If a box is not accelerating on a slope of 20 degrees, what is the net force acting on the box?

if it is accelerating, what is the net force?

The net force is zero, if there is not external forces. The net force if the body is accelerating will be the product of the mass by the acceleration.

Explanation:

If the box does not accelerate, there are two possible options, either the box moves at constant velocity or does not receive any external force to alter its balance.

Newton's Second Law, also known as the Fundamental Law of dynamics, determines a proportional relationship between Force and variation of the amount of motion or linear moment of a body. In other words, The Force is directly proportional to the mass and acceleration of a body.

If there are forces acting on the body and these forces are not in balance the body will move with a resulting force equal to the product of mass by acceleration.