In what ways is the word “work” as used infe-ju 0:yc yi, everyday language the same as that defined in ph,e0 jyf:icyu- ysics? In what ways is it different? Give examples of both.

Can a centripetal force ever2a2 uiy( db o6gg:,xxr do work on an object? Explain.

Can the normal force on an object ever v)um8lr(- icpdo work? Explain.

A woman swimming upstream 3i1:*ca yp-a kwywqj.ya*4 xcis not moving with respect to the shore. Is she doing any worc aawp xqyk*41 *ij cya:-3.wyk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic fricu3)o7x dv+z imtion forces always negative? [Hint: Consider what happens to the dishes io)3vxuz+d7m when you pull a tablecloth out from under them.]

Why is it tiring to pusr7g ppg z66f ut),wt t6qd*o b4dkz:t8h hard against a solid wall even though you are doing no wod r4gt6tq) bwtp,f6*dt ugkpo7:zz6 8rk?

You have two springs that are identical except that spring l is stiffer tho5vsp01 rg,jye i z1n8an spring ei,zsvy8rj5o1pn 10g 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide on *ku;/n t*)kzv6 euar; fhuah+/atbg8a frictionless surface (Fig.6-30). The block starts from rest at g*a*) rtz;e/8vhhau;6bk n/a+kufu tþoint 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 potentiw83nxtv- 7 uswal energy change when you ju-7un 8vwsxw t3mp as high as you can?

In Fig. 6–31, water balloons agh,bb 5545teq b irh,kre tossed from the roof of a building, all with the same speed but with different launch angles. Whie5,t4,bqb h hkb5 gri5ch one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point thn3 f 1w5+c;po39 m ppkszy8famat is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum iws fpya5p+1;m8mzofk n3c9 p 3s 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. If you compress the spring ;it;wwd7 sn+efnfzfxc ,.3b /i of,1qby pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.7qbzft1/; w c.dfnn ,o,e;+iwsf 3 fix

A bowling ball is hung from the ceil9dp a* jsuvfv6tmz6 3m8/c8*inye1nl ing by a steel wire (Fig. 6–33). The instructoufvtnpc v 1elzm*6dsim j88y n/6 a*39r 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 without pushing it. Why?

What happens to the gravitational zdu/r7c w/bxk58--hyxv5g7 f 5xeel a potential energy when water at the top of a waterfald rz7uaelkc7fe //bh yvxgxx 8w-5-55l falls to the pool below?

Describe the energy transformations whenw*8pzp3hp;re)w:6lver w a 2s a child hops around on a pogo stick.

Describe the energy transfor-dz z .bu0rv4kmations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strikirzbd k04.-uv zng a snowdrift.

A child on a sled (total mass m) starts from rest+j4bmvxbnk ak1w 5d.*k1w / ys at the top of a hill of height h and slides dow4kwywvk*.s5+ 1d b m1xbk/anjn. 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 is friction (deep snow)?

Seasoned hikers prefer to 9vf4og oy9 zrc5v.9ggstep over a fallen log in their path rather than stepping on top and jumpinvoyr g o49z9gc9vgf.5g down on the other side. Explain.

Two identical arrows, one with twice the ssm : b*nrk-onc)vo( q:peed of the other, are fired into a bale of hay. Assumin*-o:v:os nm bcn)(qrkg the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a sig 8gbzu./ 3/okepoo(ymple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking fricoypoo ./(/3ebu gzk8g tion into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped,5fhm l02zdo ushowwz69 zha5/f 057 oi can it rebound to a height greater than its original height? Explain.9 6 wz5l0s7fo5 m2zo5hfo h/hduw0z ia

Suppose you lift a suitcase from the floor to a table. Tw8p;t eujw8i*5 bcd/s he 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 take i ;bw*cts88ewu5j/dp s, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the 3o( r3hfxlb3ppower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straigh pvslcr, wozo5s (i,-:55v6fu gfdh1s t uphd ( ls5ucsovsiz,ro 15gfpv65f w ,:-?

