In what ways is the word “work” as used in everyday la1l51ohhb2 j(5nx wfm d*ays:f nguage the same as that defined in physicdw5ja 1 fh2n x(o1 hyb5s*lmf:s? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an ob.r)d+4 wvjw4g,im8 l.io; dtdstxue. ject? Explain.

Can the normal force on an object evukhaw3o4i ;nrd0z12aer do work? Explain.

A woman swimming upstrexg,oigf49+0* t i iqdcam is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on her? g4*90idioqitcg,x +f

Is the work done by kinetic frictz 6sv:sx. 7*cj :*d wi7efmudfion forces always negative? [Hint: Consider what hadz 76.xsc*f7 :wuvies m*: dfjppens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid w e51pwc2 x4mvo ;o6wkwall even though you are doing no wopm v6w2w kc 4;oe15xowrk?

You have two springs that are identical except that springkp yvnon bv+9u,ad;;6 zg2h0 y l is stiffer than sprpv2 +0d a6y bn;gh9kvu yn;z,oing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizonhhj9(bg2 p6k 9unfb5;5pfbpptal force on a block that is free to slide on a fricgb5bhpp;nb uk9 5fj2p6f 9( hptionless surface (Fig.6-30). The block 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 potent.* uz3yuhco*dzhqb 7s+xpdo)b *4 /0mr/p vehial energy change when you jump as high as youmpq 7s+ he/z/ huxbv b rd4o0.ohp*z3*)*uydc can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all an n+qlg6t 5;k,4bmdfwith the same speed but with different launch angles. Which one has the highest speed onlngk,t;+q5am4 n b6df impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poinw;f3:xuh recb)h:qxy6f( u2 yt in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will causxe r6 ffy)u:2(cwq3:hby ;uxhe it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright/c *z7jv f6sgb on a table. If you compress the spring by pressc6v/ g7z*js fbing down with your 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 ceiling by ag5;b/v95eau3odcho bjn z.5 m steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to red.jv nz; ob5eu/5gc o5mbha93lease the ball without pushing it. Why?

What happens to the gravita2a*luq): +hpmpwsq s- jj3too/bc1-ytional potential energy when water at the top of a waterfall falls to the poooqpm q+j*sjy-3/lhp : b )1o2wsu-ctal below?

Describe the energy transformations when a child hops around on a pogo stick1,t43r.fpfr, ayr omn 6muulo7* :guv.

Describe the energy transformations that take place when a skier starts sk, c-p.i oz vux g6o79irst2t-d5gpp2jiing down a hill, but after t6g9r2-pisg5p 7 z oxv,-2jpd tiocu.a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) st;m: qf*xjmqpbezz/: ez. d+(tarts 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) ij+ .zf :*db :p/emq; metzx(zqt is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log -ecwqz :: 8zejxiu+2uin their path rather than stepping on top and jumping down on the other si-:iuw juze 82+q xc:zede. Explain.

Two identical arrows, one with twice the /y)7v5pvi9xnfsp .cy speed of the other, are fired into a bale of hay. Assuming th/p xyfv)isy9n75p.cve 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 swinginbk +4b9j3ad c bi;z /;qhsfo6ng pendulum in terms of energy, (a) ignoring friction, anh/3fb kiqz; odjb ;a9scnb46 +d (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” isjf2.ko8h9 9i ann-: pwpiz(lp dropped, can it rebound to a height greater than its original height? Exiiokf(:-2w pnn .l89h9 jz papplain.

Suppose you lift a suitcase from the floor tcm+4 1h4tuim iiwkg+4wxz ct 688 :xboo a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) theb+w 4xwu6i t1 k:tccmx+4o m8 4giih8z weight of the suitcase?

Repeat Question 22 for the power needed rather than thc mtq;3j7w;nra.h ohxhk baj9t0/ o.1 e work.

