A meter stick is balanced on a knife edge at its centre. When two coins each of mass 5g are put one on top of the other at 12.0cm mark, the stick is found to be balanced at 45.0cm. What is the mass of the meter stick?
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Solution
Figure shows the forces on the stick The mass of metre stick is concentrated at CM=50cm Consider the torques around 0.Since the stick is in rotational equilibrium, ¯τext=m(5cm)−(10g)(45−12)=0 ∴=10g(33cm)(5cm)=66gm.