Question

the force acting on a ball due to the earth has a magnitude Fb and that acting on the earth due to the ball has a magnitude Fe then

Answer 1

Than according to Newton's third law

Force due to earth on ball = Force due to ball on earth but in opposite direction.

so,
Fb = - Fe

Answer 2

The force acting on the ball due to the earth has a magnitude of Fb. The force acting upon the earth due to the ball is Fe. In this case, the earth and the ball both are exerting force on each other. There is no external force acting on the system. Therefore, these forces are internal forces of the system.

According to Newton's Third Law of Motion, these forces Fb and Fe should be equal in magnitude and act in opposite directions. The internal forces acting upon bodies in a system are always equal and opposite.

Newton's Third Law of Motion is given as:

" For every action in the universe, there is an equal and opposite reaction."

It should be kept in mind that action and reaction are not clearly defined. They are acting at the same time.