In what ways is the word “work” as used in everyday language the same as tha5f wvmquq8l+z h0 p-b.t defined in physics? In what ways is it differehqbm80+lz wp-q5fuv .nt? Give examples of both.

Can a centripetal force ever do work on an object? Explat pq3-dsqa49iin.

Can the normal force on an object ever do work43h:ez:mktaz 6z+ oig? Explain.

A woman swimming upstream is not moving ll)/sb34yp k qwith respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work dsqkllp)3 b y4/one on her?

Is the work done by kinetic fri7iv47bc*pum9a; yrm u ction forces always negative? [Hint: Consider what happens to the dishes when you pull a tabl; ayr* 7 ivmbmpc9u47uecloth out from under them.]

Why is it tiring to push hard against a solid h )ji624uuo-osbrz-l wall even though you are doing no woz-obu 4s)- l26uji rohrk?

You have two springs th:0vva4 s3c;f f2f1/vq yfrubaat are identical except that spring l is stiffer than sprvr3sfaff c0/ yu;:4v1ba f2 qving 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 force on a block that is free to slidekovqxj9e zq0v +yl5 )j;tx28 l6vfba5 on a frictilvv2x;o6ajbylfx 5q v0j)9z8etkq5+ onless 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 your gravitational potential energy change when y 8vlr( uw-/bf+m k)yfsou jump as high as you can fu+8 sfvy/kmr)wb -l(?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with tjp fxub 4f3kaha:gd pga:o 9os31q7,+ he same speed but with different launch angles. Which one has the highest speed on im74 hofa39q 1u +a:gbd3kjsaog, p:fpxpact? Ignore air resistance.

A pendulum is launched from gz:vmpc-; sg k6-1 vhha point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will vhm shvggz:-6 ; k1-pccause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests g)7zygu9qpo64hv g -rupright on a table. If you compress the spring by pressg oru9yg6-g7q4)v zhping down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33k,fi 0o:rre lt.2a+ om8ai g0t). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release.2i i:t 0f,ralmer0toa+g8ko the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top onqxv,f9d)p fiovbefo:* arhe d1 4 1-+f a waterfall falls to the pool bri:bp ,n4ea 1fv fxfeh+*d19 d o-qo)velow?

Describe the energy transformations when a ching:m 0lfc 8g7: zeie0zld hops around on a pogo stick.

Describe the energy transformations that take placez3l97djjme;w3.7dvbu b. n ip0qyq 7)vy fnj. when a skier starts skiing down a hill, but after a time is brought to rest by sty. wyp70e j3 m77l) zbdn .9vj.q f3njdv;ubqiriking a snowdrift.

A child on a sled (total mass m) svpot yuj8a2s/dx9i7k( ctk0 0tarts 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) 2k x0(/ak0j9dvo8 titpu7c y sit 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 thahx2 -vxj fnm7( j c6zw,ms(4jhn stepping on top and jumping dow(mfjvcx42 hm 7- ,6nxw s(zjjhn on the other side. Explain.

Two identical arrows, one with twice the speed of 07d, oqwb* kj2)m5gjemc 3dlhib;0 j lthe 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 farther than the slower ql 0k*ji5b7em 3 wgdd0j)ol2hjc b;,marrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (ajzg8l*hzd9ehr qjmx(r5.1 2)mr6s wp ) ignoring friction, and (b) taking friction into account. Explain w86xj.m rq 2 z*h(ejrglw)r d59hzsm1phy a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height grears6z- ( uwo b21ts2qkthn.6 diter than its original height? Explatsnz6 .sr-qh t6(i2uob2 wk1d in.

Suppose you lift a suitcase from the floor to a table. The work you do onf- lms03jt0/oyg6 scl 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 take3llt / 0yfm0so-c6sgjs, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for thp9vyvx6 n(eor(sy 5*t e power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail thanyl j9z6 urg/,auy th8x *t*vlp17ocb 2 to climb straight up?b1 ,uvp*l8ylgc2 r7x uh yo96j*aztt/

Recall from Chapter 4, Example 4–14, that you can use a mu/ pqdj*q 2*w46gjenpulley and ropes to decrease the forqgwjne q* *p/m 2j6ud4ce 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.

