The diagram shows a uniform bar supported at the middle point O. A weight of 40 gf is placed at a distance 40cm to the left of the point O. How can you balance the bar with a weight of 80 gf?

Anticlockwise moment = 40 gf × 40 cm

Clockwise moment = 80 gf × d cm

Clockwise moment = Anticlockwise moment

80 × d = 40 × 40

⇒ d = 40 × 40\over 80 = 20 cm

Therefore the bar will be in balanced position if weight of 80gf is placed at a point of 20cm to the right of O.