Q 11-06-244JEE MainJEE Main 2017 (8 Apr)Easy
In a physical balance working on the principle of moments, when $5$ mg weight is placed on the left pan, the beam becomes horizontal. Both the empty pans of the balance are of equal mass. Which of the following statements is correct?
Answer: (B) Left arm is shorter than the right arm
Let each pan have mass $m$ and the arms have lengths $l_L$ and $l_R$. With $5$ mg added on the left, moments balance:
$$(m + 5\ \text{mg})\,g\,l_L = m\,g\,l_R \;\Rightarrow\; l_L < l_R$$
The left pan needs extra weight to balance, so the left arm is shorter than the right arm.
Solution by Sreeraj P, M.Sc Physics