JEE Main 2019 Physics question
Two forces P and Q, of magnitude 2F and 3F, respectively, are at an angle θ with each other. If the force Q is doubled, then their resultant also gets doubled. Then, the angle θ is:
Answer: (D)
Solution
4 + 36 + 24 cos θ = 4(4 + 9 + 12 cos θ) ⇒ cos θ = −1/2, θ = 120°. (The source key prints (B), though its worked solution reaches 120°.)