In what ways is the word “work” as used in jj.aanrgs:,h j r*b115ozfs 0everyday language the same as that defined in physics? In what ways is it di1.1r,hro: nss* jf0a a5jbgz jfferent? Give examples of both.

Can a centripetal force ever do work on an object? Exp,x2gp0 arvqu :-j,p rblain.

Can the normal force on m0+7,x z+vspusv1xrv an object ever do work? Explain.

A woman swimming upstream is not moving with respasd6a3pd it 0.vbl4/nect to the shore. Is she doing any work? If spdn i 0al b.t34d6/avshe stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consn/k 0vcgwd i*3ider what happens to the dishes dv/k ci wn*03gwhen you pull a tablecloth out from under them.]

Why is it tiring to push.q:7 wj46sp:xzsu,czrc pfbs0f w 26y hard against a solid wall even though you are doing no j06 pzy76fsw42pwccbf. s su, r zx::qwork?

You have two springs that are idf s9,8em7 ufi x/1iycventical except that spring l is stiffer than spring7i iuxm9y/cs1 e f8v,f 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 const6dk,/ f7hh ds7qikpv+ant horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts frofvk/hs,+q7 d76 ihpdkm 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 gl,j *trw3n/s oravitational potential energy change when you jump as high as you can? jsornl/w,*3t

In Fig. 6–31, water balloons are tossed from the roof of a building, e46x n98e yhnjall with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistay4xj n 8he96ennce.

A pendulum is launch mzdh1xm3;3jfsa* d (xed from a point that 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 direj adx*dm fx1h(m 3z3s;cted 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 compret+5qy -ww iq x-769p1 vvxrmzuss the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of 9vuyw7-65+i-zmt 1x wqqv prxconservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fhn.m* 6bghfr.gg-rz1t- xdk+ig. 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 supposed to release t+gn. t h-mgb-kgrz1d hfxr. *6he ball without pushing it. Why?

What happens to the gravitational potential energy when wate4lkd8g) c/yhx rd t.g 8bs/h0ur at the top of a waterfacds//8u0hldt4.gy rk8gx b )h ll falls to the pool below?

Describe the energy transformations when a child ho:gqj;gtb 6m r4ps around on a pogo stick.

Describe the energy transformations that take place when a skier starts s,qk1fu,yma 0 jkiing down a hill, but after a time is brought to rest by s,m fkuy, q0j1atriking a snowdrift.

A child on a sled (total mass m) starts from rest a*p mdh yfja1(r )8p6pzt the top of a hill of height h and slides down. Does thpfa mh6( ypj8d*)z1rpe velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers preferj)o0dlsw,g: 1e,hxpxw n7z (q to step over a fallen log in their path rather than stepping on top and jumping down on the e:xls1jqgz0( dwxph w,,)o 7n other side. Explain.

Two identical arrows, one with twice the ud3pqc h(ym2: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 farther than the slower arrow? Explain. ( pyhdu32cmq:

Analyze the motion of a simple swinging pendulum in terms of energy, (a) if(,*7 scalx fegnoring friction, and (b) takielx(fa7 *s,f cng friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebgvrmg g c7vt(omz8-if2h *u9 a- p.y;gfh4(ebound to a height greater than its original height? Exp7m c;rh2-f(gtye bvzg8h i-.mvfp g(94*ga oulain.

Suppose you lift a suitcase from the floor to a table. The work you do (78uvm nwx 2d,oiu5vyon the suitcase depends on which of the following: (a) whether you lift it straight up or along 8uxidw52n(yvo , vm7ua 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 2m 1rx0*bd1iit j78a7 cengq *wf*rnmthe work.

Why is it easier to climbl+ 6vx6sp xng2wxxumhnsb:2c /t- n/9 a mountain via a zigzag trail than to climb straight u-s nst96mlxnw6hvxu+2bp:x /2nc /gx p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to decrq xiva gt3b8-g(fy:ov 1 d(tefsa6(m(ease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope v6td 8f (g3(g(-b1 aoa:exvqf yi(mst must be pulled up? Account for this, using energy concepts.

