Question

A metre scale of weight 50 gf can be balanced at 40 cm mark without any weight suspended on it.

1. If this ruler is cut at its centre then state which part [0 to 50 cm or 50 to 100 cm] of the ruler will weigh more than 25 gf.
   
2. What minimum weight placed on this metre ruler can balance this ruler when it is pivoted at its centre?

Answer 1

a. Cut at the centre (50 cm). Since the C.G. is at 40 cm, the 0–50 cm half contains more mass than the 50–100 cm half.
0–50 cm half weighs > 25 gf (the 50–100 cm half weighs < 25 gf).

b. By principle of moments
50 × 10 = w × 50
w = 10 gf