In what ways is the word “w88*d7 folwv.twpd(ih k0u.owork” as used in everyday language the same as that defined in physics? In what ways is itwo . v8idt*hwpwlkd.0fo (u78 different? Give examples of both.

Can a centripetal force ever do work on an object? Expk8hqts 3c qgj8xu3mr2lp;j 7y:; zpc/lain.

Can the normal force on an obwxo (,qek 70by.dv0/bv no-r fject ever do work? Explain.

A woman swimming upstream is not moving with respect to the*;s3 p/ucw f ;sov v7qt7fg)iv shore. Is she doing any work? Ifsp iv /7vqo;)gt u3v*7f;cf ws she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider fh0gal3w , u4fwhat happens to the di,wu3h lfag04 fshes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a sol /zebl*9twk;)ms k vrd mw8(7jid wall even though you are doing no work?7(svmt)k8/zwr9kbmej* w; dl

You have two springs that are identiu..xc * e3fwugcal except that spring l is stiffer than spring 2 .x3f.cwueu g*$(k_1>k_2).$ 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 forcph79:+m zq syueuvp:dh 0k*r6 e on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and byhs9dm+uy:hpu6r 0q7 vpez k: * 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 gravitai0ppl ,tz3o8ptional potential energy change when you jump as high as you c0ppzi ,oplt83 an?

In Fig. 6–31, water balloons are tossed from the roof of a bf m0wss .u lt282trt0 cg1qc/n38jw avuilding, all with the tl tu2s8. qa0r /2c03vwcmw1jfgt sn 8same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest po :s0kxhs7 odhgmck3*2int in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest7skh3 c0:xd g som2k*h angle from the equilibrium position? Explain.

A coil spring of mass m rests upr2,lo4iogof cu ,j*c;ce.ba7h ight on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, usin ul*hca7ecj ,4,o gob;2f.ocig the law of conservation of energy.

A bowling ball is hung from the ceili bm4r fd65wyd3ng 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 suwy dmfr435b6dpposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the u.h5 kn1d93ryg kq:m1ur4m rn top of a waterfall falls to the nkku1r3g nhm .rym5r9 1:4uqdpool below?

Describe the energy transformations oe j5lf* +bs6twhen a child hops around on a pogo stick.

Describe the energy transformations that take plj(hjoa 3 nn96z .pul(kace when a skier starts skiing down a hill, but after a time is brought to rest by striking a 6j3ln(nzk9( oup hja.snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of ;-g sjn .oh g qo2z 38wjhl-4v;bmphn)height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and ther28 .bh ml pzojn ;jg)3-hhsgw4qo ;vn-e is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step ow5;+xyp a m1upver a fallen log in their path rather than stepping on top and jumping down on the otheuwa5m; x p1y+pr side. Explain.

Two identical arrows, one with twice the speed of the other, are firednu7v2d6e,lzl4j z f 6n into a bale of hay. Assuming the hay 27n djll6f,e4z u6nzvexerts 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 simple swinging pxmf y.qj*cjslk g; -d ),lo3d5*g toxelx)*:tendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain whyxqxcxs3 ;. *)-:e j*ol,tmjg ylldk*g ot)df5 a grandfather clock has to be wound up.

When a “superball” is dropped, can it rulzjs1a8d hzps b5t9y/a: g 99ebound to a height greater than its original height? 9su as: /j gy9dh8zzt5b9lpa1Explain.

Suppose you lift a suitcase from the fg*t2kcj+ +j*gysojr; b x mom;j0j.1lloor to a table. The work you do on the suitcase depends on which 1j0;jxojgl sjy +;*m2*+jmgorb t .k cof the following: (a) whether you lift it straight 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 needem5pn i;6geut q9q-v( ld rather than the work.

