In what ways is the word “work” as useu6gr. lm 3rpp1d in everyday language the same as that defined in physics? In what ways is it different? Give examples ofr613grlp.mpu both.

Can a centripetal force ever do pt 0sug.up xwkw,ja(*ggur,87.qzy6work on an object? Explain.

Can the normal force on an object ever do wyi)+ ebtnx;6lbz66(y1spcy b jtd z: 0ork? Explain.

A woman swimming upstream is not movinc4hbk5guxwl 30h d,zwq-03th g with respect to the shore. Is she doing any work? k3zc3 4 h0hhx u 5-wl,dgtq0wbIf she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negat,tdlszvnr 9 xpc2j+w(wu( ,3mive? [Hint: Consider what happens to the dishes when you pull a tablecloth out froul x(3j2(z,t9, r w vpw+cmdsnm under them.]

Why is it tiring to 2 lfc. fbv;i3kwq8:;yato*sepush hard against a solid wall even though you are doing no y.lfkb;8waft q*2 ve:3 soi c;work?

You have two springs that are identical except that spring l is stiffer than bld*x z qu.x)0spring .b d*x zqu)0xl2 $(k_1>k_2).$ 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 free to sapxv7 fc. l+y;d i8t8pf.d z:nlide on a frictionless surtd ;z.cxf+f ydpn7 ip:v88 .alface (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 potenmnr2*q:idqjq 4 k63letial energy change when you jump as high as qlmik3 j2eq:46* q dnryou can?

In Fig. 6–31, water balloons are tossed reww96(af- c3rxwth.from the roof of a building, all with the same speed but with different launch angles. Which one has the highest sr3w6 e (w.xwfcra9-htpeed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above in4+l1hsh jea;e* ;d jfts 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 directe+ ;h1e ef had4slnjj*;d downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compren*kor(7g9nj0o zauu-8y, bmy; wz5,kxt *kd hss the spring by pressing down with your hand and then release ig -xy5uo*k o kzmt,a,w7nd;zuj (0yrnkb98h *t, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiwjyddz)iu 53w;+uwu 8/soaq. ling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to relea3 w w5+ d8yd.qsw) j/iouu;uzase the ball without pushing it. Why?

What happens to the gravitational potentigtvbdf2p3a v-cu gjso10/7-7f/ ic*nu le ds.al energy when water at the top of a waterfall fall c 73c-v adeion/vtlj/- gu0fbg2 sd .f7u1s*ps to the pool below?

Describe the energy transforcc3r6yfvculk3p2z 9u0d/ 7 sg mations when a child hops around on a pogo stick.

Describe the energy trafc:j7sl ar - k.x+z5hwnsformations that take place when a skier starts skiing down a hill, but af-fc.l5 +zwa sh7krj :xter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts fr6 :enajqo+a v.zbkx;lj3 c3 p9om rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there z 6ba+plxonecv3:a j .;k93jqis friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in ti7hejcy :bci: (;p/yyheir path rather than stepping on top a( c ;y:jy:byip7ich/e nd jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the tl4k ci,ft -u2other, 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 farther than the4 u2 titf,kcl- slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of ey ul4pdld120 yi+n.jonergy, (a) ignoring friction, and (b) taking friction into account. Explain why02 ylp.yliju1 d4+don a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gnsib 1v0p u)( kh4se-rreater than its original hk iue(s0hr-p 4v)1s nbeight? Explain.

Suppose you lift a suitcase from the floor to a taba3f +* lij,mulle. 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) ,i3aull f*j+m the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neededk vm2;f e s)j*fpyz8n. rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb st(y)gtzr g15 k*ee,uw r)pu1xcraight u 1erztpu)u c(1,5 xky wgr)ge*p?

