# Two identical particles each of mass M and charge Q are placed a certain distance part. If they are in equilibrium under mutual gravitational and electric force then calculate the order of QM in SI units.

#### As the given system of charges are in equilibrium,

hence Fe=Fg

Fe is the electric force between the charges which is

repelling them while Fg is the gravitational force of attraction.

ie. KQ2R2=GM2R2

or , KQ2=GM2

or , (QM)2=(GK)

or , QM=(GK)12

as G = 6.67×10−11Nm2/Kg2

and K = 9×109Nm2/C2

(QM)2=(6.67×10−11)(9×109)

or QM=[0.7411×10−(11+9)]12

or QM=(0.7411×10−20)12

we get QM=0.86×10−10 c / kg