In what ways is the word “work” as used in 8ad-no b w+)/ ee5y-w*mrw jzkeveryday language the same as that defined in physics? In what w*wz /obnwwrd ake +5j)8em-y -ays is it different? Give examples of both.

Can a centripetal force ever do work on an ob)n uvrtalx:9t)daph. -g6dtot f1 8u/ject? Explain.

Can the normal force on an object ever do work?gh*n5kjv (30zpdp9 axwpc93j56 r vjm Explain.

A woman swimming upstream is not moving with respect to the shore. Is she d m s9t;(k:gtvmoing any work? If shtm:mt sk 9(v;ge stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider whaw)5kc-p m2 0yvdz /xvht happens to the dishes when you pull a tableclo2vp-) 5vc/wkdh 0ymzxth out from under them.]

Why is it tiring to push hard against a solid wall even though vn l5g qg:v4b1wr-zkex+f6.k b1kp,w you are doing no w-61 w5bbf+ek1 wg kxv.lpq n,rv k4g:zork?

You have two springs that are identical except that spring l is stiffer j1bo1p;rfz,40,1s g h drtycqt k..o 4qw9kiq than spring 2 1yzd h41 co9qb . r4sp0tk;. ,,g rkf1tqiwojq$(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slsfj/3mlgws/ 0ide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by jgl3ws/f/s 0mthe 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 changeub 9+-xhfgx1x e8bumsf 3+l,mgo)3bxg-7gp u when you j1- uhe 3bgm,fbfgmxu ls+uo-g )+x7x3p89bgxump as high as you can?

In Fig. 6–31, water balloons are tossed from tdit-nhgwd--bx8 l)y ; he roof of a building, all with the same speed but with different la-; )8t-xlgn-bdyidw h unch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from*3egm7 g 5tcmx a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajgc7e mm tg*35xectory. 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 you compress the sprin9auwdrfm3z 4o/t9j z-ik 4ou 94q t:kng by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation ozt u/a:9u4omin jk- rd 4zw99k3fq4o tf energy.

A bowling ball is hung from the ceilinc *- ra1ggfwr5g by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury taw51r *ggc-f rhe instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at thz+yzoe16s z fw2/n*um e top of a wate/u2+z*zo efmnyz 61 wsrfall falls to the pool below?

Describe the energy transformations when a child hops around on ; gde80b jkpaw2:,ckr a pogo stick.

Describe the energy transformations that take place yrc 2hnn 9mtwv,5-,2,h j-yenoyv pd.when a skier starts skiing dow-y,vte ,ydy2rp.2nv c 9 o5mjhnn- ,hwn a hill, but after a time 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 o4 sd;p)l 0ixa(idxcwz 2e6;kof height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is frictp;zxe(;2xoiawl )sd6 0c i k4dion (deep snow)?

Seasoned hikers prefer to step over a fallen log 0xndp1z )qf;n:i v zvac.9r-o in their path rather than stepping on top and ju 9c- xz0 d.fi):na1pnvoqvr;zmping down on the other side. Explain.

Two identical arrows,a,cgf c d ;)pyo1d3g(f one with twice 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 po )dapg cfy1dc3;,gf(enetrate how much farther than the slower arrow? Explain.

Analyze the motion of a siml5 bg5-w/g 0gyabp9 jwple swinging pendulum in terms of energy, (a) ignoring friction /9-0agyw5j ggbl pb5w, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than itq: .6;sza) sf( ytkobes original hei:az.) qt( fko;eby6s sght? Explain.

Suppose you lift a suitcase from the floor to a table. Tl3gg fo af+.7bhe 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 timfa.3gfgb7+ o le it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the padqzs (6i kg vbaz47 0a 85r8braut*g/ower needed rather than the work.

Why is it easier to climb a mountain via a ziqo3qsgf.w9d xwh0k4 )gzag trail than to climb straight upq43o gwk )9qdsf.w hx0?

