A particle of mass m kg moves up a line of greatest slope of a rough plane inclined at 21° to the horizontal. The frictional and normal components of the contact force on the particle have magnitudes F N and R N respectively. The particle passes through the point P with speed 10 m s^-1, and 2 s later it reaches its highest point on the plane.

1. Show that R = 9.336m and F = 1.416m, each correct to 4 significant figures.
2. Find the coefficient of friction between the particle and the plane.
3. After the particle reaches its highest point it starts to move down the plane. Find the speed with which the particle returns to P.