In what ways is the wor:kp4n kwu+lx/d “work” as used in everyday language the same as that defined in physics? In what waysluk/n+:x4 pwk is it different? Give examples of both.

Can a centripetal force ever do work fudw +0( jz/4e.:d5r bz hn7(pvufgeuon an object? Explain.

Can the normal force on an object ever do work? Expehcyck-vx0 g xa 71(z (yiut95lain.

A woman swimming upstream is not movi0uv, 4-mn7ylkzpwyw 0ng with respect to the shore. Is she doing any work? If she stopkmzw4,wu0- ply07 vyns swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider;w:x)q lg qs0; + bkta9tmvn6u what happens to ;;+aqlt :snu)mvk qgtbw0 x 69the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a efa1sp3u x ftu i55,7isolid wall even though you are doing no workes5 7pff5 ax1uu,t3ii?

You have two springs th o 2pf 4,idtz9c(u5zgnat are identical except that spring l is stiffer than spring 2 i45f2(pgndu9czt,zo$(k_1>k_2).$ 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 t8a9, l bwyxau+ds 9g8vo slide on a frictionless surv8a+dsb,9gy x9 lwua 8face (Fig.6-30). The block starts from rest at þoint 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 potential energy change whwau a. )/ dklju)8qq;nen you jump as high as you c).kqd a)w;q8lan/uu jan?

In Fig. 6–31, water balloons are tossed frok79 s(krxmkxe) /1pe60rnf rim the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impae)k0/ekn7x19 ixfrrkmps( r6 ct? Ignore air resistance.

A pendulum is launched from a point that is f8hfl)w6 e9 gibh fh/;a height h above its lowest point in twofg ;lfei8)f/ 6 hwhb9h different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring by,2jusfrzfq ,w 61o (kf pressing down with your hand and then release it, can the 6 ,fr,qjkzfuo12 s(fwspring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inv hl k6-- 4su q,ai1, b/nt3ik2iabakistructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposq2 ,a- ikslvb,- 16aua4 iik tbki/nh3ed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water ujtyw1d a+ +h)at the top of a waterfall ua hyd+1jt)+ wfalls to the pool below?

Describe the energy transformations whvxo3 d/7a:ipcen a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier oxn ihsx:umvo67. dj56 0 ko8qstarts skiing down a hill, but after o5d068kh jmi 6s .ooxnqu7x:v a time is brought to rest by striking a snowdrift.

A child on a sled (totwwh cn t4vj ln* +jznk*qp hwg30p4-57al mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the anglet*w 3-44 0gwj jhcplkq5+vnzw nph7*n of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fpkt 9dsq:n*r 3 ;s)ertallen log in their path rather than stepping on top and jumping down on the other side. Explensrt)3; qsdp :* t9rkain.

Two identical arrows, one with twice the speed of thet5jq bgk,)* il3eflv6e. 0jmx other, are fired into a bale of hay. Assuming the hay exerts a constant e,iv6f0bx5j ke3lmljtq )g.* 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 pendulum in terms of energy, (a) ignv(j t +yhtp3ivsj5 v.pkl2s8)oring friction, and (b) taking friction into account. Expv+ ttl)sp3 kp825j yvji.vsh( lain why a grandfather clock has to be wound up.

When a “superball” is dropped, can ;zng* i 0;1 wekmu62afmxt4op it rebound to a height greater than its original height? Ex01a;kf*zm 2tpw ;xe mgu4n6 ioplain.

Suppose you lift a suitcase from the floor to a q0u8s5. m*yt vbt7iikz.nmm(table. The work you do on the suitcase depends on which of the following: s57t.bv(zqim.km8y * mui 0tn (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 needed rather than the work9yjlqa4 8 yawnr/: nw4.

Why is it easier to climb a mountain via a zigzag trail than to climb strqt iup ky ,xnnrso38.07i,q k6aight upk.80txnyu ,3okiinsq6 7 ,prq?

Recall from Chapter 4, Example 4–14, that ypykm6m 2n*3za ou can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must32zn km 6*apmy be pulled up? Account for this, using energy concepts.

