Question

A uniform metre rule of mass 90g is pivoted at the 40cm mark.if the rule is in equilibrium with an unknown mass m place at the 10cm mark and a 72g mass at the 70cm mark , determine m

Answer 1

The equilibrium condition

$$Mgd=m_1gd_1+m_2gd_2$$

Hence

$$M\times 30=72\times 30+90\times 10$$

$$M=102 \:\rm g$$