In what ways is the wou5q3( *o lnx/s lu-qfprd “work” as used in everyday language the same as that defined in physics? In what wqx u3 5*(nu/pllf q-soays is it different? Give examples of both.

Can a centripetal force ever do work on an objecj9k)a t g/dw h.gtl13:jt5sq ft? Explain.

Can the normal force,q q /;o6+6tuw:b;4deqo5 owcoc ghdc on an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doing jpo he 72+cxb(any work? If she jh 2 eo+cp7(bxstops swimming and merely floats, is work done on her?

Is the work done by kinetif /sgn,tpu*gw10vf 5 lc friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tableclotw 5gv*fulpf,0 n1g /tsh out from under them.]

Why is it tiring to push hard against a solid wall even t asqf,k0:ri8h hough you are doing no f0rk h8s,a iq:work?

You have two springs thaxl8lm9 eu*(;u7j2wx(gxj d ncsc;we6 t are identical except that spring l is stiffer than spring 2 jex7gnuc lu (l jd; 6*(sw8 ex2cmwx;9$(k_1>k_2).$ 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 constaj dxwmw2(91ua, lk6r:qig,lrnt horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30rwakmj u(rd2x19,,l li 6 wq:g). 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 potential energy chwfbita1w6 g2 k n.7f-kange when you jump tf6n.k7b 2w-g fikwa1 as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of *)pqhcwz)8 wm0tk enj j(r/y jzsr53:a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.w* h zpke8w srq5m)3c(jt/n:jjzy0 )r

A pendulum is launched from a point that is a height h above its q73a zqle-kr6phjo vtz. 5w--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 thov5 wz7tj6p-zahq q k-r l.-e3e trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. Iwe/e.t ( wcj4z3 w2uzlf you compress the spring by pressing down withw z(.ec 4utzwewjl 3/2 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 a steel wire (Fig. 6–33). The i*qvdk5 p vrn6:nstructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushin 6nvpdqr5 :*kvg it. Why?

What happens to the gravitational potential energy when gh6jnyz4*qrf)s 66 hvwater at the top of a waterfall fallsz *vs 4ghq h6n66jfyr) to the pool below?

Describe the energy trankqka /6 .swn-lsformations when a child hops around on a pogo stick.

Describe the energy transim* fw 6dg9b6i lyg0j9c)apc )formations that take place when a skier starts skiing down a hill, but jpay0fi6b9 6*mccgl)d)9 i gwafter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top offidj2eg dz *8lylm45, q/e1p2idx i3 k a hill of heighty,d 4 i*z m3lejx/f5q22di1ped8g lik 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 friction (deep snow)?

Seasoned hikers prefer to step over a fallen logf2kqc,4 fdq*i g wym )ix44b6p in their path rather than steppi q4 2i x),wdfifqcmk4y4g*6bpng on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into v jfg.+h*w zw/e+i4coa bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetra fo cgi/w+jh+ ez*v.w4te how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in 8npku4xuuu4twa20 v+ terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfawvu4nuu2+atp 8u0 4xkther clock has to be wound up.

When a “superball” is dropped, can it rebound to a hei:bsl0ca: 2t7u kuk)kn ght greater than its originau2n :ktu70): skal kcbl height? Explain.

Suppose you lift a suitcase from the fy ll d (cxrig;ga57+e 5wvo.)y*v gq9zloor to 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) the gi y (zex;ygwg* o )5c+lla9v7r5q.vdweight of the suitcase?

Repeat Question 22 for the power nee6e qtj bugswvz 7r)2)/ded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straigiygw6j); :zzd ht upyig;wzdj) :6z ?

