In what ways is the word “work” ntw*:gr): vku*on0 ycas used in everyday language the same as that dey :tvgr*w:*n)kn0u cofined in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on ay4ki923 bymjn2sbh. en object? Explain.

Can the normal force iy6 z3s)v; .ix7 femgk43v almon an object ever do work? Explain.

A woman swimming upstream is not mhju*;s e(qm2 xoving with respect to the shore. Is she doing an(s 2mxhue*qj ;y work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider whag3 81nxr1d rnst happens to the dishes when you pull a ta318gdrn 1snrxblecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are d;7v. * hv. t8o8y4kloro2iba q yqdq)j uid*y9oing no workqqld oy* b hr4.ay9o 78kv8itu*;2).yjvqdio?

You have two springs that are identical except .yo w7gwhxynl1e +4 y*m*ym8m that spring l is stiffer than sprimoy*yeh1lgw. 4 ywn*y+ 78mmxng 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 forcejxoq/- uj2pgwdyg*sd n 994 /v on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time x4uv-dy on2g/* dj9sg9pw /qj it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change whe,s nlzi/s6w z1(q ib* jpvb5o*n you jump as high as yol6z5zo*sib w/ s j i(*pvn1,bqu can?

In Fig. 6–31, water balloons ar8nwy.c nulgl(ux419ve tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the48.(gly1w cnnul ux9v highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poin2 db7k-ww mgv(t+zm4xt in v(-k gxzmtwbdm7w2+4 two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table.qiknx6w8 z:z, sxb* i7 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 iswn6bk ,*8: zx zqx7ienergy.

A bowling ball is hung from the ceilin9utamv3c qe8yy)px*c7k2 i. v g by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nu)9k mc iqv v27yap.xyetc3*8ose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of q,7fvlvbi;3v a waterfall falls to the pool b7v,b 3;l ivvfqelow?

Describe the energy transformations when a child hops around on a pu wbll*y, :.nyogo stick.

Describe the energy transformations that take place when a skier starts bd3edo**g/ m 8u*acpj skiing down a hill, but after a time is brought to rest by st/8og 3j a*dcumd*p*e briking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of,6euokh /xki1 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,6kkhiexu1 o/) there is friction (deep snow)?

Seasoned hikers prefer to stl/+:zz gav lnr/4vx,:)qejnfo ; hvz3ep over a fallen log in their path rather than stepping on top and jz)o:/r 3,h/ xn+zg:vzna;lqv v4j lfe umping down on the other side. Explain.

Two identical arrows, one with twice1sfve-m9g* lv cnvdie g :8o(4 the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, cv*(sv 89dn o4vgi:e -elmfg1 the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum 8djt1lsy2g 0wrne. u( in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wou8(u w0syl. 2rdt1engj nd up.

When a “superball” is dropped, can it rebound tonia o-d h-sj+rb8t. m(ra(1ba a height greater than its original heraht(--8jid.b on(r b+saam 1ight? Explain.

Suppose you lift a suitcase from n21k rntw(r.xthe floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it st (2 rwtnk.xn1rraight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than tx.kc f./8kbjwhe work.

Why is it easier to climb a mountain via yb*k 0c9oa,ys gh 0p ae;st8i+a zigzag trail than to climb straight u*+sba;ah 0gs0o eky yic ,p8t9p?

Recall from Chapter 4, Examp5) b7b)i(upipfp jkt,le 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for uppb(7)if5i ktp), bjevery 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 gravitationala5htcyk yc07jl rc7* 5 force when a 265-kg pile driver falls 2.80rtyylckah75* 5c0 7 cj m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 kmv0b*bi5c3(m3t(j:l n nazbkhlp)8 m high. How much work is reit (m0l3 (8* bmach53pbvjknz nl k:)bquired?    J

  A 1300-N crate rests on the n1x d aa a-;t*dsbfwq7w8u2c1floor. How much work is required to move it at constanqan8*1 1cwtuxa ;7dw sad2-f bt speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate+kl-b tnxw sm403d9gowj :q 6c5ygxn4 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was n3w 5w jytqbl+6gn:9-omgd x 0k44s cx0.50?    J