Recall from Chapter 4, E k7vtes+x4 l* jptkh3(xample 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Figh k*3j esv7+(ltktpx4 . 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 done1ldwqv6)u cj31 p*dzoog4 y/l by the gravitational force when a 265-kg pile driver falls 2.80 m?qvpol1g/ oz 4dlj *3u wdc61y)    J

  A 65.0-kg firefighter climbs a flight of st.h08 l++;dqdynocm v kairs 20.0 m high. How much work is requiredv.++8mcy ;lqd0 nodhk ?    J

  A 1300-N crate rests on the ftrbn/g*+u5 8i:bh5xl+ebc q n *1wgvmloor. How much work is required to move it at constant spe5xc wl b*henn5mv8: bbt gg +*ur1qi/+ed (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 cratsm p. e kfk-m9eve9l3;e 10.3 m across a rough floor without acceleration, if the effective cof3v9;eek .p -kmmel s9efficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a ra(z 4t4 ,9r*bx -zguqa(l qtu082edcknary/c yte of for 7.0 s. Find the net nxbr/ez( (k9 z8lt 4a4dctq r*cqua2yg0 yu,-work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lit y9dw)m;;zw,x 4sobhe flat on a table. How much work is required m;;h9wb)oy d4stzx w ,to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff object;70,c 6 rfrjvde:inql s we might not otherwise be able to liff. Show that the ratio d l7 fr jc,0rn:6qie;vof 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° inclinyek3mxw)z 6+re and is kept from accelerating by a man who is pusxr6) +mkez yw3hing 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 massb81sek-x e*p q+ tw3jt M an acceleration of 0.10 g upward+ q8k ws3bjpe -te*xt1.    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 theyh08 lyc+je va )gz, hnw.eyjw+7 9h6s distance 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 objew25m 1kn tqyrs w:9(ndct, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the w t nk1 (ry2dm5qn9:wsobject (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particlei3kh241 mstwc 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 h26i qrpa7d2 (exa2l6xv bss(oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is 249(qcy91om qlyjmvr 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 to stop acx20le j6n t3yn electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105kmnah+cmkbew,(x410a m/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bowl01d ( v6qbhbz9mdl/ k whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the ar9z6 1/lvk dml(db0bq hrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveli r *osfacl6,mu 3x*jipk7ge9 *ng 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. Whgexm6u**o37s*crlj ,f ipa 9kat was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by wakxem)hz ga5;7 a0 )tohat factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction time.;a5tog z)mea7 0hkx) a

  At an accident scene on a level road, investigators measurwx/*p ffxvi9qz(nz+0e a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient /9zxx (wfp 0vqzn if+*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 pitched at By the time it reaches thtj 01wzm a5/pye plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of j py5/zt0a wm1air 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 5qxc k+i/4jesh 8aqqy/wa )q )straight up by someone who does 80.0 J of wq/c5aqxqs4+ei hy /kq8 )a)w jork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 mm,ks 27k /u41dyq00sl (e 8g,fivoqbi(me vqw vertically with an acceleration by a single cable. Det,2 (7,4/1fqkb 8v0qysmki 0wovudl g(qmeei sermine
(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 /co2z3lx 0 n4 oiakn1hstiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of po1ikn0ox z on c4la3h/2tential energy?    m

  A 7.0-kg monkey swings from ojo*.p(y 01qd fkvz qy;ne branch to another 1.2 m higher. What is the changyyv qfz1( kq. *0ojpd;e in potential energy?    J

  By how much does the gravi)g y,nv+lvdz;b 9 ;m5vedno/utational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m zu 5+d/ym, dnb vv)n;logv9 e;during the jump?    J

