The resultant of two vectors ` vecA and vecB ` is perpendicular to ` vecA ` . Magnitude of Resultant ` vecR ` is equal to half Magnitude of ` vecB ` . Find the angle between ` vecA and vecB `?

Explanation

Since ` vecR ` is perpendicular to ` vecA ` . Figure shows the three vectors ` vecA , vecB and vecR` angle between ` vecA ` and `vecB ` is ` pi-theta`
` sin theta =R/B = B / (2B) =1/2`
` implies theta = 30^@ implies ` angle `vecA ` between and ` vecB ` is 150.