The device shown below is Atwood's machine. Assuming that the masses of the string and the frictionless pulley are negligible. The masses of the two blocks are m1= 4.00 kg and m2= 6.00 kg.

A: What is the magnitude of the tension in the string ?

B: If the blocks are released from rest, what are the speeds of the two blocks after 3 seconds ?

C: If the pulley is NOT massless, how would the acceleration of the blocks change? (increases or decreases) Please explain your answer.