In what ways is the word “work” as used in everyday language the samez6e*uonk d 2,diq,22 mxau4rh5 w tkdne*u s*9 as that defined in physics? In wh*2d e hm 4dud29,retxiwnouksz5kun ,a6 q*2*at ways is it different? Give examples of both.

Can a centripetal force ever do work on an objecyjvv6 a.g6. 0h:ys ( ht*dbp:dp0zbvct? Explain.

Can the normal force on an object ever do work? Explain iaiew l6xvs /x17:ctbm/xyk8h;gl 7 3.

A woman swimming upstream is not moving with respect to the sflprbz( c89 +ghore. Is she doing any work? If she stops swimming and merely floats, is worg z (pbr8+flc9k done on her?

Is the work done by kinetic friction fok2fj+xcc tmy11, yx;qfcr 5z/rces always negative? [Hint: Consider what happens to the dishes when you pull +qkjx/ f c; yrmczc1x1yt52f,a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even th2ou w :)hwnjr+)hvx -12pxsohough you are doing no work?j)w2xhho1-o:+ rhsxpwn)u v2

You have two springs that are identical except that spring l is stiffer thanyz*) ef 1rn;ar spring 21ezn*r ) yaf;r $(k_1>k_2).$ 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 x4t,x )s8xt pafree to slide on a frictionless surface (Fitx8ps4x t,a x)g.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 potential energy change when kq*o+w qh;v4f you jump as hig;qoh+kv*4qf w h as you can?

In Fig. 6–31, water balloons are tossed frok4(wr.xv b 5u n2ryy4qm the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore a4kn ( xr2b 4qr5vwu.yyir resistance.

A pendulum is launched from a point .6o1vvvv j dl4that 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 alongojv641v dl v.v the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compreske/ yj q*kq;2is the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservati*kyj/ ;e ikq2qon of energy.

A bowling ball is hung fr.2 + c7zpcfmp4+ ikncpom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball baci m kc.cnf+ cpppz274+k and stands 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 at the thl)pqq 1eh0r9,c9*n7s+wh czmqi y/p op of a waterfall falls to the pool be*yr iph0h+wez 91 p9nqcqh), 7mc/qlslow?

Describe the energy transformations when a child hxq0ya)+m v9q sops around on a pogo stick.

Describe the energy transnl+ wz n*z0cnv+d* ox5.yj ,keformations that take place when a skier starts skiing down a hill, but a*d clxn+voj.+yen,w0 zn 5*zkfter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) staxa4oaz -4bsm1py ftjiwp 1l,h11h t6- rts from rest at the top of a hill of height h and slides down. Does the wx,itbthly 4a- -a4 f16 1jpmhp11zs ovelocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in thek,lu) rv,c bi4am /+cqir path rather than stepping on top and jumping dowa,mv)+k u/ il4rc,qbcn on the other side. Explain.

Two identical arrows, one wit q-lqq-xx/k36l,uwum*q9k,knxf0h9p0v a or h twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a con*wxvxuk ,3,pfqq a-q9kuq0 h- rx/l6ml0k9nostant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum dkv1 x5hbg8,l in terms of energy, (a) ignoring friction, and (b) tak5dg1k,8lxv bhing friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is doof 2q. 1r,. iklyzte*ropped, can it rebound to a height greater than its originz.y*,ok2 et1 loq. rfial height? Explain.

Suppose you lift a suitcase from thbn y2/o vvg4v d:/-f-m(sb wfce floor to a table. 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) the weight of/no:4-(v -sbv/2v dfygm w fcb the suitcase?

Repeat Question 22 for the power neejw 6l g4*d v8lxbw(4yeded rather than the work.

Why is it easier to climb a mountain via a zigzag trail thaoc7y:0 kt7tnww p1rqmpqm)+ x1j6p6 vn to climb straight uon :ptwm mw)+rcqx16 k717pj6y0qvpt p?

