In what ways is the word “work” as used in ez 6j ;8eitm36if 7urknz ,qre9veryday language the same as that defined in physics? In what ways is it different? Give ee n68ki zi,96zj;qfmr u73rt examples of both.

Can a centripetal force ever do wo9f:r lvsf sdbqfyzb9c0z*441 rk on an object? Explain.

Can the normal force om3jqp/ (tkjvx6:so5 af hgy6fznb+/ 8n an object ever do work? Explain.

A woman swimming upstream is not movingwh:vwtt, 7i1: zxaq 4n with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done o1 :z4wvi:7ntx, wtha qn her?

Is the work done by kinetic friction forces always negative? [scn( :wj5)og) ) wajkx7jrf jcfbg37.hw b c.7Hint: Consider what happens to the dishes when you p.a:(kbcfcwbo)r 7 5j.jfsgwwh n)gc j773j x)ull a tablecloth out from under them.]

Why is it tiring to push hard agai6bph)u mo)wv0;cnu8 inst a solid wall even though you are doing no wor)m6inu)0; 8 ohwcbupvk?

You have two springs that are i) 2xsbq n hx;(bbbx3gh: +j1ladentical except that spring l is stiffer than spring 2 b( bn x3g2x:h+bsblhj qxa;1) $(k_1>k_2).$ 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 blpy3 bnzv/u )6o *qa)u-y a,igrock that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the timeuua n)ygqp b)ir,-/yo *36 vaz 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 muctca0-pz g: is 66c,zgfh does your gravitational potential energy change when you jump as hp ct-fa:gs660z,zc g iigh as you can?

In Fig. 6–31, water balloons are tossed fr6cjps9vglp mw x9t72(om the roof of a building, all with the same speed but with different launc2mtl7s99 6pjp (xg vwch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heig2mqs; ;/jk cdiht 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. Which laudqim;s/; c k2jnch 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 fh5,o+r bd1e2wgxw3 zpressing down with your hand and then release it, can the spring leave the table ,3+f 5xwwgre2bh1zd o? Explain, using the law of conservation of energy.

A bowling ball is hungxs 8cs* j95j0ug(kq,yzts/fp from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to releasjtpkjs 9 c*x zfqu/s,0g 5(8sye the ball without pushing it. Why?

What happens to the gravitkji yb,jk*3/ oz6 f2etational potential energy when water at the top of a waterfall fal, kt*f32e k6zbjoiyj/ls to the pool below?

Describe the energy transformations when a childrfl73 uo()gu2px9 spb hops around on a pogo stick.

Describe the energy transformations that take place w,ag-4 7c g)f baw tqxh41kqw:chen a skier starts skiing down a hill, but aft a74acg1kqwqgtc-bhx ,w 4f:)er a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts ffmmxfzqeq 14f *kyt04 o64 (bvrom rest at the top of a hill of height h and slides down. Doeq0kzy*ovm1 4xf 6qb 4( mf4etfs the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than stepp60kt9s:gjy hping on top and jumping down on the other side. Explain. y6: gsk0htp9j

Two identical arrows, one with twice the speed of the other,h)mf5 9pjfkwgrr26x4 i yqd* k803too are fired into a bale of hay. Assuming the hay exerts a3im9d6 5*rwj8rfkyhgop4 xoqkf 20)t constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms o:s,aiwzw q2 1jf energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to b,ijwswaq z12: e wound up.

When a “superball” is dropp ry3if -uhc4(ued, can it rebound to a height greater than its original heir(-c i4yfu3hu ght? Explain.

Suppose you lift a suitcase f/r(fmobj 5o;20o o xbbrom 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 it takes, (c) the height of the table, and (d) the weighto ojmb o fxbo;/r250b( of the suitcase?

Repeat Question 22 for the power needed ratherb l;a,x5;u 1fuhb+5 gayl0qbci ln.j* than the work.

Why is it easier to climb a mountain via a zigzag trail than to clim-8o lcsyp osk/kfjk6,z 9h 7g2b straight uzfgo -plc6h kjs/,ko7s89 ky2p?

