7 A particle starts from rest and moves in a straight line. The velocity of the particle at time \(t \mathrm {~s}\) after the start is \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\), where $$v = - 0.01 t ^ { 3 } + 0.22 t ^ { 2 } - 0.4 t$$

1. Find the two positive values of \(t\) for which the particle is instantaneously at rest.
2. Find the time at which the acceleration of the particle is greatest.
3. Find the distance travelled by the particle while its velocity is positive.