Question

Two vectors of the same magnitude have a resultant equal to either of the two vectors. The angle between two vectors is

Options

• cos^-1 (-0.5)

• cos^-1 (-0.4)

• cos^-1 (-0.3)

• cos^-1 (-0.6)

Answer 1

cos^-1 (-0.5)

Explanation:

Given, A = B = R = a (let)

Let A and B be two vectors and R be their resultant, then
As, resultant, R² = A² + B² + 2AB cosθ
⇒ a² = a² + a² + 2a² cosθ

⇒ `(1+costheta)="a"^2/(2"a"^2)=1/2`

or  `costheta=1/2-1=-0.5`

or θ = cos^-1 (- 0.5)