In what ways is the word “work” as used in everydayv l.e)x-5ipqp0qzeli u8 2pg9 language the same as that defined in physics? In what ways isepq8zgq.5i-vu el0pp l2xi )9 it different? Give examples of both.

Can a centripetal force eve/n*ak mp a2swu516n6ys)v hgfr do work on an object? Explain.

Can the normal force o0(2f2j cdhkxfob p g-9n an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the sk3r+g 6 eevre/hore. Is she doing any woeervk+3 e/r 6grk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hin:0vaku* zlyow,k5.v2k1i pipt: Consider what happens towplayki 1 vzi: k0pkv.*2,5ou the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a sochk6 vjc(,:w ilid wall even though you are doing no work? cj:ihw,( 6kcv

You have two springs that are identical except that spring kyrnk k:w 6hu(gfr2lnt8.t,/e+ 6 jojl is stiffer than spring 2 2r6ojj8n +/rhtn :(yk,fk k.w g6tule$(k_1>k_2).$ 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 if1gt p*u. i.ja block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A,*.ii u p1f.tjg 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 :+oe w(m pie/ rxz1pf5when you jump as hi(/1xpw mf +pir:ze 5oegh as you can?

In Fig. 6–31, water balloons are tossed from thg3doqq d:(8 g7nqb. ure roof of a building, all with the same speed but with different launch angles.dgrq ou: 3 (b8g7.dnqq Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched fr+/ 4tenj 5ydna (rsz8uom 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 trajectory. Which launch will cause it to swing the largest angle frsz5j n8aunye +/d( t4rom the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring by - 9ma hk)wb nf(2 uif*uucyv,.pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of en9i2yvw( ,f-*kb uu umf.nhca)ergy.

A bowling ball is hung from the ceilig ccx4o+h )u8 buxy4n0ng 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 the inyu u hcxc8on4+0) 4gxbstructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when wate4yupdi9 z5 1sy6pyo 0br at the top of a waterfall falls 5 y0sz41ioy6 ubdppy9to the pool below?

Describe the energy transformations whh9 wkwg-7vv s h9v)wkwt:+lxym4r0.i en a child hops around on a pogo stick.

Describe the energy transformations jr4n(- k ay2 fsi o3yamu:k*k1o7yqa3that take place when a skier starts skiing down a hiljk* n7kfmkusa q( :a 3i2-3ryy1aoy4ol, 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 wop5o:j+ho o hwgen +b12s1 p,of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (pp,:5ns1o+1j+owohe2h g bow a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log0fcn9y (sr/ bu in their path rather than stepping on top and jumpins09(n/crf buy g down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired inmplv.dz-2a 5bto a bale of hay. Assuming the hay exerts a constant frictional force on the arrodlb-2m pz v.a5ws, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of enecq/t,fp bovu 1 9nm)w:rgy, (a) ignoring frictiof,)u9q/ bnco:1w pmvtn, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound if jvw ev. i :f30 s7vpbah;a99,xp7zsto a height greater than its origina9 fw;z3bia 9ejvfi07 p7vhvasxp ,: .sl height? Explain.

Suppose you lift a suitcase from-l +gsc pw* )wdee(bc/cp)02iw j)whu the floor to a table. The work you do on the suitb/ecs c2-j(pw) *wcdhiwu)pg wl+0 )ecase 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) the weight of the suitcase?

Repeat Question 22 for the power needed/ow0yg9 ,aaq t rather than the work.

Why is it easier to climb a mouhirlw.zr:b6n 2*gx9cqj :sfs : 5zig5ntain via a zigzag trail than to climb straight up?nb *jgrir5zch5lg .2:i:6s qfx :z9ws

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes tong5u 3c6n- ow-zgcu2u(yzd7d decrease the force needed to raise a heavy load (see Fig. 6–34). But f52gcd-g nu( -u 7ydun3owzc6 zor 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 the gravitational ujh 55subqm, ltyo7*jwh 0n+.force when a 265-kg pile driver falls 2.80 m 5l o b,jqhus0u+.jhw 7m*n5yt?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wor y: p6o)zmr:jk 6vrhf,k is required?j :zvypkr6 mr)f :h,6o    J

