Question

Resultant of P vector and Q vector inclined at an angle theta is R vector
find theta if magnitude of R vector=mag of P vector=mag of Q vector

Answer 1

Solution :

R21=(2P)2=P2+Q2+2PQcosθ

(P)2=P2+Q2−2PQcosθ

Adding them 5P2=2P2+2Q2 or 3P2=2Q2

or PQ=2–√3

NOT SURE ABOUT THE ANSWER

Answer 2

ANSWER:

R vector = (p^2+q^2+2pq*cos theta) whole root

as p=q=r write all p and q as r

therefore, r = (r^2+r^2+ 2r^2* cos theta ) whole root

taking square both side as in rhs their is square root

-r^2/2r^2 = cos theta

-1/2 = cos theta

therefore theta = 120 degree