In what ways is the word “work” as used in everydayj p:+k cyt:txuoj29e:m1 * tmh language the same as that defined in physics? In what ways is x*y +: :t kj2p1tjctme mho:9uit different? Give examples of both.

Can a centripetal force ev-5gplnzvu 4j12d .kfwwwf / y)er do work on an object? Explain.

Can the normal force on an object ever do work? 5oxq0qy9n-acf a h+db+n / x:uExplain.

A woman swimming upstream iswuv8tn4s vq6w9)9s pxk(2 yky not moving with respect to the shore. Is she doing any work? If she stops swimmin)9k 92n(wksy6w t8uv 4yvpsxq g and merely floats, is work done on her?

Is the work done by kinetic friction forces wmd6 c9 7xdqvx,w*k5dalways negative? [Hint: Consider what happens to the dishes when you pull d67mq vk9xwx,5 *dwcd a tablecloth out from under them.]

Why is it tiring to push2 7ro mi;5ap*2rzbj+ps wd: bh hard against a solid wall even though you are doing no workr2 jp ;idzh2br o*bpa:5mws7+?

You have two springs that are identical except that spring l is stiffer tvu63ilucy: ouv mn+;*gc)g,y:a -um i han spring 2ii g n+vu cl3-;y: *uymmg:, auo6c)vu $(k_1>k_2).$ 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 horizo 1.9jn): x.eu lcm9q a7zoyowmntal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from resmolw). c.u179y9o qj emz :anxt 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 d ;r 6s6tj8hius*o6(rkq d7 wwuoes your gravitational potential energy change when you jump as high as you can?w(u ko;ijht6w*s6 d78qu6rs r

In Fig. 6–31, water balloons are tossed from the roof of a building, alllu);)i ilffpo 2p r,u; with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resirp) )p iufo,;l;u2flistance.

A pendulum is launched from a point that is a height h above its lowescx+*qhhhij; ae)m2 m.jn 98e mt 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 trajectoj 8cijmnxa )mheeh .m;h*q2+ 9ry, 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 tabl7bj6k owfpn9erd2u, :e. If you compress the spring by pressing down with your hand and then release it, ca6,dep7 ubr:wno2 j9fkn the spring 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 in,vb o -nen8tq 6bs,to1structor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to relen16tot,v s oq b8bn-e,ase the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top 7 lz9/-)k yxgx-vyl4 uhm ja6mof a waterfall falls to the pool beg y6l4x/)79mvy- h xuk -alzjmlow?

Describe the energy transformations when a child ho6bdl1y plx * id,rr;5zps around on a pogo stick.

Describe the energy transformativfzi yfp; u3ydmg0/8 xd :w(45nj: sivons that take place when a skier starts skiing down a hill, but after a p:/4:u8mv y3;nfdxs5 i ivd(yfgzj0wtime is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest allxcq s3yt rmt/5) 9s4t the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow) 5s/t xstm39yc)rq 4ll?

Seasoned hikers prefer to step over a fallen log in their path rather than step5iezujn w2lul1xpr8(d w2 t5 *ping on top and jumpu8pr2w e51 unllt w2dxji(5*z ing down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired intwt7k5t f; z-ujo a bale of hay. Assuming thek-7u t;tf5jzw hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple sv:n.1k / pbletps-r* dwinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound u dk ne/*.1 :rlpvbt-psp.

When a “superball” is dropped, can it rebound to a e+ e8,7v s yqo(vdp4vnheight greater than its original height? Exppe(, ysv7d4qe v8v+on lain.

Suppose you lift a suitcase fro/3fev roqb x67m 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) t/qe 7bf36vox rhe time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the podn c.6xa hk5) q4enrk,wer needed rather than the work.

Why is it easier to climsr1 h3;iye:lsx w a2n,b a mountain via a zigzag trail than to climb straight u; i nlw 1aesx3s:r2,hyp?

Recall from Chapter 4, Example 4–14, to/d; q:q:brmo)ml3. rom+rb orbr /8dn(ug3p hat you 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 must boor/(+rg:n q3 l/ruro o;.:8pmm dmd)q3bbbre pulled up? Account for this, using energy concepts.

