In what ways is the word “work” as used in everyday lang+iju+31,nxfv 1xfuam uage the same as that defined in physics? In what ways is it different? Give examples1nx1f,3uxiv+uma+ jf of both.

Can a centripetal force ever do work on an objec odiof*96.o nxt? Explain.

Can the normal force on an object ever do wor*jafz nb 8m46ak? Explain.

A woman swimming ups;z3 j/m ;5,tmfsen wlrtream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done o3zw trf, ;l/;en5ms jmn her?

Is the work done by kinetic friction forces always negative? [Hid(/ 9 -yd tc,aleebau1nt: Consider what hapteba,u9 d/ y(cad1 l-epens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though i *ofn9/1 mhq 6v2 ojdvhfkulc.l8yz//i69i oyou are doing no work9holi/nvoy//* cld8kvf6o2 i juz.qi9hf1m6 ?

You have two springs that are identical exc+i*q ctel+1rcto- m t5ept that spring l is stiffer than sprinl+ci-1*eq rttmc5+otg 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 horizontal forces nn9gfo(a//yn zp*j( on a block that is free to slide on a frictionless surface (Fig.6-30). The blocf/a*p9 zy((nnsnjgo/ k 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 change wz4 5amm.fa* tlhen you jump5a4 mfmat.*l z as high as you can?

In Fig. 6–31, water balloons are tossed fspupfr3/ o+8 nrom the roof of a building, all with the same speed bs+3ruf8ppo n/ut with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poinj(8olk56d rju cin, :v,*ackpt in twuv* l o kdc(c8i:jrk,a6 np5j,o 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 position? Explain.

A coil spring of mass m restsy6 qydu29xjgbtk i5igxzq9 r/-q,i /2wc a1k5 upright on a table. If you compress the spring by pressing down with your hand and thenkqg 9xuii/5b/k qc5zy2jqagw,rx6 y 9-dti21 release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceili 7p kq9zi5a -t;x3 +0eh8sekfwd0n exung by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall0- pfte8xd9z ;qe0e5au k3whs7i +nkx with the 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 energ zfi:djd 1e)l2.y mje4y when water at the top of a water:. 2lz4f iyj)1edjde mfall falls to the pool below?

Describe the energy transformations when a child hops around on a pogo svg7i8o fl,vpc6 ;e z96,(w k y:wh7 cxw3viddmtick.

Describe the energy transformations that take place whenxy2*)puha8t6b m;ff z a skier starts skiing down a hill, bu2u*z;)mp bay6f8t hfxt after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at ( *cmd 7 8dx+vnr.ajmkthe top of a hill of height .+8rkm7m(d v* c anjdxh 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 euw* pcw ;84offnv*)dfallen log in their path rather than stepping on top and jumping down on the fnc w ;e4)8dwu*v p*foother side. Explain.

Two identical arrows, one with twice 9vn9c-:.ebmtmhb, 0 b;wg n uwb tek74the 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 penetrate how much farthhwmb e9 cb bbw -9g70 :et4m;vnuntk,.er than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (aosvk(lcg8uw*o-0d 7 )*p i; t 8olkiyx) ignoring friction, and (b);v *itk x)oldksy 87gwu-oc0*8l pi(o taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than lzsye8 pj* 0m4mbni9hl5 k2n;its original height? Exl;9m0mninpe4 8b*khy 2 j5l szplain.

Suppose you lift a suitcase 5dcq.1 -z4esiq7 s ngafrom the floor 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, anqs1 s 4ae-qng5cz.i7dd (d) the weight of the suitcase?

Repeat Question 22 for t v8ws0j3a)qxmyudz ;0he power needed rather than the work.

Why is it easier to climb a mountain via a zim 4qr):pi(1ux+mx33w zq zdvigzag trail than to climb straight uxzp3ixu 4q:()1w zr3 q mid+mvp?

Recall from Chapter 4, Example 4–14,drxn-ik 7v 7(hj1qhv6 that you can use a pulley 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 mk7h nx6vqjdrh- 7(v1iust be pulled up? Account for this, using energy concepts.

