Question

A scuba tank, when fully submerged, displaces 15.7 l of seawater. the tank itself has a mass of 13.7 kg and, when "full," contains 3.00 kg of air. the density of seawater is 1025 kg/m3. assume that only its weight and the buoyant force act on the tank.

Answer 1

The problem is asking for the buoyant force.
The first step is to know the weights of the tank and air. Tank = 13.7 * 9.8 = 134.26 N Air = 3 * 9.8 = 29.4 N Total weight of the tank and air is 163.66 N 
To know the buoyant force, we must convert 15.7 liters to cubic meters. 
1 liter = 1000 ml = 1000 cm^3 1 m = 100 cm 1 m^3= 1,000,000 cm^3 One liter = 1000 divided by 1,000,000 = 0.001 m^3 V = 15 * 0.001 = 0.015 m^3 
Then compute for the buoyant force:Buoyant force = 0.015 * 1025 * 9.8 = 150.675 N