A 50 kg and a 30 kg child sit on opposite ends of an 80 kg see saw of length 4 m

Question

A 50 kg and a 30 kg child sit on opposite ends of an 80 kg see saw of length 4 m. Where should the fulcrum be placed so that the children can sit without their feet touching the ground?


I know that the total torque of the system adds up to zero, and that the equation should look something like this: 50x = 30(4-x) or 30x = 50(4 - x) but the fact that the see saw weighs 80kg needs to be factored in as well, and I don't know how/which side to add it to and what sign.

Can someone walk me through the steps of this problem? Thanks.

Explanation / Answer

you have to consider the torque due to the weight of the see saw also and this weight will act at the center of mass of the see saw i.e at 2 m from any end 50(x)=80(2-x)+30(4-x)

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