A railroad car with mass of 5.0 10⁵ kg collides with a stationary railroad car of equal mass. After the collision, the two cars lock together and move off at 4.0 m/s. (a) Determine the initial speed of the first car. (b) Determine the amount of momentum before and after the collision. (c) Determine the total amount of kinetic energy before and after the collision. (d) Explain what becomes of the "missing" kinetic energy.