  How much work is done by the grav i 6zky333f.aq/wkaqlitational force when a 265-kg pile driver falls 2ak/q3lf6 .3 zk3aiqyw.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m pqzs0 djj2 s,:pcdx-2;y oixnor+2d+high. How much work is reqp+2dso:oqj+,s0;-2c dx zjxi ypdr n2 uired?    J

  A 1300-N crate rests on tf0f bm o6v6 mz2+k4vxihe floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction f0ffx6z m2+ivm6 bo4kvorce of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers dox8z;z(d 8uqi.pb6ym c (horizontally) pushing a 160-kg crate 10.3 m across puq ymb 6.cixz d8(z;8a 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 force across a floor at a rate of for rhm5 a;1z hall*+x3mb 7.0 s. Find the net work donz5 m* rbxa3hm+1lhl;a e on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fi ;0s,hbmas0ulat on a table. How much work is requi0u0 ;i bas,shmred to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can hvny2hwe)968*xp mp l be used to liff objects we might not otherwise b82hy w*lhpv npx)69eme 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 accelerc8 6 uof eq*2aqu/uu;wating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The eff6 *a;fqoq wue/uu2c u8ective 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 mfg ln v*6 +h:jozpv+y*ass M an acceleration of 0.1yo6fp*+z+:h*glv vjn0 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 distance o523,3ty t6i;koa7pj cv/llmx m/ pelaxis 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 axvt 373sfdf/g eis, varies as shown in Fig. 6–37. Determine the work done by this force to mofevd 7/3sg3tf ve the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle ac 72jasz7ztnc/ 6g(kh:irxy -ns:vxr )ts 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,o dvt mu+g3-3l an oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its svihptv5 e+i5 2peed 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 electro/ pgfw+;xx:8kakt fe 7 lyud07n $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 travelinmgm9 y m(r4pgxx .8*tlg at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow 9u 5y+2wb2nh+dfh0ylkdg . br whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the+ f9 h 20+2dw hrgndby5uly.kb speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3 dqe/2(sath6+h- nf fy2m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average forcsa/tqh-y(h+6fdnfe 2 e exerted by the ball on the glove?    N

If the speed of a car is incrisd e+9j;e n,j(3ayg cixwv +9eased by 50%, by what factor will its minimum braking distance be increased, assuming all else isw g9 s9 3a;+ix(jejv d,eni+cy the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid fslo.m-w+b/0xld ae nhk09 z3mark 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 t.9 0h-zxkdw0 am3el+olf/s bnhe 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 a8nbfu++*i yvr- j e*gdt By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate thjgn*8e-rd yuf i+bv+ *e average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doesdo(:q-bc h4/cr hf.pk 80.0 J of work on it? Neglect akdchp - r.oq:4/ (hfcbir resistance.    m

  A 285-kg load is lifted 22.0 m vertical *0y 0gm6re**bqjkj usly with an acceleration by a single cable. Determine r0m*j yjes **gkqub06
(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 Howm*-cyp+;bt w o much must this spring be stretched to stoc+* pby-;two mre 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to anotherl1z)w1t4j-vxs sh/c a 1.2 m higher. What is the change in potential energy? 11 lvt4w-ss)az /jxhc    J

