A uniform ruler is pivoted at its mid point. A weight of 50gf is suspended at one end of it. Where should a weight of 100gf be suspended, to keep the ruler horizontal?
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Solution
Let AB be the uniform metre rule, such that C is its midpoint. The metre rule is pivoted at C, such that AC=50cm and CB=50cm. 50 gf weight is suspended near A.
Let D be the point of suspension of 100 gf weight at a distance of x from C, so that the rule is horizontal. Left hand side moment, LHM=50×50=2500gfcm.....(1) Right hand side moment, RHM=x×100=100×gfcm.....(2) To keep the rule horizontal, LHM=RHM 2500=100x⇒x=25cm. ∴ 100 gf is to be suspended at a distance of 25 cm from mid point (or) 75 cm from the end of the rule.