Since the air has been removed, there are no opposing forces acting on the feather. The feather moves in a straight line.

So, we can use one of the equations of linear motion. We know $\displaystyle s = 2\ m $. We know that the initial velocity of the feather is $\displaystyle 0$, i.e. $\displaystyle u = 0 $. $\displaystyle a = g = 10\ \ or \ \ 9.81 ms^{-2}$.

$\displaystyle s = ut + \frac {1}{2} at^{2} $

$\displaystyle 2 = 0 \times t + \frac {1}{2} \times 9.81 \times t^{2} $

$\displaystyle 2 = \frac {1}{2} \times 9.81 \times t^{2}$

$\displaystyle t = \sqrt {\frac {2}{\frac {1}{2} \times 9.81}} $

$\displaystyle t = 0.639 s $ (correct to 3 sig. fig.)

With $\displaystyle g = 10$, you get $\displaystyle t = 0.632 s$.

I hope that helps.

ILoveMaths07.