A particle starts with an initial velocity of $10.0 {\mathrm{ms}}^{-1}$ along $x$-direction and accelerates uniformly at the rate of $2.0 \mathrm{m} {\mathrm{s}}^{-2}$. The time taken by the particle to reach the velocity of $60.0 \mathrm{m} {\mathrm{s}}^{-1}$ is _____.