Recall from Chapter 4, Example 4–14, that you can us v0:wj hlj,ogttd19d2e a pulley and ropes to decrease the2gtd:lvhj1wot, 9j d0 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 2, qi dd75bbo,moj51ec,h6wj/,joud a65-kg pile driver falls j,d5m 7di oebjaw,ouq5dcob/ 6hj1,,2.80 m?    J

  A 65.0-kg firefighter claap;bp6ayl (4 imbs a flight of stairs 20.0 m high. How much work is requir( p4aaby6l;aped?    J

  A 1300-N crate rests on the floor. How / ,zp1;g/jq.q r2 zyawo.k rilmuch work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 Np/ rja2;z.wqyq,1. orzklg/ i,    J
(b) 4.0 m vertically?    J

  (I) How much work did th+rx1 l(sqae8m e movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough flooal(sq+8me 1xr r without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratnf r*v(zj8wgs f o+b3bpzl9 . ;azm0c5ed by a force across a floor at a rate of for 7.0 s. Find the net workcgvbn;9+3l5j*fzsorw pzb8 a zf0m .( done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mut5q5n 6a ca*0c:jgnarch work isac0tcn5* argaq5j6n: required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be us15 1jb+je4u/ l4fnitzuengp: ed to liff objects we might not otherwise be able to l1f4/tjjg1i une p:n u4b+ez5liff. 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° incline and is kept 256ejgqh1db3m (8r tiur2fyxx o ;m5afrom accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coe25gmh boja1dq2u8i5mfx;3 xytre(r 6fficient 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 requj l1z)q+ w;96zt8xrjsatqj* d ired to give a helicopter of mass M an acceleration of 0.wlrszjj9; z6xt8qj+atd1 q )*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 linear od,1.;h0a lc+8ala hug mib9r 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 iakcm.gw-t 2 . qx3s*yuj93lxx axis, varies as shown in Fig. 6–37. Dcu* jlq 3txsa.mkx.9gy -32iwetermine 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 exerte 3sbph,r(6kjdf.t s3 vd on a 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, antuozc5v +c4v 0je8u0k oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor ha:nyml,u7f.j6vh-d(xe6 ,esh x 9ctivs 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 elecycca2:d q 2x4 nuw(:cptron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 d -c ebzx)os889go.qv bone to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fromh p+x83a my:)ew -smhs8iv9dk a bow whose string exerts an average force of 110 N on the arrow over a -ey)vwd8h s :pimk 39xa 8m+shdistance 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 fielder’s glove backward ,s, 0brw:f+hdw2h el/mc9c td s/5rm k25 cm when the ball is caught. What was the average force exerted by the ball on the glovems t0+wk cmh:/ebrw,5rf c,dd2/9 lhs ?    N

If the speed of a car is increase532.3k fzg uh0gyncnkd by 50%, by what factor will its minimum braking distance be increased, assuming all else is theh .nngzcgk35f203 yu k same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inv;dj6 hy;v 5zeu. v v exuq;u *81ud-ehpv+2yboestigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetivo-u*de6x1v8;juph z.ybvu+h d ;2ve ;e5u yqc 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 g5jsw pc(q c u3*o0*hkthe time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimatg3sw(j0pcq*cok h* u5 e the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone wzc3a(4iplye v; 5llg6 ho does 80.0 J of lela(6z l3i4p5gc; yv work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertici 7xs0.y2 hid*tb j+mgally with an acceleration by a single cable. Deteybi. 0isthd2mg7*+ xjrmine
(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 c3y l0 )jcppy(zonstant, k, of 440N/m How much must this spring be st )0y(zl3py pjcretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings fromyybb (1l9g obn i;/ jj3fy09vm one branch to another 1.2 m higher. What is the change i;j0 y y9n i9vl1y m(/bfbgbo3jn potential energy?    J

