In what ways is the word “work” as used in everyday language t7mj n/t6 gvnf + o3c l+pzpq/dij*,ar+he same as that defined in physics? In what ways is it different? Give exampfnv*mo6,lqc// a+z7+jp3+gr t dpj niles of both.

Can a centripetal force ever do work on an object? sgq j:6c1w c)sExplain.

Can the normal force on an object 6j3m iyzc7(9z xuo*qink5m 6bever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she d4 8vlil9 n/dv sll1g+za9gfc60dq tf5 oing any work? If she stops swimming and medlffn 9 tilgz+ 81dvqal/lvgsc6 5490rely floats, is work done on her?

Is the work done by kinetic friction forcek mjggp;z .( q1+fm,k iriuc83s always negative? [Hint: Consider what happens to the dishes when you pull a tablecfqg. 1mmi 3i8p ,zr ujk;+kgc(loth out from under them.]

Why is it tiring to push hard against9 yym l;ya n2fhf/e, 13tu;vbt:9kwm * g*zxgn a solid wall even though you are doing no wo9 ffg;*1enmht /y3n g;tkzywlyam:9u2b , * vxrk?

You have two springs tnc ;9lih/5(i9btiwp m 6mp8h ihat are identical except that spring l is stiffer than sprin9timhlpi m; p9wc5 h/8ib6(ni g 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 o*wysd 51dab k ix4*as.x +ym2in a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a dda+ *w1*2yibyxxs4mi5 ak. s 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 s)6 yw8ie 8zh8hw, qp6bjzvq1 when you jumh sq8 w bz6pyh,8vq8i)1e6zjwp as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a bui :afsp+sr e((*(bs,hzsaw cu: hj;-mnlding, all with the same speed but with different launch angles. Which one has the highest speed on impcmz hfj((u s+b;h :a(rsaen*p s-w :,sact? Ignore air resistance.

A pendulum is launched from a point thatiey0c qw j9 -e-p3lt y,st7k/x is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the 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. Whic lic--y9,0eqts pxwy3 /jkte 7h launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests uprighvumcm ec9n28(i1 2pd,/lawpv t 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, usid1mcm plinwu/8 e9c(v, 2p2avng the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel lqiz 5nvg.,a *z8 xk(hwire (Fig. 6–33). The instructor pulls the ball back and stands ag( .vnkxiz qlgh8z*5,a ainst 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 potmeii 06 ejsf()ential energy when water at the top of a waterfall falls s)eje0f i(m i6to the pool below?

Describe the energy transformatio7met(6: ts0mlwv . ngkns when a child hops around on a pogo stick.

Describe the energy transformations that take place w iv4:cwg8 h-,v tuj5pghen a skier starts skiing down a hill, but after a time is bro ct-pug4hiw8gv,5j v: ught to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a h.k;n3df2q( 8v6x h0hbydzjt sill 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, andbjq kfv83.ht0; 2d sdzyhn(6x (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rathe-u l: obc5.t)v1y)eek1 bncu38twmuu m:xc 2pr than stepping on top and jumping down on the other s8eu1bxym:231uwou :etnc m5c ubpv -tk. cl))ide. Explain.

Two identical arrows, one wib(:s h refa3.bth twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farf(r.3aeh s: bbther than the slower arrow? Explain.

Analyze the motion of a simp9isnhh1jut 2:yez u+.le swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking f+ihnuj 2: 1uthy9s. ezriction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebo)9lvt/b ni.l pw/a7 siund to a height greater than its original height /7 nvwba9s il/.lpt)i? Explain.

Suppose you lift a suizsdfg )51x(sv hx*w- mtcase from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time dh 1 (5x -s)gvwmsfz*xit takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed 7b41xvy d0hqu rather than the work.

Why is it easier to climb a mounta1sy *ng)lnl +-fub)d vin via a zigzag trail than to climb straight us) dby-ll+ *nv1fn g)up?

