1. The problem statement, all variables and given/known data A rock of mass M with a density twice that of water is sitting on the bottom of an aquarium tank filled with water. The normal force exerted on the rock by the bottom of the tank is? 2. Relevant equations 3. The attempt at a solution The answer is Mg/2, I understand how to arrive at that by subtracting the buoyant force which is equal to mg from the gravitational force on the object which is 2mg. but shouldn't the normal force on the object be different when there are different amounts of water pushing down on it? Since the amount of water is not given shouldn't the correct answer be "impossible to determine from the information given?