A metre rule of uniform mass distribution, with weight $W$, is balanced horizontally by pivoting it at the $25\,\text{cm}$ mark and applying an upward force $F$ at the $100\,\text{cm}$ mark. A vertical force $P$ acts at the pivot to support the rule. What is the magnitude of $P$?
- A$\frac{1}{3}W$
- B$\frac{1}{2}W$
- C$\frac{2}{3}W$
- D$\frac{4}{3}W$