  How much work is done by the grayq.un 0f g6f ,uwrj9a6vitational force when a 265-kg pile driver falls 2. .f,u gfwau066j 9nqyr80 m?    J

  A 65.0-kg firefighter climbs a flight of staibbneo 6ukl .)u. v74qxrs 20.0 m high. How much work is requirednbk.eo uuqv4.b)67xl?    J

  A 1300-N crate rests on the floor. How much work is required to7xy z t-eb x5yqc9p) f0mfv)p1 move it at constant speed (a) 4.0 m along the f ef9) qc1 p5-y x0tyzfbmvxp7)loor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally(v yo *an0a td+ciorq07 2gl1x) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of frictioq 7nort2 x0iv1cg*(0ao adyl+n was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor atrq-v*x 3m. jrt*9w zoq a rate of for 7.0 s. Find the net work done on the boxzvo.wrmqt3- *xjq 9*r.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How much f+.8 yw +vhp xwtutg;*work ih8+yf *t gwtu.v;xp+ws required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects webfr m:5q- bifgrs61d1o)a,u f might not biuffa611qor ,m:)rbdg s5f-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 is kept fro z,(-inrh d5uqa(3oio m accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effidhz uoo,5i(q3r(n a- ective 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 helicyho,0ep3 7j5rf:5 u oyk(ai0,scbkw vopter of mass M an acceleration of 0.10 g upward. uve05r kjw,3phoy sb:7,0 yif5c (koa   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 * r8jdem4zrbqc3l 1ae84.ttf linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis2; qjor*hz40ae: trln, varies as shown in Fig. 6–37. Determine the work done by this force to move the obj4* e;zrtq0nro :ah2 jlect (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 a/bno *e -dd)gyev2uw, tn)zf1 cts 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 molecul(, pi f9hmi-9qdi1 xzte, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by w 1ko3t*)*0h sqeza,jjg(-avsolu c )hhat 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 ankxfl y,s*iq7 d6lg-bpz: g09e 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 traveling at 1w7ey:8v(4xj vtg1o nt05km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110xp9dvd y0wgu.: j )+utm4zst8y 6hf3jf v6vg9 N on the arrow over a j9w:6v vgpu 96fjf4u0x)th38zsdt .ym +vgyddistance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) trz yg4gqh/7vx s +ou( rni7f11gaveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. Whatno r+4qg(7g yx v7ufi1s z/g1h was the average force exerted by the ball on the glove?    N

If the speed of a car is 7/gf6oi6lblc on4 /ew increased by 50%, by what factor will its minimum braking distance be increased, assuming all else i6wo beo //il lng4cf67s the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure 6a*qwm176 zvp lnx/hb 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 locked) the brak7n1*ml/hwq zax66 vbpes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg ily xd1e( i d:)c 3k2jdc/py0tns pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the aved2)(3ty0cix:epdkdcn j l/ y1rage 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 straightwci b ykc. *4.j0 ;tqz kgqa(.hiv43qu up by someone who does 80.0 J of work on it? Neglect air resist4bk(yc*v ;j iu..wc3h.itq k0qg4a qzance.    m

  A 285-kg load is lifted 22.0 m vertically with ai4phb 9f wr/(on acceleration by a single cable. Determine pih (w4/or 9bf
(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 s68 -bv9; ppw2 alxhf1c-sxjvhtiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energh8v--x 1h lpcfswxba62;vjp 9y?    m

  A 7.0-kg monkey swings from one branch to anwysn vj,gj 006other 1.2 m higher. What is the change in potenti gw,j0nsjv6y 0al energy?    J