  By how much does the gravitational potential energy drw1n tqppx12/6o 7keof a 64-kg pole vaulter change if his center of mass rises about 4.0 x1k pwdt216qpn/r7o e m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 k: sug +4y ,) tmf40kkcelk,qpcm/h when it strikes a horizontal coiled spring and is brought to cku,k m+c,q4t s)l :kf0pg e4yrest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-d,i:i b409,0c8gp enbiqgjw ikg book from the ground so it is 2.20 m above the ground. Whatigiqijibc wg0 e, 0db8:,4pn9 is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and clim.uk6gil*:fz70 kjku l+1 cql .qkb5/.wf xuoibs to the top of a 3300-m plk*07j+1uqz.bo iqul /.w5ug k.:k ifk l6x fceak.
(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/mxso5z9of5 c-a hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end oozfa-xs 9co55 f the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a 0waich4l*ohday h7: 1 vine hanging vertycah di:h40 alwo7h 1*ically 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 frictionlef 3*;zz:mg tk0 oodqb*ss 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 c k5hb//4z/ imhqxd3i-7v uhxa frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational pg7o8w ys)73cqiksci 1otential 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 woici1g qs yc8) s3k77with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a pm b:2fiwvx 1*7pg4mq elatform with a speed of w21*4qmmxe 7ibpfgv: 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 stiffnes n(b.g-*:aoyidu(ldp s 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 ball when releaslpdiu yo-.(bad g *:(ned?    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 lmo mgii7w5z 0,ooped track shown in Fig. 6–39. If the block is to remain on the track, even at the top70wig5mm,oi z 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 stiffness f 5m xmv0y4oyo6bw-vr/d/-rbconstant k), Fig. 6–40. The block is given d4bvwy50/fxr o6 rmbm -y-/voan 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 :iobg,4mc i41at7 elpjumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calbt im1caoiegp 4l :4,7culate 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 point 1 where it;8v a5dlzw0ly is released from rest. Assuming no friction, calculate the speed at points walvd ;50l8yz
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12maz0p q528( 2pphfhxk m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the0d 6vt6ux+w8)/yffcrdy b z3j 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 shourw +byjz8du)xcf6 /6vtd0 y 3fld 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 upjbz+3j. bci/purz 6v 4 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 7 8ve4qopualn9 vwj96+l4g2e g,c x6wd650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How mucj + g9que cell6,x 4gwd9wonp46vv8a2 h thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends an h4gj r* 8tjw*h/;vxt slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was *j*jh t/x 8nr tgwv;4hgenerated in this process?    J

  A ski starts from rest and slides down a-ghvspd8 43+ xc9frh2fsdj+ yjy : z+s 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 tf*bwj( 92.j/kzyjld c /y)onwhe 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 lqluot q2kc*y(94- l7 /twced height of 1.5 m.9- ceqtwo 2u /t*( llkc4dlqy7
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant hs8n(2x k z7neoorizontal force of 350 N. For the first 15 m the floor issek8 o7n zn(x2 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 co 4* p7zvoiq- fqjvd)+6*utr;i*kjzj + ed 3auuaster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, withr)6pi dke **vqv*zuidjo a tu-;zu+4 +q7jfj 3 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 )vi8gv4h zf etn .8sl*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 attap-xr na2yrsq 3 *x(u1bp*rca,ched to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretcrqa cxx-2pauy **3npr (sr 1,bhes 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 ver: )np 0ow:tv85dyba7xaq4 e2l,qm oe ty light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from th ):7dopaql4 :ottm,b5yx n8qa02evewis position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (massro b ugzx/1l )ra7fl8p: f(wd3 of 980 kg including pilot) that was launched hor)z/px gw7alorr1 b:uf8l f 3(dizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor49q01cb vlcx4u 2bqxc to lift a 315-kg piano to a sixth-story window 16.0 m aqx1cl42 90cb u4v cqbxbove?    s

  If a car generates 18 hp when traveling at a t ibi6a xtu)6 t0uy0w0steady 88km/h what must be the average force exerted on the car due to friction and air res6ty 0)a0uiui0 bt6xtwistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is th lvhyyq14 f )loqu,hnl /ca amz702z)r+(t1hfe average power delivere +ruzqyl vf4)t o/ynhq(f1l,hlc0 )ha1 zm7a2d by the engine?$\approx$    hp

