In what ways is the word “work” as used in esh;moujoni yi9s tiu 9 -)96z/veryday language the same as that defined in physics? In what ways is it dij) 9i9ts/m i-9synoou;hi6 zu fferent? Give examples of both.

Can a centripetal force ever do work on an object;kny+, glt q-29 njzwc? Explain.

Can the normal force on an object eve6yo*hkfci:s - r 7y:ifr do work? Explain.

A woman swimming upstream is not moving with rd/37 ehkn u7wx:o,jw-ecqym99ow/r nespect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on he oqwe7,uh w7n yex/:o/9n -k9r3mwj dcr?

Is the work done by kinetic2 + g(/rwaczjl friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecjcr(g2/wl +za loth out from under them.]

Why is it tiring to push h..oxwagph o.v* sca7*9 c hj+4s dn-sqps ;wn:ard against a solid wall even though you are doing no wo +jn.w cac: ad vps. nsh7x-**;gsoqhw9p4.sork?

You have two springs that are identical except that spring l is sc,xqoxtzvl ;5 c c60-ttiffer than spring 2 xc ,- 0tctvox 65qzlc;$(k_1>k_2).$ 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 a2shvq. d8rb 9j block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and brq2dh v.9jsb8 y 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 energx;d h 9xcur1;jfwxt:.y change when you jump as highc;wrutx. x 9jd;:fhx1 as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wi7x vkbi/* jw7nth the same speed but with different launch angles. Which one has the highest speed on impact? Ignonj bw77x/ k*ivre air resistance.

A pendulum is launched from a point that i)nu fm1 zp(hf 35ymm5cs 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(mum1fhzn 3fpmy) 55c 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.

A coil spring of mass m rests upright on a table. If you compress the spring by o e(q p,rdp3:sawv 1e)pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of enew(,so1)qpad: r e3e vprgy.

A bowling ball is hung from t6(vl*6 dv o1o ho8qwezhe ceiling 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 release the ball witveol68o ( *dovqwhz16 hout pushing it. Why?

What happens to the gravitational cb+h q)k6es( v:e0vlwl./ylf potential energy when water at the top of a watee vqf0y 6wcbelv+.(l)k:/ s hlrfall falls to the pool below?

Describe the energy transformations when a child hops around on a ph5b (,vd45 axmxqxr: ekx ,i1qogo stick.

Describe the energy transformations that take place when a s+x g/u,5o c-m9iesu; c6nsyy m5c+ hnckier starts skiing down a hill, but after a time is brought to rest by stri5osmexh y69nc s-+n +g5iucm c/;u,cyking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of he*er)p4 ,ag;w bg yc3wnight h and slides down. Does the velocity at the bottom depend on the angle of the hill4 bg;* a3ry )wgwe,pcn 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 ratherj.im i fb)*sfc)wo*rcpa+9c v 0 ed.7u than stepping on top and jumping down on th j+ii0su)7*f.*cpwao9 vecd) .cfbmr e other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired i ry-al- l,*gignto a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the sl la-glg*,yr -iower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (at+m*hm 3; opqo9iw 8eh) ignoring friction, and (b) taking friction into account. Explain why q+8ow3 *hom9;pe i tmha grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than itww v :vcg6eh1-s original height? Explchw: vgw1 e-6vain.

Suppose you lift a suitcase from the floor to a table. ;rn24 bfwe5oqhunj t2 3 zd,t;The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the h52b j4urtz32 ;twdo;nnqf, e height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the gr4e5 ougqzx(( p2mo4 ap2u4mkuq+)uwork.

Why is it easier to climb a mountain via a zigzag trail t26bzhz n bqeu+p1was i z;0;z nu+i,. tuw4;swhan to climb straight u n z4bz u 6a1i;;we2.,swwzpqhui+;nzus 0t+bp?

