In what ways is the word 922mn)y quwhgjkug3v) y1wo 0 “work” as used in everyday language the same as that defined in physics? In what ways is it differentu yu yn0vq)2h g19) kmog23jww? Give examples of both.

Can a centripetal force ever do work on an object?s dlsoz8 k.-qk5kj6)7;jx/( )ot0 iwr gyupr y Explain.

Can the normal force on an object ever do w1ok6fl2r9 .)utie ui1fq wu8rork? Explain.

A woman swimming upstream is not moving with respect to the shi:7x js a.me1w*dm iqwch)5 9eore. Is she doing any work? If she stops swimming and merely floats, is work done o1i7) mh.qcw m:eis d9x5awj e*n her?

Is the work done by kinetic friction forces always negativkj)(.hh(y d wre? [Hint: Consider what happens to the dishes j rd(h (y)hkw.when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though youh p),-vvk2 jzv are doing no work?p2)-vzj,h kv v

You have two springs that arem. rv-r*hnv2x (g7f1 i:xzmkk identical except that spring l is stiffer than sprin:.2mix- 7rxkf1kgz v( m *rvnhg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constl 1gqv7ze d;lpgih ,3*ant horizontal force on a block that is free to slide on a q1ghp *7e;,zi v dll3gfrictionless 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 potential energy change whet49 +/shic zktxc)e*pn you jump as4ek)c hxt/z +tisp*c9 high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all / 64fcsngre*b with the sn / gbcsf*4er6ame speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launchq 3jhtaze**y:ao(u f 9ed from a point that 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 from the equilibrium position? Explain :(q3zey *aaho*ut fj9.

A coil spring of mass m rests upright on a table. If you compress the spring b o j35lz 5 0rz08b ceop9tajhyrb-h6l.y pressing down with your hand and then release jh 8y5a0ll6e-o ht3.jbrc95bzzp ro 0 it, 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 (Fig. 6–33). Tt zt(q.b0 /, e-/0 uvrzhavfujhe instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without0tq.tf-/u b,h/ 0juvzaer( vz pushing it. Why?

What happens to the gravitational potential energ16h r0ce-ph h:5p9skxz0ytq xy when water at the top of a watxy-hk5h1tpqz r p 6 9s0e0hc:xerfall falls to the pool below?

Describe the energy transformations when a n -u+gf fp:yp;child hops around on a pogo stick.

Describe the energy transformationmj brlf2 lewi;5. 1a4vs that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdr l;a ljefw mbvi2.5r41ift.

A child on a sled (total mass m) starts from rest at the top of a hill of heighrsjn)l 3j; l;ga;ed6ut h and slides down. Does t;d jj; 63)s eulanr;lghe velocity 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 stepp+msi8*l *7y-ksmd9orhb fe1 o i gn:+ over a fallen log in their path rather than stepping on top and jumping down on the other side. Expsgfmb + yo7:e+ *o i8knmsridh*l19-p lain.

Two identical arrows, one with twice the speed of the other, are fired into a zoegtj6 /id t3,n 41klbale of hay. Assuming the hay exerts a constant frictional forcezj3edtk4 t,61lon/ ig on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms ue e+v/* 1s -bglq3v odxtaw2k9h0vo vqp9:c 7of energy, (a) ignoring friction, and (b) taking9e:c kbo0qu/ vv v21 79-* t devpaoq3w+slhxg friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greateem n,/ niry:bsr. ur -7gr-po)r than its original height? Expla,er p-:.by n)i -rs/gu7mornrin.

Suppose you lift a suitcase from the floor to a table. The work yo vs,t8g qwhq4)u do on the suitcase depends on which of the following: (a) whether you lift iwhg t,)4vqs8q t straight up or along a more complicated 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 t2wlu5,ax x;us he work.

