# Oscillations of a mass on a spring.

A mass m suspended from a spring of constant k has a period T. If a mass M is added, the period becomes 3T. Find M in terms of m.

T=2pi(m/k)^(1/2)

I know that the period varies as the square root of the mass so the mass M should be 9 times that of m. The answer is M=8m. I dont know why it is 8 instead of 9. Any help would be appreciated.

Thanks

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