question_answer 17)

A metre stick is balanced on a knife edge at its centre. When two coins, each of mass 5 g are put one on top of the other at the 12.0 cm mark, the stick is found to be balanced at 45.0 cm. What is the mass of the metre stick ?  

Answer:

As the metre stick balances at 50.0 cm mark, its CG must lie at this mark. The 45.0 cm mark is the CG of the metre stick + 2 coins system. Let m be the mass of the metre stick. Distance between 50.0 cm mark and new CG   Distance between 12.0 cm mark and new CG   From the principle of moments (for equilibrium),   or