Question

what is magnitude of the buoyant force?

Answer 1

Archimedes (a greek mathematician) determined that a body which is completely or partially submerged in a fluid experiences an upward force called the Buoyant Force, B , which is equal in magnitude to the weight of the fluid displaced by the object.

Answer 2

Archimedes principle, states that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant force the magnitude of which is equal to the weight of the fluid displaced.