Recall from Chapter 4, Example 4–8f63uxyjf eopq8 pv/h, *0q yj14, that you can use a pulley and ropes to decrease the force needed to rj ph0 fquo*j ypqf8/y8 ,63evxaise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational fo;b+ k947yic x:ptal v: +xurcirce when a 265-kg pile driver falls 2.80 pki;ct: a+4i7ub+yvl9c:x rx m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m higheu o yp *y+r5nk1)niwsn+8zj+. How much work is requi1spk5reo+ znjy+ + 8*uwy nin)red?    J

  A 1300-N crate rests on the floor. How much work is requir5oqrw8q gr2+;vk2 tnoa j-2 tyed to move it at constant sr8 wgno jt-yq 25 ovtkq+;a22rpeed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) *tvhw03xurw- pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective co ww3u*vx0thr- efficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor avwkg7;pc km62 fb;fw +t a rate of for 7.0 s. Find the net woffpw72cm +kk;6;v wg brk done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Ho8h a ok8x8c9cdw much work is required to sdkx oa98c88h ctack them one on top of another?    J

A lever such as that shown in4:l:gebj ps, 0sxts(xre x/i 7 Fig. 6-35 can be used to liff objects we might not otherwise be able to :e xesx,4 rjp/0lsxts:7bgi (liff. 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 ande 2b;,mdm+ meamu wd9(oj-/k t is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient/u-2;(o9k, m me+dj embmatwd 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 acc1ow(nl7lx.o ub kh0+w x(i4p82 uodadeleration of 0.10 g upward. b h ilx((.pl0uod78kaxu ow+owd 412n   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 dis- gtj0lb psnfl p(ze;c)h*/.2im kda0tance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along thvbeac.; ;sl. ee x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a)c sav.;b .;lee 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 pdbc 2m)kd3(dgc-f9 k aarticle 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, with mas +r mm,+v 7 qoisk6k)*cm dx vf*wts,8bzlst*7s 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 cm,c e9bu29iilhd34as,xsd2 is doubled, 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 5vgu944qags i7) vlm m(kp l7yto stop an 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 travelaow0wa05 zd,qing at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an aveaw3,kja woeem - 8,8qdrage force of 110 N on the arrow8-wq wm,ej8 o ,eka3da over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves (n4x xrrr 8i5 b,9og jry2ltt4a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the gibl 4rtxrro492n8xy( jt5rg ,love?    N

If the speed of a car is inc8jcw2:gkf f3nreased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the drive 3ngfkwj: 2f8cr’s reaction time.

  At an accident scene on a level road, investigators measure bobr/g 558 (:1tkgr:l ckwu ika 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 whe (wo5tb5gkk/r8ilu:k gr:bc 1n the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0pk; pjrcv4 , ktt9z )p,,sb6ue.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average foru,,e)p krckb4t,t;j vp9zs p6ce 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 dosxsbyn. z i(cu84bqmy/0 7t- oes 80.0 J of ( sqo.7 /xbzcmys-y 4nubit8 0work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratiof,u +62oiawmgnnm c 5m/vu17on by a single cable. D cm6/+gu w, iv1m ofm5anu7o2netermine
(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 440N/n a1gdobol30* m How much must this spring be stretched to store 25 J of potential * 1 3nbda0ooglenergy?    m

  A 7.0-kg monkey swings from one branch. ruz8wik.n.9ae:m3 vd- pzzy to another 1.2 m higher. What is the change in potential :uz8dn .p-3 avizw.yez.k9 r menergy?    J

  By how much does the gravitational pot ummm n/: ;1cojfe*/aaential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jum*m/1mce:uno;/ a mfajp?    J