Recall from Chapter 4, Example 4–14, that you can use9 w)td2lna4 dz 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,2dznlaw)d94 t how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational f()* g*nr s nshv:ekctwc(x+-;e5cefi orce when a 265-kg pile driver falls 2.80 m?:h)-ekcs*g*5 fxs (eeincvtc w;rn( +    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much workfaix:h)a)f).z-wua o is required.ua)) hz f:w-fx)aioa ?    J

  A 1300-N crate rests on ,lxg - xstvnrs- *7qjauz5q+,the floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a frictjt* 5s- q+ ,a-gzls7v,uxrq nxion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horqa, zx:y,9c enizontally) pushing a 160-kg crate 10.3 m across a rough floor witya,:9 zn eqcx,hout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of 4;c laes,cb 1ma .mk-,l; sj lamke(a* for 7.0 s. Find thekjksma4 .;1cca;e lla* a(,- ,mslbme net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Hb x +h8n6ifj)eow much wo6hf8)x+ibn je rk is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 ca;3c6o :: rbdk/qn( l-pzuqx phn be used to liff objects we might not otherwise be able to liff. Show that the ratqrhk-op6 zubqx p/d;: (c3: nlio 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 from3,uwp3vy;xoch 5os h 51h-rpl accelerating by 5ho hshu3l 1xwp35c;oyv, rp- a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force requibw,q :6bugmt2 red to give a helicopter of mass M an acceleration of 0.10 g b,t6:q2g wmb uupward.    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 distance axis is linear a)c ik4 1rmuvma20 wzqohz4s:6nd 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, a55afw9c +caq.tk,m xlcting along the x axis, varies as shown in Fig. 6–37. Dete flaac5+ctw 5q.9xm,krmine the 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 aqb3j(/ g++ skv etwhn6 particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with misy/u* ;b( )-m.t(gwfj mi rsoass 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, byopx )lkx)/6w:jbo h,4oj1vsos7c*zi what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop 9 pjr:2 shy6rpan electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar t 8tr 5ksx +t70zncx6i;fgk5 lkraveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fronx./9id idd7(- kyd7fwd wak5 m a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. W(d .dw7-k9d y k i/dnaix5fdw7hat is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a f-4nbpv;s1wzxx.l l60 avp n;g ielder’s glove backward 25 cm when the -vxg.znxb ap6 l04;sv w1lnp; ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what (u a7x;ft dwz9j,q xv.factor will its minimum braking distancexvd7; ,.f9 (zxaut jwq be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene j bk:gp-i4 y 2ovb,8nxon a level road, investigators measure 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 detepg xok yb,48 j:i-v2bnrmine 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 thej mx9 8gvhtrbx c::w8a1i; p3j time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate t1 gb98w vt 3hpjjima:xr:8x;che 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 whomb(m 7 f7gkmd0i6:gysqkb+w i 7c7.qu does 80.0 J of work on it? Nei ugk kw0i (mg77+sd: qcmyf77bq.m6bglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with7yy (n a2ijxlz0g )+x 2ci/ooe an acceleration by a single cable. Deter ol+xig 2in jy)ax7cy oe/2(0zmine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must thiss p-:3aj79b;*xa uxc3xt edd 3mf r,dc spring be stretched to store 25 J of potentb,p xdcam;73*dj9x3cu :x3rs - tea dfial energy?    m

  A 7.0-kg monkey swings from o / jl b apdjj5ra+;hjnw*(3zg1ne branch to another 1.2 m higher. What is the change in potential b djj1z;5h*+rlaw naj g3p( /jenergy?    J

