physics
posted by paul .
A girl 36 kg occupies a seat of a swing that this subject by two chains 20 m in length each. If someone drops the girl from an 8 m position below the highest of the swing. What strength exercises it on the girl when she passes through the point lower?

she drops 20  8 = 12 meters
her los of potential energy in the drop is m g h = 12 m g Joules
her Ke is then 12 m g Joules
(1/2) m v^2 = 12 m g
so v^2 = 24 g
force up on girl force down on girl = m a
F  m g = m v^2/r
F = m (g + v^2/r)
F = m (g + 24 g/20)
F = m g (1+24/20)
F = m g (2.2) = 36*9.8*2.2