JEE Class main Answered

Man and platform constitue a system . In the absence of external force, cenre of mass of the system consists of man and platform does not move.

Hence if man of mass m moves with speed v then platform moves with speed V in opposite direction so that we get

m v + M V = 0

V = - (m/M) v

V = -( 60/180) 2 m/s = (2/3) m/s

Hence if man moves with speed 2 m/s,  then distance moved by man in 6 s = 12 m

The distance moved by platform in opposite dircection in 6 s = ( 2/3) × 6 m = 4 m

Hence distance moved by man with respect to ground = ( 12 - 4 ) m = 8 m