Recall from Chapter 4, Example 4–14, that you can use a puldz/(h )i59mp gw8znxlley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34).)9mzh il8w px5gn (/zd But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a db()qob /a/ gi lz r8urh4+bz(265-kg pile driver falls 2b+rid)l8g4( b(/rq ou/zh azb.80 m?    J

  A 65.0-kg firefighter climbs x;a0r3 ( (qmmwr uhj8va flight of stairs 20.0 m high. How much work is requ30( xa;mrjrmvh(w uq8ired?    J

  A 1300-N crate rests on the flxeg csh72 pv3i6t5zloj 0-p x+oor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction f 2-i5ep0xp +zg3 htj vcs6olx7orce of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) lvmw-0bkf3s 1io :e8 7ozj 1rzpushing a 160-kg crate 10.3 m across a rough fv10 : 1lojzksem -37i f8zbworloor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acgtx ayxjbmx+9 1.dd49 celerated by a force across a floor at a rate of for 7.0 s. Find the net work dond9tx.ajx y41 9gmxbd+e on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on atyrznf9qm10r o +q0 pyz)a4 *n table. How much work is0y)rar4+ o9n*z qy0mq tzpnf1 required to stack them one on top of another?    J

A lever such as that shown in Fig. 6ftx214nmgw 7m+v*-urig qn1d-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio tn4u2*d1wrq7x 1nm v g+fgmi -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 fro:gz)/g,:f97gtqi9s+ eogt tyjy p- nom accelerating by a man who is pushing back on it parallel to the incline (Fig.:sg:-tqe zyog)tt,g 9oi/nfjpg 7y+9 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 requix5za,(7wk) 7j, es4sc okrjzored to give a helicopter of mass M an acceleration of 0.10 g77sxoj,sko cje,w )z5arzk4( upward.    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 th,h kwq3eyc. y6fg+ ,3camp8ske 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 objefvzeaalf: 6 7xc4+b 7tct, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this af6 x4f+: a7bzvt el7cforce 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 a particle b: mw txnzr6e 8mmg,+acdh*r4j;*b..bm.ksj 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 ox)u 36he4 jdjea4s3vr zygen 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 arrowr 1dyxxgz-g/6 flr6ee 0u2 wso0u;1m o 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 tb 6r+at/mck.ao stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250v v)6 oqb kkog;;px6*q-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an -t2lf:7tm,s zi m i)bnaverage force of 110 N on the arrow over a dist2 -nilmt)7fbs:i m,tzance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 c: bzfl(wla7q0 m when the ball is caught.z0f7q wlbl:a ( What was the average force exerted by the ball on the glove?    N

If the speed of a car is ji9f ib6i;:thw2ld: p increased by 50%, by what factor will its minimum braking distance be initwhfb: 2 9piji ;l:6dcreased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid m88./s usmvikp ark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car vkm88 i/usps.’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time itctpk 0p7:m5,o m,mncy reaches the plate, it may have slowed by 10%. pn7,c mmty0p5cko: m,Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rockw 72+y am8 /qt 3m8qerywvnl,x go if thrown straight up by someone who does 80.0 J of work oln7wrym/etm 3a 2q + ,8yxv8wqn it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically wimuko );gtlh65 28wcta8bos c)th an acceleration by a single cable. Dete8 u)k8asog) 5bt6wo 2lc h;tcmrmine
(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 springds ydg3u0p8d. stiffness constant, k, of 440N/m How much must this spring be str3d d.0 ygs8updetched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hi37s1t4bgn y 8 2vw98oiwgzmul ,)kbbrr7lt s 7gher. What is the change in potentialw2tv8l 77ro91 tnu8riwz,)s7b s g byb 3km4lg energy?    J

  By how much does the gravitational potential energy of a j0//fcv,n )e+ /ied l 3zpzext64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump? eidezefpj 03 zvnlc) x/t+/,/    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it stri(ix7-ez.kc1z bg.3uisw u4 z okes a horizontal coiled spring and is brought.c iew(.z4 o71zxuzi-b 3gsuk 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 -/ z5vhrqt3 cza 2.10-kg book from the ground so it is 2.20 m above the groundqzh-3 z5r/t cv. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation ou,:2vy wvox2d f 1600 m and climbs to the top of a 3300-m p2ovu:2y, dvxweak.
(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 vertiy p j2u;gl:9am,3/pkmzghe:k cally next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of thep9l, : :;g2eguhm3 kmz jay/kp spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is 08sqs,h.ob: , lzsuhvrunning at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwao:s, uhlss0z.b q,v8hrd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, s*4oo rniag i2t3w0ks .jv /n+plides 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 giv/s :mlg:(rohomgi6p * uty74aen 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 kinetic energy is transformed into :l dk4(aml+zc gravitational potential energy without km:la(cd + z4lthe 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 verlq0/w)dro 5z, w/luk stically upward from the top of a platform with a speed of 5.0 m/s. (wr z5,usk )0/ lwdo/lq$\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 95;c:krfcp/dyq 8i c l)50N/m is attached to a table and is compressed down 0.150 m. c fr8 cq:iyd) p5;lck/(a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped trac zq g)l)tq4lt/k 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 what mt ll4/g)) qqtzinimum height h must it be released?    r

