A $40,000$ kg freight car is coasting at $0\mathrm{.}650\frac{m}{s}$ with negligible friction under a hopper that dumps $90,000$ kg of scrap metal into it$.$ What is the final velocity of the loaded freight car?

$0\mathrm{.}359\frac{m}{s}$

$0\mathrm{.}513\frac{m}{s}$

$0\mathrm{.}200\frac{m}{s}$

$0\mathrm{.}650\frac{m}{s}$