# Buoyant force/density problem

1. Mar 3, 2009

### jsalapide

1.A beach ball has a volume of 0.050 m^3. How much force would you have to exert to hold this beach ball completely under water?

can somebody help me plss,,,,

2. Mar 3, 2009

### redargon

what have you tried so far?

There is a template for homework questions and a seperate section.

3. Mar 3, 2009

### jsalapide

I learned that for an object that is completely submerged in a liquid, the density of the object is equal to the density of the liquid.

I used the formula p=m/v to get the mass of the ball. I set p as the density of water which is 1000 kg/m^3. The answer I got was 50 kg. Then I multiply it to 9.8 m/s^2 to get the buoyant force.

Am I correct???

4. Mar 3, 2009

### PhanthomJay

This is not correct. Look up Archimedes principle.
For all practical purposes, the density of the air filled beach ball can be neglected...that is, assume it has no weight.
The buoyancy force is 490N upward. What downward force must be applied to keep the ball completely underwater?