A particle of mass 5 kg is placed on a smooth inclined plane making an angle of 30° with the horizontal. The magnitude of the normal reaction of the plane on the particle is [Take g = 10 ms⁻²]

The normal reaction on a smooth inclined plane is given by N = mg cos θ. Here, N = 5 × 10 × cos 30° = 50 × (√3/2) = 25√3 ≈ 43.3 N. Option A (25 N) is the error of using sin 30°, and option C (50 N) ignores the angle entirely.