In what ways is the word “work” as used in everyday language the same as that grwi1g6y qsa nxnhtm.x4;; ++ defined in physics? In what ways is it different? Give ex4; nyx1 .ig6w xatn+g; hrsmq+amples of both.

Can a centripetal force ever do work;wgk wa.5gm2 i on an object? Explain.

Can the normal force on an object ever do work? Expbt d dvsj,fo k43tdybuc.c0c ,j5 j-,.lain.

A woman swimming ups uo az:1)m9mzwaw tb)thn;*p 7tream is not moving with respect to the shore. Is she doing any work? If she stops shmuzoz baw:m1 a9n) ; 7p)t*wtwimming and merely floats, is work done on her?

Is the work done by kinetic fiirc bpn6 uv2:7 g.4juriction forces always negative? [Hint: Consider what happensiujg.pnbu6ivrc4: 27 to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid lg1c1;fyo :w (wi xrylcpp6)7 wall even though you are doing no work1p r p67w(ly;gxfl wycc)o:1i?

You have two springs that are identical except that spri;cvjuye(wme 4i (sjesr11 5k) ng l is stiffer than spring ;m411 e()u i(5s krcjeyjvesw2 $(k_1>k_2).$ 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 horizonnc z84nkr *)gntal force on a block that is free to slide on a frictionless surface (Fig.6-30). The bloc4rnncn)8k*g z k starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change u 3- f5yy4ismnhcl;(bwhen you jump as high asnub h-f ; c54ilymys(3 you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all withd0. u uwb9m m,nw0a8 we51gv *uectkm5 the same speed but w,ubt 95k00vc1d8wemuenwu *wma.gm 5ith different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lo2t-qxyy2 *xnkwest 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 pe- yynt 22qkx*xndulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If 7 .lr5nlqgr+wa/qo7 c you compress the spring by pressing down with y l/+roaqc7gln.5w7 rq our hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the cq*z6j q06ltagpd ;bo2eiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. Tqopl 60d6g;tz 2*jbaqo avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential ee l:i*xtmu* 7mnergy when water at the top of a wate:7t*umm* lxeirfall falls to the pool below?

Describe the energy transformations when a child hopagft -+g;f hv2s around on a pogo stick.

Describe the energy transformations that take place when a ski *6;1nzagbsb:lgk0 0 tfyhhp fb-x0.ier starts skiing down a hill, but after a time is brought1 ;0:h h-6ibfgn0x t.z*b gkay0bpslf to rest by striking a snowdrift.

A child on a sled (total hzaoe tq cy9tdfhq--q1lr48 ,/b,s+ bmass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no t- +,dcof/h,4y8h bq1r zqbesa lt- 9qfriction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a foh y* qa9;ybz(bwx4 1gallen log in their path rather than stepping *yyobwazb;9q4x gh1 (on top and jumping down on the other side. Explain.

Two identical arrows, one with t/r a8:3) eosqxd pw;oxwice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower ar/8eodaq 3; )rpswx: xorow? Explain.

Analyze the motion of a simplldc zh zp9 i2mq; 42vc79zql0xe swinging pendulum in terms of energy, (a) ignoringp9hq;l4 md29c z07iczx qzl v2 friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can :.q pf*lnwjx7t0 re)b it rebound to a height greater than its original height?b )qe*x7l:.nf pjrt 0w Explain.

Suppose you lift a suitcase from the floor to .ekb;2c vl:5fth ii0,kym, aia 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 thibf 0;yiv2:h5k m, .kei t,acle table, and (d) the weight of the suitcase?

Repeat Question 22 for theede o.r(h7*ac ;wxl 9x power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straight h0gt-n7soyi csa4 8rfx,ub34w u9yd ;u4u4 x70h;y-d, 8oacns uistby39frw gp?

Recall from Chapter 4, Example 4–14, thatnz2f, vmd 4g5v47hbv g 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 be pulled up? Account forvgnz bv4h2d 7,mvg5f4 this, using energy concepts.

