How Many Electrons Are Needed to Accelerate Two Spheres at 25.0g?

[joseph5640]

Homework Statement

Two very small 8.55-g spheres, 15.0 cm apart from centre to centre, are charged by adding equal numbers of electrons to each of them. Disregarding all other forces, how many electrons would you have to add to each sphere so that the two spheres will accelerate at 25.0g when released?

Homework Equations

F= abs( (kq1q2)/r^2)

The Attempt at a Solution

25(9.81)=245

(245)(0.15)^2 = (9.00x10^9)(x^2)
(5.51 / 9.00x10^9) = x^2
2.47x10^-5 C = x = charge of one sphere

(2.47x10^-5) / (1.6x10^-19) = 1.55x10^14 electrons in one sphere

The answer's wrong :(

 

[gneill]

You've used acceleration ("245") where you need force. What force is required to produce the acceleration 245 m/s²?