Question

A uniform metre rule of weight 10 gf is pivoted at its 0 mark.

(i) What moment of force depresses the rule ?

(ii) How can it be made horizontal by applying a least force ?

Answer 1

Given,

Length of the rule = 100 cm

Weight of the rule = 10 gf

Pivoted at 0 marks

1.

We know,

Moment of force = $Force\times Perpendiculardistance$

Putting values

$Momentofforce=10gf\times 50cm=500gfcm$
2.
To apply the least force we obviously have to make the perpendicular distance highest. Hence, the least force should be applied at the 100 cm mark.
Thus, by the principle of moments

Moment = $Force\times Perpendiculardistance$

Putting values

$500=Force\times 100=5gf$

Hence, the least force applied will be 5 gf.