In what ways is the word “work” asgrv7brmct3(28z( .ibzx w*b x used in everyday language the same as that defined in physics? *3t rgibxbb(rzm8(v.2 wx 7zc In what ways is it different? Give examples of both.

Can a centripetal force ever doz.cpgsj5 xk15(sddx * work on an object? Explain.

Can the normal force on an object ever d(6nt tytca s8t 7+e(sso work? Explain.

A woman swimming upstream is not moving with rep dylofd8+qsa+7pj+ae yu) ,5 spect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on hs5y y ,pp8q ujf+ ++laeaod)7der?

Is the work done by kinetic friction forces always negative? [Hint: Consak: ga lki3 1r/al)5nxr((zfgider what happens to the dishes when you pull a tablecloth out from under themagiznrx: lal /rgk) k5(3 f1(a.]

Why is it tiring to push hard against a solid wall even though you are d pkns6:atto,id0o 2k0 oing no workt0pn02o,a ki6skdo : t?

You have two springs that are identical except that spring l is sti(eno l l8qg/u;ffer than sprin/e lo;q 8(gunlg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is freedj;qlr05(c+47bb ig+)xt d2k gc imlh to slide on a frictibd0qgc)jlm24 g (i+7rki t;ch 5+ldbxonless 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 youdm3 0dp+mh+9 v-wr eour gravitational potential energy change when you jump as high as youdopwe+3d+ummr- 9 h0 v can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with t9ateawe.lwn 5rjma g;9 /t/m:3x ni0-d(aicthe same speed but with different launch angles. Which one has the highest speed on impact? xea ldt/9a gtm njr/- 9n0taa:cemw;i3 .w(i5 Ignore air resistance.

A pendulum is launched from a point that ik-5uhwgx0sea rgsi9 g2+2tcx/x t75e s 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? Exx9etw esa2/h +7u5ig -0cx2 t5kgsrg xplain.

A coil spring of mass m rests uprlyf*q); (fwso *wu 9sjight on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energyslw )o*( f*ujsqfwy; 9.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The in,n nau9ctxogug+t 9, nw,njqi 5+)2zw structor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed tu)aiw 9,g,tn, ojx5g+qn2 t zn 9cnuw+o release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top o.2:w2xre;x;fadba ljcus* ; of a waterfall falls to the pool belosxda*w acrj;b;xl ;:2uo. 2ef w?

Describe the energy transformations when a child hops aro)d rh)+-tdahc/6g:akt) l jjvund on a pogo stick.

Describe the energy transformations that take place when a skier starts skiiv-mlwr* e3 j; ccj0+ ifno*1h*zb2rmlng down a hill, but after mc3zrw-l oflc*nj1*vm+2 bi0 r;h* ej a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heightw.w *8apots, myb;wv 7 h and slides down. Does the velocity atwv p;7b aw.yw8om,st* 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 their path rather k qsfl*we8,g7 than stepping f e*w,klq7 s8gon top and jumping down on the other side. Explain.

Two identical arrows, one witc1 k;tps h vk:j:a26 e(decy.yh twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much v cstycy:e 6k a;. 1kj:(dhep2farther than the slower arrow? Explain.

Analyze the motion of aiua1-b nitdx (t 09q+x simple swinging pendulum in terms of energy, (a) ignoring friction, a+i iq(xxt9 -budan01 tnd (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than itst2a9auw* +niy origia+iy*uan2wt 9nal height? Explain.

Suppose you lift a suitcase from the 12 0 qx,whmv:ua6c azlygm/s+ floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it u 1xg6vwm+,ha amzs:2l0c q/ ystraight 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 neej4x wnfr*,q+t5 3mia:o 5tlpu ded rather than the work.