  By how much does the gravitational v 02wsu3 vrueta7i b 8gc34e8ypotential energy of a 64-kg pole vaulter change if his center of ma08avwisueu vr7g382tc 3y b4ess rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontalv(q f.9ljhz;2le7bz h 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 spring stiffness constant of the sprih2; 7(fb.zl ejhzvql9ng?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.z4/a6 3jvkb3 ryd mowyl8u 4 (pub/ko720 m above the ground. What is the potential energy of the book re(/y43ov8opzkwdy / 6 r4bj klabu um73lative 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 the top of z i.c j33rgi*ia 3300-m iz.c iji33rg* 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 ruln2xb cwy.0qh: tqd 8:ler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with tht2 qn8d .hwbqy: 0lc:xe ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s.i yey r+ y;g hbgf5mv.r3gb*8uun.,ttp m4q/) and grabs a vine hanging vertically frr f./qgn8ty5hb.g;*,3 bt4vugmue .ypi r+ymom 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, starting from rest, l yjh6s rx9dk6 yi3.i4slides 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 frictd 5 dt)qdwla3g.;3fe +ua iap.u70ontionless 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 -dpqbnzvsd/ fu5n e4b() ev4msa1,(stransformed 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/nd pvsm bz s /qase5) 4de(b1-v4(,nufs.    m/s

  A 65-kg trampoline artist jumps vertically: o cj2phwp,l4 upward from the top of a platform with a speed oflp4 ,wjpo2c: h 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 c5d/kk+ n afp8y1 je.r ; qc9hz6 zfa*)qp+lrqhonstant is 950N/m is attached to a table andr+ha*qay)8l/ q1f+d kkn p; hfrj9qpe. z6 c5z is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m sl pfth59 +e3kbxides without friction along the looped track shown in Fig. 6–39. If the block is to r3k+p9f 5e tbhxemain 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 ablzqt *)+tih7ttached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial di7ht+liq *tzb )splacement $x_0$ 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 jumpvcu(-4u wvc: q))nvgv s from a bridge. She is tied to a bungee cord whose unstretched length is 12 ) uvcqc)nvv (w:4gv-um, and falls a total of 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 poin vzeim*;br23 j+k r*gmt 1 where it is released from rest. Assuming no friction, calculate thezm*mr 2;ker+v*3bji g 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 at an wss bkbay0/rb0w18n1 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 t2p7;)ul;bpe ajy v)jkr 5udc(he 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 w 7pp;)ekj; )d crjl(vauuy 2b5hen brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 x(n t (supx32n$^{\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 direc 527 nllhyac3m3k nbn7tions, collide head-on and come to rest. How much thermal energy is produced in this collision5kn na7n hb7c3m2 3lly? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slidein oi91 z5jp2l 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was genera25oi91jni zlpted in this process?    J

  A ski starts from rest and lpvi8jy2rvq*1ljh:4 slides 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. 1 6xkeou4nn qru3.am1xrj/p:6 g2i jn
(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 1.5 mw,o m16q51h.k tesa:dl ke c74z uwlp3.ect6 suwd 3ol,.e5mph a7k4:wkql1 1z
(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 acro/,brkwlt/s g5 w/h.q rss a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the ,t .wgq/w5sl/br k/rh coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in *wp5;mpbi3 ;grv.j* vam, w) ;uqs gnfFig. 6–41 passes point 1 with a speed of If the average force of frn5;* mpg;; s)wg aq,vbijfm*.3 uvwpriction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot +/zq)b 4c kt:.mrvwkiof 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 spriskkqt+lf5 8o -a-gltit k (,l+ng (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5 if(kk-lt8+ q t,sa5lolgt-+k .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 attachexy 3/ g.t *iu3irygamf630md dd 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 foa/ yyi0 m. fm63*ggi3ud3xrtdrce 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 used1 oktmjhx 28+c6ckq*h a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been ihqhm+ t*kjc2c6o8k1 xn 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 to a sixg;edrqlo( glf .9l95a th-story window 16.0arf99ll; 5gq.eogl( d m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the ave p;(:omoia,u;vctlvd t yb9 :a6m -;iw8k-cklrak;lmy (i; bvv:6ccpdt;:m -8iklwu o -ao,t 9age force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95bq 1md buv k(*nnjv/x+)grg4 0km/h in 7.4 s. What is the average power +v vnj1 g(q0kbrmn/g4du)bx* delivered by the engine?$\approx$    hp

  (a) Show that one Britisopkt;hf *1 mxfk1i 9p(k+vl2sh horsepower$ \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 expr t0id;52r4 rosr,lamn5 w) bb+pe p0yem*;pdressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slow(c0 pi*jqe4x qdsq80q s down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car jiq (dps4xe80c* 0qqqtraveling at a constant 75km/h.    hp

