QQuestion
Akash takes a uniform metre scale and suspends a weight of 2 N at one end ‘X’, and a weight of 5 N on the other end ‘Y’. He then balances the ruler horizontally on a knife edge placed at 70 cm from X. Draw a diagram of the arrangement and calculate the weight of the ruler.
Exam-ready answer • 03 Mark
✓Answer
The diagram of the arrangement is shown below.

Given,
Weight at end X = 2 N
Weight at end Y = 5 N
Distance of X from the knife edge = 70 cm
Distance of Y from the knife edge = 100 − 70 = 30 cm
Let the weight of the scale be W. Its weight acts at the 50 cm mark, 20 cm from the knife edge.
For equilibrium,
Anticlockwise moment = Clockwise moment
2 × 70 + W × 20 = 5 × 30
140 + 20W = 150
20W = 10
W = 0.5 N
Therefore, the weight of the ruler is 0.5 N.
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