Question

Two masses, each of mass `3 kg` are being held `7` meters apart on a table (neglect friction). They each have `100` microcoulomb of excess negative charge, what will the initial acceleration of each one be when they are let go?

Answer 1

There are two forces between them

1. Electrostatic repulsive force `(F_e)`
2. Gravitational attractive force `(F_g)`

`F_e = (kq^2)/d^2 = (9 × 10^9 "Nm"^2//"C"^2 × (100 × 10^-6 "C")^2)/("7 m")^2 = "1.84 N"`

`F_g = (Gm^2)/d^2 = (6.67 × 10^-11 "Nm"^2//"kg"^2 × ("3 kg")^2)/("7 m")^2 = 1.225 × 10^-11 "N"`

Gravitational force between them is negligible when compared to electrostatic force.

Therefore,

Acceleration `= F/m = "1.84 N"/"3 kg" = "0.613 m/s"^2`