  How much work is done b; hfmr( q4irkk-g :t4iy the gravitational force when a 265-kg pile driver falls 2.80 i4h:k fmkr;(4rtg-qim?    J

  A 65.0-kg firefighter climbs a flight of staird g/7/tzw1viqg p9f. qs 20.0 m high. How much work is req/ 7qfg qzipv9dg1t/w .uired?    J

  A 1300-N crate rests ot0d d(+1j uyspn the floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a frictionj1u0+ptd( yd s force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the moversr srzkoti( .rp5;su+ 1 do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleratuipr o(r;z1 5skr.s +tion, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is aox) 8)e sgrot1ccelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the box.)s)gr xe8o o1t   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fle5 gyq6muyup+dc5 w )*j 2so1wat on a table. How much work is required twuwp o sqm 51eu+ gd*65)j2yyco stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can bv1eoalah9f6k67 gomu l -;e;me used to liff objects we might notm 9u;lefaogaho 6;klv6 e- 7m1 otherwise be 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 id(j+w9ki 0k4z q )4asqwrsg6j s kept from accelerating by a man who is pushing back on it parallel to the incline (Fij4w ja(gwk+s i k)q0rz6q94sdg. 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 maspb,b 9llk r6f/s M an acceleration of 0.10 g 6 pl /kbrb9fl,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 m:k (l9oav(qq the 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 object, acting alon58s)f9fdsp r/ibo e0thlr 8k 5g the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) o ss 8lrb5rdf08k/ fpte5ih9) 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 iw2 nfdgv-,,ds x +)oxdn 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, with m4col w6sl1 kg0ux/1erass 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 facyt/v,jg(t r0rlx6 x+ctor 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 anv do3wvphsv4hlwn-mu * -(.z( ur2t e3 electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-h6 wu0ka6mccf,lg rg c16.0xikgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired frog8wtq4)c dj yo ldjbw,;0j)w *(s) s5ux+ajtqm a bow whose string exerts an average force of 110 N on the arrowydwt(l;*s xcd4 w ust,)8j j0jjqq )ba+o )5gw over a distance 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 backa)rs bj(7whuv 9qvpm, lv+. :tx5gf 0oward 25 cm when the ball is caught.0w5+r ,j aq:(9 hxpv.v7b l)vmusf otg What was the average force exerted by the ball on the glove?    N

If the speed of a car is increase;6t; lkc;+x.tor am4qs y ps3md by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same?;.+ ot ks6m;p;yc4qr mxa3tsl Ignore the driver’s reaction time.