  (a) Show that one Britis/r cucs/(d+wddqy a 79cf.qt on2tk3* h 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 expresse(hlq.,3cyhrm/hi: cy 7v mi9nd 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 from to 65km/h in about 6)xcy.f iujjr(b3z /tq (*qq( j.0 s on the level when it is in neutral. Approximately what powej z/ 3 *yrq)(jj c.(qiutbqxf(r (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h?hck2pinxmc0) (l 8imyg4r e+- $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion takesn30na*b ad;:vkz)b*c 5m oool 1.5 s, what averag )3k*;o:cnlba z*5nm 0avob doe power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What*ttofka ,wm4ax 7 wn u;g+gn3) output rating (wattsx t3;f w7*kwg4na ),um+gnato ) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stacd4id a*-fjt/lh*.w9t ;nuc airs in 66 s. The au.c;f9nt ld4tc/d haw*-j*i stairs 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 climpzry4-0y( vzvb 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 186 zsfz)oxw k4,n )eynzjah) 520 hp. How steep a hill can it climb at a constant speed of 75km/h if the frict4hwkxnzfjzz)so6)en 8 ya)5, ional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able un ;.fb2omv6f to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction u.m2 f6bonf v;is 0.45?    hp

  A bicyclist coasts down a e g6c8l:u xok tra0vw,jt0./l7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are desi) u6/27kx zov.pr f,*hanrqypw2ph e8gned 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 ramming ik h8,/fp)n*wpyez r .r7ah2p v6x2u oqnto a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library -zasbas e(6af 7x4r3bthe first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the averse4 a7-f saa3 zx6bbr(age 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 famous long jump (Fig. 6–42)zq3awkx0 *co* in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of *k 3*qxzc0woathe arc?   m/s

  The block of mass m sliding without fric6)tp z dcazbj+.)d 7yzm7*pgition along the looped track shown in Fig. 6–39 is to remain on the trackycjzd*6t)db zgz.p )7ai7 mp+ 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 jumpiw4o8 h.xlgq 6w3t +ating from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity wo3h86awgq .il x+t tw4as 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 tw q:wl eiik ss405a2xnm-1 bx;o a horizontal cord of length L whose other end is fixed (Fig. 6: ms2i;b51 nwix0-ewxqa kls4 –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 mountayxrg yy6 o4n8*fy,k0a in. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculate kgxya6y4 oyn r*0f,y 8
(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 huge sc 9*ibcrb.b1wg1 gx5j pring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 tmi4l avy7 lx, 0ej4mc,hat its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the powe ,l0j4imm el,av47xycr needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fl ,:)xu,ju7d, m(zk9xsmr nrm alls vertically 81 m before striking the turbine n ms(d u9uxr,rj )mz,xlm:k,7blades. 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), thee pgycjwkne;9i )*3-i xsua65 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 neede5e iu ceaj i;g)9w*xns-y63 kpd, 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 convw7vk ( 54zzxdaert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1 dz45vz7k(wa x000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 454h1n e4fi jew/.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 scabhrp :6 ua-o:hzvt xd+7.4fxp le, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the d xxuzho6f:pa 7 r:p -v+tb.h4scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabsm wao ufr-y 8cp30y(a. a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velo0rafyop.8-w3c u a(m ycity 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 inl.v-l yukvk1rb8t ,)jrb+ l2 i 9.0 s. What minimum power output bl82ku bvri1v, +.l-t)jrkly was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Wnmyskd 6)2qk;ehh 0e04 h0s8x wnjlx-ater is pumped by reversible turbine pumps from a low to a high re02h;x y-mhn qss0jld 6480e)xnhkwkeservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut eil0 /qkm- dad0z 2ap+bj z2i)in half. What is the spring stiffness constant for each of the two resumi /0aei2 z 0-2)+akdbjlqdpzlting springs?   k

  A 6.0-kg block is pushed 8.0 m up a * xild,;;:asna0hq dvrough 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 indc s- ulayr e6/1l(,ae 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional loy1se 6(c-/dlaru ael,sses.    s

  In a common test for cardiac function (the “strecqa vr:)0iu ncu kcb8)xb2*p( ss test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill i) q(i 2v c8u:ccu0p* xakb)brns 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 verrfgqbj8zgw3o (.e nhmt+/(8 rtically upward a distance of 500 m, what was its velocity when it left to+88rjwtgb 3mqfr( n(/z. heghe 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 wate bq39y 4k4, s9v5 s+b)-ztss cynxttcwr wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up kv,nw+t9 y s )s-4 9cttbyq4zx3bss5cto 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