Two masses of constant velocities collide with each other. Which of the following quantities are conserved ?

Force Torque Momentum Velocity

Momentum

Initial momentum : $p_i = m_1 v_1 + m_2 v_2$ Final momentum : $p_f = m_1 v_1' + m_2 v_2'$ According to Conservation of Linear Momentum, $p_i = p_f$