4. Two 30 kg blocks rest on a massless belt which passes over a fixed pulley and is attached to a 40 kg block. If coefficient of friction between the belt and the table as well as between the belt and the blocks B and C is μ and the system is released from rest from the position shown, the speed with which the block B falls off the belt is: 2m 2m 30 kg B C30 kg 40 kg A (A) 2√2 m/s if u = 0.2 (B) √√2 m/s if μ = 0.2 (C) 2 m/s if u = 0.5 (D) 2.5 m/s if u = 0.5​