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