizonpbnfrpur+c836hg- np (j pd8,tal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at 6pdjnhrp r+p nuf 388cb(,pg- 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 gravitationalsmpbn4wj0erbxiq *x0)(dc;ys 2f7l 0 potential energy change when you jump as high as b0;*lb xi)qcwp ye r0sm7sn4 d02fxj( you can?

In Fig. 6–31, water balloons are tossed from th s./n425 t9szz :i omuisra(v wxd+5nye roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ign5m5xi z/ t o s:2nrwa.(+d9isvus yn4zore air resistance.

A pendulum is launched from a point thf +6sze0. hqu,bfm vy pyamar06(t,7qat is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle.,afrb6+6m uvhty 0 ems q zqa(f,70yp from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress t2e3j,sl 2w 0ovgz5npyfx;6 h yhe spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the 2z vlnpjxywg3 y , o;25s6he0flaw of conservation of energy.

A bowling ball is hung from the ceiling by a steel wi/;y js:6zmfwsbubl 4xe (47cbre (Fig. 6–33). The instructor pulls the ball back and sta sbfj;s:x4(mzu 4yw7l/bec6bnds against 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 energy when water b0 3owsm9b3 3sc wzm 6a,it(mtkh2s5z at the top of a waterfall falls to the pool be(wb5hto6ai92cs ,sk3zms3mm0w3tb z low?

Describe the energy transformations when 9+/ay4j8v j qd j,b*kl(szdhoxp5 sd 6a child hops around on a pogo stick.

Describe the energy transformations ta5 b(s gp w1+khy,oq(dhat take place when a skier starts skiing down a hill, but after a time is br+ sd,hqw((1kay pbo g5ought to rest by striking a snowdrift.

A child on a sled (totk1 ztb6*h+ i irzt+i2x;txy wm(ck8n:al mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no frirbit 628 x1(i;t+zm ky *zxchw:t+kinction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in th3vj5 -2 romvb5bd-zdq f:v 8eeeir path rather than stepping on top and jumping down on the 53j : rvzd 2d-e8ebmvbo5 v-qfother side. Explain.

Two identical arrows, one with twice the speed of the other, are 4y5e. vsz1+prxo )y eqh60jib fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farthe) vi ry5o14h+eyxbsqj6z.p e 0r than the slower arrow? Explain.

Analyze the motion of a simple swingwvrd*kx c1 k/z9r0;or ing pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain whvo0r ;*9kr/kr dwxzc 1y a grandfather clock has to be wound up.

When a “superball” is dropped, candxtb/d,v4,-y:z gad o it rebound to a height greater than its origin:axod,dygvd- , 4zt /bal height? Explain.

Suppose you lift a suitcase from the floor to a table. The work ,*snh 8 r8,wqqv rjgc;you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicn8*qj,wvqc8r hs,g ; rated 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 the o/hi7x t 0o9evwork.

Why is it easier to climb a mountain via a zigzag trail than 7 zeoptx6th2r ;u-j-fq4ntn8to climb straight up? jn4qthzxe2 ofrut;-t-p6n78

Recall from Chapter 4, Example 4–14, that you can use a puve0 (x1t7z lv)rwyhn48lsn/f lley and ropes to decrease th1ys v0znflvh)xnwrel/(t 8 74 e 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 concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fa,n7qq qoxz7, alls 2.80 m?nx aq77z q,,oq    J

  A 65.0-kg firefighter climbs a flicb 8o/k+rzl. /b bgf 0uifjilwp+.99vght of stairs 20.0 m high. How much work is requi/+cjk bb lrzp +8if0uilgo.f9.v/bw 9 red?    J