Why is it easier to climb au;nkqposqj 1 ik8p ;5p32-zcj mountain via a zigzag trail than to climb straight up? k-ozspq5; 2q jj;ipc3kup1n8

Recall from Chapter 4, Example 4–14, that you can use a pulley and rp g.is x:7r l30dq5xkdopes to decrease the force needed to raise a heavy load (see Fig. 6–50sxd :l3.gd pxq7rki 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 forcz z9 -mrm( qn 4q7smmykt*fxz6ir9g86 e when a 265-kg pile driver falls 2.809mnrx6kmrm 647gt8sm(q9 zqyz fzi-* m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much workiks )u/ dpvx;jowno9o n6 w.k7b6i8d: is required:.bios no9x68u;6/kowj w pkdidvn)7?    J

  A 1300-N crate rests on the floor. How much workl9ff+5* oolds k*c1df is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 23 fsolodf 5*fc91 d+l*k0 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) push33yflw;m.d ayaj 85a ding a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50? y3.5 aymdw8 a daf;j3l   J

  A box of mass 5.0 kg is acce; fnr *1doag dg(x0fs68:ahc alerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the boxcog f;nd r x:sa0ag(681hfda* .   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tabqdh // jh5b e7vjy4wm0le. How much work is required to stack t5q /jm4h0y edj/ vbwh7hem one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we migh5gvvha*yxe e2 mdpd;p7 hj168t not otherwise be able to liff. Show that the ratio of outxem d h28dvae7jpg1;65 *ypvhput 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.dg,amk3v z0n rsj), n-6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effectg amdzn,-)k,jr 3n0s vive 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 helicta5r1g1wa eutg9m pwd 7*p3r7opter of mass M an acceleration of 0.10 g upwardw1ad91utrwg mp77 3pg*et 5a r.    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 that ab0lk wrf *w 0+(/kzf+c-by as87+el:nq rmbe$d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shownq:y 81 r*1vuk7w +wctyra0ibp in Fig. 6–37. Deter wt:rwav 8*7b+1yc1qri0ukypmine 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 particle acts iur d5:;vjx jad 0ci1-ou;a7cdn 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, anry)+awhk :+ lhl4 xbp2-q 2pqh 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 has ij) 1.m yo*kwi(q, wnoets 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 anc ra9+ljv/vc0 electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105k38mlu mtnz9o9/ sa/ekm/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exeriw hdgv.y 0(gt ogr5v(.wnh2j *gzd r:n+q70xts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leav(*vdq rt.5 0go.h w0 7h2w+ngixzyj: dnv(rgges the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm51*ojc/ j ervp when the ball is caught. What was the average force exerted by the ball on the glo1 p5jojv /c*erve?    N

If the speed of a car is increased by 50%, by whn2qz8ruz bk 1-do x ;w703eydyxv2v+fat factor will its minimum braking distance xo wv k 0 31rby28-xzyqvzd+2e7n;fd ube increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, in4*f g8n c48hveqqbd s9vestigators 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 driverds8*f nh8qb94vg qc4 e slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.kgh t g*+12vdb25 kg is pitched at By the time it reaches the plate, it may havtd gh+* vkbg12e 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 straight up by someone who do3s,s +n;o(pvn .odl2so zmbn,es 80.0 J of work on it? Negl+z(dn23,oo bnl spvo;mns,.sect air resistance.    m

  A 285-kg load is lifted 22.0 m vert;ia7j4n(m3oeritbp + ically with an acceleration by a single cab;jer4(i7b3 tmi+opa nle. 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 44.phcl sbz(- kg- (r7iv0N/m How much must this spring be stretched to store 25 J of potebk- vz (- (rg7icplsh.ntial energy?    m

  A 7.0-kg monkey swings from one branch s3 gxiff*26rq03djk u to another 1.2 m higher. What is the change in potential enersq30d* 6 u2xrgjf f3kigy?    J

  By how much does the gravitational potentialxhn,n ltn7f,0w,8 xby energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 my 8nnlnxhf x,,,7 wb0t during the jump?    J

