posted by mike .
A block attached to a spring with unknown spring constant oscillates with a period of 6.0 s. What is the period if the mass is doubled?
The period is the same. If you do a proof with different equations, the mass of an object doesn't change its period. However, if the length of the spring was changed the period then would change.
When you do the proof, the mass ends up canceling out of the equation so it can be ignored.