  At an accident scene on a level road, investi9:a( z148wo8omzv wvc9n oj xngators measure a car’s skid mark to be 88 m long. The accident occurr4c9 :w8z9vawnozx1(ojmvo n 8ed 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’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the times,b l7aocm5 o: it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the5cl oa7os :,bm 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 does 6.m6 pc v(rnx6,q-undkjr-so 80.0 J of work on it?k 6 .qvnmrp6-nx,cuojs(dr-6 Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cab/ 2inc ew+:jp;hu8gc hle. Dete wnijc:/h; 8+euh2cpg rmine
(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 stiffn2enobr+x0 g9 hess constant, k, of 440N/m How much must this spring be stretched to store 25 J of 0ehr bo9g+2x npotential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wha+ un:t+zq-hhi)h; zubt is the change in potential ener+ t;+ qb-z hu)h:uzhingy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter0uzh qoozx*cw1+ 6pq8 change if his center of mass rise*cz zqu 10+xqo8o w6phs about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizonta*thk +zm)p, : buymeo;l surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought ty,mb);u hte mz +:*okpo 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 ground sa l-qyoalu 0455ffmr/h ydtcw :*;qq,o it is 2.20 m above the - ayqfadchow5y5lrfl tq* /40u;:m,q ground. 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 ele7u(xlxmyxr vm+ s(u+ h7gcm*)vation of 1600 m and climbs to the top of a 3300-m*g+y(muxhcrsxmlmx7 7u( +v ) peak.
(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 verticallyltyw8hh(-a3bk3l n :x 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 th3 t-hay h(kxnw3llb8: e end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a m -;(cavk xtz*vine hangi (cvt *zk-;xmang vertically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frl-hrcez4b)sh u0bm b ;y./d0lictionless 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 gik:),jic 2 6 aa (dz-zhkzt9twcven 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 int90+3l j .0wkp flc9wux1 ncwdao gravitational potential energy without the aid of a pole. With what minimum speed muscfw0+ kjw9d0xu. 9apl c1w3nlt 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 vetd*xru ,yv 13xzz/iq+rtically upward from the top of a platform with a s+xuzd3/r tzy, vq*1xipeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant i.nbwn)ej-h mp 0hm ;e0s 950N/m is attached to a table and is compressed down 0.150 m. (a) p m-;.0nmnwb hj0eeh )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 track shoeqd spxydth h:3b2j6v-fq p 8d9l j+/8wn in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radiuhpq:h/8 de j93t+x-bp dvfy8j2l q6 dss is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end1dhy z0rjgk) 0*.iwp m of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initird g)jw .z1i *kp0hmy0al 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 bungee cord (hbs-twyrpi ;my5 (g so* qi2zekk;18whose 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 lawi;y58sp*w;qh2m sg -zeryt oib (kk1( applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shtk,cb 3h1p iod;4jqzo p5rx1 uv++p)town in Fig. 6–41 is dragged up to point 1 where it is release1v1pc5 dih ; +q4)r pztooptj,b3x+k ud from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thtn-rvp / f*)mvrown with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of. gzsp4vo l /au;*r)xo 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 undergo an acceleration of no more than 5.0 g when*r/v; zolpasuo.xg4 ) brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to hes:h-aah9d : +2zjq qcycle up 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 h-un 6dd:mdk1 95km/h in opposite directions, collide head- khd-m6dd: u1non and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a l.5 y tzgqesg2z+5 rd19slc: kspeed of 2.2m/s How much thermal energy due to friction w+ce:1k2s q gdzlrs.5y 9gzlt 5as generated in this process?    J

  A ski starts from rest and gow2)zvh 8du6slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the gre3g;/oj vfmb +ound.
(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 er0 lc0bs5ak 4it bounces back to a height of 1.5 m. 0a0cr5 le4kb s
(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 withgl+92 ex)ixt 4nxdm9ft zz)i9/mux +o a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15uxx92dm) zxt +nei 4x/9io+z g )t9fml m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coasur )0td grbe sgej1h1/mo,r(9ter in Fig. 6–41 passes point 1 with a speed of If the average forcsr( e0tgbrjue, hmdo1gr/ 19)e of friction is equal to 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 rearrc kj2e giqm8f(2h) (ches 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 horew k; eawz/5x-izontal 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. W/eakw xe 5-;zwhat is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizont -/ictlg 1kh cer4hwd5s, c:zuo*)-t;o,es i bal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this po- hc,s;w s*ot5l,ccitee4h) z/-rkod1 big:usition, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used aam 8crni/x78c y+ufo:h+ j,jy “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What mufc /xc8jyhoj:yra8n+ i,7+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 t0q)8z4xkvmt yo a sixth-story window)my vx8k0 tz4q 16.0 m above?    s

  If a car generates 18/ 6g .c7 xjlkbx ifx7 nq;7lr4n.a+yyh hp when traveling at a steady 88km/h what must be the average force exerted on the ;x4 7/qay7xh gf.j. yin+ l7nkrcxb 6lcar due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95kui53v k8z3spam/h in 7.4 s. What is the average power delivered by the engine?vp ak3 53ui8sz$\approx$    hp

  (a) Show that one British houjxes6.vu,6 so:9a v brsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hours.” 0irz .y lj gg*j2 *ji-.ar9n)gajd zi*
(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 115f /qtx46 ,ecss0-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (wa tx,cqs/4 f6estts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp rj()1my(v d qcmotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s3-e5ov up: tcu If this motion takes 1.cp5-o u:v t3ue5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.h.f v706ooe vdq t(m(/ttu y6s0 kg of water per minute through a height of 3.60 m. What out s(v6yu6fo q/v7m(do0.tehtt put rating (watts) should the pump motor have?    W

