What is the buoyant force on it (in lb)? (Enter the magnitude.)

Question

An ebony log with volume 13.4 ft³ is submerged in water. What is the buoyant force on it (in lb)? (Enter the magnitude.)

Answer 1

To determine the buoyant force on the log, we must first understand what the buoyant force is. With any buoyant force, the magnitude is equal to the weight of water displaced by the object in question.

In this case, it tells you the log has a volume of 13.4 cubic feet and is full submerged. Because the log's volume is 13.4 ft^3 and it is also fully submerged, we know the volume of water displaced by the log is also equal to 13.4ft^3.

We can use the mass density of water to determine the weight of the displaced volume of water, which will be equal to the magnitude of our buoyant force.

The weight density of water is ~62.4 lb/ft^3. To find the weight of the displaced volume of water, simply multiply the weight density by the volume of water in question.

Weight of Water Displaced = (Volume of Water Displaced)*(Weight Density of Water)

Weight of Water Displaced = (13.4ft^3)*(62.4 lb/ft^3) = 836.16 lb.

So, we now know the magnitude of the buoyant force acting on the log is equal to 836.16 lb