One of the strings at end Q is cut at t = 0 and the rod starts rotating about the other end P. Then
At t = 0, angular acceleration of rod about P is 3g2L.
At t = 0, angular acceleration of rod about C.M. of rod is 3g2L.
At t = 0, acceleration of C.M. of rod is 3g4 in downward direction.
At t = 0, tension in the string at P is Mg4
MgL2=ML23α∴ α=3g2L∴ acom=αL2=3g2LL2=3g4−T+Mg=M3g4∴ T=Mg4