The two masses (m1 = 4.96 kg and m2 = 2.90 kg) in the Atwood's machine shown in the figure below are released from rest, with m1 at a height of 0.800 m above the floor.

Question

When m1 hits the ground its speed is 0.203 m/s. Assuming that the pulley is a uniform disk with a radius of 13.3 cm, calculate the pulley's mass.

* I tried using PE intial of large mass is equal to KE final of the pulley plus PE final of the small mass but I am not getting the correct answer.