A particle of mass $2 \mathrm{~kg}$ is initially at rest. A force acts on it whose magnitude changes with time. The force time graph is shown below. The velocity of the particle after 10 s is
(A) $10 \mathrm{~ms}^{-1}$
(B) $20 \mathrm{~ms}^{-1}$
(C) $75 \mathrm{~ms}^{-1}$
(D) $50 \mathrm{~ms}^{-1}$