  How much work can a u1-ua,p:xnym3.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7sw: -u 7h/ypa+9jp: a l/uhlhm.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was developedu /hh apyllawsjph/u:9-+ : m7?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3, ;b b8oj(wi8skj (lwb.60 m. What output rating (watts) should the j;8bi bw ,(w lsk8jb(opump motor have?    W

  During a workout, the football players at State U. ran up the stthb8gcyc k4 9*adium stairs in 66 s. The stairs are 140 m long abhc9ckg ty4*8 nd 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 cyclistbd/t: mwd*c gv1o 8)dtprb-t, 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 120 hp. How2mt.o .2,s.zigtmv as steep a hill can it climb at a cons2 a ,sv gomms..ztt.2itant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be ab2iqx /z8a7yy)xhhjq6 le to drag a 310-kg box along a levxi /6q7 y8j ahyx)q2hzel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downsr4 2i cfs,l-nak5/l u 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) bumpers” that 4b8j8x p 1dutly(t z)s7ylau 3are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanenty8 pj d1baul(s7ut8 tylzx)3 4ly 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, abeclyd+9/m,g2ar -2 e s 7twbond the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and alybg / a9eo-+s2 bt2,er7mcdw n 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 t+ 9bve;w4v/nqm m 0ctOlympics shows that his center of mass r+b/vw qc4t e0mt;9nvm ose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopw28qr5d:wc1 r*kjjji ed track shown in Fig. 6–39 is to remain on the track at all times, even at the very to:jwqcrw2jjdr 5i*8k 1 p 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 fri8f3sg j(c p1oom an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilo(c 8ogsjif13 pt’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 whose other end int 74 ua8sw,z/bf.lgv s fixed (Fig. a,u.vswg/b 8z4tf7n l 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is9e wj ) sawr9i+gj, 1xex gtbzo;uq299 made in 5.0 h starting at an elevation of 2300 m. Calcul jwwrxu 1oqe ,2x)9+;99igg zastbje9ate
(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-kn2yuv p*a turp .-3vc+g elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims ty:4 ciup5xedc/k y,k;hat its lifts can move 47,000 people per hour. If 4c: ecku d,ky ;yi/p5xthe 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 zew)grdzfvb 6*8g mv,o2 y+a, and falls vertically 81 m before striking the tuegg v+ m*r,z z) wb,y8afv6d2orbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vpx zm giu*dz. *,3;uqmertical 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 nz3 ,p*;*z m dmuxiqug.eeded, 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 canq 2tk *qmmyc50l:3iggdy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by3*lqg gt 2mk:q0y5imc one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fire0(l 9rki dtr3kd at 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, th5( 9nu*rs r2sl kt6gyme spring inside the scale compresses 0.60 mm, and it tells you yoursusg5lny2* 9ktr mr(6 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?    N

  A 65-kg student runs at 5m/s gramc)b d5aimxj(joa(* 4bs a rope, and swings out over a lake (Fig. 6–45). He releases the rope )a ((xic mbjj*m45o dawhen 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 verti ,/bqhthp82w m9s5 emzcal distance of 5.0 m in 9.0 s. What minimum power bm5epw2thhm9s,8 / zq output was used to accomplish this feat?    W

  Some electric-power compa 0)/7wn qlukmq -4twhqnies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour bk4w /-qtl w7qunhq)0m y 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 s vhwi r0*e71blpring stiffness cons 7*r0wb elh1vitant for each of the two resulting springs?   k

  A 6.0-kg block is pushevhnh *q74iwnohst u+*f878op d 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 sw itv 8z /dn)m8jh5t(c, how long will it take to accelerate from 55km/h t 8/h8)dtvnm5t izcw( jo 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac functiongnc1j 0vt4n 1atsz2*5c t0m8drpwk +i (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whe pt+ dgwk4rtcjannvm*t z8 1cs502i10n the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distanceivxzfh)/55 enzp qj6fp;0 y u/ of 500 m, what was its velocity when it left the volcan5ipjzevuh ;f/y0 5q n p)6z/fxo? $\approx$    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 1+qifud+l )lh2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum powefhlld u+) 1i+qr output?    W
(b) What is the speed of the water as it hits the wheel?    m/s