  How much work is done by the gravitation5b14sw(*rrtesfv+ ( v6: bfync *me2dyojv8gal force when a 265-kg pile driver falls 2.8b5 fe (d(s w4v*frtn*cvj86evo yg b1ys+m2: r0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is+zmp. y 9q h(lpdyz/jhsi6ba2 x3q57n requ ipyzq+ .a s27nxzb dhl5(6/pqhy39jmired?    J

  A 1300-N crate rests rbrp,rvev5,zh6+ mj ,on the floor. How much work is required to move it at constant speed pzrv,h j,rv m+5reb6 ,(a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3 mkby79d2gqo;cw5l s :x across a rough floor without acceleration, if the efo5b: sxldy2gq;79wk c fective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force axcek t67+q a9dcross a floor at a rate of for+c7a6d xq9 ket 7.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table; r m wda/nong3h0fy;.. How much work is requiredydrn./fa0 ; n wmogh;3 to stack them one on top of another?    J

A lever such as that shownm/* ybw kgrdt7(wpot(;yc06k in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of/wdw*6oyr( kt7 tg k(b; p0mcy 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° 6qhwlet87k)2)qj vpj 8gfyc - incline and is kept from accelerating by a man who - vq8fw2 7yeg8c)qk)6ljthpj is pushing 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 required to give a helicopter of mass M an accel x3;9r- obo uk3:*;d acapwjrveration of 0.10 j;cwk :o xd* ravu3a;bor 3p9-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 axis is linoc7 x991ow* hvn jhc9.s 5pdzhear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. 6–4fj 2x 00*rt/uab akrf37. Determine the work done by this force to move the object (a) from x=0 m /0u4ar*bfkft xra 2 j0to 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 lygrt9d w4lq4)p:bu3 v 9oid2on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxyshe m mfp+jx s-/c+0l4gen 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 arpbjuxu,:g i okxb-*tle 2 2yx48c(jq9row is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electron2y o(wznu 6o8n $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-q4x vwov;p/ 2/p) lozqkgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whosgz :6ay 7 ly3cz5dhskp;h *tq0e string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is thl qzsc:67;530khhgap dtzy*ye speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3/68xcapo u5d19zjcjz 2m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the bx8 96zjd5za/j1cpcu oall on the glove?    N

If the speed of a car is increased by 50%, by what farg ybyb3t;b f- izirx6(k/*c.ctor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reacyt(y-kb.grb ;x b3f ii*c 6r/ztion time.

  At an accident scene on a level road, investigators measure a car’s skid mark to sw/p)ql7)ks;n6mnzr be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slamms)n n wlsq k;zrm76)p/ed 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 time it ry.o7yy9b rd q)eaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch,) d79yo rbyy.q if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock 2blw56gp )uyk go if thrown straight up by someone who does 80.0 J of work on it? Neglk6g5l wbu2py)ect air resistance.    m

  A 285-kg load is lifted 22.0 m vertwj1 ;jc; jyu84ipsoy8ically with an acceleration by a single cable.w8 p yuji 8jjy;c1os;4 Determine
(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 st dj kl/y1e.7fgiffness constant, k, of 440N/m How much must this sprinkdly7 .j1 /fgeg be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to anothernavt c0*n1 jmq5kd+. q 1.2 m higher. What is the change in pote.j md*c1+vnq0ka 5qtnntial energy?    J