Why is it easier to climb a mouni x i:e dl1rdsw7gm+a ae g:q.68q;.rttain via a zigzag trail than to climb straight up 6ai srdxi1 ;mwgt.ar:qed7:e.+gl q8?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to da;vico8qk ty7z09k t -ecrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the lo9a ytc 8vq;tz i-ko7k0ad is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the grto1 m8x(cjo fkqs *;wb)hr24u avitational force when a 265-kg pile driver falls 2.80 m? bfwkr4)o(hm 8j2qs ; 1uoxc*t    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 mv)4uiad hl 4tsp: /jr1 high. How much work is required?: )lj4u sp/1haivdr4t    J

  A 1300-N crate rests on the floor. How much work is req c6mq -dzn6 ck8dmw2js+*;fn euired to move it at const6 j; m2+fcnzqs-mde 8 dwkn*c6ant 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 bnrbe(6 g e;o0do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of r eb0on6g(be ;friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by av-13wda0*8x rmno7qcq ic lyu1 z1/wu force across a floor at a rate of for 7.0 s. Fily1dcqcz1auu 3*18r7wi q mnx/o-vw 0nd the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. e lalwy4.rc1x nub+b9u, m2;gHow much work is required toe4 2,mnbr awly;.9cb+ulu1 gx stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we might no rrcb/y*9bm: at otherwise be able to r bymcr9*/:baliff. 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 keppvz7wuj:8 dv+t from accelerating by a man who isw7zdv+vup8: j pushing 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 helicopter of mag eo +6zmutu0n+x0bffccp;64 ss M an acceleration of 0.10 g upward.;guoxe04m+ccp60 z6 unbff+t    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 thatr de fft/s e74h8g//si $d_{\mathrm{A}}=10.0$ 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 alongrzgq00vf w:rk/c3k2ki(s f y9 the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the objecrfzks09yq /f2 w 3: 0gkvcrk(it (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in thes:3 qcezr 90jf $+x$ 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 oxwiu w 798z,zsdhp7hw *ygen 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 doublm hdm/cthqt9bg: 18z:ed, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop mcoe.mn:f211i +fo va(opf5dan 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 sto y.v79k;zz kk*qt (8goayaua) p a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts a3ejjbl4*e:/ zrxg: orn average force of 110 N on the arrow over a distance of 78 cm. What is 4rjg bzx3ele:j/ o*: rthe speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s m;; e)9by lsjz8i5unzhog.6wxm +xq8z oves a fielder’s glove backward 25 cm when the ball is caught. What was z; eijxxu8n;o6s.z+5) my 9 wb8qzhglthe average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50l7bw,+pwo .mqy3p m*c %, by what factor will its minimum braking distance be increased, assuming all else is the same? Iq.bpwlc+,oym m 3* 7pwgnore the driver’s reaction time.

  At an accident scene on a level road, inves:(uk 0c 4kgpystigators 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:ukgp(0 scky4y does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at t6y694 )bbn pyq.ottz By the time it reaches the plate, it may4py)t.69yt bbo nztq6 have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown striuest *g) ).mrdf /co)aight up by someone who does 80.0 J of work on it) )mo)trgi esu/f d*.c? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an ap6ozzpedp j -(k eocfl8*;q 76cceleration by a single cable. Det 6 z8k6poeqop-lcj*(;depzf 7ermine
(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 stiffnebl;a a6d;cj3-ly n.zcmt ;0wrss constant, k, of 440N/m How much must this spring be stretched to store 25 J of c; tmzw06ja.nlr;acb-y ;d l 3potential energy?    m

  A 7.0-kg monkey swings from onek,ro9ca9i7ce ay 9z 9j branch to another 1.2 m higher. What is the chang9 ,z 99 rek7yc9aaiocje in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter cha(c/ oue+ clfi)nge if his center of mass rises about 4.0 m du+fl( e oi/uc)cring the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = u- q e*e6(rcau7qby/ ijbg48s/*ee bg:rzw.x 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 constanqsrqzjie.ub e (rwgc: b/86*ux*- 7ey/4agbet of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m above tilfg9z.xat y;rto1)o *o 8 d1the ground. What is the potential eto1 r)91*z otd8fioxga;.tylnergy 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 elevation of 1600 m and climbs to +(o oq/ p0q. 0gnnmcycthe top of a 3300-m /0 ncn0yom.o+g(q pqcpeak.
(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 = 53o9*ly93jrf ca-mbs m 0N/m hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?9fo 0rbl- cm9s*3 ayjm    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and gy ig53):.h)h;hg z megfzmxs)rabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwar g:sh.zymh;)e)hxm ig) z3f g5d?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a friu7 yi6azsl6 yq7 :3fssctionless 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 givenczjfa*,(*5-ut jq a eg a shove up 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 transformed int-9s1saabxqy8; ep1 y eo gravitational potential energy without the aid of a pole. y1eqa9-sp1ax besy8 ;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.    m/s

