A uniforn half metre rule is pivated at its 30cm mark. A mass of 50g hung at the 45cm mark keeps the rule horizontal. determine the mass of the half metre rule

150 g

Explanation:

From the question;

Half meter rule (50 cm) is pivoted at 30 cm Mass of 50 g Pivoted at 45 cm

It means the mass is 15 cm from the pivot

Mass of the meter rule is always at the center of the rule (25 cm mark) Therefore, the mass of the half meter rule is experienced 5 cm from the pivot. But, According to law of moments, clockwise moments is equal to anticlockwise moments when a system is at a state of balance.

Therefore;

Assuming the mass of half meter rule is m

Then;

m * 5 cm = 50 g * 15 cm

m = 150 g

Therefore;

Mass of the half meter rule is 150 g