  How much work is done by the gravitational force when p8r(eq -8obfi a 265-kg pile driver falls 2.80 m?bofq -( pr8ie8    J

  A 65.0-kg firefighter wwo4ypw;b nm+n ive,7ox)3 -eclimbs a flight of stairs 20.0 m high. How much work is requirn;,v+3xmoowen 7 yp4w )-iwbeed?    J

  A 1300-N crate rests on the floor;3);faa qm lowle0c h9. How much work is required to move it at constant speed (a) 4.0 m along the floor against a f;wf c 0oha3;9e)mll aqriction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do 5 ,n/ :j dl6ddt9fidmf(horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50? n5 dfli/mtd9d 6, :jfd   J

  A box of mass 5.0 kg is accelerati0;:cb-fan sb ed by a force across a floor at a rate of for 7.0 s. Find the net work done ocibb0 n;:fsa -n the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How much xst,zjf4 f8 7ocym53e womyt34, o5f xec8jf zs7rk is 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 wj cy0vf p3e: t)yv wlin7woaeyg5fc) k09o(89e might not otherwise be able to liff. Show that the ratio of outpwi3c5 p weyctykv el)7fyf)n8a9 vo0 0j:g (o9ut 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 downb*eljebiy,xy + 9,n ownu6,g ( a 28° incline and is kept from accelerating by a man who is pushing by y6(nn*uw,l j9x g,b,eoe+ iback 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 required to give a helicopter of masse56jur f)p6 )gpcms07r ph 3dh M an acceleration of 0.10 g upward. )e6pu c phrgsr p 50)7d6hfm3j   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 ann7a- q c40k;3qug 3 l0drpgp +sqwl/lnd 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 ) j xjc( wvr6i6v lmunp2c pe;r0;y)-zaxis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x ;u-n(z6vjvrweym p p0rc6) 2c) xil; j= 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 rk vo/ 52u8wbqacts 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 mass of9v+c58n 4tvwhiz e -3ba xyu9u $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed incye-e ;wvrw- lb* t-uhd p4jv*r.gn.i ,reased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an )h 5t fe0jtnvts3sy a(* +zs6bicaj1 /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 zig 7-i0 0sr:ob sd*mt105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force 8v,5oh d mip 3iyv-xg,of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves thh y5vopv,g3-xmiid8,e bow?    m/s

  A baseball (m=140kg) ktgc4 cwkva zd+)fe 1o-( )sj;traveling 32m/s moves a fielder’s glove backward 25 cm when the ball is ec w-g ka )kds4z1ovf;+ctj)( caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50% mzgfx ,fal*:9rkek;i xi ejs2: /np,/, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reactirx :p;g ln/ : aj2i9ikfkz*s,m/fx,eeon time.

  At an accident scene on a level road, investigators measure a car’s skid mm9u gzkd3 8wr-ark to be 88 m long. The accident occurrekm8-9 dug 3wrzd on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg i bkn i3319tybhg* zyk*s pitched at By the time it reaches the plate, it may have slowed*bhtgib1z ynk3 3yk *9 by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kc uf,*:3mwk59kppggnwe tw8 5 a q7-pyg rock go if thrown straight up by someone who does 80.0 J of work on it? Neglectntk5w358 wcpep*ukqwg ,9f7a: gym- p air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelerationx qhi9 iw os3(9d8ii9c by a single cableiq8x9h iw 99id s(i3oc. 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 440Nl bhy/.x, 8ioz/m How much must this spring be stretched to store 25 J of potentia lh8yzio.x b/,l energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wha nl77e3*e ttdst is the change in potential energy?d*7tese 73ltn    J

  By how much does the gravitational potential energy of a 64);-mma,y wadmkz:-q8o( l iop-kg pole vaulter change if his c yo:q ,mad(ak8m;o)p-z liwm-enter of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontaupu;6kg)3 yi bmex5z 0l surface has speed v = 65 km/h when it strikes a ho 3 u5k xgb)y0;umz6eiprizontal coiled spring and is brought 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 frome4hb u dqx7zfv 0 v, o)cpv4)q/6kkx;b the ground so it is 2.20 m above the ground. What is the potential energy of the 7qxkx q, ev/v kbcv;p 4bu)f0)zo64dh 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 16i3zyl0rd ;9 bo00 m and climbs to the top of a 3300-m zd3b ; lir9o0ypeak.
(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/msvqsd eqjh( hv575p+-sajz9 8 hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line upjj7-+p5v 5z8eq9a s(hq sd vhs with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs 2 *x5,unp g f mi)p+ypqnf33jpa vine hanging vertically from a tall tree in the jungle. How high can shf 5im,f*p+ 3xun2n p)j qgpyp3e swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides8:r) ql3us 6 . xuohpjt**wwsu 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 shove up a frictil z 8hfs90bp7tonless 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 trxt2/nm j, ei9/ wqcz3z7 bzphkd+4qf )ansformed 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 masxzhp3tk+ qq4 9n,fji2 we )bd7zz//mcs 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticabl1m: m q43 gfqu3i5xully upward from the top of a platform with a speed of:5mq xum3ubfi 3l4g q1 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,,n ia gtjso80 its mass), whose 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-kg ball whjt0 a ,8n,gosien released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown yq*chvow76b g 3p,: ue0k2unik c+nk,in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h myhbk2 ,uc36w0k nu i+ *7, qpenkog:vcust it be released?    r