  How much work is done by theym-hj:e m(lzo.wqp 5- gravitational force when a 265-kg pile driver falls 2.80 m:mp.ze(yhl q-wmj-o 5?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How md 7:1dju5g br3ogqb8guch work is reqq:b7u3j5d8b o1gdggr uired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at coyix8fe .jagf;gi3 5 n:nstant speed (a) 4.0 m along the floor against a fricti:5g 3fneixf.a ij8;ygon force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (ho -xi yhkg9+3ayrizontally) pushing a 160-kg crate 10.3 m across a rough floor wity+9-y h3iax gkhout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a for6)fsex otoq4 0fzs;n:,wm a jby2lc) /ce across a floor at a rate of for 7.0 s. Find ffcbet;wno /q),6)ys0 a:lm24jxz s othe net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.*jsk;2cx(tug(nqu 1 vr* a;pf7 kg, lie flat on a table. How much work iu f; 1u*at;x2sc((kg*vrqj pns required to stack them one on top of another?    J

A lever such as that shown in Fig. o26 co5r*wt-siss4jy 2: pvnw 6-35 can be used to liff objects we might not otherwise b2c 2j6w:ps si5y *onowvrs4-te 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 2i-ysndl- b+5o8° incline and is kept from accelerating by a man who is pushing back on it parallel to the i- soldi+b- n5yncline (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 rex3y0d6,.feb a mrbb 1s-cq k3equired to give a helicopter of mass M an acceleration of 0.10 g r m1cs,k yxq6fb.3ee3b-adb 0upward.    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 dio)xk-, r- fysmstance 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 algc/ z* *a0dpngx-v yd5e0,x ybong the x axis, varies as shown in Fig. 6–37. Determine cb/y*n0dyx5 pe,gag - 0z*xd vthe work done by this force 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 acts in4h ro.ddok +k2 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, wqf rku2f60ox /ith 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 doubled, by what factor has i gjo 5k40our ;0:fazrfts speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stoa4e 8k(v;a,wx sox)pf p 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 12. yks/i*cjx5d on um3)50-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from arz i/ cm,cal*( bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves thr /*,m zalci(ce bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm whe x/u/rx6//wck+w nm6y ty.anzi3vi: b n the ball is caught. What was the average force exerted by the ball on the glove?iwcni 6atkw/z. rvx+ y6nm//y/ b3:xu    N

If the speed of a car isy1 /q,4x detfv increased by 50%, by what factor will its minimum braki y4tveq1/dx,fng distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measue 5h(chnys(1)m*tex4c u e .ljre 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 these data to determine the speed of the car when the driver slammed on (and lockeux.nyejc h e4 ((elc)hsm *5t1d) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg (ln4lxp8x:mr x;:s;// znbcnyd r 6x(vlz:b sis pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecr;z lmy/8n ;:rps:n4x:6bzx d/v ( (bslxxlcnting 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 rock go if thrown straight up by someone who aw5.;)r rug0kbzxetfq 9u-4u does 80.0 J of05gbz9r uu-q tax4.; r )fekuw work on it? Neglect air resistance.    m

  A 285-kg load is lifte9:etuf/ku avzk; f+v )d 22.0 m vertically with an acceleration by a single cable. Dutk+ :) 9/efvvkzufa ;etermine
(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 z)(6jxo5hag v mq.q7 econstant, k, of 440N/m How much must this spring be stretch7xv(h o.6za5 )mejqqged to store 25 J of potential energy?    m

  A 7.0-kg monkey swina2ht rm4sc -;i. jtjqez a:;gg*9du7 kgs from one branch to another 1.2 m higher. What is the change in-.gqj;;sa:ig7z etrdu*c t9 k 4 ah2mj potential energy?    J

  By how much does the gravitationadc 2wuy *fs*.m0ojha6l potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the *hu w y*60o.df2mscjajump?    J

