Torque /physics question

Question

A see-saw is balanced on its

midpoint A224 kg kid sits on the

left 1.75 m from the axis. A

second kid sits on the other side.

1.22 m from the axis. What is the

mass of the second kid?

Can someone answer this thourghly?

Answer 1

Make a sketch:

In order to still be balanced with the 2 kids on the see-saw, then Torque #1 (T₁) must balance out (or be equal to) Torque #2 (T₂). Another way to say this is that the sum of the torques must be zero. T₁ is positive and T₂ is negative (by convention) so T₁ - T₂ = 0 which makes T₁ = T₂

T₁ = Fd = mgd = (224)(g)(1.75)

T₂ = Fd = mgd = (x)(g)(1.22)

Setting these equal:

(224)(g)(1.75) = (x)(g)(1.22) [you can cancel the "g's":

(224)(1.75) = (x)(1.22)

1.22x = 392

x = 392/1.22

x = 321 kg