# A railroad freight car coasts along a level track. It collides and couples with a second car, initially at rest and with brakes released. What percentage of the freight car's initial energy is preserved in the two-coupled cars after collision?

## A railroad freight car, mass 15972 $k g$, is allowed to coast along a level track at speed 2 $\frac{m}{s}$. It collides and couples with a 41386 $k g$ loaded second car, initially at rest and with brakes released. What percentage of the initial kinetic energy of the 15972 $k g$ car is preserved in the two-coupled cars after collision?

${m}_{1} {v}_{1} = {m}_{2} {v}_{2}$ Then, the initial Kinetic Energy is ${U}_{k 1} = \frac{1}{2} {m}_{1} {v}_{1}^{2}$ . Calculate ${v}_{2}$ then plug that in to find ${U}_{k 2} = \frac{1}{2} {m}_{2} {v}_{2}^{2}$.