  A box of mass 5.0 kg is accelerated by a force acrossg99 +nran sr5jy+p n3q a floor at a rate of for 7.0 s. Find the net work done onn p9+s5jnn a9gy3qr+r the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tablec-c xtby8 u4,c)ok+jw5 jr-kc . How much work is required to stack them one on top of ano) ko-4bwjcx-ur5c+jc, t kc8yther?    J

A lever such as that shownjd; zk3+fdme- ea f1)h4u;:pysg0jz w in Fig. 6-35 can be used to liff objects we might not otherwise be able - ;u f+z;fezpd)e4a y3wshj1gj:0kdmto 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 28z7qx+u;t* jr f- wgm4z5 c*apm° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Ca ruqpm*5azf7z; cx-+*w4mjt glculate:
(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 gi1i h+fu w4mfpza)m.h:(uw 6 lcve a helicopter of mass M an acceleration of 0.10 g upward.mz w6+.(hl1wu pcfia: mufh4)    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 is6c:1e-s( 4ltue zhblyr *;v b(h-xyxl 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, ac3 :)zw z -k.yg j(3vvcrxsc8opting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x =.jp kv zw- )3:c8yz rsov3gc(x 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in thy3f 2icy hz:f1e $+x$ 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 ma9(b,rltmi ws2 ss 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 i;: 6karkqzeu0 ts 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 electxvwr*4y)e f6zx58ty7b ynv5c ron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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/h?ph-)p0qz( zqc-7rjjaz2+qp g $\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose stringxfx,bl j:9c 7p exerts an average force of 110 N on the arrow over a distance of 78 cm. What is t cf7:x9jl bpx,he speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm q k efg1rnrg/7;a)x17 ar5ow mwhen the ball is caught. What was 7)7qar15 1 gmg;fowner/ xa rkthe average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will it7nrax qy )5,jrs minimum braking distance be increased, assuming all else is the same? Ignore thex q nyr,a57r)j driver’s reaction time.

  At an accident scene 7ons;(g 32 zhoynd;f(n 4aqkoon a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient ogyz3f 7( kd2qn ao;snn(;oo 4hf 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 pitched at By the time 9 je 9ch56x5vcwx9av iit reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the disewvh 5cx9ia99 j6v 5xctance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85*zs o ohecblf6 g,d9t q iadr)539v.5n-kg rock go if thrown straight up by someone who does 80.0 J of work on it? Negf bt, zh*g9on9)dleqc55ia .6 r vd3solect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accef.x+aao -tya(gv ,gl6leration by a single cable. Dete,fgalagxvo.y t+- (6armine
(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 442bp3fjw,b rl40N/m How much must this spring be stretched to store 25 J of potential energy? bpbw, j3rl4 f2   m

  A 7.0-kg monkey swings from one branch to another x:lk;zos6x5/p* qku fa ;ubv:1.2 m higher. What is the change in potentia* kulx5 fza;v ;ox:su:q6p/bk l energy?    J