Why is it easier to climb a mountain via a zigzv3)cp5 -wzfmg sg :i72mttk n.ag trail than to climb straight up?v i3 kftmgc7:-5mg2ns.w )tzp

Recall from Chapter 4, .0r mgzmm/rp14qmz ll/monc4 ( p16 txExample 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 frx qor1.4gzcmpmml m z/ nml(61t /p40or 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 grav+wv cl 21*junmitational force when a 265-kg pile driver falls 2.1juwmc l2+nv* 80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work skeu4 i5; 4uf *bkiin6is requiresfe5i6ni ;bi4uk *k4 ud?    J

  A 1300-N crate rests on the floor. How much work is required to move it atirtqzc) mc pv25 02)ircs/lh 6 constant speed (a) 4.0 m altv c2c)h)6rmlpqiz2cr0 / s5iong 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 1spq1ml;1p/ dgi qln 0160-kg crate 10.3 m across a rough floor without acceleration, if the effectimingqs;d/1 pp10l q l1ve coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelekvl l04rlklija:c4,6azzy7 .yrj3 n/ rated by a force across a floor at a rate of foray 0r 6ij:zyl lv4akkrjc3llz7.,4/n 7.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass e, i.ji/ 0awme1.7 kg, lie flat on a table. How much work is r/.iiem ,j wa0eequired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mi4owo4bet 7lii w sa/)0ght not otherwise bwo) eai ts4ibow 047/le able to 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 and is kept from a:gcv9 e9b8o ncccelerating by c b:gvon8 c99ea man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass Mgi1 m- w..*w suvb0-dh xxm)coc4csi, an acceleration of 0.10 g upward. x im, d*i -wuhsw4)mb.c-c0v.o1gxs c    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 d:j *k9c; co znkz(uq5+qe mac-istance 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 the x axis, varies as shown in Fig. 6ay.9 n9rd )x/u 1t)aj: klslhk–37. Determine the work done by this force ).kda s 199nlrjua kht:)x/yl to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on pzx-p ;u m-mb1a particle 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/ 9ieks48t zaj, 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 a0f0opu hgj :+errow 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 to stop an electrwz52p( pwmnc0t jdd70 on $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 travelx1*u s/5nzt wxxq*8-:ygj dok ing at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exert*tio co8urf a4)wi8,q s an average force of 110 N on the arrow over a distance of 78 cm. What is theof*i)q8 4 iro8cw,uat speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a field s3u0yvtf;j1-b0 - bkcg1f ho :6odczaer’s glove backward 25 cm when the ball is caught. What was the average force exert6ghfykbsubc11o3 v00:;-t f o j-cadzed by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor 06a ujpb*6ccrk6m i2kwill its minimum braking distance be increased, assuming all else is the p60kcrk6j6*2 c i mbuasame? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measuwykb9,8yt.kf e pi3i5re a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use ti35.w tekyy p,98fbk ihese 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 th: lf-1 r9douq,mv rkpihiateg.r 5,3;e plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance betrih i-kmo 5.ru,dlg3 ;f9,rvt 1aq:peween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg roc/si 7k mgkgxlao19 96qk go if thrown straight up by someone who does 80.0 J of work gq/glxoik7k m1 9s6a 9on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m v hd u1,b,swc/.ic zcp3ertically with an acceleration by a single cable. Determine hduc z. ,ps3w/b,cc1 i
(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/m How much muz)w 8bdq6vsb 8st this spring be stretched to store 25 J of potentialvwz8 s dqb)86b energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 xw0mh-4mm6qzekh1 6fm higher. What is the change in potential enemk qwz -4m10e66 xhfhmrgy?    J

