the diagram above shows a uniform metre rule, X Y which is balance horizontally at the 90cm mark, when a mass of 0.4kg is suspended from Y. what is the mass of the metre rule

Answer:
0.1 Kg
Explanation:
Please see attached photo for explanation.
In the attached photo, M is the mass of the metre rule.
From the attached photo,
Anticlock wise moment = M × 40
Clockwise moment = 0.4 × 10
Anticlock wise moment = Clockwise moment
M × 40 = 0.4 × 10
M × 40 = 4
Divide both side by 40
M = 4 / 40
M = 0.1 Kg
Thus, the mass of the metre rule is 0.1 Kg