Question

Two small kids weighing 10kg and 15kg are trying to balance a seesaw of total length 5m with the fulcrum at the centre. If one of the kids is sitting at an end, the other should sit at

• A. 1.67 m from the centre
• B. 2.50 m from the centre
• C. 2 m from the centre
• D. 1 m from the centre

Answer 1

The correct option is A 1.67 m from the centre

$\begin{array}{c}\text{Let,}B\text{of mass}15kg\text{is sitting}\\ \text{at distance}x\text{from centre.}\end{array}$

$\begin{array}{c}\text{By rotational equilibrium,}\\ \begin{array}{cc}\left({\tau }_A\right)& =(m_{A}g\times 2\cdot 5)\\ \text{and}\left({\tau }_B\right)& =(m_{B}g\times x)\end{array}\end{array}$

$\begin{array}{c}\text{Note that,}{\tau }_A\text{and}{\tau }_B\text{are in opposite directions.}\\ \text{Thus,}{m}_{A}g\times 2\cdot 5=m_{B}g\times x.\\ \therefore x=\frac{10}{15}\times 2.5m=1.67m\end{array}$