In what ways is the i7 x+3o+me1sabc zoi*word “work” as used in everyday language the same as that definee+o7soixca1 b zmi3*+d in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an objz1 ;vksafs;r2s,1*l x 4k okcfect? Explain.

Can the normal force on an object eow h5uq fuvj ko98zp2 6fb4c82ver do work? Explain.

A woman swimming upstream is not moving wip ;s dw+dqph-+th respect to the shore. Is she doing any work? If she stops swid-d p+qhw +ps;mming and merely floats, is work done on her?

Is the work done by kinetiv s2fds7yf o7-c friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out fro2dvs77 fyo- fsm under them.]

Why is it tiring to push hard against a solid wall even though you are doing 3pem+yhf1wjjv 74 e(vno worvp+ h f3w(4e1 jjvym7ek?

You have two springs vrm7b. 3p9ivp that are identical except that spring l is stiffer than spring 2v . 97imvpr3pb $(k_1>k_2).$ 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 hor8vayynv8awnng.d) 4 a ;uu6 m2izontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and b6y4n yg8.;2w8nn dv) aauuav my 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 srea5).d8 mj8smj (orwhen ymser)5mj8orsa d 8(j.ou jump as high as you can?

In Fig. 6–31, water balloons are tossed from t m vbn4f ocy5lgscm/9h3(zf88 he roof of a building, all with the same speed but/hzobm vc l3sf9 yn8fc8g4(m5 with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a p(xfgz s0* 9 owiyn6hov/0thj8oint that is a height h above its lowest point in two difv(zt fo*oh8 09n 0yxgj /w6ihsferent 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 position? Explain.

A coil spring of mass m rests upright on a table. Igv:pei n-tnb,gb..q *f you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using thegv tn -*b ,:ipqnbg..e law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inssw 3l0.f-nxevo ;9ji htructor pulls the ball back and stands against the wall with thvofh3 j-0n.9ws e ilx;e ball against 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 watom,u)m8ct/ cter at the top of a watertct /8o)ucmm, fall falls to the pool below?

Describe the energy transformations when a child hopsf+u4ey3p2*1 k/*(1v ddajbjou fi8 bb 3 qijml around on a pogo stick.

Describe the energy transformations that take place when a skn fvpqpl7sf w q )+a1v id,5x(1u:5zfoier starts skiing down a hill, but after a time is brought to rest by striking a snown qpz, 517dwuf(pfv)15s+i q xa vo:lfdrift.

A child on a sled (total (/d: +5 cibczos)dyjh mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy an/ d(b)hjci so dzc5y+:d there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rathtkt* w0xlekntk. 7*85wzju. :ttlxx 1er than stepping on tz7kt.ttk5u tnlxx ew1k.:8*w* j0 x ltop and jumping down on the other side. Explain.

Two identical arrows, one a;wdqi0p6m 2y with twice the speed of the other, are fired into a bale of hay. Assuming the hay exertsa iq0dpy;6mw2 a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms o hz 0sr6lb.k2csj(0g jf energy, (a) ignoring frictionl(0khjr 0 .cj2gzssb6 , and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a h/wo5 bw(a nvv8eight greater than its original h bn5ao w(wv/v8eight? Explain.

Suppose you lift a suitcag2 r+m-k 2tqvdse from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight u-tmkg2 r+vdq2 p 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 rather than the workubt3u bxc n(9n1c(x gv,:8lm b.

Why is it easier to climb a mountain via a zigza6eu b8w 8g j.yaaky43dg trail than to climb straight up6uea8wg3 yj8 b.ky4da?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ro r5,z7n rd;ce /-qizqopes 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, ;zrczne/7i 5-qrqdo , using energy concepts.

