Question

A uniform plank of a seesaw is 5 m long and supported at its centre. A boy weighing 40 kgf sits at a distance 1.5 m from one end of the seesaw. Where must a girl weighing 25 kgf sit on the other end of the see-saw, so as to balance the boy?

Answer 1

The fulcrum is at the centre, so it is 2.5 m from either end.

The boy is 1.5 m from one end, so his distance from the fulcrum is 2.5 − 1.5 = 1.0 m.

For balance, Load × Load arm = Effort × Effort arm

40 × 1.0 = 25 × distance of the girl from the fulcrum

Distance of the girl from the fulcrum = `(40 × 1.0)/25` = 1.6 m.

Therefore, the girl should sit 1.6 m from the fulcrum on the opposite side.