Why is it easier to climb a mountain via a zigzag trail than to climb str/tdm s2kp o jln 7c-/u(l*cxw3aight up?jscw(nl/k3/m2ct*l od-u xp 7

Recall from Chapter 4, Example 4–14, that you can use a pulley and rpu(rg vwe-+r7 qjal):opes to decrease the force needed to raise a heavy load (see( jrlwg7ar +-p:)vuqe Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done m l99* boy(j 2ye1d uz33liessj-3hazby the gravitational force when a 265-kg pile driver falls 2.80 mb9y a 1ji9l2deh(l3-z yumzo3*ss3 ej?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is.9kmrss,h1 9n5js f uc bds;l /tna8t( requirsrks. u( t9n,tls5m;8/ dn91hbsf jaced?    J

  A 1300-N crate rests on the floor. How much work is required to movebtj+y7vgz / s+ it at constant speed (a) 4.0 m along the floor against a friction force of 7/st gzjy++ bv230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers douvio/zbvh:-l)av p,v8 e riw)s12+p p (horizontally) pushing a 160-kg crate 10.3 m across a rough floor ww + 1p2ervb)lhv/,vup:izpv) s-8oia ithout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated bf5- jtwsv u*x2n brcl4j,;)iby a force across a floor at a rate of for 7.0 s. Find the net work done wx -2vb;u,c45j* )bjrftlsinon the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kgaxa vf52 9/aj2hdz1 xw, lie flat on a table. How much work is required to stack them one on top of9a25h wdaxxfj1/z v a2 another?    J

A lever such as that shown in Fig. 6-35 can be used yvb5a9 o8hc d9; urp8kto liff objects we might not otherwipb8o 9v9hkau5 r8c ;dyse 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 kepv8z;aec1x*i ed:oul 5+zgli 5 e6s,o:b d po1ct from accelerating by a man who is pushing back on it p6e 1z:eupgll5d:*o ce 5 z i81bo;s,io+vxcdaarallel 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 mass jyl65u z1ddo+ spsi1.M an acceleration of 0.10 g upwarodsizl1.p 5uy1+ s6djd.    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 vyt2x1dolhh; h0* r bn6n1q f5axis 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, +(qn5ahh4-mc3f mh oc acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force ocnm5f4h+ h3-m(hac q 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 particfue- e9jn+fa; iff8+ele acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygegg5*c)3j p epyn 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 doubled, byl4e(t2x2j okw/o wp +-ngkb+o(yd(u g 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 ikurw 90pi)v/gdz2,dh*l5 ny*i cox+ 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 tr0y)-1ph )wja npiw fm6p w6)ixaveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exe9 8ltu6jhix* frts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrowh 98*t6fiuj xl as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32jmtu w3pc23 1rvp-wse09 e4+ cvx*tmpm/s moves a fielder’s glove backward 25 cm when the ball is caupe*c4m v-r30 c9s wxmt+ w3vpu2ejp1t ght. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor wkpa4 ah3 i890. xfetb+n-)kbzzrf2puill its minimum braking distance be increas8zka bakxp0p teinb24fu3 +h9z)f- .red, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid /38d 6akg;tm hzqdmi; 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 m dkag8zt;q;h3/6 mid (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass ofta gepjdhow m)fo :vvw iuf3 tz1,:c9 (;86vz: 0.25 kg is pitched at By the time it reaches the plate, it may have slow91 if3cpe zu h6wga, d:v)( w:ovmtot:fjv;8zed 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-kg rock go if thrown straight up by someone w o pi l5c1na8-jpg72pnho does 80.0 J of work on it? Neapn7 85pg 2n- jlcpoi1glect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically withc5(7q;iyrt:dtn s4 )yiyt g do/ v:-i-hihrc ; an acceleration by a single cabldn5(:s- corir i)tti; h:t dh 4qiv/yy -;7ycge. 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 stiffnecnt ) klu5ds -y;hlp*po c+)j(ss constant, k, of 440N/m How much must this spring be so+(j ;htncll)5k)d*sp-y uc ptretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from onpet;jj w1r5 *se branch to another 1.2 m higher. What is the change in pojpt*s ;5jw e1rtential energy?    J

  By how much does the gravitational potential enet,/h,tg/z e4(pbsh6* u8l tzrf smu(orgy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m duringz( l,b/uer,(shgof th*6 /sp4ut8ztm the jump?    J