Recall from Chapter 4, Example 4–14, that you can use awu-dz:a:*sl8 w yitv uh) av,2 pulley and ropes to decrease the force needed to rai : tivw8:d, wu ly)uh2va-*zasse a heavy load (see 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 by thxja 6o19px x:qe gravitational force when a 265-kg pile driver falls 2.80 m?qx:oxx1p a9j6    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high.9 q)*a*gu i ynacp88zc How much work is requiranuaqi8c y 8z9p g**)ced?    J

  A 1300-N crate rests on the floor. How much work r3o0jd+q;dk 2ec*mivis required to move it at constant speed (a) 4.0 m along the floor against a frjo2c3e; m 0*kq+v drdiiction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hx0uwv,bdq9h2* r:hke orizontally) pushing a 160-kg crate 10.3 m across a rough floor withoutq: kvh hxe*wd9ub0r ,2 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 floord80 hz nng8a3oj p9q)g at a rate of for 7.0 s. Find the net work do 0onj8nd 8 )gqphz3ag9ne on the box.   J

  Eight books, each 4.3.dh)e /dpi2dj t)ypj+ cm thick with mass 1.7 kg, lie flat on a table. How much work ish2p j+.ejdp)dti)y /d required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used tapsy9l*e: t*ifotz h3 4j3*t w8ur( zho liff objects we might not otherw4oari9**st8(p: w ylzj 3z3ht te fhu*ise 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° incv.*:ahs140xm 0cz0pj jd*n evs-vhmh line and is kept from accelerating by a man who is pushing back on it parallel to the 0*djm1nscea0h- * :v0mvx.s4 hp v zhjincline (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 o2ko 11d/t8 wsuopuo0g5)kjr ef mass M an acceleration of 0.10 g upwa1tok2epw1ou8gu ) 5sk jord0/rd.    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 tvif-,fks6 sv4; sw r;tper 6)xhe distance axis 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:7hl4,45n *z kpqebg cw,pk ww along the x axis, varies as shown in Fig. 6–37. Determi 5bl4wg:wq 7z,kkpew h4 *nc,pne 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 paryo13ab pgfy,2 em88 ztticle 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,fixjt- uy1dy6e; s - ;l5 j3mj2s;wmgn an oxygen 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, by what factor has its sp(x-l:9lx t.)57xvfbwhurdlt y d+(dc eed 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 elect/+ds61x pihzy w63qth ron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 at0.6i hobt4 8anct(ti tc-rc: i 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an av vp1bjsv6 02e ue.pgz,0of ky1erage force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow a1p062bkgsyevuz. j, p0v1ofe s it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm w369c(olap p lrvke9jht 5j- ,vhen the ball is caught. What was the average force exertek 5 r ,(9v3he9tp c6voll-pjjad by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimumn wr:i s/d+* -i.krtq6diam2w braking distance be increased, assuming all else is the same? Ignore the driver.rn+w /ki i-rw d:6m*sqdti2a’s reaction time.

  At an accident scene q -g8+g8g7mjym,mrw1s 2st-j idh br4on a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s8 ry2rdj-81 gtwb,gq ih+ 47js-gmmms mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches th d5 );ypr1cteyi/4hz y+,jjffe plate, it may have slowed by 10%. Ne 5ed1y/jif,yp4 ycjhzrt) f+ ;glecting 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 someoni( uefi d(ip-:e who does 80.0 J of work on it? Neglect air re i (ie-pufid:(sistance.    m

  A 285-kg load is lifted 22.0 m vertically /fftpjlv1 m i5l slpg940d.9qwith an acceleration by a single cable. Dete dmf9gf5p lp40l19sjvlti/. q rmine
(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 1i hzco8.i:a pff(6 czuslm-o 5 sa7mmn9h8/ystiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energ/ao-suahf spmf5lm8( 7chn. z6y: m8 1oiz9ci y?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the *yrk/r6 q8i+gl cldj 8change in potedjglk8 /i86rr l+y *cqntial energy?    J

  By how much does the gravitational potentialf4 x6pgamq+:x energy of a 64-kg pole vaulter change if his center of mass rises about 4. a6g:xfqm4px+0 m during the jump?    J

