Question

The resultant of two forces, one double the other in magnitude, is perpendicular to the smaller of the two forces. The angle between the two forces is –

• A. (a) 120⁰
• A. (b) 60⁰
• A. (c) 90⁰
• A. (d) 150⁰

Answer 1

(a)

$\overset{\rightarrow}{P}$.($\overset{\rightarrow}{P}$ + $\overset{\rightarrow}{Q}$) = 0

P² + PQcos q =0 and P = $\frac{Q}{2}$

\ P² + 2P² cos q = 0

or cos q = – $\frac{1}{2}$ Ž q = 120⁰