  How much work is done by the gravit.:wo+s 0 w* f/gq;qk9jl eyezjational force when a 265-kg pile driver falls 2.80 my/fqs0.j joez;wq 9 ek*+w gl:?    J

  A 65.0-kg firefighter climbs a flight of sm/w4. p a:jcxpaj(s ,g:lhja8tairs 20.0 m high. How much work is requiredp. :4jx jajp:( c,l/ hmg8asaw?    J

  A 1300-N crate rests on the floor. How much worxye9) 84h ftwbh;aut- k is required to move it at constant speed (a) 4.0 m along th-yfutex )b8;4ha9 t hwe floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3mnbj18vfc .z 6 m across a roughc.6bjm fzn 8v1 floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor /57.bx b18sz kchjjrevc4.yy at a rate of for 7.0 s. Find the net work doxhj51kjyyb 7 .rb/ ez.4v s8ccne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mucfp e yi84t6kh3h work is required to stack eh 4y3f8pt ik6them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objectslr3 jizqtw)4v 8:uo1m we might not ot8mz:t4u 3o jqv l)r1iwherwise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acceleratinfl4+elu y z4d7g by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coeffill ye4f7+u zd4cient 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 helicoptr46lmlxu e4 5ir+aoj (er of mass M an acceleration of 0.10 g u( lre a+j4 65lrmxi4oupward.    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 is li6k 3w -j(l ps/amzhite0fv1r5 near 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+sui yy nqaid :vae*0+ 6le: idtqy+-. axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 1nu++vqd:eyyaael y is +-.: 6*itqid00 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 padv3 9jf* x sjkj/)mrtjmc7 f /we78cux)0wqi0rticle 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 ox u)b2eym+hq9 6mpcd.3 5vvg4u(djnp mygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its s m /n-b5cobwbw;a w8l8peed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stoyjv u.n /rzx.:p an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcarz 59stl73i hlg traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strj1b * /spgj.qqing exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leav/ bsj. g1jqq*pes the bow?    m/s

  A baseball (m=140kg) traveling 32mx;no15w,jaf1 r h:zos9crc 9u/s moves a fielder’s glove backward 25 cm when the ball is caugcwzrx9u fa9conr, 11 5o;h:sj ht. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum rd, :qrd.kwl8braking distance be increased, assumingd w,.:qdlrkr 8 all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’ssykf95 d3 j8/;tryknat) 1b v8ptaj2a 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 th/)a8dt5ytprnt18ak9 y2 a j;3sb vfkje 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 is pitched at By the tiky:4w7ou cpa1s qmm(hvvm32f,k5br. me 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 pitcher is rqha y1ms( .:,cwb m5kfm2 p7vv43ouk about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up 0heae e bq*-f4by someone who does 80.0 J of work on it? Neglect air *f0ebq4-eha eresistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single kqj,b975tchkg k:cu-iw-o j8 : mz.hjcable. Determine i8zt- :.bgq-co7kju9k5m,j hkchjw:
(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,*tc tj2ffcz oa5kxft (ru 876. k, of 440N/m How much must this spring be s tfr zc2a* .7xftotf5c(uk6j8tretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch topamb2 sbw7m ): another 1.2 m higher. What is the change in potentmmpa):27 b sbwial energy?    J

  By how much does the gravitasec-k drfk3;rw*q1nb)-/oel0ts v;h tional potential energy of a 64-kg pole vaulter change if his cent e sd- eh; ctqkwr)ks;0f *lrv/o13-nber of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on s/eb 68e ac .4jnd8p( cnkxfs0a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distancecefan.s84nk0c e6x /( bpjds8 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 itmzt0ssp)wqxyeea 475ng*u 8 ) is 2.20 m above the ground. What is the potential energy y0ssa eenm5g8 *7upqzwx) 4t)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 a87x +qus dudff/jar1*w- ed:dn elevation of 1600 m and climbs to the top of a 3300-m 1du sj+8wdfr-*a:qdex7ufd / peak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the i ff b..ftr7ue5xm3;xspring is next to the 15-cm mark on the ruler. If a 2.5-kg massuiffm73x5.t; f. bxer is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs fy55+42ie w1mz- *gdefnjif q wu*ki6 a vine hanging vertically from a tall tree in the jungle. How high can she swing i*5nw ugemz4 wyf ej2f k6 f5+*-ii1dqupward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides do2ec71ex znzw2 wn 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 g00+f v+xbqntaqj3/g shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic ebx51o8fr : rcn(zp4 ttnergy is transformed 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 spexrpn 41czo:(ftr b85t ed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps ver cn hdj;49o3iz*(esrni1 p g8utically upward from the top of a platform with a speed of 5(r;n 8is3 e1op*czji4dgnhu9.0 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 s-ndrd 1f:6idxoj yg, .tiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give tfxddjdo.y,:6 -ign r1 o 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 withs1x(h5 d(qezrr,ss cb2ot/y1 out friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be re 5y t, 1sssr zobd/(ch(x12qreleased?    r

