Question

A physics professor of mass = 50kg, stands at the end of the diving board, as shown. The board is uniform, massive, and solid. There is no vibration or motion of the board. The board is firmly attached to two supports at the point ${{P}_{1}}$ and ${{P}_{2}}$. The professor now starts to walk slowly in (right) from the end of the board towards ${{P}_{1}}$. While he is walking, how should you describe the force on the board by the support at ${{P}_{2}}$? (i.e. over at far right-hand end)

A. upwards and increasing magnitude
B. upwards and decreasing magnitude
C. downwards and increasing magnitude
D. downwards and decreasing magnitude

Answer 1

Hint: In a system when a body is supported by two or more pillar-like objects one of them behaves as a pivot. A pivot is a segment that balances all the forces acting at that point or turns. A pivot is necessary for the stability of a system.

Complete step by step answer:
From the figure given in the question, we can see that the board exerts a downward force on the support at point ${{P}_{1}}$ and as reactive force support exerts an upward force to the board. One more support is there at point ${{P}_{2}}$ which supports the board.
The support ${{P}_{1}}$ acts as a balancing component (pivot) for the particular set. So the board towards the right side of ${{P}_{1}}$ exerts an upward force at point ${{P}_{2}}$, and the support ${{P}_{2}}$ exerts a downward force.
As soon as the professor starts to move toward point ${{P}_{1}}$ the force on $P_2$ will gradually increase by taking the moment at point ${{P}_{1}}$ into account.
Thus the correct option which satisfies the given question is option C.

Note:
For balancing a particular system it is necessary to have a balancing junction or pivot component of the system. Its main use is to keep the system in its ongoing state (rest or motion). For every action there is a reaction force present. This was given by Newton's 3rd law of motion.