  By how much does the gravitational potential energy of a 64-kg5it 5 wac9gowzv2h4y ( pole vaulter change if hi2gwh wa zo5v59t y(c4is center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfx:p) u4rp fqfz44*l ac 6oei4sace has speed v = 65 km/h when it strikes a horizontal coiled spring and i s44*oe):pzffluc6a4 4irxpq s brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg b-e)qvw y x0a9dook from the ground so it is 2.20 m above thw- ) qavdy0xe9e ground. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of l: kmoo*y 3a3/nc svk0a 3300-m3/ma lo vy*:knc03 kos 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 hangyfj +l,kg 6.7mu fo*p+pions-ho4k l6 s vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a kkoo il, 46p.ff +s7l* g-nm +jh6pyou2.5-kg mass 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 a v1ly7q2:eam,n/x x7ws x jrf7kine hanging vertically from a tall tree in the jungle. How high can she swing ur:n m 7xk 2jxw1y l,7qes/x7afpward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting frxeovfp/d mmg:u4( 3,fa9j. qrom rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a srpei /492hwds hove 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 ki -zmzmyy6 pnc44sk; pz ui1jw:1p3.pmnetic energy is transformed into gravitational potenti61-p4zzm1;p3.jpsypn4zk y uimmcw : al 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 speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from thmnpvf 7 ,ws 0o;fz+9zoe top of a platform with a speed w +;zvsz,7m0ofpn9 ofof 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 (ignorfs/rev l3u /u4e its mass), whose spring stiffness constant is 950N/m is attached to a tablu/fvues3l4r/ e and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track showxvkg 3x.r 330q+zdbxd n in Fig. 6–39. If the block is to remain on the track, even at the to3bg3vdxk0xq dz+x.3 rp of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attacheywa7afi a-:v-leo;3 od to the end of a spring (spring stiffness constant k), Fig. 6–40. The bloc iaya-wol v-37o :ef;ak 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 cobx e-8+5oxkuj0 3 bf a1ppli,;w- wba bungee cord whose unstretched length is 12 m, and falls a total of 31 m. c-u08 xpk+obi5w;l,wxe3 bba-f o jp 1(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 Fign m,8.ytn/9v:gnk yyk . 6–41 is dragged up to point 1 where it is released mn8k n.9 yt/vyk :,ngyfrom rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throwju-k 3qbzn)g (n with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to b- 52udqcsr+l0ynp ch4 sgu3gbws o dn9u j;*--e 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 ndn+scud9j;upu0--g 4 lssq h*rny gbc 2 5-3woo more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to 4:7k iuobbjixv.;rm3 (so6bm cycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite kv(: cd+z-gwd directions, collide head-on +:dd wk cg(v-zand come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speeaq. f8/h3m ;5w2*qobtharxh k d of 2.2m/s How much thermqat5 *2 8/b3w foahm.rhxk; qhal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down e6d5,w eqnxx;(pe si0lu3f* g 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 the ground. w 9ip4kh r1a0x
(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 2u1d24ov zso-k.0 m, and it bounces back to a height of 1.5 m.suz2ood1vk 4-
(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 hobdp6ftbo/9 cxvj(92xs u5-srrizontal force of 350 N. For the first 15 m the floor is fr9xf s( d69/ j5p b2crxsbuov-tictionless, 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 5t.6(f8vh+ ufmwkj djwith a speed of If the (f6f8jj 5. h+ uvwdkmtaverage force of 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 re5hkeuwa 9 6xjpa*by /gavc)0*aches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood blocwz kfh9)l+40kud- k uk dz** -dd:jvoek is firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is nou d9k*z+ ek-klfu) : d*whkvd4-d0zjoted 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 :-w(y2,l +wbudr7m b7 b 2mpsyow3sw ipwa6n+very 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 18d+y rbpymbplwo7w+2uaw-72ww:3,s mbn6 (is 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 shuttle used u+ywt :i+z2 cua “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider +z2c+ui: yuwteventually 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 motor to lift a 315-kg piano to a s,q5+n 4glwsbv ixth-story window, v+bs4qgl5 nw 16.0 m above?    s

  If a car generates 18 hp zhs(rnd p2x e,v*b.+gwhen traveling at a steady 88km/h what must be the averng hb+.(dx,r ve ps2z*age force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. W (f.ze7l0wyyjg p37xh9hkk(y hd -4n yhat is the average power d7l7 h-(w x .zf4jeynk9hg3py(dy 0hykelivered by the engine?$\approx$    hp

  (a) Show that one British horsepow.v-ckhrb 3 y1uer$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hoursukf.e(6b0m r2 kv (yzy.”
(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 sloao 5,dni/bn 4 tq (zbc84lgbe9ws down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what poci5,g4 nd 9z8(4ben tb/obalqwer (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.vy-6c m.d -wstsj2uf/0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-vczi 6)u(,m:9a.zpfr (wq9mest( yyxkg shot from rest to 14m/s If this motion takes 1.5 s, what average pmaf yze9x q(w:v,(p c(r.izyt 9m)u6sower was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heightq6/jlg74uu8 o fzpcvb t3 ,2i,mg 9llb-ie .yh of 3.60 m. What outitho/pv,m3jy2ub,ugqlgb9 4 -67lz8 ce f.l i put rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran u/*)9yqgcki k mp the stadium stairs in 66 s. The stairs are 140 m long and inclined at 9y *k)cg/iqkm 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 6y3ncccb2 ttw l,4xa; climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum poo* gtzx8+amfl;zqp,;q n4j6t4xx x , ewer output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frizanxx; q*t,p,lfx;t6qmoe+g44 jzx8ctional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 31up(f crgft9. 9 jn9c*l0-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45 9lccg(* ffrun 9j9tp.?    hp

