Two vectors have magnitudes 3 unit and 4 units respectively. What should be the angle between them if the magnitude of the resultant is (a) 1 unit, (b) 5 unit and (c) 7 unit.

Question

Philoid · Accepted Answer

Magnitudes of vectors a=3 units, b=4 units, let θ be the angle between these two vectors and c= magnitude of resultant.

We know that

(a) If c =1, cosθ = (1-9-16)/24 =-1, hence θ =180°

(b) If c =5, cosθ = (25-9-16)/24 =0, hence θ =90°

(c) If c =7, cosθ = (49-9-16)/24 =1, therefore, θ =0°