When a body moves on an inclined plane with constant velocity, it means that the net force acting on the body is zero. In this case, the work done on the body is also zero.
Work is defined as the product of the force applied on an object and the displacement of the object in the direction of the force. When a body moves on an inclined plane with constant velocity, the force of gravity pulling it down the incline is balanced by the force of friction or an applied force pushing it up the incline. These forces are equal in magnitude and opposite in direction, resulting in a net force of zero.
Since the net force is zero, there is no force acting in the direction of the displacement, and therefore no work is being done on the body. The energy of the body remains constant as it moves on the inclined plane with a constant velocity.