A small metal sphere has a mass of 0.11 g and a charge of -25.0 nC. It is 10.0 cm directly above an identical sphere that has the same charge. This lower sphere is fixed and cannot move. If the upper sphere is released, it will begin to fall. What is the magnitude of its initial acceleration? Express your answer with the appropriate units.

Explanation:

According to Newton's Second Law, the acceleration of the sphere is equal to the net force on the sphere divided by its mass, a = F/m.

The net force is the sum of the weight of the sphere and the electrostatic force applied by the lower sphere.

Since both spheres have the same charge, they repel each other, which means that the electrostatic force on the upper sphere is directed upwards. Naturally, the weight of the sphere is directed downwards. So, the net force is

Therefore, the magnitude of the initial acceleration of the sphere is

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