  A bicyclist coasts ddkj2pa.3ggbe 7-i dq3 a:ayj/own a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’seqlt l d+ot9rm 2g-5ap e8p c0:b3nkz 9wsbg;. cars have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the mate:agb 8 wgo;zl+m93p0 2 ekd5-qr ptselcn9tb. rial 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 into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm offtrmupv3,eq oh3.z*9ck4 ny,c the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. Ifron3*vu, 9yk.me3c hq,4t z pc the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–4l ml3z; qh w73ztqpnbh+tj/.+kmx :k12) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of th zt+ nm;m qh3 3wpqlbxt7kh+j.1:lk/ ze 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 sliding withoab jpw4fcva91z;52pq ut friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very topaqaw1pfbjz vc29; p 54 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 f/cf rvjh.5l80clcq r(-e- jswithout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, bfqe0l/j(l-8.c cc v5hrs-fjr ut survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is y9-fxiuixuy- hxw 9r0:6qr*u fixed (Fig. 6r-ux *ihxqwy-9 xfiuu:90 ry6–43).
(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.x2ei7y5dhiw a ,6gjv 2 The climb is made in 5.0 h starting at an elevation of 2300 h 2xa w6di7v2j5i yeg,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-kg elevator is 28 m above v9 lxjxkx4liaji0 s69;u lb .(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,+i5 g kiu(iv)j000 people per hour. If the av(jkg iiu+5vi )erage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verti -vaqbf9th 4y0cally 81 m before striking the turbine b-t0qf9by4ha vlades. 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 cizias;+ xa0 d*u/,oqcuw,l li +rcular vertical 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, t0+l/ouu ;qaaxidw,*z+,i slchis answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body counpn 3t,cuwd1whed )3;p(.gc,tc2rsc ld convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) c;gdus crctpw,3) ed h w c.1tn2p,(3n    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 u+(lj pqewmh* /pward 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 compresq45bxq8 -fd a,gf1fzw2 yo qm v1g52bb q0nft4ses 0.60 mm, and it tells you your5ftwxba1b5- gqg2, 8 0vfmq 1n24 4bfqzfdy oq weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out omh0-n j ,y:yazver a lake (Fig. 6–45). He releases the rope w-:,jmn z ayy0hhen 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*wh adaxuk30m . e(s5vbc7 q.q.0 m in 9.0 s. What miwk(.3 7v sb*0d.exaq mu5a chqnimum power output was used to accomplish this feat?    W

  Some electric-power companies use water (5nnaq. cf r.bto store energy. Water is pumped by reversible turbine p. c(.nn5abrq fumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffnessj-rafq5yqa0 r ccu+3ux b;* +i constant k is cut in half. What is the spring stiffness constant for each of the two resulting springs? rxc - 0 ;uyf+ca3j+auq*birq5  k

  A 6.0-kg block is pushed 8.0 m up a rough 37 tmi5qkki+- i ($^{\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 l h-.h qn;o-ne3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and negllhnq-o-e ;. nhect frictional losses.    s

  In a common test for cardiac function (the “stress test”), 2lz7;b 6:xc jwve xm3(oypg 9ithe patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle o;le:voyi(7p93b czj x2 wm6x gf 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 r2k s2-mndi 4t0 nle *mg-zlp)a distance of 500 m, what was its velocity when it left the volcan2gpns rntl0 m*dl-4kz-e m2)i o? $\approx$    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 95j,7llo 8wn.2 b yo.gt:u0 avgzkg/s (a) If this water wheel is set up to provide electricity output, wh:n. gg 7.z,toyvau 8bolw20ljat is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s