Question

A boy weighing 50 kg is sitting on a see-saw 3m away from its support. On how many meters a girl should sit, whose weight is 25kg to balance the see-saw???

please help with explanation ​

Answer 1

Method:

Consider the boy is sitting on the left side.

Let the torque produced by the boy be in an anticlockwise direction.

• Anticlockwise torque = - 50 x 3 = - 150 Nm

Now,

In order to balance the see-saw, the other arm must move in the clockwise direction.

Torque produced by the girl,

• Clockwise torque = 25 x y

Clockwise torque + Anticlockwise torque = 0

[ As the see-saw is balanced the net torque produced will be zero]

$\\ \implies\sf{25y - 150 = 0 }\\ \\ \\ \implies\sf{25y = 150 }\\ \\ \\ \implies\sf{y = 150/25 }\\ \\ \\ \implies\boxed{\sf{y = 6 m }}$

The girl must sit at a distance of 6m in order to balance the see-saw.