Answer
t = 0
Work Step by Step
In the previous part of the problem we found that
$v=20−15t^2 $
To find the acceleration equation we need to find the derivative of the velocity equation or
$\frac{d}{dt} (20 - 15t^2) = -30t $
Therefore $ a = -30t $
To find when acceleration is equal to 0 we set a = 0 and solve for t
0 = -30t and therefore, acceleration is 0 when t =0
