Ring Balanced by Surface Tension

A circular ring has radius 1cm and is suspended horizontally by a thread passing through the 5cm mark on a ruler pivoted at its centre. The ring is balanced by a 5g mass suspended at the 60cm mark of the ruler.A beaker containing a liquid is then placed under the ring such that it just touches the liquid’s surface horizontally. If the 5g mass is moved to the 70cm mark, the ring ‘just parts’ the surface. Determine the surface tension of the liquid.

We first find the mass of the ring using principle of moments (sum of moments is zero for the balanced ruler) Then we use the same principle for the case when there is a moment from the surface tension of the liquid to find what the surface tension is.
Here is my solution:


Posted in Physics Tagged with: ,