In what ways is the word “work” as used in everyday be:uw 1 ;-elbsl:vz lxb6.j0j language the same as that defined in physics? In what ways is it0l -;vs:elzbj:. be jxbu61lw different? Give examples of both.

Can a centripetal force ever do work on anjz(e r- p9fpi)v h(.; .hcd (csbpmq0m object? Explain.

Can the normal force on ayzlqwyivo0f,d ;pg5 z9 /y:uda(an; *n object ever do work? Explain.

A woman swimming upstream is not moving yzgyw-6z; ck m m.hv98with respect to the shore. Is she doing any work? If she stops swimming and merh9;c. 8y6mgzz kwmv-yely floats, is work done on her?

Is the work done by kinetic friction forces amzf 1y+mn,5bc ra.z5.; yaluplways negative? [Hint: Consider what happens to the dishes when you pull 5;5ya zr..ymlz1c +,unfbap ma tablecloth out from under them.]

Why is it tiring to push hard against a solid walldhpt.y*;hhu 5 even though you are doing no wphh.;d hty5u*ork?

You have two springs that are ids0m+6ujx n*d );b1zbd*e-9 kenln a ))uvrq mnentical except that spring l is stiffer than spring 2 v)lqsnm) a n+-6rnbnjeu*)d me ku1x9;b0d *z $(k_1>k_2).$ 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 forcesly3uye :v,t. on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A,yl.3 ,vyse:t u and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy chzqigf61i/b8:9b r ud lange when you jump as high as yo ub iz b:/ifq189g6ldru can?

In Fig. 6–31, water balloonkfctkgtko 8*;. c9dd7s are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest 9c.ttd kk*87fko ;dgcspeed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lo5lm h6k7 9fi8b.nt1kqsgz k+ ewest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initiae1kln 6kf 957 8zhbgmt+s ikq.l speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tayn lcv--h,cu 7nlk(0lble. If you compress the spring by pressing down with your hand and then release it, can the spring leav0clk7(l ,ylcnu-n-hve 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 instrucj5x 5.5.5sjlf)rednp p zqs 0ntor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor issl5nf0 epq5rx. zd5jp ).5njs supposed to release the ball without pushing it. Why?

What happens to the gv.y;dyzj-y f3wx, h:a se xvncp060c 3ravitational potential energy when water at the top of a waterfall falls to the pp-c.syvy cavjy ex0f03dwzhn:36x; , ool below?

Describe the energy transformations wheng rzhc3zp5nt02+n. en a child hops around on a pogo stick.

Describe the energy transformations that g(k v*7ytj bzwr 3/rf2take place when a skier starts skiing down a hill, but after a ti*k( yf2/w7rrvb jg 3tzme is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of hei( skl-q mva; )o/ekaa-pbqb97ght h and slides down. Does the velocity at the b/a;bqa-opsqe9mabk)k 7 v -( lottom 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:qi oa4il:svi;h82al a e1rh- to step over a fallen log in their path rather than stepping on top and jumping down on the othe::1ohiil4 ;a2qlha v8si a -rer side. Explain.

Two identical arrows, one with twice the speed of the+.1i4 gcnon zu other, are fired into a bale of hay.+n14g .inocz u Assuming the 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 swinging pendulum in terms of energy, (awql;34 tb:s sn) ignoring friction, and (b) taking friction into accoun4:s3nbwqt ls ;t. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebodixfm )+/f i4,too t1mund to a height greater than its original heigh ,tmmi xit+4ff od)/1ot? Explain.

Suppose you lift a suitcase from the floor to a table. The work o7h:vyw eh 88yhz:*emyou do on the suitcase depends y:v:87wyh zoe*hh8e mon 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 weight of the suitcase?

Repeat Question 22 for the power needed rather than the work.p 3pz1wp l ;uo/e)aij(

Why is it easier to climb a mountain via a zigzag trail than pmr)(*qbgjm,r j h/v-to climb straight u / ,qp -vmjmgr*h)rb(jp?

