일반물리학 1 — Center of Mass and Linear Momentum: Problem 39

39 A man of mass \(m_1 = 80 \text{ kg}\) is standing on a platform of mass \(m_2 = 20 \text{ kg}\) that lies on a frictionless horizontal surface. The man starts moving on the platform with a velocity \(v_r = 10 \text{ m/s}\) relative to the platform. Find the recoil speed of the platform.