Recall from Chapter 4, Example 4–14, that you can use a pulley and rodg t)q7;arq f/btxf4p1w1dp, pes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for everypx4 atwq/q1pdf tb7); fg,1r d meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done u ih49t9c ;csnv 7aw3bby the gravitational force when a 265-kg pile driver falls 2.80 mbh w3atc us9 47ni9c;v?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is (zy-ax kbek t25,d2(oh;f o1w ulivp1ld2j1xrequix1y1 l2jziw ao 2b ,x;p5ev1dtk(uk2-h(f dlored?    J

  A 1300-N crate rests on the floor. How much work is required to mov55bav- 1u-p mad j(el ;9o/ksz,7 bgctis:rzm e it at constant speed (a) 4.0 m along the floor against a friction force of 230 Nrzs vm ;be z-1lg5s ai :/9jo tc,pu5-(dbka7m,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushingj6z .d :5 bhx1,pgp/zfv8 ktmj a 160-kg crate 10.3 m acrosx6zjj p1:/ fdkbvthg ,5 p8z.ms a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a fojgbfbymiz; rmv b55 t;+/xw; 0rce across a floor at a rate of for 7.0 s. Find the net work done on the box. fb;jv/ imzwr +;;yx5tmgb50b   J

  Eight books, each 4.3 cm thick with masspbe h/, e5mnq/,vfwf 7 1.7 kg, lie flat on a table. How much work is required to stack them ,q,p75h wf/v/ ebnefm one on top of another?    J

A lever such as that shown in Fig. 6-3ke7xsipgul+, :hbz/2wic/d45 can be used to liff objects we might not otherwise be xibhedw7 ,lzupig+ / k42/s:cable 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 an7 z(1vf g6vdl-m *vgtk6 jfs(nd is kept from accelerating by a man who is pushing back on it parallef(*dntj16vgs g(-kzfvlv m67 l 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 M an acceler..a bpl0anm2 *6sf s4xl)yhel ation of 0.10s n .xly)shpe4a0. af l*6m2bl g upward.    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 kk o/hllnk )04hw/-m)lte 0yrdistance 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 along the x axis, varies as shown in Fig. 6–v; 4df7 uccy:q37. Determine the work done by this force c;quy:df c7v4to 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 oijohs/r 6tpk/ 9+-bhun a particle 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 oxygen molecule, with mak*nrbtr r i(2 .p5ipb+ss 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, bk 5 n4wy* c-9+qngv;fcrhi b/1;q vlouy 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 z v3nb90ilmp0electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 f)ka, rgapq2rm3wpqq+(u)0v 5v v8iq105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 N *t. l1 6otglfje 5wdt+on the at+j 6ewd5o* f.tt l1glrrow 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 movesemgnz0,f+,6z 8 cga a0jweoq( a fielder’s glove backward 25 cm when the ball is caughg zg fn6 ,+wc8z ,aeje00(qamot. 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 c: yebplj 39.9*biif0oiltl - factor will its minimum braking distance be increased, assumingi9:0co b3-lj fyi t.lbe *ip9l all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators ukbflx03x0 + hmeasure 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 lockexl0f3h+kux b0 d) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches the 2zvysn1n.;g8 gn)eclxy+s1 eplate, it may have slowed by 10%. Neglecting gravity, estimate the average s;lg182n z s vne.1yynxg c+)eforce 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-dvswtb- zntot 8+*xkic -v2 .8kg rock go if thrown straight up by someone who does 80.0 J of work on v*vt8b. +t ixsc2-tkodz8nw -it? Neglect air resistance.    m

  A 285-kg load is lifted 22g7u s7bb 8b7mks8 d*wf.0 m vertically with an acceleration by a single cable. Det 77ub8m8*f bsg7dk bwsermine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How 6o/h .n2v 2dzghqv+fetwr 3l 2much must this spring be stretched to store 25 J of potential energy? dft/h r2e 2zo.hwv63v+n2glq    m