  By how much does the grhq*4oyx tw .5f;i(kkf8xb:nrdb g-: bavitational potential energy of a 64-kg pole vaulter change if his center of mass rises abou *f4id o:nw( b8x5ybgh ;kf rqb-ktx:.t 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v a.ar+ yf8z2h2gz2ug c= 65 km/h when it strikes a horizontal coiled spring and is 2g f.gh8z c2a+zu2ayrbrought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground s3m fr s7shbti8-d/6g co it is 2.20 m above the ground. What is the posi/7rmt8sfc- hgd6 3 btential 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 1600 m and climbs to the1x1qi-:l.-t+ d f0bdfn dwhtvuyg:a4 top of a 3300-m peak.:q+yvn-a xd4:g fhutdlw-.b df 110ti
(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 end7 t-0cfknkrn0;v 4x wb of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now at kncvr0-f t47n0;wbkxtached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spe(fjo +-d/ei*rdihxp/y l so;.ed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward? xfi.ope/+dhj/- d is r; l*yo(   m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, sli4iv r7mab /,cmdes 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 given a sho)r+ m:8ad p-4 vzfruvyve 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 transformed2c6*(v 4( mylwdpm4t* qsyzvx into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a splmp4 z 2c4t6xs*wdvmy*q( y(veed of 0.7m/s.    m/s

  A 65-kg trampoline arti snx7 .c58px3mjow qx*st jumps vertically upward from the top of a platform with a7 jn5 .8wsm p3cxxxo*q speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffnep0 *d0aqodg1 lss constant is 950N/m is attached to a table and is compressed down 0.150 m. oqdp0dg0l*a 1 (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 fr44rk;dnb d-qd7 g i2nziction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radzgr -ib4ndkd;q742 ndius 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 stiffness constanky-eml:b,ubycv v7; :t k), Fig. 6–40. The block is given an initi ,kv e-b m;vy7:ucyb:lal 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(.jte8x che :9grdl*lxru p *7 from a bridge. She is tied to a bungee cord whose unstretched length is 1. rp(lu:j xegdcht 7*9lre x8*2 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 w y72pdpo8xduges5)w4gj k8t 7here it is released from rest. Assuming no friction, calculate the spe8gpp g7y )78j 25sddkw uxeo4ted 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 adb e7ndc /e a5pvwxx;:.j 7bq8n 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 plqab- (zd3ddw,aced at the bottom of an elevator shaft. If the elevator cable s-dz (,wad3 qbdhould 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 elevator and passengers.

  A cyclist intends to cycle up a 7.mv6g tfiiy ,6x/8m ds+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 opposi:-vq w 2k2mf 7aztv7ckte directions, collide heatvfmak:q2 7cw 7 -v2kzd-on 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 s yxgyxw+7oahu6 (7u u9lide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this process?7yyhgo+69ux( 7xawuu    J

  A ski starts from rest and slides dokr83ao js o5ip.*+aqlwn 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 thntgn-8becr ;6 e ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a hur(xvy vsx)4:5 )+ zjyh8f qpueight of 1.5 mj4s fy: z8 (pvqrxy +u5h))vux.
(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 pulliu xc2;pz+e a2ed across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of fricti ae+22cxz ;uipon 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 of If ttznd(in: fnxm (: 08zphe average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance tratnn p0n x:di(fz(8 :mzveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a st(mv7 uj +e*xspeady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (ken o50ju2j1* e4abat d=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and*t ej4euna a jbd051o2 released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached tkizp+4w cewi67,x)cot ho s;nib 3s +2o 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. If3h2 wi+4 + k,)izncso6x ci7sopbtew; 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 space shuttle used a “glider” (mass of 980 kg ppmr +w;d 4p 8qo5aid9including 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 would its landing speed have been indiprm8qw;p+ado p954 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 l+7 /b *ayg8yh bl:trxpift a 315-kg piano to a sixth-story window 16.0 m aby+lap:/yh*gr xbb8 t7 ove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must bems, kxe7.vgro8s :lw. the average force exerted on the car due to fs.gme.,7v r:8s xkwlo riction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 mz* xdz*v,szuvqt* :4s. What is the avera*u m, x*:dtz vzq*4zvsge power delivered by the engine?$\approx$    hp

  (a) Show that one British hoopn3xu rq(owrjn*a; x6 7/hdn,df;u e/l c7t7rsepower$ \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 ao)(/g (1g8ncr pckr ilre often expressed 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 about 6.0 )c57knv 9l-rqy.hcrq n :td 8is on the level when it is in neutral. Approximately what power (watts ankc n)-cqqy9tdh:rv n8. ir 5l7d hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.1 mra c on/xli)wxc556t;1yog0 h? $a\times10^b$ J a =    b =   

