# Two points $A$ and $B$ move from rest along a straight line with constant acceleration $f$ and $f'$ respectively. If $A$ takes $m$ sec more than $B$ and describes $'n'$ unit more than $B$ in acquiring the same speed, then :
( A ) $(f' - f) n = \frac{1}{2} ff' m^2$
( B ) $\frac{1}{2} (f+f') m = ff' n^2$
( C ) $(f + f') m^2 = ff' n^2$
( D ) $(f - f') m^2 = ff' n^2$