In what ways is the word “work” as used in everyday language the same as ttb5u+fuk0 g 4that defined in physics? In what ways is it different? Givf5 ut+gtb04 uke examples of both.

Can a centripetal force ever do work on an object? Explahzi1 -gq.mcqxz-; p8k in.

Can the normal force on a niu+a8ui9tp b4gq2k6n object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Iz)t+p zxwrg3vwxa( 7xk)t lks i51;p,s she doing any work? If she stops swimming and merely floats, is work done on zv73a,tp();px r g wxtk+ksl5)1xiwz her?

Is the work done by kinetic friction forces always negativgw o:h;7jc u8fh7k1n oe? [Hint: Consider what happens ohwg8kuohc7n :;f j71 to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to puhria u9)8t 9fds cp8cy/ c:1rwp7:5-or ygfhksh hard against a solid wall even though you are doing no work?c5r r 8f tw91f9c riy: d-7 sku/pg8apyohh):c

You have two springs that arb 07fkc 3t()t( nwhwjze identical except that spring l is stiffer than spring 0t 3)(kb(tnch7z wwfj2 $(k_1>k_2).$ 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 thatg:v2z8, qcsp u is free to slide on a frictiosq2: z8u g,cvpnless surface (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 hmd-ya ,-m8zwf ps 5u+ikt9i5potential energy change when you jump as high as,wd8y-ht55k9 afip smu m+i z- you can?

In Fig. 6–31, water balloons are tossed xfqqf m2ect(f0y4 9/cfrom the roof of a building, all with the same speed but with differetf0xqef f2(4/m q9cycnt launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its raeigi8w6f hn :pl;, ,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. pw glfe ,ih:n8ra;,6 iWhich launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a/oopo fzan+2ayh . b72 table. If you compress the spring by pressing down with your hand and then release inzoh2b7a2po +fy.a /ot, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (4et2 h; 6hxgbbFig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor xeb6t h2bg ;h4is supposed to release the ball without pushing it. Why?

What happens to the gravitational potenti;.8k2k,n cxiqmtxs8i m0 r-pe al energy when water at the top of a waterfall fallsqn 2-k0x,mpx . metis88cr;ki to the pool below?

Describe the energy transformations when9 i00d6y4 qflr1snso u-- n vghu+;hdm a child hops around on a pogo stick.

Describe the energy tranf xqnk/vvj08n 1amfm3q2h:ef3ly 86qsformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strikinga 362q3n8y08/ j1efl vqm mfvnq:xfk h a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heigu+x 7umws0k,ght h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is i ,wg0kuus7m+ xcy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step ov 9okg 4; :yjaz62pfroler a fallen log in their path rather than stepping on top alg624 pk of;a9zry:ojnd jumping down on the other side. Explain.

Two identical arrows )qjb+;e6z kn8 to4qpbfh84 rudy7tq,, one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force ;ruztbj, y4+6 fq enodhk)t7 q8q 4p8bon the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pend ) 87qd5rhatsdulum in terms of energy, (a) ignoring friction, and (b) taking friction into accoutd ar)58shd7 qnt. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a 2gia:.3etk;i)ow*r.6 avroga jvop9 height greater than its original height? Explaiwv igporei*aa69 akg).o;32t.ro :jvn.

Suppose you lift a suitfwn45gwhj s13 8jjc.zcase from the 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 heigc j4hjgn185zfw 3w.sj ht of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed r ( 3y jtrof6kxg7reiy)w(o)6 wather than the work.

Why is it easier to climb adigazp.e. k 5k :r:fzc 9p5f4zmh6jx + mountain via a zigzag trail than to climb straight up?d 9p.arkif6hm5 z.4ckp5x:z: fjezg+

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dewfgf 6:uyessl8 u-p7sl 2 dtd;c,;o 2xcrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the loaddlu uf72-s , xgl;fd eo: cy;2ss8w6tp is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force *31cguj ow, i*ebw -c :)epsgjwhen a 265-kg pile driver falls 2.80 m?i*)1 j,e ecpjb*ucgwo3- s gw:    J

  A 65.0-kg firefighter climbs a(x3c;jmmd3y 9rp:fn wjc t z,* flight of stairs 20.0 m high. How much work is requy mx:3 npct,(jd9 cz3*;fwjrmired?    J