A block of mass m is attached to the engs.g-f t)mp8 xd of a spring (spring stiffness constant k), Fig. 6–40. Th8-x .pg mtgf)se block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge.ko s2 3qyn(+ kzv*)hqh She is tied to a bungee cord whose unstretched length is 12 m, and falls a totv)h q n(2k*o qkz+shy3al of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is drtco24cucpmq f j md070e3q l 5/rbx;i5agged up to point 1 where it is released from rest. Assuming no frictio5mr4 b0ofpelq 7 0; j5it/xmuccd3 c2qn, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed oo2mutntf8l +; vf6jdxo( -y4hf 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 be27p ig/ 7.vmqw xc7xrs placed 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 constant k should have so that passengers und./ iqcwpsm 77vrxxg27ergo 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 unz7 h.rahhv03p a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in oppositn+ umpl,+u9 cenjjmhb )s 5j14e directions, collide head-on and come to rest. Hm hujs)ncej5 jn+p, bu94l+1mow much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a sr )5*(bxfwln))s ;m0 nmioy iepeed of 2.2m/s How much thermal energy due to friction was generated in this proces )m 5n bwmeln(; *rfxsoi)y)i0s?    J

  A ski starts from rest and slides down a 2sz-6dnu 1.go *va ysn92 $^{\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 grounxq c:- wvvt)j ;cfocz:3;zrl .d.
(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 heightb x:ltx g-;3toxa..xy of 2.0 m, and it bounces back to a height of 1.5 m.. t:xxx t .ya-g;x3olb
(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, startk(t0 odp,d t0m)6nqha2 )yujg(r 1 fnuing from rest, is pulled across a floor with a constant horizontal force 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 speo,0 nug) )k(dd t0tumr1fa6pyq(2hj ned of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pas*flmv - ezt /7mk.ab*xses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, -x*mfvz /be.m *klta7 with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reac suxb.-6g a,5* m.filnak 5udn8g(tglhes 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 (k=18zao m 3.g + o-gc:2fq,norrfshj5;:gl)4rd nn0N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the co olgs- g2+.n ;f g fr)n,rhadojr4:z conq3:m5efficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attat,l9dkn 9 /db 1n4ev.ywfa:j gched to a very light horizontal spring, Fig. 6–40. The block can slivl y,g4w9dd:a b9njte/1kn f.de 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 this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights foqx-05p n7g1)io jaxhfr the space shuttle used a “glider” (mass of 980 kg including pilot) that w-h n)1q5 pxo0f7ja gxias 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 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 31 y8 q(q.7osbdr5-kg piano to a sixth-story window 16.0 m abo (qb8dr.sq 7yove?    s

  If a car generates 18 hp when traveling at 2dp l: yi.djvyar9t u/b: 2zk7a steady 88km/h what must be the average force exerted odl:92ay 72drtv. zk bpu/yi: jn the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to,v4 h.jv:*ju hxze8sd 95km/h in 7.4 s. What is the average power delivered b 84eh.*j: vvjh sz,udxy the engine?$\approx$    hp