  A 1200-kg car rolling (yo+2*+svw* dbxoerun -d hl3on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring andydxv*+(*d+ b w rus e23lhn-oo is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.w5m) .f2y lzc z0lnf8p10-kg book from the ground so it is 2.20 m above the groum lw02z).c5n 8lfypzfnd. What is the potential energy 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 e 7u8,2bwpogn,waua p )levation of 1600 m and climbs to the top of a 3300-m peak. ,2ow awbuua p)ng7,8p
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the c o70lwc(w1mtspring is next to the 15-cm mark on the ruler. If a 2.1l0c m7w (ocwt5-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 a vin 3 s*zvheviad 37hl7;ke hanging vertically from a tall tree in the jungle. Howehkhdl7izs* ;7vv3a 3 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, slides down a frictionvied aiw(bhu 2tsc 47t)(z)p6v(6kazless 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 frqmcxctj7*9m/8 3jvgx, 0 c8b+dy mvbrictionless 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’h9f6kqp yf2i 6s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the groundh2k9qyff6 6ip 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 vck2p bms,93psertically upward from the top of a platform with a speed kb ,pm3 s2s9cpof 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 (ig zlyg3a7 j h35sppb37nnore its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 37 pg ah snplz3b53j7y0.30-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 shown in Fig. yz8l.kt 8 wjy3 de6-uf6–39. If the block is to remain on the track, even at the top of the circle (who3dwyu8y tz6fk-l8 j.e se radius is r), from what minimum height h must it be released?    r

A block of mass m is att9vnq: ) a363tpx nww65jbgate9az. vy;c3h pvached to the end of a spring (spring stiffness constant 3 c)x6 3g9v:.ave ah9p;vytna3wpjtw65bq n zk), Fig. 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 jue))pwq 7-zkkph+ nfmuel*/) tmps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, andq-/zktppw l)7m e) uh*e)fk+n 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 point 1 where it tzfa 8zz29 v5s41wbz0ibrf1eis released from rest. Assuming nzv09 twsabfei5 fr1z8b 1z 42zo friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed o7 - bflzpk xlv03g;j,cus:xi 6f 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 spriqb*sj;h a t*7 0ot0vrb7whf t-ng to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of t0bwtt*07;jfsta 7q h*vrb h-o he 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 the elevator and passengers.

  A cyclist intends to cycle up a 7.8 hn o(b9j(6qwm vgmdq1 2 hgb8,$^{\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 avr*4wwuyo 2nda0l b)vw7:x 8j nd traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermalow2d7y8na0vj):wl rbu *v 4 xw energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom ve6at iib p29.s o6mx(3fk5o awith a speed of 2.2m/s How much thermal energy due to friction wa f6v639xe.(5i2m oot asbip kas generated in this process?    J

  A ski starts from rest and slides down a 22 d-;u mwf-t ompo1l 2njn.;e- z9p +aeq$^{\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 thyw6yrk6 n:25r:6n t g+vp xbzhe 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 ihl3 w02 n, awlh9e0nyyt bounces back to a height of 1.5 m. n l9al3wy ,n2hwh0 e0y
(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 pvllzt5* b /xu(.xz( alulled across a floor with a constant horizontal force of 350 N. For the first 15 m t(* .atb5lxll/uzx (vzhe floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If the :ge56wzd1n g1ke2xdp average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The did51 e2dn:zeg pg kw61xstance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12mc 6+bqa*bj;bu70zkqe jc49.m g+ehh x/s reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal sz2bu2to h2o.) qm kwvo.*9: j aczlyp.pring (k=180N/m) .o:m2k2jov. y2z*hpaob9z. wt qc)luas 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 fiygo;gxuss: : -rmly attached to a very light horizontal spring, Fig. 6–-ou;yg xs:sg :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 first swing?    m

  Early test flights for the space shuttle used a .yx7ss ad)3pk.w/ibzx c* y(d“glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h*p 7ys zi. x()dwdcxyk .s/ab3 from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg pitt i8 m*),/mr0acvueg-dlir7ano to a sixth-story win)8*ru , ct7lirmed /0 ai-mtgvdow 16.0 m above?    s

  If a car generates 18 hp whenxixf r. v4rw,eeii +(* traveling at a steady 88km/h what must be the averag,.(ivxwr* + 4eifxr eie force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates froad9i*f nkb bxic m c j1+i( u6w,3ygi2fvr)58dm rest to 95km/h in 7.4 s. What is the average power deli nd idrf1v(3* c+biwya,g)2xjmf68cu95b ikivered by the engine?$\approx$    hp

