In solving this type of problem, there is a four step method.



Step no1  Identify the system ( body on which the equn F=ma is to be applied)



Step no2 List all the forces acting on the system.



Step no3  Draw a free body diagram ( a diagram in which we consider the body under consideration as a point and show all forces by lines in proper direction)



Step no4 Finally appply the equn F=ma

now let us take an example :

Q. The inclined plane forms an angle alpha=30 with the horizontal table.The mass ratio m2/m1=2/3.The coefficient of friction betn the body m1 and the inclined plane is equal to =0.10.The masses of the pulley and the threads are negligible.Find the magnitude and the direction of acceleration of the body m2 when the formerly stationary system of masses starts moving.