Q 1 :

If the magnitude of sum of two vectors is equal to the magnitude of difference of the two vectors, the angle between these vectors is         [2016]
 

  • 45°

     

  • 180°

     

  • 0°

     

  • 90°

     

(4)

Let the two vectors be A→ and B→.

Then, magnitude of sum of A→ and B→, |A→+B→|=A2+B2+2ABcosθ

and magnitude of difference of A→ and B→

|A→-B→|=A2+B2-2ABcosθ,  |A→+B→|=|A→-B→| (given)

or A2+B2+2ABcosθ=A2+B2-2ABcosθ

⇒4ABcosθ=0 ∵ 4AB≠0, ∴ cosθ=0 or θ=90°