5 A particle of mass 18 kg is on a plane inclined at an angle of \(30 ^ { \circ }\) to the horizontal. The particle is projected up a line of greatest slope of the plane with a speed of \(20 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).

1. Given that the plane is smooth, use an energy method to find the distance the particle moves up the plane before coming to instantaneous rest.
2. Given instead that the plane is rough and the coefficient of friction between the particle and the plane is 0.25 , find the speed of the particle as it returns to its starting point.