  A 1200-kg car rolling on a horizontal zuyw8,j mk8 ug cu: d0zd/0nu6surface 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 constant of t 0zkgmj8dc0u u6yz n8/uw,d:u he spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book frvu31nyvtpaflkpd)*o5 /8eukf l+ / 6wom the ground so it is 2.20 m above the ground. What is the potentia ot 3udv/lkk afp)5lu/+f1yp nwv86e*l 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 yoxf..v6 uy(co3 vmo13 usn+k nq/2rtand climbs to the top of a 3300-mqkocmy1o n(.yrf+n3s26 u.v / vu3otx 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 springc 6a. v;re9et3c;ew*ny+ ovot 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 wv6ac3 .;*ctr9 ;+eyeovnot eof the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) a+eyd0v6 qdjxm)ore+ -7; gc svnd grabs a vine hanging vertically from a e+ edrvd 6j0; xmo)sy7cg vq+-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 down a frictionless 35llh+x,rj jmh i 8/2xc/.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 given7drg o4j i vclv5g(:gph0m yx,*m.qc ( 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 gravitxhlk- f50 kw2fational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in ox ffw52 k-klh0rder to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a p.brrcwv2 .d0 kzjz6+w iz/2 swlatform with a speedz.6 ir2vs. wk +wjb/rw0czz2 d 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 it3f)duydxem2n t6 4x ov2 1khj2s mass), whose spring stiffness constant is 950N/m is attached to a table and is covodjxm2kd efyt6 u 32n2x4)1hmpressed 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 friction along g18nfln .chqj2 j/:cmthe looped track shown 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 whaclnh m2:gc. /1jq 8jfnt minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness constan n+w)- otl+qcst k), Fig. 6–40. The bloqs+l)c ow n-t+ck 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 jum97uk60cjiu frhmhrzbh1/ 2p oxe94m ( ps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assumi phi9urb2hz m9ruhcmj/o 40xfk(7 16eng 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 pb7on gk1zzts 6u;a0i 9oint 1 where it is released from rest. Assuming no frick zzou7in g t;b60s91ation, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a tqbv 7;s v:wi.l/ 3p0uy -,n mnqy(jpmspeed 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 bo d.m o: xx;6o2qxkk0le placed at the bottom of an elevator shaft. If the elevator cable should break when the elevxo2 : dxqlmokk. 6x0o;ator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyc d(f8 il:0g8(dwg8nrg cfqcr zwim; 53le 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 massz5vk0yls-gn eov8 ,5c 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produzn5g0 8clov5y ve,- skced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wp6xr:swub bxhb.t/u . .6z;lc ith a speed of 2.x:x b zr../hp wl;us.6t 6ubbc2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22 1up2 al+byro l.s3c,tct1,kn$^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m abovug se/5 .y n-ve+dl5.i dqlg 3xfx69zme 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,.iwz *nm+bz-6nb yad . and it bounces back to a height of 1.5 m. 6 +wnyd-.i .mazzn b*b
(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 puz cv ik sj dr66y,+5jyvpld:))lled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the nextv:yjdvjs, 5d rcz )ykp6l+i6) 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coastezq0 d0(ls5quf r in Fig. 6–41 passes 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 z fql(u00q5dstraveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches *:k)rr bif-- gr,mfu w+l nix5the 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 attacheq yu0 py:a dv5r4i2*uod 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. u20:uyi ra*po5dv qy4What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block ilfbym pa- x-39s 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. If the spring is released from thi9- abmf y3p-xls position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glide21zd6ar (odkcr” (mass of 980 kg including pilot) that was launched horizontalla2rcd1dzo(6k y 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 resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-stok z-o.7j*ffecr4 x )ldry window 16.0 m abovezr*je .dl4)f x7ko-fc?    s

  If a car generates 18 hp when traveling at a steady 88km/h what9/n :;hna6l0 u(utdfi q r .lg9po,gvr must be the average force exerted on thl9l9(q.fvroa nu 0 ithp n /g:rud,;g6e car due to friction and air resistance?    N

  A 1400-kg sports car acceleratp24;fcc/zo r qes from rest to 95km/h in 7.4 s. What is the average fp q/c42ocz ;rpower delivered by the engine?$\approx$    hp