  A 7.0-kg monkey swings from one branch to another 1.2 m r1t:tsdup /1t+nl7euhigher. What is the changue p171r/ stn+ tdt:lue in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vault 3e35ynrf tx(zer change r t5yx3( zfe3nif his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontaltq6n2f. be z) e1uyikk x/j.7h surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the sprin /kftiy ..6)kexnq1uj7be2z h g?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m above so,b duuf1 f/./kc7fmthe ground. What is the potential energy of the bo,ff 1ubod./ m7fs/k ucok 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 oaks8 *0f9z .cge dgv8af 1600 m and climbs to the top of a 3300-me.0safg *8 d av98ckzg 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 verticallrois77 a8w-nmy 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 of8-wnsai7m 7 ro the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runningjq ernbnr9wog1u:zx -6 4qx.0 at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwa0zoqre1q: nu9x 4nw jxgbr. -6rd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fromc:.(b j/qny tr 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 fricti9;hfm c0o(d(w/gj4 x el.x *zgl6mfplonless 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 tr6)r6bk3d lr:ieb yh9lv . ;hrwansformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a spe ieh 6ky39.wl6rbl db;)r:h vred of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticas3.,js qf,r ee be+tq*lly upward from the top of a platform with a speed s ft3e+js,.*rqeb,q eof 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 constant iy(:aj1m.2re fs 2-k mmi h*svhs 950N/m is attached to a table and is compressed down 0.150 m. (a) What *k.rym - m s1hm:fvsaieh2j2( 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 a+9 roi tyi7b.05 gtcmzfy9 ,falong the looped track shown in Fig. 6–39. If the block is to remain tzoy.7fc0yr9 bfig,mat 5i 9+ on the track, even at the 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 to the end of a spring (spring stiffnessef4ur 5 d -inas26zlp3 constant k), Fig. 6–40. The block is given an i5rs6f dziln2 e p4a-u3nitial 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 fr( sh 7lm9/ *h sepsdfmkfy56q1om 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, assuming Hooke’s m lfh6h1/5s7pqs*m d 9 syf(kelaw 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 q.4.pmn qf9lpwts;b,/4 sw qpdragged up to point 1 where it is released from rest. Assuming no friction, calculate the speedpq.s t4qnpmb9,qf sw/;p w.4l at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s9ny(/:zxd n gn 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 pt8w c5m8*fj5(/eqjf vidg:m blaced at the bottom 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 accelera:j 8f5d8q5e gj*witfvc/m mb (tion 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 cyiddq,iq5 ;3y g9fok:ycle 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 travel3aij ym e:t v84;wag+cing 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this 3ji:v ta4 w;y agc+e8mcollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descend3 /:ev/ yv nq792-lct(atqk q *vwfsjbs a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to fr /*e:ftaq- cvny v2/kts9lq7wjq 3vb(iction was generated in this process?    J

  A ski starts from rest (xgtdz 3h/9gu(1y4 ayfk m)wmand slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree jwjnr6fa(z*kc , .3qz 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 b qf.ox6eqws b.b +,8wbounces back to a height of 1.5 m. obswq 6w8.fbxe +.qb,
(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 pulledmlh /j;h yoj+(.ys 8bu across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. Wha( .lyy8s/ m+bjh;huo jt is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6 f u 3g,025qv5 ivp:a;qfay8r ghpewn9–41 passes point 1 with a speed of If the average force ofq yg958wnarp 25p3eufgi,hvva q0f :; friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the iou-:mq+/de i8b7:ms/ 2 y wpfua6cn gfoot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light h cxih0ejynv s:fk23qa6 +0+uxorizontal 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 posit 3+2x:0kqcaejfyu 60s nvh +ixion 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 spring, +mi28+ug8w;m o)usoic m6i-kbt ruy8 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 this position, how far beyond its equilibrium position will it stretor8wi umc6 m8+o ikiu s2 -guby;)mt8+ch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mas hsr+-;4ezxsbe k2x0.k rjqm -s 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 200sm-xeqhs;+4e k .-jrkrbx z 02km/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-stormz41;pv -srs2a(u j9u*grw biy window 16.0 m abov pw4zv*us (rgsr -u2jai1b 9m;e?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be th0 j*+co 44703ufk no rqvhbhfde average force exerted on the car due to friction a3ub od0+4orvjq* 0fcnhh4k7f nd air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h iixnfm2e9 5p2z(ssj*tu e 2f.mn 7.4 s. What is the average power delivered by the engine?(2f2 xsfj *esinztmp952.mu e$\approx$    hp

  (a) Show that one Britisr9a(x0 fvbv h9h 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 “kilowatt-hoursy*h* fnor o.0kyyt d,7.”
(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 slowsdok(zyjh pu 4 0rf7q /b6wpi:3 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 travel:/63(kpbqyzhfu4wp0 d o7irjing at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do i x4t*36gs9lu3i lvdpj n 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kgg4dn)yap9y1agi;pm p7 .hx ,o shot from rest to 14m/s If this motion takes 1.5 s, what average powe1ao n;gxyp7) ,gp9h 4ydpaim. r was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heightg-c 8ywh,d+f. .hnci c of 3.60 m. What output rating (watts) si .fhgh-wc.,8 ycn+dchould the pump motor have?    W

