A metre rule is pivoted at its mid-point with a vertical force of 10N hanging from the distance 30cm from the mid-point. At what distance must a 15N force hang to balance the ruler horizontally?

A. 30cm
B. 10cm
C. 20cm
D. 25m

Correct Answer:

Option C = 20cm

Explanation

Clockwise moment = Anti-clockwise moment
10 x 30 = 15 x X
X = 20cm