What is the frequency of the bobbing raft with a 4990 kg load in fresh water?

[lizzyb]

Hi - I'm not sure where to begin with this question:

Question:
A 4 m by 11 m raft whose mass is 17600 kg floats in fresh water. A 4990 kg load is dropped on the raft.

The acceleration of gravity is 9.8 m/s2 .

With what frequency does the raft bob up and down?

Answer in units of Hz.

Comments:

??

 

[lizzyb]

ok I can use archimedes' principle regarding buoyancy force to determine how far the raft is depressed from it's initial equilibrium position below the surface to the water to the distance below the water when the load is dropped on it, but what then?

 

[lizzyb]

frequency = $$\frac{1}{2 \pi} \sqrt{\frac{\rho A g}{m}}$$