In what ways is the 4 7(cqk+ajrauzv b00tword “work” as used in everyday language the same as that defined in physics? In what ways is it different? Give7u+0 rkb( zvca0 jaq4t examples of both.

Can a centripetal force ever do work on an ,dvitncd1)) /xuqed0 +l5xp wobject? Explain.

Can the normal force on an object ever do work? Expla: ydb4tb w+a3my14x7u tpfnu-j vou8)in.

A woman swimming upstream is not moving with g2p9phkwykasjiim4 9 7f+*(xrespect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on herix *+gsph 2a99y (4kwij7kp fm?

Is the work done by kinetic friction forces always negative? [Hint: Consider whag /nyced* 1y xxl br7fn0.i8j:t happens txc lj*rg yy ib1x8 :nd7/.nef0o the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even thougtkcj+ s*7j 3xw4pof-mh you are doing no workxs fjkpc* wt 347-jmo+?

You have two springs that8+xx4ju95 m yoyl 9jvr are identical except that spring l is stiffer than spri9xyu rj m4lxy95vj+o8ng 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant h f0t0b/*n7t0o iw upuqorizontal force on a block that is free to slide on a frictionlet0q/t*u0nuf 7ibpwo 0ss surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does -qy)t0y a4udvp :qau(-0vi :bidi ms8your gravitational potential energy change when you jump as high as you c) 4vy: sq:by iamdd-pau008v -q(iti uan?

In Fig. 6–31, water balloons are tossed from the roof of a buildin zr6+)tj w *itwe/kwd-9g.txgg, all with the samz9wr6x eg wt-*ik wj+t.d)g/ te speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point ; d*6) jag+cex7 ftu8pqr4inrg r+ 1cuthat 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 from the equilibrium posi;r+p1j8i nxugtd74 ae+) fgcuc6*q rrtion? Explain.

A coil spring of mass m rests uprigh/xg:op gfe*vi.dj, ;lhij w7/t on a table. If you compress the spring by pressing down with your hand and then releas v/gpigijhjo7w/e l* .d,: f;xe it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ce svd pc/34tkp/iling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball ag /cps 4k/d3vtpainst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a w3 ;yorru ,j)tsyh 0 q;t.ilu5vaterfall falls to the po;otiv;5 yul.r)ys3rqthu ,j 0ol below?

Describe the energy transformations when a child hnk6(2u h7c ehfops around on a pogo stick.

Describe the energy transformations that take plab9g5 i;xjllj ) cbrl+(ce when a skier starts skiing down a hill, but after a time is brought to rest by striklj(li;r9x cb 5jl)g+ bing a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of hein/dbhl bv kbs2p.xb )(tw*7mp og9l(:ght h and slides down. Does the velocity at the bottom depend on the angle of the g( mb7 ol )b2:pkhbsx* nwbvt/(dl9.phill 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 log in their path rather pq 359z, egph yavpq11than stepping on top and jumping down on the other side.9pzegp35 vqqy ah,11 p Explain.

Two identical arrows, on;1/ dqmmpi1u8o8z fpgxy, )vke 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 pene;p vimd8 z1g,f )xq8y1km/ouptrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulums4 o4qg211ytzhz db.qs7 tp;w in terms of energy, (a) ignoring 4tsy4qsh.d 1 z7pgbwo2 ;1qtzfriction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can itp,4x 7dsvyq3 gk493,tgrutwn rebound to a height greater than its originalgu34s93prx ,7tq4tk ,ngydwv height? Explain.

Suppose you lift a suitcase from the fm z am56caj4ilblcm8 b70q+ *h tzaj8)loor to a table. The work you do on the suitcase depends on which of the following: (a) whether*7q)8m lab6 8 ctzmibz 5a lhj0m+cj4a 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 cvl,+ ve;ybnl(ho* bxpkrxd .; 1+gl8the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail t,s-pqz* hpjs ;h)k;tphan to climb straight us,hhj *;-st)zk; p ppqp?