  By how much does the rxc .a8h t1;m)d/,pa cqfayg2gravitational potential energy of a 64-kg pole vaulter change if his center of mass ris1)ac8a r2;hxfa ypd m,qg. /tces about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when i 8 fyilitl)ahi97r8 p6t strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffyrlfta98 86h7ii ) lipness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m abov6;+7 rsgtd gmce the ground. What is the potential energy of the bog r; 6gtsdcm+7ok relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of a (xk4tk 9lgn54zaoem4 3300-m peak. n 4(45ktmegozx a4 9lk
(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. Thb a;yve b l d7k*o-i4q-jh7do/e 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 the spring, where will thq4av;dk/ d7-h-y jobol eib7*e end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/:0bqonxhy r7ka631a k s) and grabs a vine hanging vertically from a tall :r6y0o7kqa kbnax h31tree 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 froxpczg-/4hssc g,ry 45 m rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially giiou)y3ri 1a+bzk z((pf7+mdv ven 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 gravit;)ne txw0 5.hfg6ml dcational 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 the bar with a speed of 0.w6)5d. tnem0 ; clfxhg7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward mjkmu2n; 85im from the top of a platform with a speed of n ku28imj5; mm5.0 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), bn1n;/ yq6rurwhose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30- 6/ur1ry;q nnbkg 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 tl;dpg ztd2 29 l(ty :r;lhku6hrack shown in Fig. 6–39. If kt ( ;ld h 2;2yzt9uldr6glh:pthe block is to remain on the track, 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 olspmtfge-v,)mx zj: i jihn jb01 9::n- bz18cf a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displa-nnmsfb-0:m l8z tbj:c 1j)hjz :ie px9,vg i1cement $x_0$ 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 jumpsa , l(,f7 sp2dh)n,i7mrkhx hz from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bul7fr 2k(h7 m xip)nzds h,,ha,ngee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where +w x fm(/wdg3ijwt:r/+ (yasgit is released from rest. Assumg/wxg+i/dwfj( ts(w3ayr: +ming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle4xwpvbve33 : ftm e y-(p0mb/e 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 a p7s(whoa2o7y r* w*sop nb5 ra/l1g3jn elevator shaft. If the elevator cable should breakonryb jos*wr3 *pa a2l7hs1pg/5( wo7 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 elevator and passengers.

  A cyclist intends to cyaqes7x .-epopt 4s4a/cle 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 95km/h in opposite diu nmu7 o *x y8b0,5k+vqjwusvx q;6jd,rections, collide head-on and come to rest. How much theq mxoy 0+x u ,u;vsjuqnkw57jv8d,*b6rmal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hig4ab+h pz ea4nti-s1a 0h and reaches the bottom with a speed of 2.2m/s How muc4z0 pahia+-14e tsab nh thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a onn +nb+ 7gw.c*xs1fy22 $^{\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 dropp *wxnj(jdt:bh a .i;egg3(b7oed 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 rmtdxa(qc outi; 8u2u;8al1 0 a height of 2.0 m, and it bounces back to a height of 1.5 m.80tuqr;dtucu18 mx2(a al io;
(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 conla3aw 1,ofz rs7.q-qu stant horizontal force of 350 N. For the first .q3q-1owal ,s zfura715 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed lni fg4wvo +j,,:8ig u4 ;lsodof If the average force of friction is equal to one-fifth of its weight, with;i,u44+, jsigo :8dglonw lvf what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches ;ko)+ 9qohrm3kpth j2the 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 attached4 shkd785tq 5*jwulxl to a very 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 baj5lu7 s54kqtxhl*8wdck. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached t h33e4o0urfb,g6 h(bznc0unyzx0h2b o 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. If the spring is released from zunxb b6hz(33 u g0r0ebc0nh, 2oh4fythis position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” wap1lwn9 89boddpwy*c-j 0p 9(mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The 1ww9 dcpn09j*wod9b lay-p8pglider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-*;kg ;k (w fa8tljob+*5zxx6s3gg nnt story window 16.0 m aboz6k+wnbgktof 5j a(sl;gn8* * 3xt;xgve?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be th u1xj*vdou79e k--t gje average force exerted on the car due to friction and air resistanc- g91-u7 vd*juxjkote e?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the av 65 4;fa ,e+xdtb, usz(boduxmerage power deliver+o ;dfxbud , mbex 4u5,tzs(a6ed by the engine?$\approx$    hp

  (a) Show that one Br3,:w2k9p ffv0xhqqui itish 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 i a/wuhvi1*h d3 mv29fthe 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-dd y*2x pmiyt+ckny.k- q (0i car slows down from to 65km/h in about 6.0 s on the level whe p* kdty.kc2y-(dny+iq0i-m x n it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do intq ep /n g,v3zz.8hko9 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion take* ( dfllxfqk,va. ter)l l)8i0s 1.l f, * r8l0a)flitqkxde)v(l.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a hesns(1qy 3 (ea0w5i2xkhi ol o:ight of 3.60 m. What output rating (watts) should the pump motoio2 ia kwl3yexqsh:1s(0( n 5or have?    W