A block of mass m is attached to the end of a yexs56xmb/b1j 2c9dl spring (spring stiffness constant k), Fig. 6–40. The block 1 x5d6/2c 9lesbmxyjbis 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 cord whos2 ix.xh; xe)kge unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee .ix exhg2;)kxcord, 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 toqr: *z4-f+6hmror fh g point 1 where it is released from res-f6rr+z*hq mg r4:ohft. 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 sp qwkdcs 2sro);hjq:/ 3)f k(tseed 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 b v+-n zga2tc j 7bocd18w,dtv02dz0yq e placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h aboveywd2 g tdbzdj70vn 82za qvc,t+-co01 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 kpp a p q*.syhlfaei(ap0i.0i o*66m ,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, eacqokti2ir e0nya 6w7/behw; -(h of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal entre /qbwa70- 2; i6hn (keowiyergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bott6pnbn5 ,mst:uom with a speed of 2.2m/s How much thermal energy d6n5m,btp u:nsue to friction was generated in this process?    J

  A ski starts from rest andva y v..x: m5sr.baa4r 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 fu1a *4 i.tnhzh6w-vzmg an +3rrom a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2./xvd7 9gitb 2q1 n-c u7z4epgy0r mwat /b/j9n0 m, and it bounces back to a height of 1.5 mba/bc r-n2tt g019ipn7 mg dv/4jw7 u /qx9yze.
(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, k/nbc i4 t0nn0xj6co mmirca 0:3.f)cis pulled 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 friction is 0.30. What is the3 n b0m 6:itcnmcck4r) 0xna0cfji/o. final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 t * 92jha.i,h/ldyzlx ao6st:j)7y iab 7gu7b with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach po/ 6 a7,)z*yl o:7xyi 2 .slhtdhjuagjbb9t7iaint 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot o4 /z sux hjpb/2arclvw(1: am)f 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 2c +: mgrdlm) +d*o;bix,skfpvery 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 reldr+mcops i;fkm,x +d: * 2)glbeased, 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 to a very light horizontalku3ob;ir; ; 7w1krbua 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 thuak13o; w7rb;u;bki r is 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” (;),8 fxa+dfmj)i- bi alvk5aq 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 200kkm8qd+i, i5xv);fjb f -a)alam/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+ 43 p2 feffw/ow(2xxtfdywu, a sixth-story window eyw 4+f3tf/ f wfd,x(wuox2p2 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the av2y:nn*k 3lpxw erage force exerted w:*x p3lnnk2yon the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whawioezy+2*d7arg ya2) t is the average power delivered by the eng zy ia+yor2a7)ewg2 d*ine?$\approx$    hp

  (a) Show that one British horsp*a qfcuze-n1 fr9(f w:(8nkeepower$ \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 expreso)rx7.yu 3pl tsed 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 a,q 1+p9d7qh p (v;mrxitby yy ;snqx:0bout 6.0 s on the level when it is in neutral. App0q;nvxty;rp ys qhqm9 x:(y+,i 7p d1broximately 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 ywoe(al rh j. mb+0r+8do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerat,(hwyc:qa+ w yes a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 ayw(y,c:hw q+s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3a7c m5bgk r)e8, a:wxytt w ,myi6hr7-.60 m. What output rating (watts) y ,,77:a8gm5rat bkw t6rw-)eimychx should the pump motor have?    W

