A block of mass 5 kg is held at rest on a rough plane, inclined at an angle of 40 to the horizontal, by a rope making an angle of 15 to the plane. The magnitude of the tension in the rope is 10 N. Calculate the magnitude of the friction force, in newtons, to two significant figures. (Take the magnitude of the acceleration due to gravity, g, to be 9.8 ms-2.) The magnitude of the friction force is N (to 2 s.f.).