  During a workout, the football players at State U. + vgz3-j z :z14)wn dfjwz8kcqran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an ac:wzk1)-f 3j4d qj8n gz+wzvzngle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb w q(ibev ;+ ,evrv2)nc(x lst0a 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 hill czx9p 9i30 4 tqmxkn6z7mbqcb(an it climb at a constant speed of 75km/h if xnkzb0qc43bz7p69q9m mit x(the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor:n4niq:q 7c.i3eewe n have to be able to drag a 310-kg box along a li7e.:nwi ennqq :c43 eevel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dowrqx/0w6cyv b54hmlu;d9wm g- n 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” tdjw-p ;l9(0d j6 iwmzohat 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 s lom(i;d9w -wj6 djzp0tiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm of-2m fxa5 (tbmvus vb)t)ur4kxyv ) 6h7f the ground, and the remaining four shelves are each spaced 30.074 )f x-r ykmx5vt(vma 6u)h)2sbubvt 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 books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s f q :d3tlhj), sbr7mkf0ing0p/amous 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.t,0 pmi:hf0bnrs3 qg dj7lk/) 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 3cat; ltgy ;t5uyh. b62eur -jtij ;8rlooped track shown in Fig. 6–39 is to remain o;;tacr2bgey.uu t-tjj53t8h6;y r l in the 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 after jumping from an air)a635 vtvj-8bh la x -arxbxe;craft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s m -xa-)a8x3;ehl bxv5t6a jbvrass 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 other end is fixe7d6 *xowvjm(p jep5*zfb:;k ) pmq 6zdd (Fig. 6–43). (e ppd: m5d6*qx6o*j)vj7bmz;zkpfw
(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 made v9ryao 28fu*oin 5.0 h starting at avo9y u2*aofr8 n 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 is 28 m above a huge springpe;m w wkf*c;qi :g r:,a(l;3*ozsevq ($k=2.2\times10^{5} \mathrm{N/m}$) 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 its liff9(7 e 1* gg5mojml l(kw,hjdqts can move 47,000 people pewjd(k5e* o lfq91,m(mhlg7 gjr hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m bef jyzxb8ul9u(op /u / bb;pktd*95 b(qeore striking the turbibbtj zpl;u99(kb 58/qdx(pe ou/y* ubne 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 vertics: e).;fh:jgs6lf;e fbpe:jl al loop (Fig. 6–44), the differench;s )fs j fbe. jfel:g:6pel:;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 l2 .l4rx9hm1qvx1e jkwork, how high could an 82-kg man climb a ladder if he were fueled by x9evk4 .h2mxr11ljq l 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 angle of 45n+uu.3 k8w a gfpi34s4olwsrnsn;;/ync:u) h.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale comp6cmy+lkxl*g8z+d /j f resses 0.60 mm, and it tell * mj/f+8g+llzkyd cx6s 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 peak?    N

  A 65-kg student runs at 5m/s grabs a rope, an;i9pfe x3(5klb o: f tknowx 8,6x)awpd swings out over a lake (Fig. 6–45). He rellkfw, 5x) b (fo;a3:otxikxnp8ewp6 9eases 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 athl f4k0iu)mbz0,ew5;hw qli:xb ete climbs a vertical distance of 5.0 m in 9.0 s. What minimum zq0;i4wefwb5 , :im)xlb uk0h power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pum5; *c,n, xdccpnd nj7qocb(8e f --vrsped by reversible turbine pumps from a low to a high reservoir. To store the energy produced xorcc,nvds(n,ebpdjn85-q-fc7 *c; 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 o,+:md ge4q3t1ehuvbex*2 eotp f) 1a stiffness constant k is cut in half. What is the spring stiffness constan)vqgeh b,: fopta+t3 1mee1 e42ou dx*t for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough loq;ppxw w1l323phs2 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, how loa*xjf6 oy 75be cykg2e/*qid -ng will it take to xb g- 2f6qejeyc*a5o 7kd*yi/ accelerate from 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”), the patient walks g c4) t o:z *lcsz)++9pjiaugdon an inclisd4)jgc+oi9 *u pl:c)z+z t ganed treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically 13hq; -pbi iklupward a distance of 500 m, what was its velocity when it left the v1q ;i p3kbi-lholcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/v*jp ,5usfoky7.laz 5s (a) If this water wheel is set up to provide electricity output, what is its maximu,. kpjvyus5 z *ola57fm power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s