Question

A 10-kg piece of aluminum sits at the bottom of a lake, right next to a 10-kg piece of lead, which is much denser than aluminum. Which one has the greater buoyant force on it? Please explain. Answer: B - the aluminum
A) Both have the same buoyant force.
B) the aluminum
C) the lead
D) It cannot be determined without knowing their volumes.

Answer 1

The buoyant force on a submerged object is the weight of the water it displaces ... the water it pushes out of the way.  That amount is simply the volume of the submerged object.  So the more volume is submerged, the greater will be the buoyant force acting on it.

Since Aluminum is less-dense than lead, the same 10kg of Aluminum needs a bigger container to hold it than 10kg of lead needs.  The aluminum needs  more volume to hold the same mass.

The aluminum displaces more water.  So the buoyant force acting on the aluminum is greater than the buoyant force acting on the lead. (B) .

I'm guessing this is a big part of the reason why fishing sinkers are not made of aluminum.

Answer 2

I think that the answer is B