## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

We can use conservation of momentum to find the final speed of the railroad car after the gravel is loaded. $p_f=p_0$ $m_f~v_f = m_0~v_0$ $v_f = \frac{m_0~v_0}{m_f}$ $v_f = \frac{(10,000~kg)(2.0~m/s)}{10,000~kg+4000~kg}$ $v_f = 1.4~m/s$ The railroad car's speed just after the gravel is loaded is 1.4 m/s.