1. The problem statement, all variables and given/known data Find the number of kilograms needed to pull apart evacuated Magdeburg Hemispheres whose radii are 25.0 cm when the barometer reads 760mm of Hg. I really don't know where to start. Could someone walk me through it? 2. Relevant equations Unknown. 3. The attempt at a solution I read somewhere that an equation to help is F=pi*r^2, so I made 25.0cm into 0.250m, and made F=pi*0.0625... but that doesn't seem right.