  (a) Show that one Br8 ctom h l.0,/(8lj7qg fukoinitish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt80bsi h;d /3x(th fceiue6zq( -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 yaqf*d3r;hvxyhh p4(etc 05 0from 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 constant 75v h4*x ;tp0 rqye hay53hf(cd0km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h89qlk9 mx t vt )ein.idu:b*b7? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rf pi ,fl g0sj.h6b;rryb(se(j2.ka b/est to 14m/s If this motion takes 1.5 s, what average power was develope;6(lsb/f,fjrh0srjb peik.( y 2a g.b d?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of c)w;a0nt f1: d6b ab:zypdqn 2uh09 pa3.60 m. What output rating (wattf2haawp9u: 0; nz yp:d1nqtcad bb)0 6s) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium staif.nt7llj(2 uh rs in 66 s. The stairs are 140 m long and inclined at au( nt2lfj7hl.n 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 c j c xqi0v9:6aegf0k6ulimb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hillww8tk9)6l ks r can it climb at a constant speed of 75km/h if the frictional fk8srt 6 lw9kw)orces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 3hebv1r;t:(b i03zcpu3 -zxfl 10-kg box along a level floor at a speed bb3:x rv-; pu 1 c3(zlhezif0tof 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.ga*6 odzi7ub b7w qob6-il;c 2zqw0b0g4 b 8vk0 $^{\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 bel ;d( hwt+bop1 ow.:uuilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the efd1l to (+u.w eowbph;:fective 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 sh )k.i*nwy zy6fvsp)e5z,um1 i4+apihelf 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 book*+ipzyizk e y6)va,1 nhiwm4s. fu )p5s are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s *lka lmhn, qrrs;m,px35ydy+g ,;pc.famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the l,c5, 3nkx*;rpa yd rs. g+lmmhpq,y;top of the arc?   m/s

  The block of mass m sliding without fri 8auk o5*c3axxk rj:/jw6dab1 ction along the looped track shown in Fig. 6–39 is to remain on the track atr8wukaxaj c :/6b 13xj*aodk5 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-8/;aav xmtg k//(ccpmlld )k parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but suxccl;m v( )gk8ma/pat-/k dl /rvived 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 oop4 9ail e(wo6 jatn d49s59ttther end is fixed (Fig. sj 4n5 4patlie69 ato9t9odw(6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is ma+w gw83(lnkq d 2k-vb1(z hccpc2) dtade in 5.0 h starting at an elevation of 230n 8 kbc +d(wvzkh1ct)-3aw p(2 cgq2dl0 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge springzy::+5vghhj k ($k=2.2\times10^{5} \mathrm{N/m}$) 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 iaepw y0jysw01+r p//cx 9oc w1ts lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) 10pr0wc1ca9w y sy+p /x j/eowhigher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at-kcs8k8- cc.v jbmm+e the rate of 650kg/s and falls vertically 81 m before striking the turbine bla.j sc 88 emmkc-k-c+vbdes. 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 l6( mn d4nkd:vioop (Fig. 6–44), the differenck(dvnd i 6n4m:e in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into ,lsqz)ry+m p ov+m8 q6work, how high could an 82-kg man climb a ladder if hy 68+pmqr+)svzqlm, o e were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward anggc ; iv*0cu 6+v 3pzc.x3diald5pmz.xle 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 px,p+5n smc 0dscale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now id05,x pp ns+mcf you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out o;ph):fyb8nt u 0wb )auver a lake (Fig. 6–45). He r:uhw ynpbu) )bf;a80 teleases 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 vertical distance of 5.0 m idv bt7t6 o;)f6 wbi7i/m da,dxn 9.0 s. What minimum power output was used to accomplid; awti 6 67i/) fdbxo7mbtvd,sh this feat?    W

  Some electric-power comh xxf0dnv)w :sh1 41fjpanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1xf n jf0dhws4)x1v:h1.0 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 consr*1 //wsji(00b vklk0 ykmaj qtant k is cut in half. What is the spring stiffness constant for each of the two resulting sprik akq/i0rs0b0wjjy ( k/1vml*ngs?   k

  A 6.0-kg block is pushe-t 6wj0 *6rorlrzo6rjtse i ++d 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 accelerate from 35km/h to 55km/h in 3.2 s,6d bgxvs3f3 8l how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fr3f6dv 8g3sx lbictional losses.    s

  In a common test for cardiac function aov-x(d s(k m,(the “stress test”), the patient walks on an inclined treadmill (Fig. 6a, ( okmvdx(-s–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 verticalfh5q 2/ k5lpyrq(,3 xvuo5ljply upward a distance of 500 m, what was its vj3u,(pxh 5o2lp5yf q 5q /rvklelocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate ofhp9: er aol* qf;w(xv*( jiuv3 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power o r p3xq9uhv*a(e wf:vo;j(il*utput?    W
(b) What is the speed of the water as it hits the wheel?    m/s