Question

5. Block A, with a mass of 4.0 kg, is moving with a speed of 2.0 m/s while block B, with a mass of 8.0 kg, is moving in the opposite direction with a speed of 3.0 m/s. The momentum of the center of mass of the two-block system is?

Answer 1

The momentum of the center of mass of the system is

$$p=m_1v_1-m_2v_2=4·2-8·3=-16\text{ kg m/s}$$

if we assume that the second block moves against the direction of the x-axis.