Question

Two vectors, each of magnitude A have a resultant
of same magnitude A. The angle between the two
vectors is
(1) 30°
(2) 60°
(3) 120°
(4) 150​

Answer 1

Answer:

R² = P²+Q²+2PQcosB

here B is angle between P and Q

given R=P=Q=A

A² = A²+A²+2AAcosB

A² = 2A² + 2A²cosB

-2A² + A² = 2A²cosB

-A²/2A² = cosB

-1/2 = cosB

B = 120°

so, answer (3) is correct