A 220-kg wooden raft floats on a lake. When a 75-kg man stands on the raft, it

Question:

A 220-kg wooden raft floats on a lake. When a 75-kg man stands on the raft, it sinks 4.0cm deeper into the water. When the steps off, the raft vibrates for a while.
(a) What is the frequency of vibration?
(b) What is the total energy of vibration (ignoring damping)?