  By how much does the gr t m 6)uoz,ftj((f*ptyavitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m duftpz,t)om y* 6u f((tjring the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h wxao8k 2 9od;(s5qzk5coeq+ d e1 gbmw7hen it strikes a horizontal coiled sp1dq5 qaoc9e;be+x25wgs8o(k o7kzm d ring 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 the groungt 9e0 joc).xad so it is 2.20 m above the ground. What is the potential energy of the book relative j. 9x 0g)cteaoto
(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 1cthte1vou5p5 kwf; t*yb62 nelevation of 1600 m and climbs to the top of a 3300-m p cfohk5w ty *;t216n5 1vpeubteak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler.f p awf,q-b/ v;0j;wei The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is nowvfwb;f j,/0-eiqpa; w 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 mvn kbp)wfj0 -o 8(aj(grabs a vine hanging vertically from a tall tree in the jungle. How high caj(nk )baf0 (m wv8poj-n she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from r j0pym ys/-w;e,fgrd1 eaf57uest, 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 givej15chkcg4y qy.zv (+yn a shove up 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 :h cb.oy. bgk(kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.1b:h..bc( oy gk0 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline arteg:1.au3m5eexw .joj ist jumps vertically upward from the top of a platform witjg mxuo5w1.: ea.e3ejh a speed 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 (ignovym r.h( .w;;uer*hcn +sih6xre its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed do(.h.us;hc m;yenhr*x6wi r+vwn 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without fricgw6t8 p3 ci.+ljw/gb7m if2v stion 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 is r), from w/jic w il .86mgf7wgs2+pbv3t hat minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness constpu j0y l ,.,( myhb0a71 )bufchwcpc(vant k), Fig. 6–40. The block is given an in,bj .pchl17hcumvb,wa yy(p)u0 c (f0itial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungt4xba)*dai m xnl6a6mx,e8q. ee cord whose unstretched length is 12 m, and falls a total of 31 mt bx6d,a lx) 8a*4aqmx.imne6. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to p(qmfl(ep w(+snnh 36 yoint 1 where it is released from rest. Assuming no friction, calculate the speed at poih+ yneqw(6s n3mlp ((fnts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle odezba7if .dh6:, g; g-i)djbo;l 9zerf 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 at1ll(a4ulof bl7kv y(9 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 thatofb4ly19vk7(u a(lll the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up-c1dqmmx znu-c xf/eva54 7*c 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 765/k;z z21hxweimwd7.)zejz8 . fbq y8m0 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal enewwqzhm) xy / 87 zez2jm.fi18.bedz;krgy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a s( 72pc7nkp. ) kbwhwtqb7m,g ilide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to f 7.p ( m7 cb2tkqb,hgpiwn)7kwriction was generated in this process?    J

  A ski starts from rest and slidm,q-rzs4n5 rp7bt + lces 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 kj ovwp71gf piu26.,otree 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 bounces back to a height/bpqn/sn noyh yb3:/e(jx b45 of 1.5 m. bh3/jp yb q(/ 4 5eony:nsx/bn
(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 acr j;9xif +yr:bloss a floor with a constant horizontal fo;r bifxy :9lj+rce of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coasteil;hdq:p .2hcr in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal toc .qh :l2iph;d 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 reac 21pgawxlk gl.smrfapg n(/d y9866 f,hes 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 :+ppgp97cmq j a very light horizontal spring (k=180N/m) as shown in Fig. 6gpmq 9p7p+jc: –40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horiz :/g)ys)sn ohpyq0qu: p+x5ojontal 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 sygquqpp )ojy ns0xso5:)/+: h pring 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 udp duo,cx1-cnq09w 7qnmdt h6+ l(1tesed a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m0h +1tum1 p(nddcxt wo7q,n9-d 6ecl q. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story xng- 8n6naa rgq .ivx; 1maz..window 1nrxn mxzn.qav .a1;8.g g 6ia-6.0 m above?    s

  If a car generates 18 hp when traveling aenb.1x bk9rgkc- v) *mns(xv +t a steady 88km/h what must be the average force exerted ong c nn.9v ex-)xk*r+1(sbmbkv the car due to friction and air resistance?    N

  A 1400-kg sports car accele*fl .yp7.dtwjzowijp:2l6g( rates from rest to 95km/h in 7.4 s. What is the averagejplldf iz.p 6(. 2t7 o:jgwwy* power delivered by the engine?$\approx$    hp

  (a) Show that one British horsqktacz 6n2gk3, 41 ge) lp0wkpepower$ \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 zu *hhre(zh15 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 8la6 i)wuwa,2;kwucb1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constikwcwu6) ua ,2la 8wb;ant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 z-i 0 ed8dgli)h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motiovq j,e fnrg 8-5sapkwo7 qki+t:uc2,;n takes :-ov eks fk8apcw7;,nr q2qt5u,jig +1.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.6.ojj)rma hoi .y97a h70 m. What output rating (watts) should the pump motorjh my7.rh9oo). a7i ja have?    W

