WAEC Physics 2015 Theory — Question 10

Model answer

A floating ship is balanced by its own weight and the upthrust acting on it. When the ship is unloaded (off-loaded), the upthrust would exceed the reduced weight of the ship, making it unstable and prone to capsizing. Refilling it with sand and water adds ballast weight that restores the balance between weight and upthrust, keeping the ship stable and low enough in the water.