Question

Two people are sitting on opposite sides of a see-saw at positions 3m from the fulcrum. the person on the left has a mass of 50kg and the person on the right has a mass of 80 kg.

A.what it the net torque on the see-saw?

B. Where would a 40kg person have to sit on the see-saw in order to balance it?

Answer 1

(A) The net torque on the see-saw,

Tnet = 80*g*3 - 50*g*3 = 240*9.81 - 150*9.81 = 90*9.81 = 882.9 N.m

The direction of the torque is towards the downside of 80 kg person.

(B) From the given masses of the person, we can assume that the 40 kg person will sit on the side of 50 kg person in order to balance the see-saw.

Now, consider the 40 kg person sits at a distance of 'd' from the fulcrum.

So, in order to balance it, the net torque should be zero.

Means -

50*3 + 40*d = 80*3

=> 40*d = 240 - 150 = 90

=> d = 90/40 = 2.25 m

So, the 40 kg person will sit at a distance of 2.25 m from the fulcrum.