Recall from Chapter 4, Example 4–14, that you can use a pullor , 2+ rx+wty6os k:abuq(mx0ey and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts. : +qrot,x2u0xo+6rwsmab (k y

  How much work is done by the gravitational forc8u(hl *5kqdea e when a 265-kg pile driver falls 2. kd(qe h8au5l*80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How a+ at pg:rp-8dl:0pnh much work is re :p rpdnt-+p80ala:g hquired?    J

  A 1300-N crate rests on the floor. How much work is requiroez,74o4 yaffex 35az4mx b9 ved to move it at constant speed (a) 4.0 m along theb y,z 4v9oxz5e ax amof344ef7 floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) w 53d ,gz27huuvkph8 h0r/v tqpushing a 160-kg crate 10.3 m ah8,3u/tv rpwdgkqhuvzh 0572 cross a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acc: y jp)hqv2-owi 0iiy7aw8xr+ elerated by a force across a floor at a rate of for 7.0 vaihq:yi i)+ y p-wox7j20w8rs. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with num8x.dv(+; ucuk.g g mass 1.7 kg, lie flat on a table. How much w+m(cuu k. dnvu .g;g8xork is required to stack them one on top of another?    J

A lever such as that shown in Fo8b0 dfj8f;;y s xqqs6ig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that o6bs qsfyqjf088x; ; dthe ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept1zhrd8 v 4che- oc 02awq-m lrd5i()cm from accelerating by a man who is pu)2 o 1i--q dwhlrcmhr5 dmc0e4 8vc(azshing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force requirem1wlkx6t -rm3 d to give a helicopter of mass M an acceleration of 0.10rmwmt x3k6 l1- 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 ve181zh)v9cu e.wu l kwfti 52distance 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 thkq6 b q6jiixud(09 xz8e x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the objekzq0ji9 8xq6 (b6d uixct (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 the 9eh(2*a d 9uxibf hh5g$+x$ 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, wi n,a/+av5eww8),j 4au bjuhmqi h r8b(th 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 speed incre,e 9, kjhg /o6+ork3l t7gkcpyased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elecldbg zp:p+mu; 2u.ob5tron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 a bta8 ejzije xozil1 f8r861 o77yr2j,t 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts anyg )x.y 5l4lzjcrb:)ow7g0 vk average force of 110 N on the arrow over a distance of 78 cmjbl:7g.z4 xyg5 y wo)k)r0lcv. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) tra5b 1(sdh qf/ .k4-w eu0tkvadtveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the k-5we./qh(a s bft4tdd0vku1average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum braat6nkx)hb-bq7z cd pf64vb (4bv4a b5king distance be increased, assuming all else is th (54z c4vbb) qf -64 7habbvbpkdxat6ne same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inveorv2j y+ wliu1u7j w)-stigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficienti ju2ow)1rju7vy+ lw- of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg i2bub:m3m ux,ys pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcm2mub, uxb3: yher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown st)gfw1cda w e4y)h )u0rro2n ,lraight up by someone who does 80.0 J of work on)alu02d) ghy1)r owwenrc,f 4 it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a s3 0zz9lj qzuwju .d39kingle cable. Determzz39j.q 30w9lzj dukuine
(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 much must-y,n(s. bz +/p-z olw 0/hmaw*xmeewi this spring be stretched to store 25 J of pote h /-+a0bziwn xe-.se/z(,ypwmo mw*lntial energy?    m

  A 7.0-kg monkey swings from one branch to a1 hz6/mqjj ba6nother 1.2 m higher. What is the change /jh qabz61j6min potential energy?    J

