Question

A uniform metre rule balances horizontally on a knife
edge placed at the 58 cm mark when a weight of
20 gf is suspended from one end.
(i) Draw a diagram of the arrangement.
(ii) What is the weight of the rule ?​

Answer 1

$\bf{\underline{\red{Correct\:Question:-}}}$

✓✓A Uniform metre rule balance horizontally on a knife edge placed at the 58 cm mark when a weight of 20 gf is suspended from one end.

• (i) Draw a diagram of the arrangement.
• (ii) what is the weight of the rule?

$\bf{\underline{\green{SoLuTiOn:-}}}$

$\bf\implies\:(i)\:$ Weight mg (W) of rule produces an anti- clockwise moment about the knife edge O. In order to balance it, 20gf must be suspended at the end B to produce clockwise moment about the knife edge O.

$\bf\implies\:(ii)\:$ we know that the principal of moments state that when a body is balance ,the total clockwise moment about a point equals to the total anti-clockwise moment about the same point.

$\sf\therefore\pink{{Anticlockwise\:moment = Clockwise\:moment}}$

$\bf\implies\:w\times\:(58-50)=20gf\times\:(100-58)$

$\bf\implies\:w\times\:8=20gf\times\:42$

$\bf\implies\:w=20gf\times\dfrac{42}{8}$

$\bf\purple{{\implies\:w=105gf}}$

$\bf\therefore\:The\:weight\:of\:the\:rule\:is\:105gf.$