yaar simple hai......tumhe bas angular momentum conserve karna abt the pt of obstacle......

initial angular p=mvR/2 +2/5mvR=9/10mvR

final angular p=(I about the point) W(final)

=7/5mR2 *w

equating initial and final ps we have....

final w=9/14W ......

i amnt very sure abt the final ans.(ekadh silly mistake hogaya hoga)

but the method im sure is correct....

rate if useful.....