Recall from Chapter 4, Example 4–14, that you can use a l4y f)8u jev5kpulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter tj ul4v85ye f)khe load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg v c0k3etxnm mic0 8h:2pile driver falls 2.80 m? kv:8 2 30thc0cnie xmm   J

  A 65.0-kg firefighter climbs a flight of stairs 20.cc8sn,o sltl:mq+; , p0 m high. How much work is requ so+8 q, n;lmtlps:,ccired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at constow4rl+z: :lx +buu5ow ; mq+o:eou(wdant sp:+ul(4q:woe r oubzwxl;o+ om5u+wd: eed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers d6yuwiy: z ,kf xc4u*rv5z1vz8o (horizontally) pushing a 160-kg crate 10.3 m across a rough floor w*,cyzu5z 1yk wvz6v:8xif4 urithout 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 formp ks5+x7, 0yiysuub k1p8r o, 7.0 s. Find kp s8+1xs 0ypmuikyub r,5 7o,the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flata08 poe:q/s gnzfu o8*jug4 2ucem8 w3 on a table. How much work is required to stack them one on top of anm a*oe usuew2:z 8340og8jfqn8upcg/ other?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects w2gp58a m oalh-a7i 3yie might not other5oyip aga8h2a7lim -3wise 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 downex )v immp d76;h szik0d)1xf( a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (F vx)(izsf )k6md ei7d;01mphxig. 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 givn 4fkwx1w0:g3 skg9 lfe a helicopter of mass M an acceleration of 0.10 g u 0w4gw: 1skfxk ln9g3fpward.    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 a) yek l-dtv:..d rluwws n(h4;xis 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 along the x axis, varies as sho-qkv l8jj j;c:wn in Fig. 6–37. Determin :jck8jl; v-qje 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 a particle ahn1rp o7 si. y4g*vrny s/iaqq3k8/ y8cts 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 - lsuy14vm8/e,om8i tv* pwe qoxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubl1dab 9vn( mr ybqk5m9o:*mvc.ed, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electron kb0chg75xx p xhm+1.,s :sirt$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kgcaj: q lcwkb130t2g2bzi r traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strinves )9 xleay)agz /n-(3i bkv,g exerts an average force of 110 N o v9l (s3-iaxbvey)z, /ge)nakn the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travd00zpt2c ;wxw78i g5/u:ou nvea tt(neling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glove?i nzt8x7w o(vg2 ce :0/utw;t u0a5pdn    N

If the speed of a car is incrh bd;0(n 3f rl yx;x;wo6wyc,seased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ign;w;rxc;xob,(d3yh nylf0 ws 6ore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark/)nsq0v 9eh gk 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 th0nk e )hgqsv/9e 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 pi b; zrl ffxs-fu/*n;u3tched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate thb*uf3x snu-/rf;lf;z e 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 sebung7a23a y +omeone who does 80.0 J of work on ity2nag +au7eb3 ? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m verticaltmw/ybl:plcphu*o e (qt*1e pb1y3/u ;zl a4*ly with an acceleration by a single cabl 3muey/:l */z 1u; *by tlp*pqalohc1tb4ewp (e. Determine
(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 r5by tq:;.dthlw yx *5must this spring be stretched to store 25 J o5dly.* w;rqyt5 : xhbtf potential energy?    m

  A 7.0-kg monkey swings from one branch to anot ff+md ev6d1i, m0mtv;her 1.2 m higher. What is the change in pti;v ,m0defv+d1fm m6otential energy?    J

  By how much does the gravitational potential energy oydrl4+p);u6fp4 t eg f-s5zglf a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the y ;d4 eufp+t-fs 4glg5p6rl)z jump?    J

  A 1200-kg car rolling o ll5*k -zdadupig z o..x19si,n a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constand-i zsll.zakd9ug o.*,1p 5ixt of the spring?    N/m