  A 1200-kg car rolling on a horizontal surfacen ,la9l5 sfn*fy-qrv. has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant o l5*nnfafyqvr l,9s.-f the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so ihh3+ l3idpftvraj ),4xv/r)zt is 2.20 m above the ground. What is the pote4z) h/3 ,frixvra+3)vldthjpntial energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of og+uhoh0 t5, / yj5vbz1600 m and climbs to the top of a 3300-m peak. zy5thjho5+0/gob uv,
(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. The end of the s7kmdozf c gh)p(u1w9 ji6r4,kpring is next to the 15-cm mark okg c)94kmdw rh(fpjo67, ui1 zn 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 jknr*sp;d p1: 9q wh72;gwlvdtop speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwars:297vdk1p lw hp ;rgqjnw*d;d?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a fric).5e,wc kg q0z;(zxfpvn f y f/ xo5.gm)riqd7tionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionvagt:hj t0qx5/b9 f9zless 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 gravitcjq3jg;h+t 9f ational 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 2.10 m and cross t9 jq+gtjfc3h; he bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jump67w ;rnjzs-u hs vertically upward from the top of a platform with a speed of 5.0 m/s. (hnzsw r-u7j;6$\alpha)$ 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 constantzx 6r)cuni u/nb /hbwa*, u0p, is 950N/m is attached to a tabl/wn*x0zurb 6,ha,p)ui/n u cbe and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction nuxc/(w/p -mx along the looped track shown in Fig. 6–39. If the block is to remain on the txxnmc- wp u/(/rack, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffq mmb e7s 6)p+-q 9h.a4anoezkryt j01ness constant k), Fig. 6–40. The block is given an initial displaceme eb -+m1ko 6)amqajqs790n.hret zyp4nt $x_0$ 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 bungee cordr313wp,os/; iv uj9 p jbw2pyscm9vwzsz:/ a) whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law appl/vmoussc3;z9:2jj pw)ps bizy, vra/wwp91 3 ies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shqz(en9ls y2lx1 cz /*n7p.jsoown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the spezl 2n1* jn ozs9clpsxq/7e y.(ed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 1,gklyfb 4 hd1(2 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of abtvzkj;3 x78kn elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevat 83bkzk tx;vj7or and passengers.

  A cyclist intends to cycle up a 7. s(;9 ocftw(y2de43 oeb7oqk dbv mw..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 ,t)d ;vks*r0oo (v (+acl aqkqs-imc:9g b(ookg and traveling 95km/h in opposite directions, collide head-on an(rgso ;k(+ -:lsc9,idmvav *bo(o k0ao)qctqd 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 andhtd80-a ivjr8lc gl i320rp9j reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proceslt0 0rd2a-ic39l8v hjij rp 8gs?    J

  A ski starts from re aj171 qh.g-xgfbmr 9me1d z1yst and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dcrtha)y 4et +cb.g;/qropped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 wyt1)bb np 6)qc-asn(pvq 54mm, and it bounces back to a height of 1.5 m.p(t64c) -mq bsw)y1v5nba qnp
(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 c88wet-pnkuw3z ku8t( v+ia 0ponstant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m pi3e wuw(u+-znt8k88 tpk0a vthe coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6-pnd:uvlr*l)07v ur0d w;nfa–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with wha;:udnrpn0 ldlw- af7vu)rv*0t speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of nygz i4;wpn9b8a( s rg6k9me/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 verya 8jppecaag+9ico/( sg;d)6 v light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coe8+)e(caaj spgi6 d;acgv9op/fficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly a5:nojq1ib vm ocu 9+mrfi 2d33ttached to a very light 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. j53o+mo: n bd3fi2c rvq91muiIf the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spac7 )+qd iyyw3vce 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) Whi+ yv)c 7d3qywat 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 6gcgwq reec;k6)f 8 (gsixth-story window 16.0 m aboec6gr8qec6 wg)g;k (fve?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be tr0zbfrg 747sihe average force exerted on the car dus7 4rr7fig bz0e to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avc,4amb:j0 x7x20vf iw n )jfjoerage power delivered b04ofc)ma 0fi: b,jnx2 7 xjjwvy the engine?$\approx$    hp

  (a) Show that one British horsepeiuo6 u2:99c +etvqm bower$ \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 exp- 84kp4 yn wj s 5v03ydhq*oqu-rmfk8oressed 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 from to 65km/h in ab2bkcw ,b9 3 ezil4sho 72zmej7out 6.0 s on the level when it is in neutral. Approximately what power (watbwzmhc k942 ,le2 e7z7jo b3sits and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor dh1hq)o)m* n rpo in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s Is mr ggh9 )t-/x,say;vf this motion takes 1.5 s, what average power mt)vg/ s-;xrh9,sgy awas developed?$\approx$    W

