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A coin is placed on a horizontal platform which performs vertical simple harmonic motion of angular frequency ω. The amplitude is increased gradually. The coin will leave contact with the platform for the first time

Asked in JEE Main 2006 · Wire, tunnel and contact-loss systems

Answer: (3) for an amplitude of g/(ω²)

Step-by-step solution

The platform can only push the coin upward, so it must supply the downward acceleration ω²y needed at displacement y using gravity alone plus contact.

The demand is greatest at the top, where the required downward acceleration is ω²A.

Contact is first lost when ω²A=g, i.e. at an amplitude of g/(ω²).

Why the other options are wrong

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