  A 1300-N crate rests on the floor. How much work is required to move it atf 3 pjbv1t 6uzi14j0po const1puo4 3j0ibv1 6t fpzjant 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 (horizontally4he(p*b k fpdau;hj3by q19kw/0 7eeu) pushing a 160-kg crate 10.3 m acrosu*j9h7 y;b 40 eapefw/(p kdkhq u13ebs 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 a6vbo qq u)2 x1 pzy9pco.t9wdgh,7f k d+rk:0i force across a floor at a rate of for 7.0 s. Find the net 7q b0r19.pyogo ,9 xpd hkwcf2:v uid6z+)qkt work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tabl: kp)ve:o vw-ee. How much work is required to stack them one on top of aov:) k-pe:wv enother?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects(a y+a 9wa7eis we might not otherwise be able to liff. Show tha7ay(es9wa +i at 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° in(ujuu6hv x4x;x .0 b9bd,jhvb cline and is kept from accelerating by a man who is x v6u4,hxvj(0.b;ubh uxjbd9pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a,-p1i *tr*w 0 ljzp0wokt g4pj helicopter of mass M an acceleration of 0.-rp*wj01,pttzp4 o w lgi0*jk 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 and thatv:8 tvredy33q bj 8*os $d_{\mathrm{A}}=10.0$ 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 objec x4l hr*mpd+znijyt 1n7-e kz;/j*:ipt, acting along the x axis, varies as shown in Fig. 6–37. Determ**kryni/41i;+jezp :lznmp t j7-xd hine 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 a partic5(lwg3ymc k. 9rmlqw :le 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 h*k+w.bklatyr ) x64t 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 whrhab1zoozh 1af-/+ or7 fmp6(at 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 elslc;zm6z(b,g 3miq+ a ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-nte r06 -/.tznhlsl .1lqp:rt kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a b1b q htegk0 +mkw0/(4nzjw6avow whose string exerts an average force of 110 N on the arrow (jt+0wekgv n/4wqkz1 ah60mbover 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 m)z jd:x)df , y uqrbvbdhm0::h 2wo*,voves a fielder’s glove backward 25 cm when the ball is caught. What was the ave:j dyud0,whqx*b m:rhvd:vb2o f )z,)rage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will 4jl9jvkp(2d9ftf4sc, a/ j mcits minimum braking distance be increased, assuming allfj /c9mk2 vpt(c4 dl j4a9,fsj else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inr *ks-,j,z vnuvestigators 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 speed of the car when the driver slammed on (and locked) the brakes. (Wh-snk,,j*vrz uy does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time vj9 c ;t-a(eshit reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance beth (ja- tce;v9sween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rof 5d 0d;8maolzck go if thrown straight up by someone who does 80.0 J of work on it? Neglect airdfz ao80l5 ;dm resistance.    m

  A 285-kg load is lifted 22.0 m ve p1dhr;+c1pi4 mni7emrtically with an acceleration by a single cabp dmcnmr 7h11;4i+eiple. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 4//sg x7p(frf lh w8 ok4(ql-go40N/m How much must this spring beflpwo7g8 h/k l -(rq/4g(fsxo stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thec3;-i+3lpaeil -fcd y change in potential -3eilcp d-clfyi3+;aenergy?    J

  By how much does the gravitational potential energy of as rv aa8c nn9 kikgz,j62/pnhyst9416 64-kg pole vaulter chang ,ztk9ck2nr8snn a6 ghyp/ai1s 4jv69e if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whe x81i,7oyanij n it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 a 7,i 1oyj8xinm. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg bot gzx8/d6nqu (ok from the ground so it is 2.20 m above the ground. What is the potential energy of the book relat(qt u6n8 /dzxgive 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 k* 94j6)+c ryvr.es)e(arze)nom l n um and climbs to the top of a 3300-m peak ( z4mynu)kc +erel.*oa) 9rrsn)ve6j.
(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( eu u)ke4qxa3o;+nk i ruler. The end of the spring is nexta+4keo3xi; n(k)qeu u to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs g8f)-d ktm 0vca vine hanging vertically from a tall tree in the jungle. How high can she swing0 8)mtf-vd gck upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from reufy-(wabo+( 8 m pz1pust, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionle ,vst 2q/cpwru4;x qf9ss 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 transformed intod87s/hn gk8b y ijn56i gravitational potential energy without the aid of a pole. With what8 j6isi/n kby8d57 nhg 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.    m/s