A block of mass m is attached to the end of a spring (spr ii l7hu mk1 d,aqap68f*)wxr)ing stiffness constant k), Fig. 6–40. The8i q h*fpm67d)awkxri,au 1 l) 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 jumperwv)yvge 6 shyd **9n8,3sypjt jumps from a bridge. She is tied to a bungee cord whose uns 6g)h*tj eyv98y3s*w pyns vd,tretched 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 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 pe2 l i d*-l(.;0mk gunyj. twoujgve6+oint 1 where it is r j2+je .n.*k ;m- oldgv(tw6yuil0gueeleased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with 78u lgp)s n ;8xywxye g4:ar7op y3vv/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 designi: jo.0rx9 t 0xs efyghokub84)ng a spring to be placed 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 acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and h9o fyjg. 0uosb)k8xrxe04t: passengers.

  A cyclist intends to cycle um 1 hqnzy3(vj:mw ,g5tp 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 an; 30; d2 z tyi:zp5u3acdwppngd traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal e2t 3w;gd0updyz5p p3z cin a;:nergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slcm isz+bi m.)kt7qgh96r)bg* ide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to zb9tig s7)*mkcbi .+)6hmgqr friction was generated in this process?    J

  A ski starts from rest and slv)qr t231nlgj ides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above thsz ;yu6/kqok1 e ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a ).-ers4 hl9axug-m d lheight of 1.5 mx-)de l-r guls.49am h.
(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 fhezo u9.tkf; s3s8hk3rom rest, is pulled across a floor with a constant horizontal force of 350 N. Fortzh39hks.;3kue f s8 o the first 15 m the 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. 6–41 passes point 1 x*92/w fw pugs x;fdb1with a speed of If the average force od*f upgf ;/9xbxsww 21f 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 foot of mtqz8kur771p0p 5 hnsgp(x9b 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 horizontal sprif+t9t9d 3zg i io-(syd; rg6hjng (k=180Nth( ytjo i3f;+ 9-gr 9zgid6ds/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light hoi5zamx hxh c f136o+l-rizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how fa16of5hh-xx+i cmla z3r beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass ofue6lp9uet a:1 980 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 o 1tale: pueu69f 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 3152uebv yp1ie8(q(xw4o xhn(cfnra9 ,. -kg piano to a sixth-story window u1rvbieh,eo9n4 2(cpx(.fy8( axwnq 16.0 m above?    s

  If a car generates 18 hp when traveling at a 4pp4z2iq27+vs0e4nrzpwtqpa j 1 z 0msteady 88km/h what must be the average force exerted on the car due to frictio+aiq 0p q s0ne2pzpp4jzwz47 2mv1rt4n and air resistance?    N

  A 1400-kg sports car accelerates from reky8 ;ayv,r4kdlf; t:y st to 95km/h in 7.4 s. What is the average power delivered by the ;4kfyy8vt d y; :rl,kaengine?$\approx$    hp

  (a) Show that one Britirsn*agz 6pyen.8rf (5 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 expre nlaahyw-p ++4ssed 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 lfaqfm3f4 x.3,uw m-owa -(iq her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is neede-4iuflmoaw- qa,fm(xwq33f. d to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-h 5tyf0 odczy 6-8:agn g5logz5fz) ou(p 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 mofkh*r5 y9z ll2tion takes 1.5 s, what average power was developed?l9lrf hy5 *2zk$\approx$    W