  A 1200-kg car rolling on a horizohf7rqd v( u10antal surface has speed v = 65 km/h when it strikes a hori1q fh(0uadv7r zontal 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 cri36f s(f(chthe ground so it is 2.20 m above the ground. What is the potential energy of the boic3( srfh (fc6ok relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of p yzvcrf5 ov ;j16ds1,a 3300-m peak.ysvv ,1d5p 16; rfcjoz
(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(*rz vaslyv.ba z1cnrp7; r. 4 ruler. The end of the spring is next tosb7r;zrv*yc( 4z 1alvrn .p.a the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine3 wbewl :jp9f b.z37ic hanging vertically from a talf piw.w7:l3cj9 bezb3 l 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,n/-8dmbe*k p( f* skx2vm8jgc 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 ubb5ha/d5xz z,)*eh h f3qc8 ckp a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitation-q tj *h2 y8b.ft1qff.ka5tspal potential energy without the aid of a pole. With what minimumtf. jq y*s8.btk pf25-htqf 1a 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 the to 0 w s,v5fep;rz.80y1nzr odymp of a platform with a spe8ypowy0;r m5dzs,1 r0zf .n eved 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 sprib0lj(zu9x oq0;k g kr.ng stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when jx(br0l o k.0z9gk;uqreleased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides wk+ et4v4h *vx /onddbbv lq566ithout 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 circle (whose radius vtkl /ob4*v eb5vdd6h+ 6 xqn4is r), from what minimum height h must it be released?    r

A block of mass m is attache6h7r )hh w.vu ayi; hsju8a*n,d to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial di a yhv6 *).,jhas7;ih huuwnr8splacement $x_0$ 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 v1:ud7 )yzdp xs8jy4p 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, assumsp4: v)8jddzy pu1 y7xing Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where i / 5xqgq1a xh/wfe5nn-t is released from renw5/5 xqx-1nhaefg q/ st. 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 speed of 12 m/s at an a 2 + w.+ pfmj.om:/j*jwetjwyengle 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 pla+;l0up k 35do-la mnjn;y y.ytced at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness consty.jdl+0y;-ykup ml nto3n 5a; ant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up ahmoz2r,v tl7pq 67(pa 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 opposit46l ,rzcacb;tq s.5-p:gm c fke directions, collide head-om cak.lzb grfs5,q ptc- :;4c6n 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 )m7 zd 4xbkvw-reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was genv-zxb w)d74mk erated in this process?    J

  A ski starts from rest and slide9(sr5c1vm*tr4f cl ies 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 *o7rqr1 qk*muthe 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 bounces back to a height ouj9 td jx7rokb i/n 8*13g)-4 qqyrkagf 1.5 m.qoguk- 1* j3 7idj4by)r8rxt gkaq9/n
(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 cv4d7 al+gwv g2 vj/-aeonstant horizontal force of 350 N. For the first 15 m the flov-lea+ j7/gdg42v wavor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 wg .pr-v7k7+sy wpcvu 2ith a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.urp2 cwvv7yk-7ps .+ g0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the lhllm u(t5h6( 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 horizontavdonk-3eyn v-b tz :2we6q6 s8l spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring3--6v y2 dvbkw:6 zoeqsnte8 n system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very a;4,;ootsa( pw7w,w)mo u a yelight horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from 4;ya ;, atwamsw )(7w,ooepouthis position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for th ycirb*9jv4b d50cfc2 e space shuttle used 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 sci20cfb*y4 dr cj5b9vpeed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth- qd0,xutw6bjr .s. ew9w8nxb q2j ,y(mstory window 16.8,buw .9j sxw.bjq0(dqe xrywm t,n6 20 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be theaaejvt, rtb 1af) yb(r33p y)qg/an74 average force exerted on the car duer3b1/ag)rt4a3eafj, ty()v 7 pqabyn to friction and air resistance?    N

  A 1400-kg sports car accelerates from y6k qo6t4n; ovrest to 95km/h in 7.4 s. What is the average pow k 6o4q6otv;nyer delivered by the engine?$\approx$    hp

