Maximum tension in the string T = mg

            = 30 x 10
        
           = 300 N



          T - mg = ma

From the figure

       300 - 10 x 10 = 10a

$\therefore$    a = 20 m s^-2

Thus, the maximum acceleration with which the stone can be raised is 20 m s^-2.

Given,     s = 10 m

and         u = 0

$\therefore$       $10=\frac{1}{2}\left(20\right){\text{t}}^2$

$\Rightarrow$         t = 1 s