1 A particle \(P\) moves in a straight line and passes through a point \(O\) of the line with velocity \(2 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). At time \(t \mathrm {~s}\) after passing through \(O\), the velocity of \(P\) is \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) and the acceleration of \(P\) is given by \(\mathrm { e } ^ { - 0.5 v } \mathrm {~m} \mathrm {~s} ^ { - 2 }\). Calculate the velocity of \(P\) when \(t = 1.2\).