  A 1200-kg car rolling on a horizontal surface 9(j/,psc 5zmjv2b krnhas speed v = 65 km/h when it strikejvpc2/9z(k bn5j , smrs a horizontal coiled spring and 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 2.10-kg book from t7 j+)fo 2osgu7ktx3cpx :y lc 6,xm;jphe ground so it is 2.20 m above the ground. t ;f xm7jxp:,y2pkg x3o76)l oucs+cj 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 1rc5(r ijr8 p w*oa/4+o x-2qrlr8yfos600 m and climbs to the top of a 3300-m o8o/5il - 8yr jw4c (2rq pa+rro*frxspeak.
(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 no hoy 6e, 77kwx548g jqghws9hangs vertically next to a ruler. The end of the spring is next to the 15-cm,q7gxwo5j g s8h yo 9wn4ke7h6 mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan,4kwqrsn1 b8a8 is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tr4ak8q8rbw ns1 ee in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startr a(fzza20(q6go( tin hmx8s 2ing from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frij:.a u t,f8ccyt2ty/qum46r7 0qjrlnctionless 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 khhkdi(5mq. -hinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must5qd khhm(ih. - 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 from the top ofom-n; / (( vijv56wiipwnh4c k a platform with a speed 5(iop(v6w;cvm/knnwi- i 4hj of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constantjfmj)6) g q/cp is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball wqcjfg)mj 6/ p)hen 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 tracdz gnmt1j :/tdt46. 5r2zsc ekk shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radr dzcttjm4gnz t1:ke .d/652 sius 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 sayl v5,iga s+;tiffness constant k), Fig. ,sgai+a;5 y lv6–40. 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(,irme(u,qv dt8isucso-.a* a bungee cord whose unstretched length iu. (, i sid8csrq,-ot(*mueva s 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6:hl 5odoyt- mwa mu;h .4 5hg(zn(7zgh–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the spe-g 4t7h :mzhhnw5 alu;oo.ymhg(5z(ded at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 1w2t3vb5q / m -k3gr ixnbs,l7s2 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bot .wit 3d;y-7*mvxfk w p53hbxhtom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total dwyk- 5 3*f wmp7tvixx;hh.b3mass of the elevator and passengers.

  A cyclist intends to cycle u laehj6w +9)ls3 wtrf- jrg f1+x4/urup 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 travelmapbg3fnv 5-+g i vooe.(d 3w9ing 95km/h in opposite directions, collidn35 o9 vp-gw3ob.vg( die +fame head-on and come to rest. How much 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 with gjn p0()glz .qa speed of 2.2mgz ()jq.g 0nlp/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest an 0y 01jljek)7tymq.sfvvsq + *d 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 fromg;yso *6.leoflf1/esz :-t xt 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 : ,xzn-b5n6vqw8k6mrm/ fiuy bounces back to a height of 1.5 m.6:v8 -q i/wrznm f56 mxkbn,uy
(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 withdy/zgd*o4j(ehc e1x0 a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, g1h(j/oyx*4 d 0cdeezand 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 coasinin; 3l,t h:o )8tim 3t)vwykhobh.,//lvioter in Fig. 6–41 passes point 1 with a speed of If the averai3:/lnthiiot v3bm ,;.)i voy/o k,h l8hw)tnge force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 146g x p0ecy0kq8.0 $^{\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 lignf o(m4ur mz,2xlh9s1ht horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 , urfsxl2mz9 h(4m1o ncm 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 3; -l3+kib ph+j-lcre hm1oiv attached to a very light horizontal spring, Fig. 6–40. The block can slide alo1h3- vco mi-hlbej3 ip+;r lk+ng 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 bfd59 zpd4s(;a kt /k1qpdd -v“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 spez skpad;1t(pddk9/5-q 4bf d ved 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 moo am76x/lp:hj ;az g-ftor to lift a 315-kg piano to a sixth-story window 16.0 m x7a6;z m/ao:fhpl-gj above?    s

  If a car generates 18 hp when traveling at a steady 88km/hqha6z1a 245ogvxhr ki3od1 sco p8**j what must be the average force exerted on the car due to frictiog 64kr1a apjc25zq**sohh1ood8 iv3xn and air resistance?    N

  A 1400-kg sports car acceler .wmi 2hjnx( - fu9n7s+8oc1 qud*hyosates from rest to 95km/h in 7.4 s. What is the average power delivered by thym9d 1(jiqh n8u n sfh *2o.cx-7+owuse engine?$\approx$    hp

  (a) Show that one Britishuj w8sgl:be/udsob +dmn xc 49;f2 .u, horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-ho nl9 d)gsmgi-2urs.”
(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 11b 8v3h. r5 ay8.rz8pcsd3a qwb50-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what .s38 r z3.8vcrabwd5hyaq b8p power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a jzl sza8q/s g6m93z5 (4g wfco3.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg sho:ilcgv63 yh0tgg. g ,i-2k16k ymr juzt from rest to 14m/s If this motion takes 1.5 s, 2h6.:ygv ic3u0g,k6lmy k-1jirg t gzwhat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water 2ln )jx7f)d z./ejidf per minute through a height of 3.60 m. What output rating (wat).n7diex2/ j ff ldj)zts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stairs inl43he;lk9:lx n0r pm7, qd nox2p6 nmj 66 s. The stairs are 140 m long and inclined at an anq ;xj m0r7el l6pdmp2n 3 hxln,49o:kngle 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 a 6.mb s ll;cn)/i70 $^{\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 2n 1pwbb:a)p1: tl1it d(soava hill can it climb at a constant speed of 75km/h if the frictional forces add up to 6 an1p1 a (i1bws2tbtol v)p::d50 N?    $^{\circ} $

