The forces opposing the motion of the device are "mgsin θ" and "μN" where N is the normal reaction From the diagram, on resolving to components, N = mgcos θ Total opposing force = mgsin θ + μmgcos θ = mg(sin θ + μcos θ) = 100 × 10 × (sin 30° + 0.25 × cos 30°) = 1000 × (0.5 + 0.2165) = 1000 × 0.7165 = 716.5 N