Question

What must be the charge on each of two 100 kg spherical masses in order for electrical force to be equal to gravitational force?

Answer 1

Electro static fore=F=Kq1q2/r²  
F=Kqxq/r² ----------(1)[q=q1=q2]]

According to law of gravitational force :
F=Gm1m2/r² ---------(2)
Given that Electric force equals to gravitational force.

Kq1q1/r²=m1m2 G/r²
q²K=100x100 xG
where k value= 9x10 ⁹Nm²/C²
G=6.67x10⁻¹¹ NKg² m⁻²

on substituting values we get,

q²=10⁴x6.67x10⁻¹¹ / 9x10 ⁹
=10⁻¹⁶x 6.67/9

q²=10⁻¹⁶ x 0.74
q=√10⁻¹⁶ x 0.74
=10⁻⁸ x 0.86
=8.6 x10⁻9 C
=8.6 nano C