Question

The resultant of two vectors, A and B is prependicular to the vector A and its magnitude is equal to half of the magnitude of the vector B. Find out the angle between vector A and B.

Answer 1

Resolving vector B into two rectangular components we have B cosθ  along OC and B sinθ along OD.The resultant vector is along OC.

R = B cosθ [A.T.Q.]

R = B/2 = B cosθ

or, cosθ = 1/2 or, θ = 60°

Hence angle between vector A and B

= ∠AOB = 90° + 60° = 150°.