Solving MA: Sum of Forces = Mass x Acceleration

[Oblivion77]

Homework Statement

Homework Equations

Sum of forces = MA

The Attempt at a Solution

I already found the answer to part A, which is 10kg. But for part B I am not sure which box to draw my FBD on.

 

[Doc Al]

But for part B I am not sure which box to draw my FBD on.

Since you want the acceleration of body A, analyze the forces on body A.