. A uniform half metre rule can be balanced at the 29.0 cm mark when a mass 20 g is hung from its one end


A uniform half metre rule can be balanced at the 29.0 cm mark when a mass 20 g is hung from its one end.

(a) Draw a diagram of the arrangement.

(b) Find the mass of the half metre rule.

 

Best Answer

(a)

(a)

Figure shows a uniform half metre rule PQ which is balanced at 29 cm mark. Let M be the mass of the rule. A uniform rule has same distribution of mass throughout its length So its weight Mg will act at its middle point which is at 25 cm. The weight mg produces anticlockwise moment about point o. In order to balance the 20 g (0.02kg) weight is tied at 50 cm mark which generates clockwise moment.

(b) Hence from the principle of moments

Anticlockwise moment= clockwise moment

Mg(29-25)=0.02 g(50-29)

M=21(0.02)/4

M=0.105 kg

M=105 g

 

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