  A 1300-N crate rests on the floor. Hoyohhz/7k n* phv,m,r2w much work is required to move it at constant speed (a)k7vzrhh2,/ yp,m hno* 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movd()xgj;y*7*jpe 1zlmh pmyp .ers do (horizontally) pushing a 160-kg crate 10.3 m across a r1pj x** jyl;m d z7gy)m.e(hppough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratedv *zi a,(kv9jauz30edgt1 1mo by a force across a floor at a rate of for 7.0 s. Find the nio 1dz,*u9(vmz ae1k3tjg0va et work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tableq 0b9 fcy*pf*.x.yoh e. How much work is required to stack them one on top ofxhyp.*c9f. 0 yoqeb* f another?    J

A lever such as that shown i, bl1 k0 itb5)wwrwrb*n Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force, ,wbrwrt 1l)bk*i0bw 5$F_{\mathrm{O}}$, 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° inb1tcmt2crp;-a 3*,b s ul2sslcline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The -3l ;pr ssb*csca2 ltbtu21 m,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+ gs5bzwpqu3 a0 .ont-s:.g cm to give a helicopter of mass M an acceleration of 0.10 g upw:gsu- t0 sp +cnwo zb3a..gqm5ard.    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- 2rdf0z 7 a1umy9gnbf is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, bx-r hozc 2 z(oy)0o+zvaries as shown in Fig. 6–37. Determine the work done by this force to move the obxz by-c2)ohz(o 0ro z+ject (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts in gl-rn l,updm;,ycywh. . x.e 9the $+x$ 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, wmg hr02sx)xb ,ith 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 fac0vqdpy1 u/7 n8,km jwutor 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 electron7h4:bxfct / dd $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 (o *zi cwb9zl jb/f5z+sz, 8ic105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averagejp k(( h,ayhy+ force of 110 N on thekp(a h+hj,( yy arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 253ja3 , hoqr+oihx)wh- cm when the ball is caught. What was t+ ho xq3o w,h-h3j)iarhe average force exerted by the ball on the glove?    N

If the speed of a ca s jsdf.:l-d*ghq8*y mr is increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore : slq.hgfj yds-d* *m8the driver’s reaction time.

  At an accident scene on a level roakrgw vg9dnpp; i55(g )6nxe8 yd, 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 doexpn gnp8;y5id(k 9r)5wg6egvs the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at B,x9t,qro,k g.bnhg y;y the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resisn ,.h 9 k;rqtbgy,,goxtance 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 who does 80:w/2c um:w s7bnleq9 l.0 J of work on it? Neglect air resistan:qwsl2 nb9c ewlm7:/ uce.    m

  A 285-kg load is lifted 22.0 m vertically with an anqi+ho-70 yi blor j6-u5kv .icceleration by a single cable. Determine k-h iyrb 765 .u0j+-vloii noq
(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 constanes):)b tvr ti+p 49 wg.tdqfl 8*7zpdot, k, of 440N/m How much must this spring be stretched to store 25d* z.9+qf4b8 tso)) :pwpv edtrtgil7 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to anothkjmrhgnpmc 2d 7d41/9er 1.2 m higher. What is the change in potential e2dpj h m 941mgc/7kdrnnergy?    J

  By how much does the gravitationalam1w-r /so3xk potential energy of a 64-kg pole vaulter change if his center of m s/-xmak3o w1rass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizon h*rvudve 73bn.9r-7tnskj w:tal surface has speed v = 65 km/h when it strikes a horizontal coilrj -7*rwst97nv: b.hdn3ek v ued 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 from the ground so it is 2.q mhgj0fbj (1(;8c.sszhjzz+20 m above the groub+1(zgz(zm ; jj0.j8 sfshqc hnd. 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 and climbs to the top of a*/6ioic g:2s5o2ta+ughr-yru .wngd 3300-m peak.h . *i6sct2 yo:-+g25nrwur/uiog adg
(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 ke2c9/rj i0a )i5ukhv 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 scaei2)/hk5j0 ukir9v pring line up with the ruler marks?    cm

