A light beam is pivoted at its centre. Two weights are hung from it as shown in the fig. The beam balances horizontally. What is the weight W?
Question 1 Report
A light beam is pivoted at its centre. Two weights are hung from it as shown in the fig.
The beam balances horizontally. What is the weight W?
Answer Details
For the beam to balance, the principle of moments requires that the clockwise moment about the pivot equals the anticlockwise moment. The 6.0 N weight hangs 0.40 m to the left of the pivot, and weight W hangs 0.60 m to the right.
Taking moments about the pivot:
\[ 6.0 \times 0.40 = W \times 0.60 \]
\[ 2.4 = 0.60\,W \]
\[ W = \frac{2.4}{0.60} = 4.0 \text{ N} \]
The weight on the longer arm must be smaller to produce the same moment. This is the same principle that allows a lighter person to balance a heavier person on a seesaw by sitting further from the pivot.
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