  A 1300-N crate rests on thg0a1/vp/ qu bpe floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forceugpv 0q/p /ab1 of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushingt5i e g7h.tssb t,(h7s a 160-kg crate 10.3 m atitsgh.es7( ,57hts b cross a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a flo/et (rvat2 x3mz xxl).or at a rate of for 7.0 s. Find the net workmx(tv2 zet ./rl3)x xa done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Hof2f* y*i9c a5b q;aenfw much work is required to stack them one on top of;e i 2n abyf*c*9f5aqf another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects k jx/y:zs+jt- we might not otherwise be able to lif: k-y jjt/zx+sf. Show that 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° inc1z9u t9 19* 6n kvnjegmbqu;pyline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effectik91b ;z jymeu*61pqvnnu 9g t9ve 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 ajboe:a:wb 3+odio8p,8tih n ( helicopter of mass M an acceleration of 0.10 g upward.(8+twoe8di no,hbabj: io:p3    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:n, -dsbg o0kzxtv+p+uz2 y/t 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 jaiqj3,9su (cgpz-v3 axis, varies as shown in Fig. 6–37. Determine th3c zi(qsj39, jguvp-a e work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particli/7yt3u 154 w)uq pv zne1vaewe 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 of w*0n6)y: t bcf+aiwgl$5.31\times10^{-26}$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 faf)4 lz0 e/-ldk ug 1w6cuphpb-ctor 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 ull6mp3w h07 dstop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar 5ldljt:v,j:li 9a a/d ewe*h/ traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string g87ihjj- z n8cn *tn:hkq(dz9exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of n*hhi(8-jnkn: 9t qdc zjz87 gthe arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 251wb kz0nzn3+b cm when the ball is caught. What was the average force exez b3+n znw10bkrted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor /u:ie5;23 ld(g jjqnslu- nybwill its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s rjgy/ed2-ni: uj;u l(5 q3ns lbeaction time.

  At an accident scene on a level road, invt k zg0/7n;7extn , o(2e ikc7qnaoiq:estigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coeffi7eq n/2k zktg7,i xcq;7toni(an0eo :cient 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 yuuj tqtlq0v ;i8y7s4by j-66qe)gkg;ig1/ tof 0.25 kg is pitched 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 distaql0;j;6 s4-u6gj7q1gqk) b/tg t8yy y tiivuence 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 s xakf8.c e zphff/m3 7ts7 b+au9b3/haomeone who does 80.0 J of work on it? Neglect air res/f/p +m7xbaht7ha ua fek 9zc3s.3f b8istance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratiot(yx0v+el( gcgs/*d mn by a single cabggetmx(0*+d ( yl /vscle. 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 stiffnzhqcxwnm kbzi-95587rb 4dh. ess constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energy? n5dzq.m5bz hcb xw89h4-7irk    m

  A 7.0-kg monkey swings from one branch to co2elq p8a nnlm1:24l another 1.2 m higher. What is the change in potentialcml221lp:n q8ole4 a n energy?    J

  By how much does the gravitational potential energy of a mcc7.-uwt8li 64-kg pole vaulter change if his center of mass rises a utmwclc.7- i8bout 4.0 m during the jump?    J

  A 1200-kg car rolling on a 7i2vg i ga(rd+horizontal 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 di7i ga+rgv2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the gt:o 9 z; qupnqh:5yuy:round so it is 2.20 m above the ground. What is the potential ene5 p ho9q znuqu;::y:tyrgy 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 elevpo9jt*gyd41 cation of 1600 m and climbs to the top of a 3300-m4t1dj* cpy9 og peak.
(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 next to a ruler. 5*wd+qz1 -nvkc, v8ppl h:c roThe end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached tch q +dp,1:8wkl5vr- znpv co*o the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running ay 0ls ki4o1n:gt top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How hignlyk4 :i1 sgo0h can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from r6 y baye85tno *s,dfc5a 2a/wxest, 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 utum. r zf )n7l8y0(iwap a 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 transf n8ohv:09lf)4iv7 rkddmui :y ormed 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 of 0.7m/s.li0r v7dmik9o8fny4du: h): v    m/s

