The question is an illustration of related rates.
The rate of change between you and the ball is 0.01 rad per second
I added an attachment to illustrate the given parameters.
The representations on the attachment are:

---- the rate

First, we calculate the vertical distance (y) using tangent ratio

Substitute 100 for x


Differentiate both sides with respect to time (t)

Substitute values for the rates and 

This gives


Divide both sides by 2


Hence, the rate of change between you and the ball is 0.01 rad per second
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