A block of mass m is on an inclined plane of angle θ. The coefficient of friction between the block and the plane is µ and tan θ > µ. The block is held stationary by applying a force P parallel to the plane. The direction of force pointing up the plane is taken to be positive. As P is varied from P₁ = mg (sin θ – µ cos θ) to P₂ = mg(sin θ + µ cos $\mathrm{\theta }$), the frictional force f versus P graph will look like