Question

A uniform metre rule balances horizontally on a knife edge placed at the $58cm$ mark when a weight of $20gf$ is suspended from one end. What is the weight of the rule?

• A. $10500gf$
• B. $105gf$
• C. $1.05gf$
• D. $11.6gf$

Answer 1

The correct option is B $105gf$

As the scale is uniform, so the weight will be balanced at mid point i.e. 50 cm of the scale.

Let, $W$ be the weight of the rule.

Using principle of moments, for equilibrium, sum of moment of force on left side of knife edge is equal to sum of moment of force on right side.

So, $(58-50)W=(100-58)20$ (as moment of force $=$ force $\times$ perpendicular distance from fulcrum)

or $W=105gf$