  A 65-kg trampoline artist jumps vertically upwardpk ptkr5gfe5-7md +m/db d4yobg+. 3q from the top of a platform with gem b -k/3dmofp bdt45rk75+qy +d.gp a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffnessw9rba)5 n--rw rlwmrawu7 r8* 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 released )7l-n raru awbmw8w- wrrr*59?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides wss.) vx cse(b-ithout friction along the looped track shown in Fig. 6–39. If the block is to rem-vs.sbs(xc) eain 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 spring (spring stiffness constank+la-7c 3. syy dd1gh 1arb4mmt k), Fig. 6–40. The block iy4al7s d-m dk1h3 b+.cmg1rays 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. She is tied to a bungee cord whose o ci dt6;jo+s)unstretched length is 12 m, and falls a total o+ot6o)j; sdic f 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to p8o plt(xdte io*md8 -y3a1 wx)oint 1 where it is released )p8x83a(to wd1y-moti xd el*from rest. Assuming 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 speed of 12 m/s a4ys /gyse( xd +by9(yxlviz)5t 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 springf5)eqb)dm2er-;9 cftbumoqe, ) ac*m 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 acceleration of no *meb)cf5uo e-) db9mc ae2qt),fmqr ;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 u6kdzy 5r 4u :qpnk;e1pp 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 9z5a9-pxi3 fs v5km/h in opposite directions, collide head-on and come to rest. How much thermal energy izv3fx5sa9-p is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m highov fw8*8 k 1vepv6*rvv and reaches the bottom with a speed of 2.2m/s How much t*r6pev*v vv 88fwvok1 hermal energy due to friction was generated in this process?    J

  A ski starts from rest and sli rkezq+8sv4 0b( 4czteoxn8 3zox 5(audes 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 dropped from a tree 13.0 m above the ground/f8or lvuvsnsv7+q;3e+k 8/wm krux8.
(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 he2p+2rtg3rbiwxo7 ix* ight of 2.0 m, and it bounces back to a height of 1.5 m.pb327*ix2org wi r+tx
(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 acr8/m hhnr+eg ky5y7:ai oss a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for thea+ hikh7 m nyy5/rge:8 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 poih4y;spn *dt kth3 w25ant 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what5p4th 3* ks2tda yw;hn speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s:t(lt vn kwm +.lmg::n reaches the 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 very light horizontal sprinz4+ v :b 81;hjtcunv8f . tf+/vnkclmmg (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turn8jnb 4mv t.ku:c+c/zh1+l;nfmvf 8tving 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 lit,*k7cy9jow x3u0arv8 qsi 4a ght horizontal spring, Fig. 6–40. The block can q 3jk rc7at y8, u09aoxw*vs4islide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glidaf;3 5lr q,zdd h*8pnxk*aix; er” (mass of 980 kg including pilot) that was lau5li qkx*;r3, x 8zh*fn;pda adnched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg pian 5n en-hsv42(mwycvu7o to a sixth-story window 16.0 m ab5wnvuhy7ev2(m -csn 4 ove?    s

  If a car generates 18 hp h,uh d)t4l;f y( uki+3qc6tfgwhen traveling at a steady 88km/h what must be the averag6f ,tc ylq4;uh d(u)kgth3i+ fe force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whaihq go90+ xzpip898rp t is the average power delivered by p8riqx8+pzg9ho9p 0 ithe engine?$\approx$    hp

  (a) Show that one British horsepu jgkyn7m s1fcw fcdp;vg..+j.w 2+,hower$ \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-hourzzd*q6j iy :w0s.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.0gzxh: h0jdiw:oc;8m) s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling ch :dhijw 8o xgmz0:;)at a constant 75km/h.    hp

  How much work can a 3.0-hp md 3vty:7mc66db6 oh tsotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from re1q;h gc1 8x7ngrg zpi0st to 14m/s If this motion takes 1.5 1z0qnxghpg 7 ;grci81s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m.+em s udr4ykq52:oi 2z What output rating (wa4o2u2rm dyks:q ie5+ztts) should the pump motor have?    W

  During a workout, the fotacdi:ee f)ihevs88n-*; f1n* l/ fis otball players at State U. ran up the stadium stairs in 66 s. The stairs a:hnc vd;e f*s18 li-f8/ is)ea fni*tere 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 c.v6(i y: ttbekh:v1;n ye0g kwlimb 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 120 hp. How steed-3 pow+ca;uw p a hill can it climb at a constant speed of 75km/h if th+p wa ;u3wo-cde frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg b 8 dbk obrb2;z*uhn,/zox along a level floor at a speed of 1.2m/s if the coefficientdh ;/ rbo 8kunzz*b2b, of friction is 0.45?    hp