  (a) Show that one British horsekr285/wbi9xauzdu m he/q 0 s;power$ \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 ofg/dyd 9)zxwj/r+rm6e ten expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-k:(ua hq)2 1)hx kpullfg 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 :fuq1hk la2)l x )ph(uto keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.p15i h:mmpm5i0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from lxn.i0/ 4)dokl b z/xdrest to 14m/s If this motion takes 1.5 s, what average power was/ki)x. dzl x0n/l4 bdo developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height o r:/l ,tp/ixpbf 3.60 m. What or /tp x,bl/ip:utput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stairs i+)zhvr f)rug* n 66 s. The stairs are 140 m long and inclined at an angle of 3 f)h*+urz v)rg2 $^{\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 cyclx,kv;h b;c )xyist climb 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. Howtcj a3*oyauy 0qf69g7 steep a hill can it climb at a constant speed of 75km/h if the frictional forces add uatgcf*9uyj y0 67o 3qap to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg bon bddijxo,-om;t 23: ox along a levelodmx ,-obi3 njot2:d; floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dozi n. ; +g4rb o7u 8rhusjn;rujsl13:mwn 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(8k6py bv((r 2oegm/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 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 thevrg ey(bop26( 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, and thwu-b x/tw/ w7je 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 required to fill all the shelves, a/uw 7x btwjw-/ssuming 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 5cuwryjkuwrc m-3b*ps- )-- o1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at larjm5p uub -kw3*w-cr-s)- yoc unch 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 tracv*h.w ec5oe,d k shown in Fig. 6–39 is to remain on the track at all times, even at the very tod .eocv e,h*w5p of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircr(s7/ wwliz;h va/yy) fk0 .uraaft 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 te v0yzl. /7 u fy/kaih;)w(rsawrminal 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 fryt*xs 5e5)(i5 ir peis fixed (Fig 5pys55(ixr* )fetire. 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.bfe*) d3lla sx+uq) b; The climb is made in 5.0 h starting a b);blx3 e+sdla) *fuqt 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 j+0.5 6fkifgfj b*jww when 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 mo9kwjr; -olbo 4jn /h;fve 47,000 people per hour. If the average lift carries people about 20; 4-9w;rfoonh/jb ljk0 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 vertic5* pf4jxidyu0i f6d0kally 81 m before striking the turbine blades. Calculateij 6k4duyf* ipx0f0d 5
(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 (r 3cr) lixgoevke x(;v*9q/ h,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 *r(k / q)hg cxleroivx39, e;vlong 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 d1m0eorbo)z z 1hho -6hirectly into work, how high could an 82-kg man clim)1 boh o0 om1r6zeh-zhb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 43 muvlsu2) dme0(s.ku5.0$^{\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 6, d5dtbq( znc;,gma zscale, 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 of 1.0 m, what zad dn,,tq5 b6(cg ;zmdoes the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabbm(( f3 ywc5ru. )w5zl+mr pv,q3mm ims a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his lbvw 3c yr( 5rwp.3mi zm)u(m+ 5mfq,mvelocity 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 climxkq 6mmzlufe--- *,qk bs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomple kxfmqq*-ml z-u-6k ,ish this feat?    W

  Some electric-power co)wx,lzx;, 04wnu p bpfmpanies use water to store 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 120-Mx; z,u4p,pwl0n )wbxfW ($120\times10^{6}$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 halflrhnka*ezr */i1uh 4 ) ek;tv.k8*ydr . What is the spring stiffness constai; vd4k)rr uar.8eyhk1 nh */*eztk *lnt for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m k7 :zw xrxq1d;xnz61k6tm ew;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 o+. an1uq c8h 5dkh-naow gpsp-a ./k+will it take to accelerate from 55km/h to 75km/h Asun + 1nhaahgkwqk5+pp a.c-sd.8-o/ osume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patienti7 k/hs/w2rlt g tpx+4 walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whsgw7+k4r/ip/t x hlt2 en the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a dvn-rt5 as2 7mflud1cp, ;wb/jistance of 500 m, what was its velocity when it left the l7-d,u2 5bjmc 1fs p ;wr/vntavolcano? $\approx$    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 watuay ( uvccqh77z1s m+0er wheel from a height of 2.0 m at a rate of 95kg/s (a) If this whu y vz7u1ac7sq c(m+0ater 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