Question

The working for a body of mass 50.0cm is suspended at the 20.0cm mark of a uniform metre rule. The metre rule is adjusted on a pivot until it settles horizontally at the 40.0cm mark. Determine the mass of the metre rule.

Answer 1

Yes

Answer 2

Assuming you meant 50.0g (not cm), then consider the mass of each part of the bar as a point mass at the midpoint of its length. Then if the bar's mass is x, then
(.4x+50)(20) = (.6x)(30)

Answer 3

up force at 40 cm = (m+50)g
down force at 20 cm = 50 g
down force at 50 cm = m g, the weight of the stick
moments about the 40 cm mark are 0
so
50 (40-20) = m (50 -40)
1000 = 10 m
m = 100