A uniform metre rule Mass 80kg is pivoted at the 30cm mark. Find the mass that would be placed at the 50cm mark for the metre rule to be in equilibrium.

Answer 1

We can start by using the principle of moments, which states that the sum of the clockwise moments must be equal to the sum of the anticlockwise moments for the metre rule to be in equilibrium.

Let x be the mass placed at the 50cm mark.

Clockwise moment:
80kg × 0.3m = 24Nm (due to the pivot at 30cm)

Anticlockwise moment:
x kg × 0.2m = 0.2x Nm (due to the pivot at 50cm)

To be in equilibrium:
24 Nm = 0.2x Nm

Solving for x:
x = 120kg

Therefore, a mass of 120kg would need to be placed at the 50cm mark for the metre rule to be in equilibrium.