  By how much does the gravitational potential energy of a 64 rrw)uggy- 9jl 8z/j:q-kg pole vaulter change if his c q9: 8rzr- gwujg)/yljenter of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed1 )+rglv jq* k9ae)o(4whhefv v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m.vvgoe)( 1*w+ ajk ferhq49l)h What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m abovexy,t13 tbc;, z l4tbmt the ground. What is the potential energy of the b3,tyt;zt1t4 xb, blmc ook 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 elevgs 47 ffbp44fzation of 1600 m and climbs to the top of a 3300-m 4p7z44fgffs bpeak.
(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 verticukx);v f +wo l.*my3bx5ckz9ually next to a ruler. The end of the spring is next to the 15-cm markuk* wblvou xm+zc ;9yk.x35)f 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, ik6xkd*j d65n0xp v db2s running at top speed (5.3m/s) and grabs a vine hanging vertically fromn6dk* kdb6pdxx 02vj5 a tall tree 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, starting from rest, slidea+0 cgjf2- rbds 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 frictionlef5mix,d62.fikf c8 b56 zsxfh ss 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational az 8ecn)q5kb.6 fx:udpotential energy without td. a 5f8c6nxb: ez)qkuhe 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 from thes(awf0 ty)x75 ds(7 jm,sozoo top of a platform with a speedyo 0axoj mdt(75 os7 zs,f)(ws 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), whont spwf0k+:; +elv i+ fvjpf-(se spring stiffness constant is 950N/m is atv pj+fpeikv-(0ff+ n:s +l w;ttached 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 e mk0 f,cgw20mwithout friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the cmm2,0ke gw0 cfircle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (895 en o0:p.:lxjz ib ooyv8zyspring stiffness constant .oj5:0ynpzb89lxi zv:8 oeyo k), 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 jum9uo cinhj6n8603l9d gd fuhe) ps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law appliesiuf h)90jc68d6ul9ndhneg 3 o. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig.4f saxh;/7qls 6–41 is dragged up to point 1 where it is released from rqa h /f4l;s7xsest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spee .uzb:j vvx ,p9z4h tu.55+(vzp qo5dlf9fwqdd of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottomnj09ma0u9w sb vr.;qk 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 tha aw0us;90vqj rnbmk. 9t 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 a1) ;c+m .au)2a sbfctmm tdg2e 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 765pc8qq j*11 xcc0 kg and traveling 95km/h in opposite directions, collide head-on and ccjxq*q1 pc8c1ome 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 3.5wm./tpma 1)zg m high and reaches the bottom with a speed of 2.2m/s How much thermal energwpa1tz )/m.mgy due to friction was generated in this process?    J

  A ski starts from rest and s c5*chdim8x ,blides 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 the grougf- 7jjwu*cyk( p -c6rnd.
(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 bp g.6q);dtiforh 1os8ounces back to a height of 1.5 m. o1p8g . rifst6;hd)oq
(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 flotsgl3ujzmz lm:9le w;r,k )1a+6 *-hr- huhywor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the w;sw-:aty6u1r zu9gek 3lm,+hr jl-m *)hhlz coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. gs45arycz,1a6 4fjmp 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it r4 ay 5jm 64fra1czgs,peach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s x6sizz5 b:*wx- 0qa erreaches 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 spring (kt-; yoj 5zjkt8=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 bjtk oy-;z58t jack. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very ligqyvf;-ejt4 n:uii 36xx:(n, ntce 1spht horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A -:nf:n4i3cxt uj,i t;1 6 pxesnve(qy 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 ae:kh + xgh3ee m1os;;p “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 in the absence of air ;e1 ge3o ;+mkh epx:hsresistance?$\approx$    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 piano to h 9qnu:4 s b0aw*bksd;a sixth-story window 16q 4b dbhu; nss*w9ak:0.0 m above?    s

  If a car generates 15 aj s;t6z;c6 ;;soxebncfy+m8 hp when traveling at a steady 88km/h what must be the averas6;tn 6f myo+e 5zc;c bsa;x;jge force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avee,vy,m,hr8fo+rj)eq 6x*lu l rage power delivered by the enginehl, e,,lemfy8uo*r6xr)qv j +?$\approx$    hp

  (a) Show that one British horsepo0ijy/, x3mrli1lax9 8 fvmn/ower$ \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-hou9hs hv v wahbkl68(unev+ +*3ers.”
(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 d p53 vml0uy9sk err9x;jrh; .hown from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and j;5rlks xu; 9yp0.3erm9h rvhhp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp m6yj nfrr fo4il 41sn ei00o2b/otor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg s(swfpfo*q19t/4q h4xo2l pes ;lz 1i jhot from rest to 14m/s If this motion takes 1.5 s, what average power was developed?9ft12;o*ol/ jwi s pxqqef4 4hs( 1zpl$\approx$    W

  A pump is to lift 18. k*, ;gfhl.k b8y1efjb(swy3bcv a 3)i0 kg of water per minute through a height of 3.60 m. What outputyi.;vwk3lyaksbhbbc3 (*eg , 81 fj f) rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. rd 0,opboa0rli43aysc ,e ;3iwmyl w 7, srfi1(an up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an o 0w;padyaf,o 3s w(3ib70my1l4silcrr ,, eiangle 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 ee68- lmz.aw *fdap/p+0oj, fh hs.zq6.0 $^{\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 ofo+s.uxw*p9l d+ h8qs u 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional for9du h+ wulpxsqs.8 *+oces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drah)ux kw/h -r-ag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction isu-xwa/)rhk h- 0.45?    hp

