# Archimede's Principle help

My professor briefly went over Archimede's principle and assigned some problems on it. I do not know how to attack it. Here's the first problem he gave:

A Ping-Pong ball has a diameter of 3.80 cm and average density of 0.084 g/cm^3. What force is required to hold it completely submerged in water?

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OlderDan
Homework Helper
APool555 said:
My professor briefly went over Archimede's principle and assigned some problems on it. I do not know how to attack it. Here's the first problem he gave:

A Ping-Pong ball has a diameter of 3.80 cm and average density of 0.084 g/cm^3. What force is required to hold it completely submerged in water?
The buoyant force is equal to the weight of the water displaced by the ball. You can find that by figuring out the volume of the ball and multiplying by the density of water. The net force on the ball is its little bit of weight, plus you pushing it down, plus the buoyant force, and those add up to zero.

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Doc Al
Mentor
Start by identifying all the forces acting on the ball, including the applied force. One of those forces is the buoyant force, which Archimede's principle says is equal to the weight of the displaced water. (The buoyant force is the force that the fluid--water, in this case--exerts on a submerged object.)