Question

If mi+2mj is a unit vector, then the value of ‘m’ is A. 1/(√3) B.1/(√2) C.1/(√5) D.1/2

Answer 1

Magnitude: |m i + 2m j| = sqrt(m^2 + (2m)^2) = sqrt(5m^2) = |m|√5.
Set equal to 1: |m|√5 = 1 ⇒ |m| = 1/√5.
So m = ±1/√5. From the choices, m = 1/√5 (option C).