@Alroy fernandes
here is the complete question
Arrangement of two block system is as shown in the figure . mass of block A is
and mass of B is
A constant force F = 100 N applied on upper block A . Friction between A and B is . and b/w B and ground surface is smooth , then find work done by frictional force on block B in t = 2 sec if system starts from rest

For block A

N = mg
=
For block B