Block A with mass 4.0 kg, sits on a friction less table. Block B, with mass 2.0 kg, hangs down from a rope connected through a pulley to block A. What is the acceleration of block A?

Answer 1

f = m a

the total mass of the system is Ma plus Mb

the total force is gravity on Mb

short cut ... B is 1/3 of the total mass , so the acceleration will be 1/3 of g