  A pump is to lift 18.0 kg o/ .53p4mrpam rz4 dgsmf water per minute through a height of 3.60 m. What output ratingzap dmspr/43r. gm 4m5 (watts) should the pump motor have?    W

  During a workout, the football plkq/7*mdg6 be nb8 wwd3*qzl6vayers at State U. ran up the stadium stairs in kqd7*/wb6*vde 6z 83gqn l bmw66 s. The stairs are 140 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 cyclistqlhd3*bu /ttf4 klb+ 4 climb 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 hilllc9j g m,nffjbf *8r9q,rn5u,y2j 3sh can it climb at a constant speed of 75km/cn rbjf,j fns 3yjl95,h*fm92g8rqu , h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box alon, is0 zppb; j.3gh mjsfp0n5s3g a level floor at a speed of 1.2m/s if thjm0sihn ;b0 3 g3pp5ss ,jfp.ze coefficient of friction is 0.45?    hp

  A bicyclist coasts dowt,t0u ;v b8d0b ;uiugen 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 *ql ytpww r;7ni1r/g fk/, .anbuilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid walla /witnpf7/*rq gy1;r.,n klw ? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and thh 2o70hrwy hyg y,t*.se 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 boryhs 2yg,h .0w*y7oh toks are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics0 f7eg2 bmk(i73cfi es shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did h07fs cfb(e7k2m3i ie ge 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 without friction along the looped track nsi,z 7y 9equ;rrq3ybsda:41shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the lo;q7,z9nr3 q4e1 yys idbs:ra uop 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 ,xsfic4q (yg, aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor i y 4x(,cq,ifgsnjuries. 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 horizonta ujnpmkykdd 0pr a, +c4m3*a;5l cord of length L whose other end is fixed (Fik j;3cy5n* pm,dd4ap+au k m0rg. 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 climbsmf 5ri(ba6zolzu) c17 to the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevat5)l7u i( rzm oazc6fb1ion 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 brean+5scz+f (zq .uly2gsks 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 i9*t9r yirr,w cn California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (verty rrwtr99ic* ,ically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the r pjk(pswi, lk9 907ropate of 650kg/s and falls vertically 81 m before striking the t pikj0r 9,wkosppl9 7(urbine 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 verxm9 7.y kxx-/0 0oang xhj)nimtical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum /okj)x0mgnm0xi-hxna. 97 xyneeded, 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 directl f-uk,b/ayma 9y into work, how high could an 82-kg man climb a ladder if he were fueled by /am, faybku-9one 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 aluf 85 jzh dm 0ykfzcw2)p258y ;-aelgt 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 scale, th.w w+0y5sqrk te 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 itq+0tsw wkry.5s peak?    N

  A 65-kg student runs at 5m/ l 5r kk;ta4j qa kqv72j9ne0e:fcsi(zsy100ds grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. ek4;0z7yd0 es rsjj kkqiaq0at : 2fv5 l1n9(c
(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 (0nlf a-;q(mf d(i+ car1n7aenaq;o vdistance of 5.0 m in 9.0 s. What minimum power output was i1a fa+-nda(q0nfev (;( acqr ;mo 7nlused to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by rd0mnq.yf; jh*zxw 3o(eversible turbine pumps from a low to a high reservoir. To 0zn*.;xw q hojmd3y(fstore 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 consta4fp sx9 gs(wvup8 c8*mnt k is cut in half. What is the spring stiffness constant for each of the two resulting springs?89fp4uwpc *ssmxv ( g8   k

  A 6.0-kg block is pushezfq)sz4o:m e+d n2 px gz91qc2d 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 35kljk2vyo)k8f( 9cwo 6w,boi d+m/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglectjlko2)f vo,9(8ko yi+w6wb dc frictional losses.    s

  In a common test for cardiac functft5sbq* ;ju3ye./ lm lion (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required fr .julletf b;3mq5s/y*om 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 verticallin 5l*hx9l( 3wv ro8)z0vxnq cjjd4s6y upward a distance of 500 m, what was3(iwr9n 8z56 sj0c o)4v* dvljlhxnqx its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a watr9) 6b i0xr*b jz*faqgrsq6u7er wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to providu9)*qa7 *jrbi6gx6qrfzrb 0se electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s