Question

suppose two 4 newton forces act on an object in the same direction. what is the net force on the object

Answer 1

The answer is a total of 8 Newtons.
Imagine that those forces were two small rocket engines, each one producing 4 Newtons of force. One motor would produce 4 Newtons of force and the object, if it can move, would accelerate at a = f/m, force being 4 N. attaching 2 rocket motors would now apply a total of 8 Newtons and, with the m remaining the same, the rate of acceleration would double: 2a = 2f/m.
Hope this helps you understand.