F.4 Physics question.

The answer is B. The vertical distance between the objects equal to d during the fall.

Explanation:
As there is no atmosphere (air) in the Moon, so there is no air resistance for free falling. So, a (acceleration due to gravity) is a constant throughout the journey.

The initial velocity of the two objects are the same = 0

Let s1 be the displacement of the lighter object, s2 be that of the heavier one.

For the lighter object, apply the equation:
s1 = ut + 1/2 at^2
s1 = (0)t + 1/2 at^2
s1 = 1/2 at^2 m


For the heavier object, apply the equation:
s2 = ut + 1/2 at^2
s2 = (0)t + 1/2 at^2
s2 = 1/2 at^2 m

So, the distance travelled by the two objects are the SAME thoughout the journey.
Therefore, the vertical distance between the objects are equal to d during the falling.

B.

Same uniform acceleration on the moon surface;
No frictional force on the surface of the objects as there is no air on the moon. So the objects will not slow down themselves.

B.
Because the acceleration due to gravity have not change, thus two objects will fall with the vertical distance d.