  During a workout, the footbaljv9ph 3mxr av5+k5lzr+w0:kd l players at State U. ran up the stadium stairs in 66 s. The +k kz h w9 :vm+5xrjr3vp5l0adstairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist c2-ebdjzjhj 90g7dpi 9limb 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. How steep a hill can it c/rk7 j,v8ad;qa pf60p uh-gvslimb at a constant speed of 75km/h if the frictional f07sukj6fag, v vdq;r-8p ph/a orces add up to 650 N?    $^{\circ} $

  What minimum horsepower mu7ky 8):tindkp st a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient ok7iydt: kn) 8pf friction is 0.45?    hp

  A bicyclist coasts do*:sb*/hvxwz8 qy kat lm,aa:8wn 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 hav obh y))/*0vbkle( wfse built “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 vb/ he* s(of)bwy)l0k 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, and the20diw ioaj6 3e remaining four shelves are eac e3o0 ii6jadw2h 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 to start? $\approx$    J

  A film of Jesse Owens’s hn v;+qqr-;/ k5aadkjfamous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch poinv+rqaj a/-qk nk5d;;h t to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m slidinww9 8xud5y16efi. gfbg without friction along the looped track shown in Fig. 6–39 is to remain on the trac59g w.i1 x 6fdubfyew8k 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 370 m after jumping from an aircraft withoutt )ha3/iih, jm 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 a,ma )/3 jithhind 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 ;pa;vsjokog5+4 cm /4kljriqk;+8 k ha horizontal cord of length L whose other end is fixed (Fig. 6–43) / kohka vsr4c ;;+l8j; 45jkipqkom+g.
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is madei9ulxcfrdwd 6 s-5 :3y in 5.0 h starting at an elevation of 2300 m.syfw-cr lu356 : d9dxi 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 2y(r0jtf, )3q(g tocwe 8 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 47,000 peo7m2 8ibx v1pthn.:rl, qj et-ople per hour. If the average lift carri eptjtiqr l-1x,27hb8.n:m voes people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m belucc:j5*v1 v(;pe xb vfore striking the turbine bladb l1c:5vvcx p; (juev*es. 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–chfm.2y u *s tpt4.ig/44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your spee*g2h/y sticp. .tmu4 fd 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 convert7*tz n aq1poh5j+/tlb a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000k*j+ pa/tz ot1 q5nl7hbJ)    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 at9ydc0 k bh+h4smihe0: 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 sprr;;bgfsgd5kw9 ut wq7a o.:7 uqw0 2yying inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the 02 wguay7qw grq59y k7s wu;o;.bt:fdscale 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,by,5j ))adla z and swings out over a lake (Fig. 6–45). He releal),5y) djabz ases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg v6k4g5x9wsbif 2 s*wjathlete climbs a vertical distance of 5.0 m in 9.0 s.jgs 6 b5*k2xf9 vw4siw What minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water srjcs5.2qss+x zz7 l)is pumped by reversible turbine pumps from a low to a high reservoir. s x75s)qj.cs +2rzsz lTo 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 st/vh sop4ctxtsq)(da6s(z *t0 iffness constant k is cut in half. What is the spring stiffness constant for each of tt h sv*(sx t4s(/6qapod0z) cthe two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m upm 1c,m q*6/ ,ej fivy:vkxap1x 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 tj1:( 6uazlwxe 5 lk0tto 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the pow0 lxw (kzae51j:ut6lter stays the same, and neglect frictional losses.    s

  In a common test for cardiac funn xm1na6o;1l/n q7wjpction (the “stress test”), the patient walks on an inclined treadmill167 /amjnn1 l; wopxqn (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically9mw8u1- 4c) ptrebvj y upward a distance of 500 m, what was e18c rj-myput)bw9 v4 its 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 frobjoqz, pc e7k w4071j*v t(tglm a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is itwjt jqpc*et7blo 70,1kv gz4(s maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s