  A bicyclist coasts doh:fvr2m3ow6 b eao8z6wn a 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 cars have built “5mi/h(8km/h)v(xxqep 2j3y- bumpers” that are designed to compress and rebound elastically without any physical damagev-qy(epj x2x3 at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remainiega.,rn8 se ;psqmt72q; q hi/ng four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the ./q s gepe2as,nr;q7qt8 ;him 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 pou 7*z h7rh5qa*pip 35z+ uipthe 1936 Olympics 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 at lau7h*q*piz5a+ z3i hu o prup5p7nch 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 ts ry0+* ctmn.d;)baj rhe looped track shown in Fig. 6–39 is to remain on the track at all times, yr+c* rta;.b )j0n mdseven 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-;a6a+ inqrjf;6 bi9u leb j8i0 m after jumping from an aircraft without his parachute opening b9ii- lfj+ ;qi j;aue8a6r6bn. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whos)qkw14vrzj4e ,x5 .fs,r3ud 7 nmno tye other end is fixed (Fig. 6–43) o1w4 n 3evquks yr,)zrmfjn4.d,5t7x.
(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 2m::unhyz; j ,yrz c-otop of a 3700-m-high mountain. The climb is made in 5.0 h starting atz,:o-nj2 czu; mhyy:r 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-kgo8i+hox/ ,dyb 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 claimm508vs, /*h0necatwa bqx w k:s that its lifts can move 47,000 people per8 aq *, /tkb0nsx5:wc w0amhev hour. 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 and falls vertically 81 m befol)pb ufz;4nytl /p4- rre striking the turbine blades. C;lp-u4nflb4rp y)tz / alculate
(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 z*abg/w,nsjq(zruc *ui4o8 9n .l/oi coaster with a circular vertical loop (Fig. 6–44), the difference in y//9rju* (*aoi 8quglcn zsi4bwo. zn ,our 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 you go through it.    mg

  (a) If the human body could convert a can(zhtg rw(:a9 jdy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000((hj9w:atzg rkJ)    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 a2nd3h0dl.1l*zjgdg wb6 vk9v t an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses 0.60 mm-j fc d+1xmk/,*bihso, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?/f iod,h1 k+s mjbx-*c    N

  A 65-kg student runs at 5m/s grabs afx.r7 mpvgko :g1:(cz rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is (:fco r7.z:gp1mgv x kzero.
(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 9.0 uli-b;e-*lzb 8nt4a ns. What minimum power output was ltbelnubia-4n* - 8;z used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water i(jqg9 0zm,hakcy )k-;v sm gaip01m;u b* ho+ts pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 12mh a kmgu0i; *19z0yv,cp(b)g ;qkot jm-sha +0-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 84e 5otx: 4r523ch1cugto(p iegxecwconstant k is cut in half. What is the spring stiffness constant for each of the two resulting s g cu8 e oi545etpoxrh43gt:12c (ewxcprings?   k

  A 6.0-kg block is pushed 8.0 m up gq-a 51/8jhun: k q,plpocs 926lxg fda 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 froh0kk 1s+otwe ,m 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losseskotkh0 1 w+,es.    s

  In a common test for cardiac function (the “stress test”), the patieir; ,q+ 1c5ytqdn1c atnt 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 t+d 1cqrtya;5 n i,1qc15 $^{\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 di3b i t( 3,4jexqce7(cxxk:p8w cir 1gnstance of 500 m, what:3481piekx7 bx x3cg,i wqjnrctce (( was its velocity 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 water wheel from a height of 2.0 m at a rate of 95kg/s (a) If9r (w hdjjqs70q,d sf6 this water wheel is set up to provide electricity output, what is its maximum power outsfd7,jrw(qd 06s jhq 9put?    W
(b) What is the speed of the water as it hits the wheel?    m/s