  A 65-kg trampoline artist jumps vertically upward fro.; c3cvx4:wayg8u durm the top of a platform with a swda ugy4.;c8 :rc3uvxpeed 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),u7ken3t w)vh(9xp-c yil 31 qx whose spring stiffness constant is 950N/m is attached to a table and is compres -3xc3 evut)( n71ki wp9hqxylsed 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 slides without friction along the looped trackqi 0m) )j+u0u(p ejanm 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 minimum hepimqu0aje0 )( n+) mjuight h must it be released?    r

A block of mass m is attached to the end of a spring (spring(( efnuwkq7b:l /h*iw stiffness constant k), Fig. 6–40. The block ilf n (ww (7uh:*e/qkbis 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 idr .t 99bkn4nzs tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculat9k zt4brnd 9n.e 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 showtjmm-z)nsg , 0m ussi*wv -s yt t43v9-y9fmp0n in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at poip s v9 uj0zmt3) y f-t0-ymtg9-4ssimm,*v swnnts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown u0hqtz 7hg.h,(qb3hp797 j2p lflqwbos 1j :ewith 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 r-o9ybq g0fc z79g vm*of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of tg fz- b 0ogqm7r9v*c9yhe elevator and passengers.

  A cyclist intends to cyd4cf 8 6h j70ghk2dnhlcle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveli :fqco6irim3+ ng 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this qcf6o+i:m 3ricollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom, h7fw q sz/2kzt6-vv7v vsh-j with a speed of 2.2m/s How much thermal energy z/ 2v tz vk,vhwqsjh v6s7f-7-due to friction was generated in this process?    J

  A ski starts from rest and sl mc/erluz8 5hh64t+otides 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 13.0dw8doa c7l9ab vpt f; g;bh+ub2z:t r6*01vhl m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, ;bv2i7d w mn:kand it bounces back to a height of 1.5 m. wkm:;bnv27d i
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant hdj7 b;g+: 3dxa qrwlb0)shon. orizontal force of 350 N. Fod7oqw03b +b;xr: hs) njdlg.ar 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 x1fha9zmk;/ )tlhrl 2 passes point 1 with a speed of If the average force of friction is equalkm fhxh /1r) laz;t92l 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 footn(k /wlajdd)at9* kvoy,jqmf2,w( z - 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 t7g2ua /sioafmg0/)ra7 6f ikjo a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted tsmffgi/ r) a ua76g o72aki0j/hat the block–spring system, when compressed 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 verym7. vxd (wxau3 light horizontal spring, Fig. 6–40. The block can slide along a table where thexwmv.( x7 uda3 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 “glider” (mass :*fbxt rgb 3m6gt-1as 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/h1*gsfg3xtb-tb ar m: 6 (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 liftsu agfj )7j63jv4tb+t) a isy-)tv0xq a 315-kg piano to a sixth-story window 16fyut) 4svagj -3 qx)7tjsv6)jb +0ia t.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be thiggc;r, g rpjf8wsd2 4o z(.8ee average force exerted on the car due to friction and air rer4rig coze28jg;sw 8d, ( pgf.sistance?    N

  A 1400-kg sports car accelerates from resv1) 5p0v puu; bo)ijkyt to 95km/h in 7.4 s. What is the average power v)i0uo; k 5jp1upyvb )delivered by the engine?$\approx$    hp

  (a) Show that one Britizm sq( *od3v32 qv6lonsh 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 ofte .q. p-*fgtuxyn expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h inidu(:o ; fv/xu about 6.0 s on the level when it is in neutral. Approxi dv: f;x/u(ouimately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.-.b-bghwv 1w47fy ipsb:+ upc8 el0iz0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shoq/m. tizh3+u igftp;)0wed k/t from rest to 14m/s If this motion takes 1.5 s, what average power //fm; +t tu)kgi0w.qihzedp3 was developed?$\approx$    W