  (a) Show that one British horsepowe+4bf kd kl3tgmoys,. i1w 6o1zr$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kil*hf3 c0x(l bsk8yd*yrowatt-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 in abowwhxa 1zducwm 8,cv m.gp3- 8z3a 48piut 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is nd3hzaux.pa 3zg-cc4ww ivw18 mm8, 8peeded to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.07,3t zvx sc qgfmtjk2/yf.8t9lyw 3 q:-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14au0n8; h kszl54 6)z4doegl - 0jvoosvm/s If this motion takes 1.5 s, what average v45h4 j6-ll0kzounes8sd) zgoa;0ov power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of ;glw3 q-xo,s c3.60 m. What output rating (watts) should the pump mo; l-3wscxgoq, tor have?    W

  During a workout, the football players at State U. rana6vb45r eo t:(afb3nq up the stadium stairs in 66 s. The stairs are 140 m lon qbabtfoe:anr(v 3 465g 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 climqeq4 33 6qoz(syqob, l(lt1ftb 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.zc(p/6j*cpc:8w)iaa axu lt; How steep a hill can it climb at a constant speed of 75km/h if the frictional ;zu a xp8wca(c *t)iljap6/c:forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor havie6bm, x 3un8w0;phob; k.sfte to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?wb8pfb;uxm 06 ;tn.k,3hsei o    hp

  A bicyclist coasts do g*qv1r tepg))wn 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” t gpwng2w d20(ghat are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently dg2ww0 (dgpg n2eforms 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 tkhs w w8 u-0flwh680y3g .pbtihe 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 heigh6iwbh8w0uw80-l k ysg 3hf.ptt of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s.(w2e b1*i 8c;m( twef4eodkgp mrk0 r famous long jump (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 he need at launch if he(r.( dteeg8wfr ;opi*m0kmck 4ebw12 was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m ljd0;4b* d 41wc duefkyv9x 3zsliding without friction 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 radiu dxld9c1 ue*wzb04vj 4fy;d3 ks 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 aircraftf5pxyg f ;sj**az9znq*8c gp 65rimt2 without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only mi m*9jn58saq2rgz*zx5y c6p*ipf t;gfnor 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 horia+pv x iv 1g0yf ox1. mi3kg/u7hzg:s,zontal cord of length L whose other end is fixed (Fig. 6–43).xi zvi1+f/ x13 :0 ugah pms7gygko.v,
(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 xd wmzfff. rlhwy165up5 ,6l)to the top of a 3700-m-high mountain. The climb is made in 5.0 h starti wp)6yfl5ux l5f.rdw,m6fh1 zng at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks whe erfs2 1l3-bqr(qi ns 8j*o dur1sk-:jn a 920-kg 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 arecm jt.ur, sx45opy+k2 a in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needxucsp 4y5 mjo,.k2t+ red.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650moy mnnl(- ;cae ks)7(kg/s and falls vertically 81 m before striking the tusca)em k(lnmo (n;y-7rbine 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 vet6,)f jnmh,,r 1rx2 1qqsdph artical 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 irqqj m1a xhp,f1rst h,2)6n,ds above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a ca lly(6pd.rd*- bbm /i7egf8uxndy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ8.l6*ilg-p/r7 xd (yuf be bdm)    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 upwarirx9p) o (a4nqd 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 scal5+y 91 wavmucie, the 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 1.0 m, what does the scale read u91wi5+ vmycaat its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings 5xlzz 4 s9cxzi)h36ux 0 s*ojxout over a lake (Fig. 6–45). He0*z xsjx uzl6ix)hz c9 xs43o5 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 cli.wbmm p vj3z39mbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplipv. b9wmj z33msh this feat?    W

  Some electric-power companies use wywfp0c 5ogm6hh*43tx ater to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced i3 hhf*pgw6 tc45ymxo 0n 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in hgv-q5;lck*q x alf. What is the spring stiffness constant for each of txkqcq gv*5;l-he two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roughymg q;a +m6bn, 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how lqzj11 wd 4y,wj+o(lxnong will it take to accelerate from 55km/h to 75km/h Assume the power stays the saw+z wx do141nl j(qjy,me, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient hf eg ko e(uf2d8ga*97walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at a*ff2k d8o9uhe7ag g e(n 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 of 79 /7hhv w7zk kkv:jsi500 m, what was its velocity when it lv77j79k ivh:/szkwh k eft 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 95k1n rli0fnp-,ybeaf(f s: gd3a b6az+8g/s (a) If :y(an + fbib1n a6rfasl,0p fzged3-8this 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