The normal reaction between the man and the board can be explained by considering the forces acting on both the man and the board. Let's break down the answer into headings and key points to provide a clear explanation.

Forces Acting on the Man:
1. Weight (mg): The man experiences a downward force due to gravity, which is equal to his mass (m) multiplied by the acceleration due to gravity (g).
2. Tension in the Rope (T): The man is pulling the board up with a force F through the pulley system. This force is transmitted through the rope and creates tension in the rope.

Forces Acting on the Board:
1. Weight (mg): The board also experiences a downward force due to gravity, which is equal to its own mass (m) multiplied by the acceleration due to gravity (g).
2. Normal Reaction (N): The board is in contact with the man, and therefore, there is a normal reaction force acting on the board.

Explanation:
The normal reaction force between the man and the board arises due to their contact. When the man exerts a force F to pull the board up, the tension in the rope transmits this force to the board. As a result, the board experiences an upward force equal to F.

Since the board is in contact with the man, Newton's third law states that there must be an equal and opposite force acting on the man. Therefore, the normal reaction force between the man and the board is also F.

The weight of the man and the board are balanced by the normal reaction force and tension in the rope. The normal reaction force counteracts the weight of the man, while the tension in the rope counteracts the weight of the board.

In summary, the normal reaction between the man and the board is equal to the force (F) with which the man is pulling the board up through the pulley system. This normal reaction force ensures that the man and the board remain in contact and allows the board to be lifted by the man.