  During a workout, the football pl w .oxg ioz+o,f6tz:um)qxu)rk b62v )ayers at State U. ran up the stadium stairs in 66 s. The stairwr+.,6qofoozu)x2t)k)iug6 vmxz b: s 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 cyclist clim u+ b/)/5w+p/f +0bagdnf s7mjp lxatnb 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 maximume(cs2/h);afq dgoh9 r power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 dreh2qfc; oh (9as)g/N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dra.o8k pjr wcaokwy 05).g a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient y 58ckj.w.kr0p)waooof friction is 0.45?    hp

  A bicyclist coasts down0p z:6ngvb6k o a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are5)0dumymz 0xrp+1m n)vke 8/f ha z4aruh-od2 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 /-uzh50 4d hzay)nmrr2 mp+de0uv fax)m8ok 1into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 y2 h(cwd)ddo2cm off the ground, and the remaining four shelves are each spaced 30.0 cm)o2hdyd2wdc ( above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 dndcw.qcfuc3afir/, 6y;0 69kbr/ h dOlympics shows that his center / u didcbq0ck;hf/w. f,n66c3r ayd9r 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 top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown izbsw+;e4d29 dqo + za+9u qsveo z:yi9n Fig. 6–39 is to remain on theuvzsdd+qw4s9b9 ; a2+zz y+ i q9oe:oe track 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 aeo g.n umqu7* clv 17g6jpz2f2k7xfi ,fter jumping from an aircraft without his parachutec ,27ge6 zmk inqxfj u.7fg*uvp12ol7 opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontals p1und) g ,pwiiolz) -(7c)ncb.7go o8kn s1a cord of length L whose other end is fixed (Fig. 1cl7 n,ci.iz n-w1uogss8a gdp noo()p)k)b7 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 thutz62c e4 o(staeuffi30l8 1 ve top of a 3700-m-high mountain. The climb is made in 5.0 h starting 4 u6o2lv(t138uifcfa0tszee 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 elevator tl 2b,y ft w((+n.grhsis 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that i hmps :f(t/zj;iv v/6rts lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power need m6;ph/rtf(vsi vz:/jed.$a\times10^b$ W a =    b =   

  Water flows over a dam at th -6x*y4;fxjrgarp k t9e rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculate 9fagrjr4p ;-x tx* 6yk
(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 circulacoui+0rmhtli zze3 vrs+e+6*/oy;8n r vertical 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 a/n8 6+rt*m i 3z lrc;oyoh szeu0+ve+ibove 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 work, hoz*rdtj:n-s dh* lky-8c s6sc 9w high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) t*-8-9 ynssd ccjhzlr6k ds:*   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 u ,/a*wg ubud*/ mnyg5yk/*ss nwe76f qpward 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 e*6cjz if9pl 0 c -zp/jt:cew4yd ouk7z5c5 o)inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its pe wz-lo5p c64:kouj9j7c z0t*edcpy zic5 f/)e ak?    N

  A 65-kg student runs at 5m/s grab0p-hd5 y0lko,zto/ h as a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is pdh 5ltz 0,-hoy ok/0azero.
(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 distatngppn,g f:ma m50q4/lb:oy0 nce of 5.0 m in 9.0 s. What minimum power output was used to acc4yl :mp a f/to,bnm5:q gp0n0gomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumpedxgsnq3u1 -6 oode bd;; by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 12osnq3b;x e-d6gu1 ;do0-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 stiffnig3 */,nful.o r,z/fzon obx.ess constant k is cut in half. What is the spring stiffness clxifnu.3orof.gbon/z /,, z * onstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough +:fx ;t;w+lt r hstw8j37 $^{\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 in9e-flx5,p r jb 3.2 s, how long will it take to accelerate fbxr9l5, j efp-rom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”)876y zln;w ens, the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is s6 ;n7wsezln8y loping 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 r .:joq7nj wd3x y:kg:nock vertically upward a distance of 500 m, what o:k nwgyjjx3d. 7 qn::was 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 watera vo94lc/(uko wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum powe9 ckv4o/ alu(or output?    W
(b) What is the speed of the water as it hits the wheel?    m/s