Apparent weight of a submerged rock.

[benjamin8462]

Homework Statement

What is the apparent weight of a rock submerged in water if the rock weighs 58 N in air and has a volume of 1.8 * 10^-3 m^3?

And then as a continuation:

A rock weighing 57 N with a volume of 2.3 10-3 m3 is submerged in a liquid with a density exactly twice that of water, what will be its new apparent weight reading in the liquid?

Homework Equations

The Attempt at a Solution

I did m*(a+g) but that was incorrect unfortuneately.

 

[issacnewton]

When the rock is submerged completely then there will be the force of buoyancy. This force is equal to the weight of the displaced fluid. If all the rock is submerged then the force of buoyancy will be $\rho_{water}Vg$ where $\rho_{water}$ is the density of the water and V is the volume of the rock. So there will be force of gravity ,mg, downwards and the buoyancy force upwards. So the net force downwards is the apparent weight.

$$\mbox{Apparent Weight}\quad =mg- \rho_{water}Vg$$