  During a workout, the football players at Susdggn76w(h5l4 pj e5 yz)kx3 tate U. ran up the stadium stairs in 66 s. The stairs are 140 m long and ipg h5 )gu54le(s63nwxyk7zdjnclined 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 climbud i5ptk88 9:- qhiyts a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. w)0yxbvg0had 5xw.du w++ t;gHow steep a hill can it climb at a constant speed wu.bgdyx5t) ww0v0 xg+;h d+a of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower6num*+evh su lvk31z6 must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coeff3vhkv se6z1 l6m n+u*uicient of friction is 0.45?    hp

  A bicyclist coasts down a 71f*him/ u g-aj.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are n- ku3uzt1t 0hu lr4q(designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid t4unl1 q0rhzt- u(u3k wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the. f kz 5/.au2gtlyymb9 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 a height of 21 cm, and an average shelf holds 25 books, how much work is requiragz2.yb5y/f tukm .l9 ed to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Oly5 r9zo yl9( dd 6tva:1uzi;idfmpics 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 if he was traveling at 6.5m/s at thi;9 f6u5zd yz dt9 dvl:r1(oiae top of the arc?   m/s

  The block of mass m sliding without friction along the looped track sho zta *h ognd +x*hp,f+9*b/rolwn in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius r.txnpa ,/ob*+dg*9 rhzh +of l*
(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 h7 zkp0 aeo-r e*uo;6u370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor inj6z0 rae;ouuk -eph 7*ouries. 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 i; biug xc9i :n4ry2ytd:lqp72s fixed (Figdcq put7i:9:bynx42lr yg;2i . 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb izak:r i088k6dd brp2jv:l-vlh: h8 wago7 ty:s made in 5.0 h starting at an elevatioy8p8h7 : zgwoa:llakhvtjr d-::6i0v r 2bk d8n 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 spr5pj+ k9pt pf)g*d2vnring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 Ca 4waj*8twwu y) n,;utplifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (; wt*naw,)84t yjuupwvertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the 0: f+nv-fj k gvkh*/tgo.8kakrate of 650kg/s and falls vertically 81 m before striking the turbi8nkj:t+fgv gfav./kk-kho*0 ne 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 los2wyd; ijw5;gvw ; 6wlmmv,blv .d(xw;t7re 8op (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your v7; m2b(jww;ty5wg6m;d irlx8 w evw ,l d.sv;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 bodyc/ y r:ef+9gxw could convert a candy bar directly into work, how high could an 82-kg yr w9g ec/xf+:man 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 o 4s 5 mlv5 yue/j4.s3ay+tzfk:wuf2bif 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scalufjo4z l o2fp2aq/ 3aec z56 6zqyg07qn w6px:e compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what d7go4z6qop5 qup/ 6 l ajfacxz3 fzeqw60y2n :2oes the scale read at its peak?    N

  A 65-kg student runs adlv)s)+a+az ct 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. +sc)zdal)va+
(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 in 9.0 o*f* 2e 0/gndgigcrk/s. What minimum power output was used to accomplish o/ng2dg*/0ke gr *icfthis feat?    W

  Some electric-power companies use water to store9bcewmjwoww2. )/ g b+ energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 1jcm /b+bowwg2)e9w.w 20-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. What is the spring eub8;)w1)dwphn2d 8 ref ewqdz:,af 2stiffness constant for ea 8hwp; e) 2edfab)n,qfez18w2r duw :dch of the two resulting springs?   k

  A 6.0-kg block is pushed 8.z9c d.vd9xm 2g0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35kfq zm1q 9 73jdmluckkd8, q99nm/h to 55km/h in 3.2 s, how long will it take to accelerate fm7f99qd3 qmd lu1cqn 8z 9kj,krom 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 patib*pvll8y1el8y+uwf)a .n g ( yent walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-k8vbweyl8.1 +lfy)*npy( ugalg 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-kgt)k -15dqerp hbp80f p rock vertically upward a distance of 500 m, what was its velocity when it left the volcaqkf p-edrp 50pt18)bhno? $\approx$    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 qj7 fr ty bnel+-d4k: xz(wof s,3*ce-a height of 2.0 m at a rate of 95kg/s (a) If this water whednl4+yo x ( e3qrffwbkesjc*z,: t7-- el is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s