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The amplitude of a damped oscillator decreases to 0.9 times its original magnitude in 5s. In another 10 s it will decrease to α times its original magnitude, then α is equal to :(a) 0.7 (b) 0.81 (c) 0.729 (d) 0.6 |
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Answer» Answer : (c) 0.729 The amplitude of damped oscillator is, A = A0e-kt, Where k = \(\frac{b}{2m}\) At t = 5s, 0.9 A0 = A0e-5k ⇒ e-5k = 0.9 At t = 15s, αA0 = A0e-15k ⇒ e-15k = α ⇒ e(-5k)3 = α ⇒ α = (0.9)3 = 0.729 |
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