Energy Conservation on an Incline

In the given case of the cart rolling down predispose and there are three external forces (the general force, the force of friction and air resistance) and one internal force (the force of gravity). The general force does not do work upon the cart since it acts within a direction perpendicular to the direction of motion. In such examples, the angle among F and d is 90 degrees and the work completed through the force is 0 Joules. The force of friction does not do work upon the cart since it acts upon the wheels of the cart and in fact does not dish up to displace either the cart or the wheels.