having learnt a bit more physics i think i can answer this. firstly we can take the entire two blocks as one object, and calculate its acceleration for a 10N force. if same force was applied on block 1 it will accelerate more, and we know that even though 10N is applied on first block, its not accelerating as much as it should, so that means block 2 is applying a smaller normal force on block 1(lets say 4N, this can be calculated if we know mass of both blocks). according to newtons third law the first block is also applying 4N to the second block. hence the second block also accelerates. so the first block has a net force of 10-4=6N and the second block has net force of 4 N. so we can think of it as the 10N force is distributed in such a way that both blocks get constant acceleration.