Question

A uniform meter rule balances horizontally on a knife edge at 25cm mark, when a mass of 30g is hung at the 10cm mark. Calculate the mass of the ruler

Answer 1

A uniform metre rule of mass 100 g is supported by a pivot at the 40 cm mark and a string at the 100 cm mark. The string passes round a frictionless pulley and carries a mass of 20 g as shown in the diagram.




At which mark on the rule must a 50 g mass be suspended so that the rule balances?
November 2002:
A 4cm                         B 36 cm                       C 44 cm                       D 96 cm

June 2011 & November 2014:
A 4 cm                        B 36 cm                       C 44 cm                       D 64 cm