  (a) Show that one British horsepoj4vc ;js)qqzl6* cmf.ia4 o k2wer$ \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 oftenbbxqv0o dkl ( cqdev24+)3+k x expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down fuw b*.p(vrtzv( zrpo5r(7l/irom to 65km/h in about 6.0 s on the level when it is in neutral. Approximatel7(ozrbir*./v(urpw( t5zl pv y what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor douv:g+j s 97:zvkp rwvq8x5 subr1(;tt in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates am(fl ni9zqn,( 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was deve fn,(z milnq(9loped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a 4 s nq-z2 eigc7er30gfheight of 3.60 m. What output rating (watts) scri 20 qz43efgs7 e-gnhould the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stmzskbb,1dybz.(o1yz ;z* 3 6nuef sn6 airs in 66 s. The stairs are 140 m long and inclinm,1szzy. es3o1d ( u 6n;*kb6zby bfzned at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 5m zi . n v6fa.ilazwe9u(q(n4m8;y uq6.0 $^{\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 u3;i hz a7iaf 6h z9lewt69+1lehv0eyoutput of 120 hp. How steep a hill can it climb at a constant speed of 7hheizl 16vly;t+ ha e6fu7 90iwa3 9ze5km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able us(z7vqwv zt-mh;1fq/x/g l;h r0)p yto drag a 310-kg box along a level flooswgmf; q-(yh/tq v0 z p)ruvlz7/;1xhr at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d( g42rooqxtv+*-:rsjnw ) cn sown 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 bucd 4xl,j0t fq8ilt “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 spftc4x 0j8 lq,dring 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, and thg hrlpy91.8hmgu;, ufe remaining four shelves are each spaced 30.0 cm above the previous one. If the aver 1,ugf9pm gu8yrhh.;l age 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 to start? $\approx$    J

  A film of Jesse Owens’s famou m* uql+/xbi+w4ua6)x.8nwe9enebi qs 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 speblwmq/ eq98 *ueai)buw+n+4 xi6en . xed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding wiygio7z pb).f .thout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radibpfg.o7.y z) ius 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 withoutr cfb/b)qx0u. his parachute opening. He landed in a snowbank, b0c xr/bq. uf)creating a crater 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*dv4-x i 0dmbs a horizontal cord of length L whose other end is fixed (Fig. 6–43). bxvmd -*sd04 i
(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. Thiyi yweh).tg;p mo/ cf/91h;r e climb is made in 5.0 h sta9;m.tyc;i/pg1 ewho / yhif)rrting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaksu )ush38kl;*j :kf9bte6,d qn*pen4 dao t(nn when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California clair 7u.u kg*dl sjn zox6,/l4/qpms that its lifts can move 47,000 people per hour. If the average lift carries people abo jsr l74*/loqpnxk.uud,z/ 6gut 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of*7ma7frg hf 44qse1mn 650kg/s and falls vertically 81 m before striking the turbine blades. qmr 4*n f7efh7gsam41Calculate
(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 vertical loop (Fig. 6–44. av;szpnb29ni r bx3+), the difference in your apparent weight at the top of the circular loop and the b9i +pbxsn; . nbv32zarottom 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 convert a candy bar dkyvk8 oe3seggj/t;i(u: nr 8 8irectly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=ge3n8/ ogj si;(uk t8:keryv 81000kJ)    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 atk5 plvq1 s*0+hig3 /xekeqw:l 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 bathroom scalexla *hw-d6iv) , the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its pea)d* -iw alx6hvk?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over)n7qx 3ci,x rnbo+ob3 a lake (Fig. 6–45). He releases the rope ibbo rox3ncx n+ 37)q,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 cle: /dtsr0 qfm7c(ic)limbs a vertical distance of 5.0 m in 9.0 s. What minimc7m0cfr :dqs)l/ei( tum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by riy*:l ukxlm2xe;f 22geversible turbine pumps from a low to a higx i y;e* kxflu2m:2l2gh reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the h kzt6+hm3 5dvspring stiffness constant for each of the two resulting sph63tz5dmh+v k rings?   k

  A 6.0-kg block is pushed 8.0 m 4l)w:mi xfyci0nj ygy9* r2 q3up 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 can acceleratevq ibut)2l xka;i0eii b 8*)r7 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 2i8urlabqi)*i0 xk;vtbe )7 ipower stays the same, and neglect frictional losses.    s

  In a common test for cardiac funcl y)eev0wsr/ 2tion (the “stress test”), the patient walks on an inclinede/lwvery)2 0s treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spek9g)sc 0ba m:ale+/adws a 500-kg rock vertically upward a distance of 500 m, what was its velocity wh+ d/)seamklg 9abc:a 0en it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate o5n(hy l y 9nv5-wod9g7,i kyx(nbwdc0 f 95kg/s (a) Ify9wcdo xi(l y0(ng,7n55 wk-nbydh9v this water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s