  A 1.60-m tall person lifts a 2.6k(zy e2 +guwz10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book z(e2wuk6 +gyzrelative 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 33009km2i r jt8rxfm;f0d8-md098x;jrt mffkirm2 8 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 vertically next to a ruler. The end of the ssuj /0mt1g:l wpring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is nswt/ml 0:gj1uow attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top y(q 4b7b ri3ydspeed (5.3m/s) and grabs a vine hanging veidby3rqy (7b4rtically 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 downwk b gqd88v(;e 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 shove up a frictionlzo6y mrvy0e/kim53.myp 03 ah ess 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 gravitattq 46halhwf,+su* b+s2e jyys1)klf 5ional 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 ba5 tbs +6l h4f* 1yyuhjwl)q+es sfk2a,r with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward 0eh46*qq3jaztp4sgn9ohr ;i from the top of a platform with a speed of 5.0 m/q p 9tjh*4ogqzianr03; s 6e4hs. ($\alpha)$ 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 constaa* awj, v5by+vf; s,ornt is 950N/m is attach svaw y;b*+5vr oa,jf,ed to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without frictip9j-jfbm;6k k on 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 (whob -m jkjpf96k;se radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spqq6c-5 u. lduhring (spring stiffness constant k), Fig. 6–4-d5uqqulc6.h 0. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee corvvt nt2rj1+;w d whose unstret21 ;tvvnw+tjrched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster ca0+k gbh6klss +gx r))rr shown in Fig. 6–41 is dragged up to point 1 where it is released frrsr h0)k s6xk+ )glgb+om rest. Assuming 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 speedkats5vwv; xo b+:)3zc4 d;e yc 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 botekt:7i j9c*4 s cs la;uc ;5ea30dwjrptom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the valst5 a;j9eur c daj3p;0s7lecwki:4*c ue 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 cy c 7qwid)*cm; 2dozat+:oop 4ycle 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 tz cs *h4;zob(.z5hmain)fgg4+ nxx7w raveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energob himsxzf.5g z(cn7) 4xw* a4+gh nz;y is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a sli( ; e(kb,ycnexde 3.5 m high and reaches the bottom with a speed of 2.2m/s n(key;,(b ec xHow much thermal energy due to friction was generated in this process?    J

  A ski starts from rest an gmrohu5hd( 1 4 b6apuv:fd3;wd slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 )c-tkepswoo2 9 ,bs g+m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height is0h nqk+ 9g/tof 1.5 m. /h kqi+nt9 gs0
(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 axpj)ifw x3 s.9x6 p2gzgy 3ym5 constant horizo)2s95f3 wxm.pyggxx iz pyj 36ntal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pass1kr9, h5qjxzm fg( i(tes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance tra,9t (1gx fmj5qhki (rzveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foott grj bc 8)1-0. 2ntsweo9lomq 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 c )kxcsobj(-9nf d vlw2k5 9z u3-fu,zx:;dpthorizontal spring (k=180N/m) as shownw ucn;(b9 5 vtjd9 )ofkdpz lsx3 kz:x2fcu-,- in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attache7q;vs y y)( .m6hwpf,pdjkzt(d to a very light horizontal spring, Fig. 6–40. The block can slism6kf. dzy) jvt7 wyhp,; ((pqde along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the h,dyw2 ifn)r2 space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resh2 ,2fywi)rdnistance?$\approx$    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 rn-)9p;uieo xq1 ( v 7: 8ky(acusdatxmotor to lift a 315-kg piano to a sixth-story window 16.0 m abov vtcu- i8x(:;apa )9(7exnkqur1ydso e?    s

  If a car generates 18 hp wh:o-py sit kc//en traveling at a steady 88km/h what must be the averagek p- cyto/:is/ force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What f oy93 bz.g+utis the average power deliveredzyutb9f+ og. 3 by the engine?$\approx$    hp

  (a) Show that one British horsep709fy t7rwxj bmz 8;u;guq -ahower$ \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 “kilowat8 il03ev vh kb(5sk mzbj0q*r0t-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 dn* 2vd q,+gvu7mcz82 ped6gx to 65km/h in about 6.0 s on the level when it is in neutral. Appgv*c2,znu8 7 dem 2qv+ gdxpd6roximately 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 szsz;aa*n 6su5)yh k4n.z3b o in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s I6ifrll 8j5bj 5w* -xu7eg 53p4fsmxw uf this motion takes 1.5 s, what average power 76jmr5 l*sw fwfgubx 4e jpix8l5u35-was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.(r1tqoz3 0n gn s+pen;z5sqs2 wf/tn,60 m. What output rating (watts) should the pump mon+r ,n nqzo1(sq 2zg3n pt/0sefst;w 5tor have?    W

