# Buoyant force problem

by kellyneedshelp
Tags: buoyant, force
 Emeritus Sci Advisor PF Gold P: 9,772 If we take the equation which you stated; $$F_{b} = \rho V g$$ The 'thing' that is creating the bouyant force is the difference between the relative densities of the fluids hence in your case; $$F_{b} = ( \rho_{air} - \rho_{helium} )Vg$$ -Hoot
 Sci Advisor HW Helper PF Gold P: 12,016 First, you must state the total weight of your system: $$W=W_{person}+W_{balloon}+W_{helium}$$ Note that your unknown volume appears in [itex]W_{helium}[/tex] Assuming that you and the balloon material contributes only negligibly to the total volume of the system, you can now find what the volume must be by equating this total weight with the buoyant force (which is the net pressure force needed to keep a volume V of air floating in..the air).
 HW Helper P: 1,471 Buoyant force problem Try adding the weight of the helium in the balloon to the lefthand of your equation, the mass of the balloon probably do not include this additional weight $$m_{helium}g=\rho_{helium} Vg$$