The resultant of two forces,one double the other in magnitude,is perpendicular to the smaller of the two forces.The angle between the two forces is

Explanation

`tan alpha = (Q sin theta)/(P + Q cos theta)`
`tan 90 = oo = (1)/(0) = ( 2x sin theta)/( x + 2x cos theta)`
`x + 2 x cos theta = 0`
`cos theta = -(1)/(2) rArr theta = 120^(@)`