Two spherical objects with a mass of 3.17 kg each are placed at a distance of 2.96 m apart. How many electrons need to leave each object so that the net force between them becomes zero

1.704 × 10¹⁹ electrons

Explanation:

The gravitational force due to the identical masses with mass, m = 3.17 kg at a distance r = 2.96 m from each other is F = Gm²/r².

Since equal number of electrons have to leave both masses, we have a charge q on each mass acting to oppose each other at distance r.

So, the electrical force of repulsion is thus

F'= kq²/r²

For the net force to be zero, the gravitational force of attraction must balance the electrical force of repulsion.

So, F = F'

So,  Gm²/r² = kq²/r²

Gm² = kq²

q² = Gm²/k

taking square root of both sides, we have

q = m√(G/k)

So, substituting the values of the variables into the equation, we have

q = m√(G/k)

= 3.17 kg√(6.67 × 10⁻¹¹ Nm²/kg²/9 × 10⁹ Nm²/C²)

= 3.17 kg√(0.741  × 10⁻²⁰ C²/kg²)

= 3.17 kg × 0.861 C/kg

= 2.73 C

Now, q = ne where n = number of electrons and e = electron charge = 1.602 × 10⁻¹⁹ C

n = q/e

= 2.73 C ÷ 1.602 × 10⁻¹⁹ C

= 1.704 × 10¹⁹ electrons