Recall from Chapter 4, Example 4–14, that you can use a t91 s iozclmxljq/ omki*)6rzi a2tf)459pc*pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for evermo/p j)zf k)*q9 1zm 9atlcir2s c6o4 i*lixt5y meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver falu hk/skwd:.8lls 2.80 mwh/k8.s:l k ud?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much l wzx ir+l0mf0t) fh89k *6mniwork is reqlz* n i0f+l8rhmkwx0 f)i6 mt9uired?    J

  A 1300-N crate rests on the floor. How much sw4q5 o lo65iuwork is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 N,55 swoi4ulo 6q    J
(b) 4.0 m vertically?    J

  (I) How much work did the moverb oipc7qu7 0low++.dsq1fpu9s do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effec du01 o uq.pqp+c97li+sfwo 7btive coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate o lz6sqekr-n z 3.f2bt*f for 7.0 s. Find the net work done ozt*.r-sfe lk3nzb 2q6n the box.   J

  Eight books, each 4.3 cm thick with mass r0ge: 0:rw ixdv ;9hdb1.7 kg, lie flat on a table. How much work is required to stdr9x : drvb:ewgh00;iack them one on top of another?    J

A lever such as that shown in Fig. 6-35 cayjjf,p+ ) -igzn be used to liff objects we might not otherwise be able to liff. Show that the ratio oj+ -fgzp)yji ,f output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept fromg35 hxob3h 0v 9 ckbz.0xnju*v accelerating by a m9cxz vhbvh00 ugkb .3ojn*5x 3an who is 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 mass M an accelek.dp h62hiyj nj-)sb; ration of 0.10 g up. j6j;phsb 2)h-dykinward.    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 thatt0oszq ()p , sdu2lyk- $d_{\mathrm{A}}=10.0$ 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 2xi10w5mwdk 9hvl q/ix axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m i2/qxi0lwd 5kw9v1 hm 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 par),qe5xr ) jwohcps g.90 sywm/ticle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, +f73xdrat; t qwith 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 h m p*4v0wndoqd7gc,pc 7j)5swhat 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 electronz9 *9usqt;mp y $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 105km/8-pyn03:0gaqy yiv 80lrxenu h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired hoxs09s.of/rq8 g 9ycrka65kuyo q( 6from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaveoqo.qc ox r6k8 kss/0u5afy( yhg6r99s the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm whem.ag 0cu-(izpn the ba(z.-cp gua0i mll is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is incren y at l,5rc9q.7pl+q;amfol2hs /l j-ased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the5 l.-7l+ jnhay;fmql,atp2q/ro l sc9 same? Ignore the driver’s reaction time.

  At an accident scene on ;r2z03+jafmm m ihlk.a level road, investigators measure a car’s skid mark to be 88 m long. The accidemz f 0jmai.lk+r ;2h3mnt 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. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is j 6vq9)zpm ihu be0+l+d/zj u5pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between u6qviml pz5)e /ju9jhz +db0+ the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by scy/+jnyyv w sr1p j/k3gm4 3a:omeone who does 80.0 J of work on it? Neglect air rm3p3wan:4/j rkvy/c 1g s+jy yesistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratio9 tjqs3jswe 8/n by a single cable. Determi39j/ sqewt8jsne
(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 gm0 2v50: mu( uuv(g g6cwexuqconstant, k, of 440N/m How much must this sprinvgm umv00x(uwu:g c5q62g ( ueg be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one br-8g 0p.n4. nlvq)deovsp 8i)j gauo -qanch to another 1.2 m higher. What is the change in potential energy?.aqov0-pe s. - ) nlj4)dgpvnuqog8 8i    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chc.a 3 r7e3ea wjf0qi:iangeij0 e7 .c :qiwfarea33 if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has s-ed2 (dv-f 5tszfqrf 2peed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What it2dd z(e-5v ff2frs- qs the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2;w+zs g+ nd.8l9ljypl .10-kg book from the ground so it is 2.20 m above the s9 l.ld +zw;j8ngp+lyground. 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 elevation of 1600 m and90;+r oxdxb p15gz lgb climbs to the top of a 3300-m peak. 15b9 zx;dl gbxr0ogp +
(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(7c sdee *nt.r. 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, wheds. nt(er*e c7re 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 vine 4yz d82qbapkzi7575wnpa twusp *,a))h qv;ohanging vertically from a tall tree in the jungle. Ho7 7k8ni5pw2t;uhbywp oavzq z5dsa* a)),4pqw 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 frictionlek1f(3:..jz rn xc4tag kh1ukbss 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 4heb gylqat,-e99 43yhuse/k 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 r51 d3g 4dqievpyy)65zc4o7kb y;gmi is transformed into gravitational potential en py eibr d4 gg;zm)k7y15vi5qco6d4 y3ergy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward frqqyeqzw ap) m4) .sa4:vk95/kn ryd1 bom the top of a platform with a speed of 5.0 m/9m a1kq/n qy5 v4.aw:))4k szyrdqpbes. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 950N/m in;v-vldbx em g:1wsc) +g8z9a*l0oczae sbvw+;cn zl *vo-d8)xc1 m:gg09 lzs attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    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 pdvqwjk6 /-4i in Fig. 6–39. If 4ikjvp d w6q/-the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to t d.elw8g+ h q45cide2jhe end of a spring (spring stiffness constant k), Fig. 6–40. The block is giveie d4 cg2ej8w .hq5+ldn an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose:.mta+rim/2g . mc dzc unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spc: 2+ g/zmmrcimd.a. tring 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. 6–4cgxjjcc 3 - n t:-(6:0 ssefomz1j4/kmhl/y sh1 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at pjn 6jl:e(4 m:ztcf -oh3/kgxsyc0mhs- c s/j1oints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of 6)tb w6rtzr-i 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 elevator shaphg94eemls-nck(06 d f dpc hge ekl69(ns40-mt. 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 the elevator and passengers.

