Auniforn 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

 

Ithink the answer would be a