CHAPTER 45 - 7

# CHAPTER 45 - 7 - K / K = ! I ϖ 2 / ! I ϖ 2 = ϖ / ϖ = (2...

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Unformatted text preview: K / K = ! I ϖ 2 / ! I ϖ 2 = ϖ / ϖ = (2 × 10 10 rev/mo)/(1 rev/mo) = 2 × 10 10 . 39. The kinetic energy of the neutron star is K = ! I ϖ 2 = ! ( ^ Mr 2 ) ϖ 2 = ! ( ^ )(1.5)(2.0 × 10 30 kg)(5.0 × 10 3 m) 2 [(1.0 rev/s)(2p rad/rev)] 2 = 5.92 × 10 38 J. The power output is P = E / t = (10 –9 day –1 )(5.92 × 10 38 J)/(86,400 s/day) = 7 × 10 24 W . 40. If R is the radius of the universe, the volume is V = ) p R 3 . We find the increase in radius from Hubble’s law: ? R = v ? t = HR ? t . Thus the rate at which the universe in expanding is ? V /? t = 4p R 2 ? R /? t = 4p R 3 H = 3 VH . The rate at which hydrogen atoms have to be created is given by ? m /? t = m H ? N /? t = ρ ? V /? t = ρ 3 VH . If we find the rate per unit volume, we have (? N /? t )/ V = 3 ρ H / m H = 3(10...
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## This note was uploaded on 09/13/2010 for the course PHYSICS 7 taught by Professor ? during the Spring '08 term at University of California, Berkeley.

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CHAPTER 45 - 7 - K / K = ! I ϖ 2 / ! I ϖ 2 = ϖ / ϖ = (2...

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