  A bicyclist coasts down ou5lracnuf 0c,iss wh//*4a( 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” that a) gw q3kh./9tg7i(yqsd dowzu1 u0/xkre 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.(sq 1w9yugq)dht3k/ zudwgo7i/x0k 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 shelng8 : 9wayo2vk1f1bun f is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor un :bk1nw9 vy1oag28fto start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6b (7zd;g ycm5a046 g adkl5knkbcv)d6–42) 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 traveling atb (6cdy k0kb z55)gkgmd ;n dva6l47ac 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped+,g;y -qf/ne fxrm7:,soqf zp1k yrsg-8z n0o track shown in Fig. 6–39 is to remain on the track at all times, even at the, yfsq rgmfyof;p:sn,rx1 7+zq-zog8ek n/0- 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 wi,- y-osp9tnmcwvp5.5lu ) gj dthout his parachute opening. He landed in a snowbank, creating a crat) dwvsmc.5tl5g9pun- ,po j-y er 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end irjfxfj7q *)ovo0no- b ;1ky i3s fixed (Figo oo- )1 *jqyfj 3kbn;0f7rvxi. 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- a:dpaat9j,5f2 hfif2 l:n5ha m-high mountain. The climb is made in 5.0 h starting at an elevation of 230fa:h 9at,df5 a2nf5jp2 i:hla0 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 elevat0t4/gz2rhj2 2mshytwor is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can m:r 40b/53 e6ospq xcjo 2xsx0) muhmfnove 47,000 people per hour. If the average lift carries people about 200 m (vert e6m/x05 rcfnss 40)um:obxjoq xh3p2 ically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam 8wr f(3qboep4d 2 nc9lat the rate of 650kg/s and falls vertically 81 m before striking tlno9e c p(q2f3d8wb 4rhe turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coas ;,bj2dj shu v+n4vkh hiykju2( 5/gt2ter with a circular vertical loop (Fig. 6–44), the difference in your appar2v4 h2/tu;,kubngkv5h h+ sji2y (djjent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could conr av:;1x ,3d+2f6fzxgqk 5 .lbia unhfvert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were f:v5 qi.zfa d knrfgfl6u3+ 2 ;,x1abxhueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwagxe 5viq7/g 1vk ,v8pprd 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 sprin9ed 3b1 7jemu4nkyla3g 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 heigh 4yuda9klbe1j37ne 3mt of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. x/ 9s(ctbixb96–45)tscb/(b9x9ix . He releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertihithne8 pisny3f/z:nk2(.m n) rv s5+ cal distance of 5.0 m in 9.0 s. Wh35m nt2r.h+ifhes(s n/v)n ink z:8pyat minimum power output was used to accomplish this feat?    W

  Some electric-power companies use watf:k lu-q)8pr,g( zwwa 0er7huer to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced hw0)we(a qz: l8fpuur7gr- k,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 cut in ha,ho.mg t oqa4f98qz 1clf. What is the spring stiffness consqcoo8 h9tf4gq 1m.za ,tant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37b,0)zu05rge-defzrv9pe a r, $^{\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 35kkzqyn ,b0di,z1h4l2c bppj6 ,m/h to 55km/h in 3.2 s, how long will it kc0jl1b nz ,qi6 ,y2pzbph,d4take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function ( r5*or)tcdocz75f(bp the “stress test”), the patient walks on an inclined treadmill (Figcod(c 5rtpf 5r)7zb o*. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 m, wh1ble)s1lzwh;bj .w3uotw b ((at was its velocity when it left the volca;olhwwwu1 (z)( 1bl3 .bjbes tno? $\approx$    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 cbaw1 chem3-k+g77 -pxou q*v 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum powerco3he +k71p-q wgc*-mxu7b av output?    W
(b) What is the speed of the water as it hits the wheel?    m/s