two block mass m$1=2$kg and m$2=4$kg are each released from rest at a height h$=5$m on a frictionless track as shown in the figure below. They undergo an elastic head$-$on collision. A$)$ Determine the velocity of each block just before the collision. B$)$ Determine the velocity of each block immediately after the collision. C$)$ Determine the maximum heights to which m$1$ and m$2$ rise after the collision. Notes: this problem uses ideas of both conservation of momentum and conservation of energy.