Core4 mapped NDA questions
Build the idea
Build exam-ready understanding by connecting the core idea, formulas or facts, worked example and previous NDA questions. Focus on why each rule works, then test it under timed conditions.
Concept
A body is in equilibrium when the net force and net turning effect on it are zero. The parallelogram law gives the resultant of two forces acting at a point.
Stable, unstable and neutral equilibrium depend on how the centre of gravity moves when disturbed.
Key Points & Formulas
- Equilibrium: net force = 0 and net moment (torque) = 0.
- Parallelogram law: resultant R = √(P² + Q² + 2PQ cosθ).
- Lower centre of gravity and wider base ⇒ greater stability.
- Stable: CG rises on tilting; unstable: CG falls; neutral: CG stays level.
Worked Example
Q. Two perpendicular forces of 3 N and 4 N act at a point. Find their resultant.
θ = 90°, so cosθ = 0.
R = √(3² + 4² + 0) = √25 = 5 N.