  A 1200-kg car rolling on fhrbbf1 v0;b9jty58m a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to8bytfv 1 9; r5hb0bjfm 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 frobb;9:vrwng+ kugw :j/e(6adjm the ground so it is 2.20 m above the v (grg w:e;ja:wd/ubnbj9+k6ground. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m pjw9x7tzr73s and climbs to the top of a 3300-m pz wt9jsx7r37p eak.
(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 verticallu4j dmxwvi:e3(s+ dc5d2gnp7 y 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 lindd352pi(gwc : jm xnes4u+v7de up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vin,u9a9 rgg v2lne hanging vertically from a tall tree in the jungle. How high can she swing uv9gnragl9 u2,pward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides downljr;7 u vsq+2muwen3 9 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 givelv;ozh94w+ .da5 conxn a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitati*qv8eggk82ji h;n 8v tonal potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s. 8k;h i2v*eq8nt gjvg 8   m/s

  A 65-kg trampoline artist jumps vertically upward fdse fdtu8 u(h937b -3fomztb)rom the top of a platform with a s(z3 73u8m dhtb- e )b9sftdufopeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness coqb o8r, .friqx+ajj30nstant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can 03r8.ibxq,r+oj qjafit 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 fhpz )h )woq:r*gc9vk. riction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the*:qpgh .wv)ho k)9 rcz top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached t)w qaf* cpr9uf+)g3x qw9so/u o the end of a spring (spring stiffness constant k), Fig. 6–40g9)rwfo su u3qqc*w /f a+p9x). 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 cord p:rw/ nzu99x.j, qiei,acws4a(5hb zwhose unstretched length is 12 m, aq,p/nj59awwxu, bc 9e4ri i. s :zz(hand 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 whe )frb x*xjbf4.re it is released from rest. A.r)fb j bf*x4xssuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angq*th4f bsi6e; g/y;3(i bb pcvpo p0(lle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom o;8ber70a*jhbya.s uzy1 + hofc*5ossf an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no f; c0 +syh5urso e1ao.b7*aj 8ys*hbzmore 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 7.8 io cy- g m)um9c6k/.vx$^{\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 a1 d(zbdbsjp )l:sk hx5c y-:l6nd traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision?-d6 :bcxs)jdys :5lpl b (zkh1 $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a y tmeh/d2yn hbypb:b 9 *73rn0speed of 2.2m/s How much theryth h*ybbr 2 e9yp:nb7 mnd30/mal energy due to friction was generated in this process?    J

  A ski starts from rest and sled,54nn 1wbfj ides 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 droppe1mav pqx rnjx y03fb3/5be2lp4zh-k3d from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.5 oxb l)/c 0mwo)m./wb)cl0)xm oo
(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 fgha 9ps8v5670zdiob hft( 56 e/nvaubrom rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionasd ztu(o7he bf 90nvib5 g/6p6hv5a8less, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes ef4xse-sq8:uu)304*w iyxwbm v blm4mp3 dr7point 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 poipus 7* vms4l w4xfb08d3b-xey m)ruq4we :im3nt 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reacheo.e6 ckqp5:hn2 w8ze-qg 9 obvs the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attago),dn rwu;;v8 9 umcbched to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table? vucobm n;) ,9g8w udr;  

  A 280-g wood block is :oqr(mya0m* l)bvo u.firmly attached to 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.q0( :ou*vbmram)yl o. 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 ea,ih623mg j4ban2m e space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally me4, ajbh6 mne23a 2igat 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 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 1w ic s,uk8xp/*w8woz :750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m abov pu88sokx/w *,:zwcwie?    s

  If a car generates 18 hp whenbyarv99q3oe u3 kc,.z traveling at a steady 88km/h what must be the average force exerted on the car due to friction a bq3c.uke,9 o9 3rvzaynd air resistance?    N

  A 1400-kg sports car accelerates frol plb9n9)xy,o*5z2b ;kd ra kem rest to 95km/h in 7.4 s. What is the average powern); 9kl kz2db,o*5 9expy lbra delivered by the engine?$\approx$    hp

  (a) Show that one British horsm)jytd)9ld s, epower$ \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 343qy mdlc:nwc0c5 ypv1sm ,p 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-k/w9oqk lt7 yb q2w8pp/g car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a const8p/t w 9wylp b7/2oqqkant 75km/h.    hp

  How much work can a 3.0-hp motor doqxx; 31k0 oqdvzdv /04f(o); vlqpbck in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If e:+qh 5d(vzkb this motion takes 1.5 s, what average power wb( e:q+zvkhd5as developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m2p3 6ak(rdj3b85u xh)ju jrj;wl nkt0. What output rating (watts) should the pump motor hav(kj;td6nuh)ju3pbwr 2j 8 035 rlk ajxe?    W