  During a workout, the football players at State U. ran up the stafl 9 x. uucrdy iqv1+j2w 7klrcxp9s*+tta0)3dium stairs in 66 s. s2vrw+li.c u9 c *qjtp)xu d+k 3yf0l971xtraThe 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 cli:8/warh88csk 6qy clbmb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power outpukdvcl3rxj 76oy61s7u t of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional f7 1 okjrs cxul6376dyvorces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box alongmnw5f;;b:kgtk p 79 gvlsf86:phyog6 a level floor at a spw l6y;kf of 7g5g; hskmgv8:n6:9b tppeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts do3z j,mxj t+n1uwn 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) bumpe) sjq)e05wmhars” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring s)jaw5hmqse 0) tiffness 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 7 w 0+(pfjs rqkati8.jthe first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with asf .taj87wprjkq+0i( 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 Owensi 4ux cdo;clf5c n ik0ag4m9b nk/-t5-’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center n4mco/dci4a9fk; gc5l 0-5i kb-n tx uof 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 in F50 n,wremy)oymudbw2 / cl -4rig. 6–39 is to remain on the track at all times, even at the very top of the loop of rab4u r,)yd 2r0/ wmcywe5-onlmdius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hp7-.q9bbk vzwzr n13 kis parachute opening. He landed in a snowbank, creating a crater 1v1 pqzzkkwr9 n-b.73b.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 horizontal cord of length L whose other end is fivj;)ovhwnmy7 .l)z;m :je e2 hyg2ze7xed (Fig. 6–ew ze.7onmh 2g);ly7;2z e m y:hvv)jj43).
(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 mountain9ixoa2c l- om4. The climb is made in 5.0 h starting at anl-a429co xmio 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 whea*el*l cu+ gx(n a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,00fdcvv ,(.y2qi 0 people per hour. If the av, iy(cd.v2f qverage 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 ve 5 ua- u*w3lnm.o9aluay 4pb0qrtically 81 m before striu50-w l4 . lou*3auambqa n9ypking the turbine 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 (F);bh1k c xnl5cr80d7zexn/czn )gl;kig. 6–44), the difference in your apparent weight at the top of the circular loop a0n8cn1g7k);;)z xkd le cr/ h5bxznlc nd 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 5nxk2d226gmmx o qh7sm0n-.tmtmh v( directly into work, how high could an 82-kg man climb a ladder if he were fueled 5 vgh2t7.mdmkm2htm0oqms6n2- x n(xby 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 anglka4m/+j aq9 xms4t bx0e 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+bsvxrm 6d)r. , the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 .mvr)d +6x sbrN. 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, and swings ort33oryihvxprn(b* * bo x ./9ut over a lake (Fig. 6–45). He releases the rope wheo*yr p3v(b x rx/3*nrbtoh9.in his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m n,sl+*jkbdh17gsas4tg8ev ) in 9.0 s. g8s +ags41bsvk t* hd ne,)jl7What minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water ist 203y)zee0vk h zgg5l pumped by reve05et0 ek3yzgg)vhlz2rsible turbine 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 half. Whac3 :lkmg34ubiykk,nq( q j/v rq*c1b3t is the spring stiffness constant for each of the twomr/lkqu3bnicyv, 4k:bjq *1 g(c3k q3 resulting springs?   k

  A 6.0-kg block is pushed ie*ntt4f,j ( b8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate frojmx 7 g 8w;7hv lm:uz5gkvcb/6m 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the 7w/x ;kub mljv:g g576mvh8zc power stays the same, and neglect frictional losses.    s

  In a common test for cs ,)d i3rq,bhsscj l z./3d/cqardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6/l/r qd sc)i3cs, h .jqdzs3b,–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-k /gm5 lvjg;wmaj50 r)ig rock vertically upward a distance of 500 m, what was its velocity when it lefv i;a 5ml0gjj 5wrmg/)t the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a zfo9 6g8 ev2m;mbntz+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 powerzn +2bg96moev; fmz8t output?    W
(b) What is the speed of the water as it hits the wheel?    m/s