  During a workout, the football players at Sy7red,yl vz5 (y vz9jnui+ax/0s j5 p3 g9ga;qtate U. ran up the stadium stairs in 66 s. The stairs are 14j 05r( uvda a,+75pg9jzl3/9yysixez; ygq vn0 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb ar48s7r ey6p p;wsy y3h 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 k wxstsk47r 8kg,dl-tsg0pa7k.y*.k hp. How steep a hill can it climb at a constant speed of 77k gpt,gs4k 7*a yssk0x 8 rwkkt.d.-l5km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to bep .lu9e( ugc/c able to drag a 310-kg box along a level floor at a speed of 1.2m/s if th(el9gcc.u p/ ue coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7nxgfcehs r/*pn)a 8/ 7 sn+x.f.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” thx44t ppg2n kynkx* i +.ik(t(u+ty hr4at 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 t uixr +tk4(y x2nt(ny.p+t4khkpg 4*ihe 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 shelfwoq*9 qam0 p:o 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 m*:o oa 9pm0wqquch 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 famous long jump (Fig. 6–42) in the v2ld6+0ykl-l)w vqxhy( yw5 km4xba-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 launc(v kyyx2m6wl +4xaw ) 0bq-5 vlyl-hkdh if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Figbe5r0/zsk: ji fuh/ o;om8 g7x. 6–39 is to remain on the oik z5: jgoh0x8e/sb/u;rfm 7track at 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 parachuse0u6p;l 9z djf /3mgfte opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass wffzldjm3;0ep6g/9 s uas 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 L6 -uo*6ea2vcefqhlalor3c 6+ whose other end is fixed (Fig. 6–43 eo6r*+36fc h a ova2luqle-c6).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is vp ;bsoqpm(m/1wg8h )made in 5.0 h starti( sv;1 )qp/w8bphmmogng at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator9b3jrlepcg ;7uu +m6*n9 snck 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 6lxa85ttf3pwf,zi, m California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needez p ti 3wm,xtl58f,fa6d.$a\times10^b$ W a =    b =   

  Water flows over a dam at txl,dvn(sj 9/phe rate of 650kg/s and falls vertically 81 m before striking the turbjvd ,n/plx9s (ine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), r0d,rvh,a3 pd 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 d0,aphdr 3r,v 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 coul +4lvbh:lw2t,cibv y5d convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by onvwtvb4,:il2 +l5b yc he 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 upwari,vnea 5q4:, owhh: pid 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 spring inside the scale f;v15ug 9 zbsyjfk5q 5compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a h;u 9kvq1z5 bfysg f55jeight of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a ro t4bm;d* etwj)pe, and swings out over a lake (Fig. 6–45). He releases thw) t;d4 tm*beje 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 vertical distance of 5.0 mu euzkhp47.- q3ex:qo in 9.0 s. What mq zoeh3 -e4:uuqkxp. 7inimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energycvk;t f6iu 2 jh9fqn:(. Water is pumped by reversible turbine pumps from a low to a high reservoi i(hq9fkj:t cu2v6fn;r. 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 spring st(k v/rxv(of-z iffnexzk/(rofvv - (ss constant for each of the two resulting springs?   k

  A 6.0-kg block is pushewuo v .9:;u itmvgqp .0fgh)-zd 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 can acsd-fto;4drx0 q)o7 /xml;8fan bc:y l celerate 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 4ft xb7dyfls;ar8od)qc 0lx o;n /- :mpower stays the same, and neglect frictional losses.    s

  In a common test for cardiac functi 2r 9rm6z1nqjpql8 )auon (the “stress test”), the patient walks on a )2rqrz6 qnp8u 9jm1aln inclined 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 spews a 500-kg rock vertically upward a distance of;wucos2va 5/ ;:u3+o s ez9*xr/oj8ez esecll 500 m, what was its velocity when it left theva 2 xo8cl95szee:+o ;/cjw e3 u;zulso*/res volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a) ty8s;9sjo*hcif xx )7ee/-my ;uimx8 If this water wheel is set up to provide electricit/jem9*;;xs7 yi )xuhm8 e8ft -osiyxcy output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s