Two vectors have magnitudes 3 units and 4 units respectively. What should be the angle between them if the magnitude of the resultant is 5 units?
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Solution
Given the magnitude of the resultant is 5 units,
So, using parallelogram law we have R=√32+42+2×3×4×cosθ, where θ is the angle between the vectors. ⇒5=√32+42+2×3×4×cosθ
Or, 52=32+42+2×3×4×cosθ
Or, 25=25+24cosθ⇒cosθ=0 ⇒θ=90∘