# Stationary Stone Bar

**Classical Mechanics**Level 2

A uniform stone bar with a mass of \(10\text{ kg}\) and a length of \(10\text{ m}\) has a pivot point that is \(3\text{ m}\) away from the nearest edge. Two weights, \(A\) and \(B\), are hung onto the edges of the bar by massless springs where weight \(B\) is hung on the edge farthest from the pivot point. If the mass of weight \(B\) is \(40\text{ kg}\), what must the mass of weight \(A\) be to prevent the bar from turning?

Assume \(g=9.81 \dfrac{\text m}{\text s^2}\).