A truck of mass 500kg is moving with constant speed 10ms^-1 .If sand is dropped into the truck at the constant rate 10kg/min, the force required to maintain the motion with constant velocity is

• A

  $\frac{3}{2}\mathrm{N}$

• B

  $\frac{5}{4}\mathrm{N}$

• C

  $\frac{7}{5}\mathrm{N}$

• D

  $\frac{5}{3}\mathrm{N}$