Hello Dear

Let me tell you that since you have already done the B.Tech in the Mechanical engineering and you wish to do join the field Master of Social Work , infact it is good but after that there won't be any use of your degree which you have done four years in the Mechanical domain you will be unable to take the full advantage of that. So better try to reshape your career in the Mechanical field in comparison with the M.S.W.

All the best