Find the unbalanced force acting on the object.

To find the unbalanced force you have to use the formula *net force=resultant force=unbalanced force =outside force).

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.