Question

You are trying to push your stalled car. although you apply a horizontal force of 400 n to the car, it doesn't budge, and neither do you.

Answer 1

Three forces are stopping the car from moving, in this case, and they are all giving a force of 400N, as well. The road is exerting a frictional force of 400N on the person pushing the car, the car itself is also exerting a force of 400N, and the car is exerting a frictional force on the road, all at a measure of 400N.