A uniform metre rule of mass 90g is provided at the 40cm mark. If the rule is in equilibrium with an unknown mass m placed at the 10cm mark and a 72g mass at the 70cm mark, determine m
A
72g
B
102g
C
298g
D
504g
Verified Correct Answer: B.
Physical Principles & Numerical Solution
Taking moment about the 40cm mark
Total clockwise moments = total anti-clockwise moment
m x 30 = 90 x 10 + 72 x 30
30m = 900 + 2160 = 3060
m = \(\frac{3060}{30}\) = 102g.
Source: Myschool Past Questions Archive (Record #33765)