Question $2(1$ point$)$

A railroad freight car with a mass of $15,000kg$ is coasting at a speed of $20\frac{m}{s}$ before colliding with a $45,000kg$ freight car initially at rest. After the collision both cars move together with a speed of

$5\mathrm{.}0\frac{m}{s}$

$6\mathrm{.}7\frac{m}{s}$

$10\frac{m}{s}$

$60\frac{m}{s}$

$80\frac{m}{s}$