  A pump is to lift 18.0 kg of waj1qmtxa1x(qha ,). bpv(v6e rter per minute through a height of 3.60 m. What oahr1 av1mbpq (x),.q6j( tev xutput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up lc7z-oj,- za9q llyh:r4s- jz the stadium stairs in 66 s. The stairs are 140 m jz7 llhl,o-qjrzaz 4y-sc-: 9long 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 climb a 6.j6ih- j a5ifkh1bv eg x8wh0;r/-uko: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 akenj5(9 oevi5 /gklk 5 hill can it climb at a constant speed of 75km/h if the frictional forces add up to5lgei/5 jok9nekk (v5 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be abd3 :xea 7ra)c;wl 2*xsyhilr6 le to drag a 310-kg box along a level floor at a speed l ;s6yehr l3x icaarw)2dx :7*of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.y6r+hh;/yv( 3keq k+ddl 0ric0 $^{\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) bumpe hxi.+jbm o/(mz/1dv crs” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by rammimi.vcbhm o+(/d /1 zxjng into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the groundtf kg* .m9qf1e, 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,eq*mf.f1 gk 9t how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympicspsmai n7id x06-s, ov, shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he nosd xi067- vma,, nipseed at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loope+egi9hbf.bu v 87zwhd.-ed1 xd track shown in Fig. 6–39 is to remain on 8fhuebg + vez7d9 i- h..d1wxbthe track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his pa /p+qgdttj+z( t 9t*gzrachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velo*g+ g( td/tp j+qttzz9city was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end 3q / lauv(jmy)is fixed (Fig.yj q3la( mv/)u 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made: /n4vajk b,rx zr2w6h in :hz6kba,v rn jw2r/x45.0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920 n29q/ acgywngut(6v s-p1b- s-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,0j8hthpv:ytx(w xh5v47p a -- g00 people per hour. If the average lift carries people about 200 mthx7-g j yhvptpw45 h xav(-8: (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rxhzwwr. k4egm2u2). h ate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculate w4zg2wrx .2 mkeh)hu.
(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 xpzsyr0h5h0x e)43pj loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size ofex yp)5rx3h0hp4j s 0z the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into worbf*.9z) dc,ceu5oq9e cdph1d k, how high could an 82-kg man climb a ladder if he were fueled bc9c ).debd 9pdefqc5 * hz1,uoy one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle6u zxuyw sj28fqe ,w99 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)iambs; y 3tx sfo,4ixa,(:ih5w u8ds inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if yoh st5i(um sfxxiyas3 o,:b d), 8a4wi;u 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, and swings out over a lake (F ccs+6pe 4wjv;gi,pi*ig. 6–45). He releases the rope ;j gpeswi c p*4ic,v+6when 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 m in p zh5a12atzh q:o3.-xzbuc)o 9.0 s. What minimum power output was used to accomplish this feat? hx2pa ozo-1 5qa:zz)ut3b ch.   W

  Some electric-power companies useytn1h gqv/q pdi :*ksk+r89d-n +d:y i water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the eneqdg+ 81d ys*y-q/:dkn9i ih+t pv rkn:rgy 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 stiffnec nx*2ldik:8hu.v e8 kss constant k is cut in half. What is the spring stiffness constant 8:.ex8ukcnk*d vi l2hfor each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 mnn,z ny;q26lq 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 l3guw;w5 kl -kmong will it take to accelerate from 55km/h to 75km/h Assume the power stagku-w 5;m 3wklys the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stressumanlafugdo *)k29rtx di8ni4 61q d 6 a/xu09 test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is slog )9tk89a/f04*uda o26x1xiln a m nu di6dqurping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distancecl-hu-,q kxdap06 4tls qz:c+ of 500 m, what was c6-slqu p+ ,:c h-x0kqlat4zdits 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 +s q/qbkw n,i3a height of 2.0 m at a rate of 95kg/s (a) If this water whe3+,b/wisn qqkel 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