  A 65-kg trampoline artist jumps vertically up44 ojxz+qpms 2jb)8 pvcj5/o: zk je2award from the top of a platform with a speed ofp cp: s428z 4jmjjak5ve+obox2/j)zq 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), whosf1 4tkslo o8lqdn 9gtlv 1xn22e*a1 -ee spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwaro1 st11*da2ex-q lvl8 nkeg fn2o94ltd 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 track showigxg:c w:0mt 9 nx,2mln in Fig. 6–39. If the block is to remain on then 2x0cx g:i9w,mmt:lg 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:9:2kpeco9kaa37 i 4vno wzdg constant k), Fo:9a34 wvd 7a:c9kzo p n2iekgig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungkds;0(h/j ilqee cord whose unstretched length is 12 m, and fs d ;(iq0j/klhalls 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 F 6/p3i,nivb/ goti p/mig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the s3p,t ipv io/6b/gi/ mnpeed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/xbzm ms:u * ins-/rz6- n9v abze;c,x0s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an eleejc (90m0wyq xt(ehpugw, )w )vator 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 ne, ))9m0(g cxqup(jtyhe0wwwo more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends tood(jjo7udu1 * cycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of m xi25y6q.xvf ws 8l7yx -yjs.vass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How y qj 6yslxxf .v2.i x7ws-yv85much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hinb qumhn6,k v2 2 f-ic0wr:e 1bryr3c2gh and reaches the bottom with a speed of 2.2m/s How much thermal energy due -f26ybinhm0,n:rru b3k c1 w evqcr22 to friction was generated in this process?    J

  A ski starts from rest ai 9bfnx,5mjv,*+7cr s t-d )iuuva6jvnd 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 dr4 .wt vruk-;5 5prqngoopped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounctjj +ir-8 jjo 08hrk(zes back to a height of 1.5 mk-o (8jhi8+ jtr0zrjj .
(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, 9i j*guvy+ 5n9c wlp*:yasqp4is pulled across 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 coefficient of friction is 0.30. What is the final speed of the crate+ca*9qli*p ysujv5g4y: wnp9 ?    m/s

  Suppose the roller coaster s5nvr.;a7mxw 2rzwn, in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its wnazv7x2sr;,r. nw5wm eight, 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 of a steady up. zjii8vqxa5b 9x*h*uy40yfq 2pt a/kward 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 f ;p4-t,ox3j0jd mjeh zirmly attached to a very light horizontal spring (k=180N/m) as t epx0 hdjjzo;j-4m3,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 turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly lfv6hsbxs9c g+40rn;attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its n+0sc;x bsl 9vfr4g h6first swing?    m

  Early test flights for the space shuttle used a “glider” (ma o 63iezmy;q sbi2shl87f *n8iss 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 halfhsm b 7eq i62o8*isyz;i8 n3ve 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 31c fc :n4gb 80lmg:-msz5-kg piano to a sixth-story window 16- lgf0sz8gcm:nc: mb4.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must1zm c9smde+;klt wq9r 4vu+:d be the average force exerted on the cal9dm4c:+ur+ qv9e;tm1 dkz sw r due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rj ;u at(:ccl 49hny4spest to 95km/h in 7.4 s. What is the averagey lja(44 hpst9cc:u;n power delivered by the engine?$\approx$    hp

  (a) Show that one British horse* au;59jwl k xqj+;xuqpower$ \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 for+/u vl n.suau8e jdh-t8re4-fm 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 thatpe f0+:5uxadf her 1150-kg car slows 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 :pfa f5+ue0dxneeded to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hpubr euc.b*w 1:3o d,gv motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion tak7cbrjz2 j(-elg :mn5g1 o( ww2i qq2hces 1.5 s, what average power was develgbh2 onrw cjizcwgqm:(5qjl(1 -272 e oped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. 3g4mfek jl9vs / fc3j-What output rating (watts) 3mj/l f4esjg - 9fkvc3should the pump motor have?    W

