calculate the components parallel and perpendicular to the plane of 150N gravitational force acting on an object on a slope at 20 degree to the horizontal

Answer 1

to keep these straight, consider a horizontal slope (θ=0°)
all the force is perpendicular to the plane, so clearly that component is F*cos0°
So, for nonzero θ, the components of F are
perpendicular: F cosθ
parallel: F sinθ