Resultant of two equal forces: find the angle between them Two forces of equal magnitude act at a point. The resultant has the same magnitude as either force. Choose the correct angle between the two forces.

Given data

• Two forces of equal magnitude F.
• Resultant R has magnitude equal to F.

Concept/Approach

• For two equal forces separated by angle θ, the resultant is R = 2F cos(θ/2) (parallelogram law).

Step-by-step calculationSet R = F → 2F cos(θ/2) = F.cos(θ/2) = 1/2 → θ/2 = 60°.Therefore θ = 120°.

Common pitfalls

• Using R = √(F² + F² + 2F·F cos θ) and forgetting to simplify for equal forces; both methods give the same result.

Final Answer120°