  A cyclist intends to cycle uywg:z7:vx 3 ;r fn.ydxp a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite dir,jg(7)lh. ym 3rrjf fjections, collide head-on and come to rest. How mymg3r(r 7 ,hf )jljj.fuch thermal 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 with0 -1ougibnj+ .c+ zda*xly m2e a speed of 2.2m/s How much thermal energy due to friction was generated in thisu* 1+.e2n b dy0i-cjalomg+zx process?    J

  A ski starts from ren.q -ea 9 h9dprkt6y 2g2vrxl f.m8iw)st and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above t k*u3pi,oqv z;he 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 aqmba gicatx,3* )u)rc 8 c)j(e height of 2.0 m, and it bounces back to a height of 1.5 m.i( 8ueqca*r)ma gjcb3c, xt))
(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 colhk1 ;:sq l9i13nrsnz nstant horizontal force of 350 N. For the first 15 m the floor is i;3qlsn:191rh klz snfrictionless, 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 p4 )dv;4k41fgl fxhtpif +pk ,hoint 1 with a speed of If the average force of friction is equal tokv4 4tki+fxdgpf)4, h;hl fp1 one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward z3(jew1+fvsw7l sv -t18.0 $^{\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 vekew7ec 0 5msgeja+1c9-e(g syry light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the bloc-e+jaey1 gk m 70c5 g9wsce(esk and the table?   

  A 280-g wood block is firmly attached to *er3suav f*3bh)nx 5sa very light horizontal spring, Fig. 6–40. The block can slide along a fa vbr*)se5*sxh33un 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 upx y-cr/6i-at,gx yf- lvq2:ik8fo , tsed a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been ing /f8- -rl2fcv- qt,xiy xat:y ,iop6k 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 3i3/;qub: hd cp15-kg piano to a sixth-story windbdqh pi:;u3c /ow 16.0 m above?    s

  If a car generates 18 hp when traveling at a stea9a6d w*t xwaz5dy 88km/h what must be the average force exerted on the car due to friwa t *a5xz96wdction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. //o xprhv eu+ fqd6tjrk h6+4*orr 88pWhat is the average power delix/rroek4f8t h 6*8pphu vdrqj /r6++o vered by the engine?$\approx$    hp