  By how much does the gravitational potential energy of a 64- go.,r4fyu lf4kg pole vaulter change if his center of mass r ry f4og.lu4,fises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it strii1t.yvtev +ox9q fnh2:r4qm 6kes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What fei:rqnv .h v4 tm6ox29tqy+ 1is 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 2.20 m av*9srx m): ef 5drsq6m kkk/d/bove the ground. What is the potential energy of the book relativ/ :rrkdqd) *kms5vf 9/6mk exse 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 ofb*7euetqv u ns66 *:xd 1600 m and climbs to the top of a 3300-m pe6b:*nuq et ud6sxe v*7ak.
(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 sprinjf d5k1m0mhc;g is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up wit km cfh0;jm1d5h the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (. .8bazz: (/qkb9cl 3riahpyg5.3m/s) and grabs a vine hanging verticgby( izrk a:b.3h./pzaq8l9cally from a 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 35.0pqmkd; c*m0u 2$^{\circ}$ 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 frictiwiu *jcb,c5 6 +wxz e-n4unpx;onless 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’fva mrobl dvq4++3*d - :4sudss kinetic energy is transformed into gravitational potential en+4+od- fub3dsmqdvsa v:4 lr*ergy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform wm ap 0mu)c123d)j kfcrux+3 swith a speed of usk xrmum+a3)3c2)dpw0 1c jf5.0 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), .zwr1. k+kvdk9 hih5svx 9wo9whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg balwvw.+k.z9o 1rskkid9xhhv 5 9l 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 shd u;qqw j4k61.zgs6vdown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), .1 6wuq kqjzgd64d;vs from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness co (7v:lc8ce ,trcjqzfe ,s4n 9znstant k), Fig. 6–40. sr e(9evnl, 8f qcc:jztz ,47cThe block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungebw(v o)m0qo4 u lth sdb1(ml3-e cord whose unstretched length is 12 m, and falls a total of 3m-w(d1lt0b4qus)olo m3v(h b 1 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to /e o) cd nn(5)rkjr.blpoint 1 where it is released from rest. Assuming no frie)5rc d.bon()krnj/l ction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle )/j8o3vs0saby4*sbs u lq 5odof 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom vco e6/o+xc8er 5v0p r4r.azh of an elevator shaft. If v8 a rroe60rc./4oexc 5hzv+pthe 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. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle upf t(*hla1g m;zmz 7m7o 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 k)93azb:. u5c 0c c/xciy vyha95km/h in opposite directions, collide head-on and co/ ix0h)acy9cb vzc :y5 k3uc.ame to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child desc hdrm 8r,isl(7m,la 7qends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction wa rli8m7m7hdrq l, s(,as generated in this process?    J

  A ski starts from rest14wmcze+ 1j+ftg3n ge and 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 t 5irb:t y-vyn7ree 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 mr31z9vn d,si:zp,. nnca8 s nc, and it bounces back to a height of 1.5 m.rs3zc1di ,npnznc8a: ,nv. s9
(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 f 6 * aiv1mhp)1y)axu3i7lcs)gupr ,emor/*afloor with a constant horizontal force of 350 N. For the first 15 m the1g,i6hx ulsa7ecifrvu))op3 1*aap)/*m myr floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. )fa 5bn6b;/nvrhv *d z6–41 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 traveled isd vr/ah ;)bz5n6b*vfn 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a st8e7cl ;wen)5fy p ovvv131 ntseady 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 lkhy)hfgsc.+*o .dau ,ight horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic frict oa*.,+hhkd csyu.g)fion between the block and the table?   

  A 280-g wood block is firmly attached to a very light hrh;gw+4o ehwordh 9:siycr5 b-5z93 m orizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N co34;i9oh-orw: cdw55 9+ebs ymhhgrrzmpresses 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 shuttzn3hp+ -aupegb+h-1d j rd4u (le 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 been in the absence of air resi-pnegz + uh (d14urph3d jab-+stance?$\approx$    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 acmre/qi n) kn nk(-uhh0-p ;p) 315-kg piano to a sixth-story window ph ) ; n( n0/mnkhqri)eu-c-kp16.0 m above?    s

  If a car generates 18 hp when tr- fpz nr;qjg o:px403,ilp3uiaveling at a steady 88km/h what must be the average force exerted on qpi0 z-j,;: 3gnrp4 pilxof3uthe car due to friction and air resistance?    N

  A 1400-kg sports car accele75s*ksq vf6 brrates from rest to 95km/h in 7.4 s. What is the averagskv* qf5srb76e power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepowe bbl,7q pg4rv4r$ \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 oftw42 3nit8n 4 8mt uy93otqxketen 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-kg car slows down f7dm.c4 2 x;fln hup3tcrom to 65km/h in about 6.0 s on the level when itc7 4un3fp;l h xct2.dm is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp 0ed ibc8lnf7xc8/;. xvn/a.wy yth p( /erd-s motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this 27a2w vfiui);wc ; h8x qeur3kmotion takes 1.5 s, what average powervuu 8;x ;a) qfc2iewhw237r ik was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a jzzq na/a lty.)wf7cr;p25o6height of 3.60 m. What output rating (watts) shoo7af 6qnp 5a y/l.;jwz)t2zrculd the pump motor have?    W

