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1109_Physics ProblemsTechnical Physics

# 1109_Physics ProblemsTechnical Physics - 450*P39.48...

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450 Relativity *P39.48 Let observer A hold the unprimed reference frame, with u c 1 3 4 = and u c 2 3 4 = − . Let observer B be at rest in the primed frame with ′ = = u u v u v c 1 1 1 2 0 1 v u c = = 1 3 4 . (a) Then ′ = = − − + = + u u v u v c c c c c c 2 2 2 2 1 3 4 3 4 1 3 4 3 4 1 5 1 9 16 b gb g . speed = ′ = = = u c c c 2 3 2 25 16 24 25 0 960 . . (b) In the unprimed frame the objects, each of mass m , together have energy γ γ mc mc mc mc 2 2 2 2 2 2 1 0 75 3 02 + = = . . . In the primed frame the energy is mc mc mc 2 2 2 2 2 1 0 1 0 96 4 57 + = . . , greater by 4 57 3 02 1 51 2 2 . . . mc mc = times greater as measured by observer B . Section 39.9 Mass and Energy P39.49 Let a 0.3-kg flag be run up a flagpole 7 m high. We put into it energy mgh = 0 3 7 20 . kg 9.8 m s m J 2 e j . So we put into it extra mass m E c = = × = × 2 8 2 16 20 3 10 2 10 J m s kg e j for a fractional increase of 2 10 10 16 15 × kg 0.3 kg ~ . P39.50 E = ×
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