Angular displacement of a rotating bar

[Robb Phoenix]

A ball of weight m is fixed at the end of a rod of length l. The rod is pivoted about a point on a stationary surface. If theta is the angle at which the bar is to the ground, after t seconds, what is the angular displacement covered by the bar, (the bar is weight less and there is no friction between the pivot and the bar)? No approximations allowed Don't let the problems simplicity fool you.

[factor-fiction]

What subject and level is this homework from?

[factor-fiction]

I'm not clear what the question means. Are you saying that the ball is affixed and the end of the rod moves down- and you want to know how far it moves (in terms of the angle through which the rod moves) in t seconds

Isn't the mass of the ball irrelevant?

[factor-fiction]

Is angle of displacement
Θ - sin⁻¹ (1/4.9t²)

[factor-fiction]

My letter l (L for length) appeared in my answer as a number 1 (one). Using a capital L for length the answer is :
Θ - sin⁻¹ (L/4.9t²)

Does this help?