  During a workout, the football players at State U. ran up the ;1vzuqdnfjzt pu;)s+,a 9t6 nstadium stairs in 66 s. The stairs are 140 m long and inclined at an 1;qvp 9t zadtnu )zs+jn f;,6uangle 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 cyclisto evw sg:*t2x5 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 maxn l(5.leipbpz)ps1q 4sm:3waa( /b u0ast7wx imum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h ip : qbt/eus)1ip ap(4l7 3 wm 5aaxs(wblnz.0sf the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowk ll-4wymp nn9 n z+rdy(: t1o-+leb8cer must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coen l-y-nwoy4 bknt:(l+r+cd 8z9epml1fficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 fk *qvcuk60 i*y7exk. $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumperfh v8pn2fqakp1 pg,1d h )q2y7s” 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 sprinp)p2fh 2dqkf v18,pg 1qhn7yag 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 the re4t9vqu) 0 t0hgr(bbst8wmp( imaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg wi9v t bigm4 rp)0tb(s0(q8tuwhth a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in))k xgk panre/6k*q: h the 1936 Olympics shows that his center of maske *a/ )grxnhkq)kp6:s rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding6vjv ebxbn)sqv/ tq*8x9az) : without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius rv8tbz va*s)b)ve 6xx /9 jn:qq.
(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 ai wlrd -o9.wp6rrcraft 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 kgo9r p6wlr. -dw 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 h;+ 3yhi8lxicx orizontal cord of length L whose other end is fixed (Fig. 6–43). 8xi3l h;i yx+c
(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 w (4wi;tmu p1-zzevfy-9 bz5aclimb is made in 5.0 h starting at an elevation of 2300 m. Ca embwp iz5a -y(z4vwz;ut1-f9lculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a hu 4o tf7r2,qbww3ws -ozge 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 47,00h8v/vd ys*g ge8a,v0a0 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neevadg *ysg /8a,e hv80vded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls ve)04nq,b2 zhh0xjufm t rtically 81 m before striking the turbine blades.j 02 f)0hxmuhq znt4,b Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), tht1), lvele f9oji:c6n e 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 speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how n6,9ev jto)lc:e ifl1fast you go through it.    mg

  (a) If the human bodphi4g ,4v88ymxfhzd2) /nbtm y could convert a candy bar directly into work, how high could an 82-kg man climb a ladder ifh8mbyf,n tvd zgx)p 4im/8h24 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 z4-i opg:x+xuij8xu)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 compresses 0.60 c2h)4rz* yo ctmm, and it tells you your weight is 710 N. Now if you jump on the oz)r4*tc yc2 hscale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grub0bz9k x ,7rjn 1gzrc+)0vlx abs a rope, and swings out over a lake (Fig. 6–45). He releasz179 0,kbxcug)0bn+zxr l rvjes 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 athlete climbs a vertical distance of 5.0 ms6h ( ig9v8drs:k eo2xqld/x* in 9.0 s. What minimum power output was used to accomplish this fe(kivrd dg9l:e6 s/o xq82 hs*xat?    W

  Some electric-power companies use water to store energy.+vz p,xlgy s.c8 r-,)xnukwm+ Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy nyl+ rz.k c-xpw,m+x8u ,g s)vproduced 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 i4z8ivh oj1b* rn half. What is the spring stiffness con8jv41o*h i brzstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed rfu4qq,iizag01qn h5 -icj59 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will it+ s hm rp+07mkm5-k1x mbd.apq take to accelerate from 55km/h to 75km/h Assume the powe+17+0r 5m dpkhk-msmpm xabq.r stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress tefnwzo8si 24, kst”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power requiredizofs4,k w8 n2 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 5biq3 *mr(okvvertically upward a distance of 500 m, what3mik 5* q(vobr was 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 from a height of 2.0 m at a rate of 95kg/s (a)dnqtt d sz+92ylid63g2o,lf8ada 3q. If this water wheel flyd3z ti+.gs2a9 q a 8d6d3l tno2dq,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