  A shot-putter acceleratesux) ks 71ov (ybrm.l/b a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, whatbbko. m)/x r7us( y1vl average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per hb v .8vi4cn9bminute through a height of 3.60 m. What output rating (watts) should the phnc.4 8v bbiv9ump motor have?    W

  During a workout, the foothty (cu ibcz17:+v4nrball players at State U. ran up the stadium stairs in vzn7 4:1c +i cbhut(ry66 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 cyclist climb a 6.idt)/xs-w*e/ *d v p7xdpc. kh0 $^{\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 ma- 2wot8:s0. etz mk 1qk(;do+cowhzzvximum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/t;( zs8o0cmowkoz.2-v kht wq+: z1deh if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to cgainqri6* / 2be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45? gi/2irac* n 6q   hp

  A bicyclist coasts down a 7k1dx(mafv* w0g; ac mqc4::xe.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” that9 au usw91wdw+ are designed to compress and rebound elastically without any phy aw uwduw199s+sical 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 wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground,s0w0p(r5mbg wfaxq:yd6ho(. and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg (s0pagyhx wdr.( mw fq5b:6o0 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.hflqa(3 ds3g 1 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch i(sla33fq gd h1f he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding witum l8*:c1ajzz/y) b tbka7v0, qgy un0hout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at tha7 ,0vju * /1ucl8 tbkg mbznqy0y:)zae 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 jumpi d8 k ijw+/knb;ybw 8f0.2ileing from an aircraft without his parachute opening. He landed in a sno yi8lw 8wbi0e2fk k+di/ ;n.bjwbank, 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 horizonm002ash0 yl4/ffiljb 4tp3ntacst-s2 ml) 1btal cord of length L whose other end is fixed (Fig. 6–4s3f 0nt c t-jm1/f0i0baspsa l2b4)y4 mt2lh l3).
(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 i,a15 ziziu9yr n 5.0 h starting at an elevation of 2300 m. Calculat 9a u,1i5zyzrie
(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 el- f kka9.br: xatce2(revator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 p8oks/9 2p hrgjeople per hour. If the average lift carries people about 200 m (vertically) higher, estimate the p rg2/oj9 hs8pkower needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically ;uhpr,y06s7k ay us:-yh pf/r81 m before striking the tf,su/;h y60pprk7-y y:asr uhurbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (qm4q0e v16jav, xk oiez9d63k Fig. 6–44), the difference in your4 q6zm,d0eak x 6e kvq1o3jiv9 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 wor homo q irsviinft3m)i((j-+-/ h l.*xk, how high could an 82-kg man ih iol i-t3o*/fqi)(-nhmv j+xr. m(s climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 4u+acncmh( 1llzz *6s35.0$^{\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 c*zlr(n4gkf+kac c*pm6f )v f6 ompresses 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 pea )n paf cmg*( kf+vrlk6z4*f6ck?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig6u, nj78mv ms2fa9gf. / gbt*sedmsv 8. 6–45). He releases the rope when his velocity is zeros 88m,vsfn/ uamfv . g6b t7msegd92j*.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance o ly+63 qx/9z xatykb;mf 5.0 m in 9.0 s. What minimum power output was used to accomqxy6 ;l/b+93tzx kmayplish this feat?    W

  Some electric-power companies uscky)h/5r e.cr tack. (e water to store energy. Water is pumped by reversible turbin)5y kc(ehckc t/ .arr.e pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in halfgkra+ -jf7vw .. What is the spring stiffness constant for each of the two resulting springs?-. vkawgf7+ jr   k

  A 6.0-kg block is pushed 8.0 m up a rougi:.af5a hxx p7h 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 long witx: m xwbh :4a;xcy99tll it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fricti x9;:4batm ytchw9: xxonal losses.    s

  In a common test for cardiac function (the “stress rvbx5wcoyy 9znn)2 (1 test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the 1ozxrny n9v(2)c 5 ywbpower required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distancmu9+gjc1s,5omrx0 06o wl zaxe of 500 m, what 5 urxaml 0sw19zmo,c xo6+ jg0was 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 water wheel fromzri620gf66 lc6lkfk y 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 power out 6rc6k6kg0lfif2z6lyput?    W
(b) What is the speed of the water as it hits the wheel?    m/s