(Original post by najinaji)
I was going through a past paper and came across this:
A small package of mass 1.1 kg is held in equilibrium on a rough plane by a horizontal force. The plane is inclined at an angle α to the horizontal, where tan α=3/4. The force acts in a vertical plane containing a line of greatest slope of the plane and has magnitude P newtons, as shown in Figure 2. The coefficient of friction between the package and the plane is 0.5 and the package is modelled as a particle. The package is in equilibrium and on the point of slipping down the plane.
(a) Draw, on Figure 2, all the forces acting on the package, showing their directions clearly.
(2)(b) (i) Find the magnitude of the normal reaction between the package and the plane.
For Q 2.b.i, on the mark scheme, it said to use the formula R(↑), Rcosα + Fsinα = mg
. How would I come to this conclusion, as my first instinct was to have R = 1.1gCosα ?