A particle starts from rest.  Its acceleration (a)  versus time (t) is as shown in the figure.  The maximum speed of the particle will be   

Acceleration is +ve till it becomes zero. Thus velocity is maximum at $t=11\sec$

 $\therefore$ Area under a-t graph =change in velocity = $\frac{1}{2}\times 11\times 10=V-0$

 $\therefore V=55m{s}^{-1}$