  (a) Show that one British horse-7zj5 r-2 7qvqlarl nlc5pv,dpower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-h(tuh rg:t 7hy.ours.”
(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 -a f .ama;4o+.g1xxyoqme s;pb /2xnkin about 6.0 s on the level when it is in neutral. Approximately what qx.-oemp k/sfx+g.2 a4oxay b; mn;a1power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mot zv gw26au68nrujike-o ei4ttz7qc x+xf( 938or do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg sz 7ji dw-1)pcgb4p-t chot from rest to 14m/s If this motion takes 1.5 s, what--gi 4tb1dppczcj)7 w average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of watw7g (8zt;c/ 9yej-/gpqwcdnt er per minute through a height of 3.60 m. What output /;cq/t 8gy7 njcp z(dwe-9 gtwrating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the sty1a aa22b5+c9d-sx e lgcn+cc adium stairs in 66 s. The stairs are 140 m long and ibe592an xc ady g2-cl+s 1c+acnclined 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 cyclis xvm .fk)w jikb4fp2/hls; c:1t climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp.h)eq/r zwvusz5 u 98w9 How steep a hill can it climb at a constantvq8e 99z )uwwrhuz s/5 speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able tp) 7m5wi r 3 hreylxly-a5;jy1ukcjd7dm;)l 3o drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficien5l;djxpy35rume 7d) ; 7i - rl3 lc1amyjkwhy)t of friction is 0.45?    hp

  A bicyclist coasts down a :2u s mp(.vy/dmy5h 7a)mwq ed7.0 $^{\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/ i27 /0+cxaovl0xmvw uh) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a cmi x2vuav+0x7c/ lo0wompression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, y eh:5 eh82fesand 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,e28h hfee5ys : 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 famousi2wqo 4hqs,8f:sn n:p 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 was s4hnnoqifspw:2 8:,q traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the lxho 4niza-ae0)o h0* wooped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of ra-*e 0hhi)ow0x 4anoazdius 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 aircbr*xll jm*)r g ne+l+9raft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor x+g+9 lnlr )mrjbe** linjuries. 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 leqon,k :nht9 0vngth L whose other end is fixed (Figh:0o ,nvnq9tk. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb hqab94 4eiwqiu4tjo87.4pxc ,wa9d eis made in 5.0 h starting at an elevation ot8q ije44b ac.qo4i4 uwe9hx9d 7p,awf 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 huge spring m tr01 ;w:jxck($k=2.2\times10^{5} \mathrm{N/m}$) 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 people:98(vbc+/e ;q kw:bd k-qxpay y;mime per hour. If the average lift carries people about 200 m (ver/9b+:x8qk q;m- mi;yb: p ykc ewaevd(tically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s an do k*.yl,a6vuz0j q.i:zkp:ad falls vertically 81 m before striking the turbine blades. Calca0ykiqud:z6zp ,o. ajk. *lv: ulate
(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 vercje)rrivb0 p lupca4t:* d +a:*x(rs. ebf n0-tical 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 — t :v f -clrpbu r 0rsaej(cx**.)+pdie0: nab4that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how/wxjf+9hgoqh 6ybkv; 8 bg6,r high coul 8 jrfh /o6ywk+9g,gq v6;hbbxd an 82-kg man climb a ladder 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 a+e* c yc.oipl8t 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 bathroor n xct6zq;0j,ldnpod7e+. v/m scale, the spring inside the scale compresses 0.60 mm, and ic, tzox+n;.v e djpn/ d6r70lqt 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 50 af:jbv ex::im/s grabs a rope, and swings out over a lake (Fig. 6–45). He rele0:v e:bia:fxjases 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 verticthy96le;;)y j i e3tkgal distance of 5.0 m in 9.0 s. What minimum power output t3hjt)i ;kgy6 ylee9;was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water c.krzu1x*o4mj3joc e,c0b)) h y hm l9is pumped by reversible turbine pumps from a low to a high resercm)y 1coe09ru ,h).3 j *kchlmox jzb4voir. 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 cp2vm3c8a56s8w esb rmut in half. What is the spring stiffnes82b3rw6 mv mepsa8c5ss constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m *g c mulc0d ) td0+pxyk-6jus2)7jci kup a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car canzm0n f0ckke 6/qi/f( apb wx-;p5v6oa accelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays tcipk kn(avoxfq6wa 5efm zp/-b/; 600he same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), th( apfkq-lb3p3u 7 pjb(e patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 akj-b3fu3pql7(pb p( $^{\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 501 fe9cvvbp0rvm 5sv07, cy,k l0 m, what was its velocity7vmycsvrcv,9l15 b ,kv0f 0ep 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 /wwhccs j8m5 suy6o6* from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up j m6 yw/csh6 58owuc*sto 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