  During a workout, the football players at State U.rz (k3 *avw6mj-skxd- ran up the stadium stairs in 66 s. The -w(6 smkd3 *-kxrzajv stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb uja6yad g5 /b4a 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 hill can it clia n7ch4gzmb o4o0p4q ( 3ec nnqub/4+qmb at a constant speed of 75km/h if the frictional fn +g0mqen bo/u7ha(czpq4 4 o3b4nq4c orces add up to 650 N?    $^{\circ} $

  What minimum horsepowe.7 h :+aerkhgyl ip,um:0tgw ,r must a motor have to be able to drag a 310-kg box along a level flooeg.athi: gl+:pm h,yu 0r7wk,r at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down3o6x:18egwpe n z+gc a 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 built0q4tt-kuwo( j bn8g5ur n**c k “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the mau r*bqnc5-n8ko wutj0 gk(4*t terial 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 thd-p,h me31 xsb6 ktw+hnupt/- e 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 books, how much work is required to fill all the shelves, assuming the boop d6 tx,t/-h 1pu+s wh-nmkb3eks are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump,*0 on8uopy 5ft l6,luk:zkgs. )ohkz (Fig. 6–42) in the 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 hel0kukfzookn.5z)tpy 6 gs*,lo,:8hu 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 fricti,/kk -h)zrm aion along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of rad)/ak,m hk iz-rius 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 jumk-f khgb uox/ j5g;xj - kf25q3cu+;exping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injehok-;;jcuxx k5 x2 ubfk3q+ /j5g-gfuries. 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 whose other end is fixedri m 0pcdth7c+nso5 :* (Fig. 6–43)ishn0m pc c*d5r:t+7o .
(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 is mat3c;4z1hw elb8 z .kidde in 5.0 h starting at ahtl8zi 4wz1 ;.bced3 kn elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg eleva 5cly+5q5qam vtor 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 that its lifts can move 47,000 peopdk r ;(mwth*1mx)tac3j+1 rf xle per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power jtx 1c;+1d kamm *tw)rf(xr3hneeded.$a\times10^b$ W a =    b =   

  Water flows over a dam at theqwj 35. lyufptge,: r* rate of 650kg/s and falls vertically 81 m before strikingj3f *.q r:w5lyg,tu ep the turbine 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 ws/)ev b)se:2 cs-8gqd cqi1t cith a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore / sbs cig1c8:qetqs2c)ve-) d 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 cgy-45 onjmy/a candy bar directly into work, how high could an 82-kg man climb a ladder if he we j/5mg-c 4nyyore 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 at an upward angle of 45l /giw;ga o+o;xd-;dq.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, thd w (.bjk 5:73b ,prupzqkp:boe spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0bukr:q p75b:p( .bo,3kdzpjw m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s graml nml+5rk3p2l/wv)h jb9(y obs a rope, and swings out over a lake (Fig. 6–45). m/nl95 y)kvr+2w(3lojpl hbm He releases 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 veuyal 9l(bqe(u 08pyh8j v;kw/rtical distance of 5.0 m in 9.0 s. Whatk ye8a9ju /q(ybvu l8hp0 l;(w minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Wbre95b4 z mzlcz0 ( g+;wqrlhr5x 7l38y- gbitater is pumped by rever7( rxrzbzzg0 55cbg93mht wr-l eb4l ;+lyq 8isible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cug- qj4plt8v w2t in half. What is the spring stiffness constant for each of the two resul 2w8tlg qv-jp4ting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 33 a1s.dux6 kwyx8og)l 7 $^{\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/hn,)9ynw r sjx8 to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power staysx, )s 8jryn9nw the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress teo3825oeyr5n s n*kpomst”), the patient walks on an 5k *ornsmn3p8 e2y5ooinclined treadmill (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 axxi e94*cn )he 500-kg rock vertically upward a distance of 500 m, what was its velocity wh ch)enx*9ie4xen 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 cjg7e;eh/wya0gr 4t5 95kg/s (a) If ga/e7 4ejrch5gt ;y0 wthis water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s