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592_Physics ProblemsTechnical Physics

# 592_Physics ProblemsTechnical Physics - 594*P20.60 Heat and...

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594 Heat and the First Law of Thermodynamics *P20.60 The initial moment of inertia of the disk is 1 2 1 2 1 2 1 2 8 920 28 1 2 1 033 10 2 2 2 2 4 10 MR VR R tR = = = = × ρ ρπ π kg m m m kg m 3 2 e j a f . . The rotation speeds up as the disk cools off, according to I I MR MR MR T T i i f f i i f f i f f i ω ω ω ω α ω ω ω α = = = = = × ° ° = 1 2 1 2 1 2 1 1 1 25 1 1 17 10 830 25 720 7 2 2 2 2 2 6 2 c h c h e j rad s 1 C C rad s . (a) The kinetic energy increases by 1 2 1 2 1 2 1 2 1 2 1 2 1 033 10 25 0 720 7 9 31 10 2 2 2 10 10 I I I I I f f i i i i f i i i i f i ω ω ω ω ω ω ω ω = = = × = × d i b g . . . kg m rad s rad s J 2 (b) E mc T int kg 387 J kg C C C J = = × ⋅° ° ° = × 2 64 10 20 850 8 47 10 7 12 . . b ga f (c) As 8 47 10 12 . × J leaves the fund of internal energy, 9 31 10 10 . × J changes into extra kinetic energy, and the rest, 8 38 10 12 . × J is radiated. *P20.61 The loss of mechanical energy is 1 2 1 2 670 6 67 10 6 57 10 4 20 10 1 08 10 2 2 11 10 10 11 mv GM m R i E E + = × + × × × = × + × = × kg 1.4 10 m s Nm 5.98 10 kg 670 kg kg 6.37 10 m J J J 4 2 24 2 6 e j . . . . One half becomes extra internal energy in the aluminum:
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