The figure shows a pulley mass system which is kept in an elevator moving up with acceleration g. Then the tension T in the string is given by

[c] Let us solve the question with respect to elevator for. Let acceleration of m1 with respect to elevator is a upward then acceleration of m2 with respect to elevator is a down. For m1, T−m1g−m1g=m1a [considering pseudo force] For m2, m2g+m2g−t=m2a ⇒   Tm1−(2g)=2g−tm2 ⇒   T=4g×m1m2m1+m2