Question

A physics professor of mass $=50$ kg, stands at the end of diving board, as shown. The board is uniform, massive and solid. There is no vibration or motion of any kind. The board is firmly attached to two supports at point $P_1$ and $P_2$. The professor now begins 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 point $P_2?$ (i.e. Over at the 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

The correct option is C downwards and increasing magnitude.

At point $P_1$ the board exerts a downward force on the support implying that the support exerts an upward force. Also there is another support $P_2$ which supports the board. The support $P_1$ acts as the pivot and thus the board towards the right of point $P_1$ exerts a force in upward direction and thus support at $P_2$ exerts a downward force.
Now as the professor moves towards the supports we see that by taking moment about point $P_1$ the force on the $P_2$ goes on increasing. Thud option C is correct.