  During a workout, the football players at State U. ran up the stadium staip fgjmtytk0s(+(l vk c 4k*(.1m7pwlers in 66 s. The stairs are (*gltmj0sl v( 4kc wppkyt1+ e7(mkf .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 c;1x)zcw a pq7klimb 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 :jo q4: sw1nzlhp. How steep a hill can it climb at a constant speed1:z:wnojq ls4 of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor jn7u3h t e.f-phave to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.453pfu-7 neh t.j?    hp

  A bicyclist coasts dow3k qku(zm)8 t e1xst1i9f1err n a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/ n3h3i5 zlv1e2lgwaqi9xr5.vh(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently dwiv ziqn9 .l3axr23 1vlgh55 eeforms 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, 6sr7a1,z9dfhl/ gcunb ok c)8and the remaining four shelves are each spaced 30.0 cm above the previous one. If the avera8k 1/lnzr6gohfu) 7,cs 9 dbacge book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Oly. bp-xc0 r7a bdeb(7nx0x7ic pmpics 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 abbax.ppc0c nb-dx e( 70xi7r7t 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 alonvh/cxto nj:tby*1 ,d ;g the looped track shown in Fig. 6–39 is to remain on thy bn*c1xv;:,otd/tjh e track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 3706i4m-vyc4 dey ,o (imh 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 injuries. Assuming the pilot’s mass was 78 kg and his terminal veloc44vymo 6c mdh(yi-,eiity 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 fixed (Fieu7df s*7qj9h gq*7eu 7j hsf9d. 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 (711s z) cucjj xpx0) ;q+ufax8jacew mountain. The climb is made in 5.a;xfzxexs)8+q p1 a wu( )jcc7c10 jju0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge sp9 t/qb e1 gydxqw2mf/6q1bsi(ring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 peoplefmf3a; fii2/ w o:6ruq per hour. If the average lift carries people about 200 m (amu6iwi;r/f3:q2 o ff vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the raerb7ncf*axr pdblov97* 29 5jte of 650kg/s and falls vertically 81 m before striking the turbinpar9olc b*rx7nfv9j*db52e 7 e 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 (Fig. 6–44), the*ni- yr mz, .m9h-vxn5.bvooa difference n 9yoi* ovax.r.mvhbz- n ,5m-in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, ho kar + ex;qapy( sl,94cpb)n)ww high could an 82-kg man climb a ladder if he 9n p)c+ lykp(xqs,a rw be4a;)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 fired7. 61q6 a35ixni cpxkx vp3fli at an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroomfeslopq /pko tkit, 41,.xs13 scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height lq1opt s oie.4k3xk/st,p 1,fof 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and so m9bd6 h +,5oz f;jbh6.wfnlwwings out over a lake (Fig. 6–45). He releases the rope w wfwh,f6djb.z96o+ lho 5n;mbhen 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 7ut(( 5 6ez//3syu1 x jeuoyspf2-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimu((tu/1 yjypuexz3 6ssfeu/o5m power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Waters/9m-v/bp qd m is pumped by reversible turbine pumps from a low to a high reservoir.pvq-d/9sm/ mb 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 c11j *9 9mhiinh6(cmi xv:z hckut in half. What is the spring stiffness constant for each of the two resulting spri 9 hhzm in1 (*:19ckixcvm6jihngs?   k

  A 6.0-kg block is pushed 8.0 mnra -ua+5,zt7sk-of b 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 35km/h to 55km/h in 3.2 s, how long 6 f7,f20ov.k,hica o ieekbv:/a bb i-will it take to ao2keav-bcii. i ,v,b7/h :f0fkb 6eoaccelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “strcg3f2tb83sgdf *i )ud jcs/k /ess test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an skb3jsdf /*fd2ucit)/cg8g3angle 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 upex o r0tcio8y70 rv0w(qpz 7j7ward a distance of 500 m, what was its 08rzriop ctjoe(0y7 wq77xv0 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 from a height of 2.0 m at a rate of 95kg/v(tb 258s6aymdw.c fbs (a) If this wat. v (y85cd6af 2smbtwber wheel 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