You have two balls of equal size and smoothness, and you can ignore air resistance. One is heavy, the other is much lighter. You hold one in each hand at the same height above the ground. You release them at the same time. What will happen?

They will hit the ground at the same time.

Explanation:

By ignoring the opposing forces i.e. air resistant, both the heavy and light balls will fall with same acceleration due to gravity (g=9.8 m/s²) and g is independent of mass of the objects. Thus both will hit the ground at the same time.