If the resultant of two forces of magnitude p and 2p is perpendicular to p, then the angle between the forces is
2π3
3π4
4π5
5π6
tanα = 2psinθp+2pcosθ; here α = 900
⇒ ∞ = 2psinθp+2pcosθ ⇒p+2pcosθ = 0
⇒ cosθ= -12 ⇒ θ = 2π3