  What minimum horsepower vys;f0ir cif: v 870by hqwzqj(z13e; must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fi v(hr0ie:jqsz1 8;7vfw; y z3cq by0friction is 0.45?    hp

  A bicyclist coasts down a 7a1uzn/je98 ml .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 mvdlevl5sz +bcp0,x.vq5 2o ;c+h*uk“5mi/h(8km/h) 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 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 malvhs.2;+*lo ,db qz0x c+ 55uvm cpekvss 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, and the remainiaytnb913w6b lng 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 alla3 9 by16lbntw the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics shows rmf,b kc)r1t*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 traveling at 6.5m/s at the c,)tkr*1mbr ftop of the arc?   m/s

  The block of mass m sli7uztw1p91um g o d-5q cfot+k1aq 29jfding without friction along the looped track shown in Fig. 6–39 is to remain on the track ug+f1c9571-9 jwpkzq utma1o tqf2odat all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his paracqxyz ci -h:k +5m2jvp(hute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilci2 5zxmvj ypk+:q( h-ot’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 fiz 2/j4hboe 6fsot: hq+xed (Fig. 6–43). 4 +eo6sjqho2tb:zfh /
(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 37m +izu)zy8 qa7l e:mn4 bf9ft800-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 48fezm ql8f:ya7unb)t+m iz 9m. 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 mfz e648uf7s ms 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 ca:jv n,e:,yirac: ekd7 n move 47,000 people per hour. If the average lift carries peopl:edk,7arei n y ,:c:vje about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and x6p;m;ul y26jku;k pv s9c j3efalls vertically 81 m before striking the turbine b;e 6c;9s3kp xl vu ykum6j;2jplades. 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 ciruv 9*vl2r4(fqdb z cse8wla,/qfz-6 t ,d u4mfcular 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 friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend ob4zl 2,( td9s,vzcfdql8 v4/fefaw m u *-u6rqn the size of the loop or how fast you go through it.    mg

  (a) If the human body could convertb/9sr7 smqfqrl3 7r1s a candy bar directly into work, how high could an 82-kg man climb a ladder ifsb mql/3r r1 fssrq977 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 at a4 v-mom5h4auw n upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the sprie:ywx. kard-l; vo) ;2mt iieo;cp+- lng 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 2riplw ;vamd:; )xo e.oyti+k;c l-e-does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6b0 zo8kqi( 9bl–45). He r lb9bi o0z(q8keleases 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 c0qn;vo .5w ki:kfx amf1k5 8rwlimbs a vertical distance of 5.0 m in 9.0 s. What minimum power out:fakn f .m1oxqk wk 8viw0r5;5put was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped emz72yvvs(; e a:g5 olby reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by agve(:losvza;27e m5y 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is t05)ib0. igtfl z tj/d8r ks4-xg*byzihe spring stii0z- *tik8zi/xrg)f sbjy 0t dlg. 45bffness constant for each of the two resulting springs?   k

  A 6.0-kg block is pus((,rspr +9 a15stqmfa f nb4xghed 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car cano)-h2 c 9gwypzfj 6jy+ 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 poweryz-c jfj gp+)yo96hw2 stays the same, and neglect frictional losses.    s

  In a common test for cardiac funu b9ch5xqp vyx+86iffl b9 ;9 ixymr5-ction (the “stress test”), the 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 a pc9 x5u l f9xmiyqxf; 5i+9v68rb-hbyngle 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-q a;o v ktc3bi;-yph;)kg rock vertically upward a distance of 500 m, what whyci;;k aq)3bovpt ; -as its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel2,nssi,7iz mmoqvx06 from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is s26 qvi o ix,7z,ssnm0met 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