A particle is moving on a straight line whose velocity as function of time is (t -2) ms^-1. The distance travelled by particle (in m) in 4 s is ____________.

$\begin{array}{l}\because \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}v=t-2\\ \text{ Or }\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}0=t-2\\ \therefore \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}t=2\mathrm{s}\\ \therefore \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\left|v\right|=t-2\text{ for }t>2\mathrm{s}\\ \text{ and }\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\left|v\right|=2-t\text{ for }0<t\le 2\mathrm{s}\\ \therefore s={\int }_0^4 \left|v\right|dt={\int }_0^2 (2-t)dt+{\int }_2^4 (t-2)dt\\ \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}={\left[2t-\frac{t^2}{2}\right]}_0^2+{\left[\frac{t^2}{2}-2t\right]}_2^4=(4-2)+2=4\mathrm{m}\end{array}$