  Jane, looking for Tarz aossikqc5r17 yx:1zo 2-x ;kqan, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall treoos5ra y7: qq z1i;1sx-2ckxke 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 fga4 4a3 w29tt; gg.d lsuk:astrom rest, slides 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 frictionless 2 .f2+c+ /(fmh jkdkqzs8.0$^{\circ}$ 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 transfo(u h,+uv 8it uv qkvl8c3zz52ermed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her ceizu5u8h q( ctlveuk8v2v , 3+znter 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 t.il (9igsupw, op of a platform with a sp i,(w9 si.lgpueed 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 (i8;wphqs v. q:ggnore its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 8.w q:svhgpq ;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 the looped track shown in Fig. 6+inp2x+8pvux0 rr; mq–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 must it be ;xv02irp+p rnum+qx8 released?    r

A block of mass m is attached to the end of a spring (spring st x 0 t/x/(eelr3b-necgiffness constant k), Fig.0rcn(lx /b ee 3-ge/tx 6–40. 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 jhrpd 6f t*,hn/aku7yl,n w4o g0hd92yumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calcul hda0t/7*p4dro,luk2whgy9 f y, nn6hate 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 d.4hn1xl.+ knrzp (do Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming .p knhl4d.ozx (nr+ 1dno friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throw4i0shb-2n/jzs hv h(dn with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the n;d/pab.74ub j g 4ep (inc/yebottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the 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. dn/p.(;gjb 4ipeanbce4 /7y u Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyc,y kf/94hmwwz 0a6bs8t v, vejle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite di ds*oz*uwdk5)rectionsd w)s uo**5zdk, collide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hig*vveog 2nwq hwwj)- 2*h and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was w-j** vn) hgweo2w2q vgenerated in this process?    J

  A ski starts from rest and slidy/vbxlem+rvr2g 7:h. c9pq4 ves down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m j lw5pb(/m0cyabove 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 bounca t*oq0 9i;aplge g/elg;g0.h9ha 9gces back to a height of 1.5 m.lhaa ige9ce 90gght;/lqg.p0o*; 9 ga
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant py6e gt* gqqz1wr,a+7horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coer+g67 1 a ,teq*pygzqwfficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of zy) c 8g36t+e5y;uko9ymi vtj If the average force of friction is equal to one-fifth of its weight, with what speed will it reach poiyetu8 ;9o5y+zytc)kg mi63 jv nt 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachg/eiklk;2a 5nes 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 ;k 1:c 9uvxfiwattached 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 c ;fk1c9:vw xuim and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal z)yfyuw3e ge/7 9yc;sspring, Fig. 6–40. The block c;s/7y)fz wu3 ee9 yycgan 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 this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space sh -pc:/nj36. xunitet ruttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have -icp6r.n etn:j 3/xtubeen 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-story w 1u25jyv 3fv5sv:myiyindow 16.051v2y53yfymiu v :sjv m above?    s

  If a car generates 18 hp when traveling at a steom av, bri(.f,ady 88km/h what must be the average force exerted on the car due to friction and air resistabvmfa,(, i.r once?    N

  A 1400-kg sports car accelerates from rest to 95km/h za/i gi+u-5d*m zy1wa; jl3wzin 7.4 s. What is the average power delivered by the enwg a1 u w/z+*aizy-jz3;d5 milgine?$\approx$    hp

  (a) Show that one Britixs ),;e(t,:n g+es q 5o0upz amprdws/sh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowa.xht;vh sy. e (y.le/att-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.0 d0.v j0j lvhe.6p pk w;5n8plzs on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a consd.zvkp hjv0 p5w l;08lpn6.ejtant 75km/h.    hp

  How much work can a 3olf1n9qt5v :e;4+j ilh wm6 oh.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14/4jfpdoc2c9fmws6.qg , cm),nuw ug- m/s If this motion takes 1.5 s, what average pon/m 4 ,wfu2g)9dcp .cgow j6q fmsu-,cwer was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per min tph;ugy-ec4 5/ual5 mute through a height of 3.60 m. What output rating (watts) should the pump motor4-pc a/u5 ;5gehtlmuy have?    W

