Blocks m_1 and m_2 hang from one string over a fixed pulley, and a third block, m_3, hangs below m_2 on a second string. Tension T_1 is drawn at both ends of the first string and T_2 at both ends of the second, and the weights m_1 g, m_2 g and m_3 g point straight down. Dashed acceleration arrows a point up beside m_1 and down beside m_2 and m_3.
