The Student Room Group

Reply 1

futureaussiecto
A uniform ladder rests in limiting equilibrium with its top against a smooth vertical wall and its base on a rough horizontal floor. The coefficient of friction between the floor and the ladder is µ. Given that the ladder makes an angle theta with the floor show that:

tan theta = 1

So there are 4 forces involved, the reaction on the wall, the reaction on the floor, the weight from the centre of the ladder and friction. Since there's equilibrium:
Reaction of wall = Friction
Reaction of floor = Weight
Friction = µ*Reaction of floor
Friction = µ*Weight

Resolve around the point on the floor (assume ladder is length 2)
2*Reaction of wall*sinθ = 1*Weight*cosθ
2*Friction*sinθ = Weight*cosθ
2*µ*Weight*sinθ = Weight*cosθ
Divide both sides by cosθ
2*u*tanθ = 1