Let, a_1, a_2 are the acceleration of masses m_1, m_2 at instant t and let F be the force acts on the mass m_2 .So the equation of motion of the system, F=m_1a_1+m_2a_2 Given, m_1=10\\ kg, m_2=20\\ kg, a_1=12\\ m/s^2 , F=200\\ N \ herefore 200=10\ imes 12+20a_2 20a_2=200-120=80 a_2=4\\ m/s^2