# Specific gravity

1. Jul 19, 2004

### akatsafa

A stone of weight has specific gravity 2.50. (a) what is the apparent weight of the stone when under water? (b) what is its apparent weight in oil (specific gravity=0.90)?

I figured out the density to be 2500, but how do i relate the specific gravity and density to find the apparent weight?

Thanks.

2. Jul 19, 2004

### JohnDubYa

The term appararent weight sucks.

Instead, you should be asked to find what a scale would read when the stone is submerged. Hanging scales (like the kind you find in produce sections) are tension force o'meters, so all you need to find is the tension in the rope and you have your scale reading (and thus your apparent weight).

So, when submerged three forces act on the stone. Gravity acting down. Buoyancy and tension acting up. Newton's second law says that

$$T + F_B - mg = 0$$

Substitute the proper expression for the buoyancy force and solve for T.