Final answer:
The correct equation to calculate the normal force on an object sliding down an incline is N = mg cos(θ). In this case, the option B: mg cos(θ) is the right choice as it represents the normal force acting on the object.
Step-by-step explanation:
When an object is on an incline, gravity can be resolved into two components: one perpendicular to the incline and one parallel to it. The perpendicular component is equal to mg cos(θ) and this is the component that is balanced by the normal force when an object is not accelerating in the perpendicular direction. So, the equation that correctly calculates the normal force (N) on the object is simply N = mg cos(θ). Therefore, the correct expression representing the normal force equation for an object resting on an incline is option B: mg cos(θ).
If friction is not involved, the net force perpendicular to the surface would be zero because the normal force is equal to the perpendicular component of weight. However, with friction, the normal force is still the same, but there is a frictional force to consider along the plane. The net force perpendicular to the surface would still be zero if friction is static and the object is stationary or if kinetic friction is balancing the other forces when the object is moving at constant velocity.