  A pump is to lift 18.0 kg t5b q cg2 f.lgo+*z g;pu-vq(zof water per minute through a height of 3.60 m. What output rating (watts) should the pump motor havez5q.v+*gfl ;( z-tog qgp uc2b?    W

  During a workout, the football players at State U. rco fkt9s.7ovf q a6::xan up the stadium stairs in 66 s. The stairs are 140 m l oq:cx .t7kofv69f:as ong 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 l,8f.-qe15 p4 3inb fvhcgzcrclimb 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 steep a hillap ce71fy hwt s*b0k3- can it climb at a constant speed of 75km/h if the fricc7a-ps 3fbhw* t0yk1etional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower vtgt qf 6ob5(fvh1(h2must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s 1gqt(h 2vo(f6hb f5vt if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down no /edcu,(-i ba 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) bumperifnb u,8 6 mac)o3pw*is” that are designed to compreaipc o6 f*n )m,i8bu3wss 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 ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library oy,v r1fpd159zcd+(; wj ;ap yoz3rkmthe first shelf is 10.0 cm off the ground, and 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 an average shelf holds 25 ozad9p j,1vo3fdy k(p rc +;m;z 1r5ywbooks, 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 19hk6*7 2vo). rv cwoaqw36 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What .aw 6*7)k co2vqrow vhminimum 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 frictvn .ko9ud/o )rion along the looped track shown in Fig. 6–39 is to remain on the track at all ti/u .r) voko9dnmes, 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 an aircraft without his paraco,pf2qqej /q7z6 1id mhute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived wei7zofdjp 12q m/ ,q6qith 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 whosgmgty;jr fs81)9+6egm c pme 6e other end is fixed (Fig. 6–43).+ mpeg8gjmm1e) yfgt ;6rcs69
(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 mountaxz 8 hkw)u1gal1f pt9(i +/v vtyb5m2din. The climb is made in 5.0 h starting at an elb iu +2t/)dl59ktyv1m ag8wzv(fxp1h evation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a x z3r+c4kq2wyz 5z(ychuge 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 thati j.epe6,h; 0aktlt95 lql9at its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the po 0j9le65t 9qalt,tih a.pkl;ewer needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s an7t os kg776lend falls vertically 81 m before striking the turbine blades. Calcuol 7es7tn7gk6late
(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 vertical loop (Fig.st2,sbp0x5yt 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or,0ps5t2xb y ts how fast you go through it.    mg

  (a) If the human body could convert a candy bar directl1:a ztd/vxr b5y into work, how high could an 82-kg man climb a laadbt x z/r15v:dder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired ,.:sl5ghypqx .e5 zidat 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 thj wq*pd.kq 7 (v,+ ;df1vuercre scale compresses 0.60 mm, a ke+,j(dd1q*;pv7 ucr.vf rwqnd 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?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out ovj:2 bc0+0 twhdlap8wher a lake (Fig. 6–45). He releah80:wph 0t bdwl +acj2ses 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 dit69vy8-(noar0ps0r ++ f iytqwzr8hxstance of 5.0 m in 9.0 s. What minimum powerst+80-oi 8 9r6+yyp 0r af( hqxtrwnzv output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumpee5)ggc) wrc upju*;qq,m 22u j)wjx1d.mhqv;d by reversible turbine pump)rc hpqudmx g q)e ).*52j2wj1;c ;mu qj,vugws 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 d2shr kr u4w(t3i0y6 ystiffness constant k is cut in half. What is the spring stiffness constant for ( rrwyh04ut3kd2is6y each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rourni4aci(u6; lv, 7kpy gh 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 : f06t.bodbf s7z yf/qa qx:(vin 3.2 s, how long will it take to accele7bfzxqavoq df/ f: b6st0(y:.rate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress tes +ir (guh5 y;sd3nwymra (y7q-e1 tax6t”), the patient walks on an inclined treadmieydi6ygy7 x+mq3 a t(au(sr n-r;hw1 5ll (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance a-e*iry buz ul5d: ucx*2tx64of 500 m, what w25-y uu l b* t*xdeca:xr64iuzas 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/ .2teck.r3m: ydx )vqus (a) If this water wheel is set up to provide electricity output, what is its maximum pow. :m2.xqyuet3dk )cr ver output?    W
(b) What is the speed of the water as it hits the wheel?    m/s