Selectividad Junio Fisica

FÍSICA, MADRID JUNIO 2011-2012 OPCIÓN B

F atracción = F centrípeta
G.M.m / r2 = m.w2.r
w = (G.M/r3)1/2 =[6’67.10-11.5’98.1024/(2’5.107)3]1/2 = 1’6.10-4 rad/s
-4
T = 2.π/w = 2. π / 1’6.10 = 39534 s
Ep = - G.M.m/r = - 6’67.10-11.5’98.1024. 3000 /2’5.107 = - 4’79.1010 Julios
Ec = ½ m.v2 = ½ . G.M.m/r = 2’39.1010 J

I = P / S = P / ( 4.π.r2) = 1.10-3 / (4.π.102) = 7’96.10-7W/m2
P5 = 5.P = 5.10-3 W
I5 = P5 / S = P5 / ( 4.π.r2) = 5.10-3 / (4.π.202) = 9’95.10-7 W/m2

β = 10 log(I / Io) = 10 log(7’96.10-7 / 10-12) = 59’01 db
β = 10 log (9’95.10-7 / 10-12) = 59’98 db

w = 50 rpm = 50.2.π /60 = 5.π /3 ,, S = π.R2 = π.0’12= 0’01. π m2
Φ = B . S = B . S . cos θ = B . S . cos w.t
Φ (t=2) = 0’3 . 0’01. π . cos (2. 5.π /3) = - 4’7.10-3 T.m2
ε = - dΦ /dt = - B . S . w . sen w.t = - 0’3 . 0’01. π . 5.π /3 . sen (5.π.t /3)

= 0’049 . sen (5.π.t /3)

voltios

1 / x’ + 1/ x = 1 / f
1 / x’ + 1 / (-20) = 1 / (40)
1 / x’ = 1/40 + 1/20 = 3/40
x’ = 40/3 = 13’3 cm > 0 imagen virtual
A = y’ / y =- x’ / x = - 13’3 / (-20) = 0’67
y' = 0’67 . 15 = +10 cm

Hay efecto relativista
m = mo / β = 1 / 0’8 = 1’25 mg
β = (1-v2/c2)1/2 = (1 – 0’62)1/2 = 0’8
E = ∆m . c2 = (1’25 – 1).10-6.(3.108)2 = 2’25.1010 julios

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