I'(t) = \frac{1000(t^2 + 10) - 1000t(2t)}{(t^2 + 10)^2} = \frac{1000t^2 + 10000 - 2000t^2}{(t^2 + 10)^2} = \frac{-1000t^2 + 10000}{(t^2 + 10)^2}