Serway & Jewett — Static Equilibrium and Elasticity: Problem 2

Why is the following situation impossible? A uniform beam of mass \(m_b = 3.00 \text{ kg}\) and length \(\ell = 1.00 \text{ m}\) supports blocks with masses \(m_1 = 5.00 \text{ kg}\) and \(m_2 = 15.0 \text{ kg}\) at two positions as shown in Figure P12.2. The beam rests on two triangular blocks, with point \(P\) a distance \(d = 0.300 \text{ m}\) to the right of the center of gravity of the beam. The position of the object of mass \(m_2\) is adjusted along the length of the beam until the normal force on the beam at \(O\) is zero.