A particle, \(P\), of mass \(m \mathrm {~kg}\) is projected with speed \(5 \mathrm {~ms} ^ { - 1 }\) down a line of greatest slope of a rough plane. The plane is inclined to the horizontal at an angle \(\alpha\), where \(\sin \alpha = \frac { 3 } { 5 }\) The total resistance to the motion of \(P\) is a force of magnitude \(\frac { 1 } { 5 } m g\)
Use the work-energy principle to find the speed of \(P\) at the instant when it has moved a distance 8 m down the plane from the point of projection.