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Question
A uniform metre scale is balanced at a 40 cm mark when weights of 20 gf and 5 gf are suspended at 5 cm mark and 75 cm mark respectively. Calculate the weight of metre scale.
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Solution
A metre scale is a uniform, therefore its weight acts at a 50 cm mark.
Taking moments about to cm mark.
A moment in the clockwise direction,
= W × 10 cm + 5 gf × 35 cm
= 10 W cm + 175 gf cm.
moment in anti-clockwise direction,
= 20 gf × 35 cm
= 700 gf cm.
By the law of moments,
Moments in clockwise direction = moments in anti-clockwise directions.
10 W cm + 175 gf cm = 700 gf cm
∴ 10 W cm = (700 − 175) gf cm
∴ W = `525/10` gf = 52.5 gf.
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