Question

Two boys and their father are balance on a seesaw. The father, 70kg, sits on one end 0.65m from the center of the seesaw while the two boys sit together on the other end. If each boy weighs 30kg, where should they sit?

Answer 1

To be balanced the angular acceleration must be equal (but opposite).
α = mg/r

So: m_b/r_b = m_f/r_f

.: r_b = (60)(0.65)/(70) ≈ 0.56m

Answer 2

actually, it is angular torque, not acceleation that is balanced. Hopefully, the acceleration is zero.