  During a workout, the football players at State U. ran utcuvc8:u412wjt/t(v 1dxt ndpl* :hip the stadium stairs in 66 s. The stairs are 140 m long and inclidc:d:( hxu *21plt841nvtw/j tvi ctuned 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 cyclis je ii srq,-9g,y.qv4jt 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 12tm*y)a2:klk5 pk. vi2ob gt1 xw7bk.t0 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictiona2m:a .v op ykxb w1b7t*kt2 ki5kt.l)gl forces add up to 650 N?    $^{\circ} $

  What minimum horsepower m *zx,b 7wlbea4ust a motor have to be able to drag a 310-kg box along a7bwx*ze bl4,a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d ai5471 q9 0t.ehea8 etrehs.)uhm ijvown 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 buil5uq n 4msni;/yt “5mi/h(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 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, assumin;nym5 q4/i sung 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 gye0 2u .+u5l l 0w948r7ragjcbaxiloh round, 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 required to fill all the shelves, assuming the books are all laying flat on the floor tor7b g0j5y h4l89.w0r+ oilcaauulex2 start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in t3k g 8/i(tyl zpse ramnb0jc147jwr ,/he 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6 ge7acnr4ks1 (3z 0bjt /ri8/w,ylpmj.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopk a- m 9u5/zvui3bl)ohed track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop ub zk9 -/h3moul5iva) 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 aircraft withoud tsw t/ v;twr,,:qr2tt his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with qr,2; twv/,r t ttwd:sonly minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other endmuwd;f u3rq1 *3 pup1d(b5nb l is fixed (Fig. 6–3q1 d3 m5n rf(d*buu1b;ulppw 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 mountabdd, i91 n p.)u)rwwfnin. The climb is made in 5.0 h starting at an elevation of 2300 mudpb , dn1)nf9).wriw. 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 elevatogb h+i8e/3jy ivri2z /r is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47, 3-m6/s7e hc8iaw s7jrzz.kbt 000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate theh3 8tb6e7rz ci/-waj m .s7kzs power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate 50tz * b hygwe4 2xjv-*q/itlyof 650kg/s and falls vertically 81 m before striking the turbine blades. Calculahyyzvbgtt05-*i/ qw lx4j*e2te
(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 ci42*eld o)q dbkrcular vertical loop (Fig. 6–44), the difference in your apparent weig) dedlbkqo*42 ht 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, how high cxe)yg. bp21qdx y,j:e ould an 82-kg man climb a ladder if he were fueled by one g.qx dej 1by:,p)2exy 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 6-batfmr1f5kz qk -//sk dd 5jat 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 bathroom scale, the spring inside the scale compresntp, 2j1v9zq/atrccr ac*wsd 9)7 ,ksses 0.60 mm, and it tells you your weight iv /)2csaqw1pt *nrt ccs9 7,9rda,zjk s 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope,rp72ftk1 r,gi -.fhpg and swings out over a lake (Fig. 6–45). He releases the rope whenk1r, pfh - 2ggfti.p7r 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.3z-g x6ljh kauc1)yq 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power outpulh qx6z ja-y1. kcg3u)t was used to accomplish this feat?    W

  Some electric-power companies use water 5s 7xt1csiqqvo 9 a2w1to store energy. Water is pumped by reversible turbine pumps 15w x2sq1 o9cvst 7aqifrom a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the sprin*vtsh3f+x+s hgvu 4z c(:ctw2 g stiffness constant fw42h vt:f( z+ h3s*tcguvsxc+ or each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a r; fy dh)6m 76hbznf0jyough 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 ac*i -g8wqd:6pxvw (bq gcelerate from 35km/h to 55km/h in 3.2 s, how long will it take tvp-8q d:qx i(* wggw6bo accelerate 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 “stress test”), the ptu 8l 8ukjhl+ zl46o,watient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the trea 8l8 w jokuhtl64u,+lzdmill 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 500v gqctp(j:7i 6-kg rock vertically upward a distance of 500 m, what was its velocg qjtv7:(cip6ity 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/zl(d 7i;qhf:pmq -(hes (a) If this water wheel is set up to provide electricity output, what is he:( zqf h-7l m;dpqi(its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s