We can find it up angular velocity with respect to time graph .
As
[tex]\\ \rm\Rrightarrow m=\dfrac{\Delta \omega}{\delta T}[/tex]
[tex]\\ \rm\Rrightarrow \alpha=\dfrac{\Delta \omega}{\delta T}[/tex]
So we get
[tex]\\ \rm\Rrightarrow m=\alpha[/tex]
We need the slope in order to find angular acceleration