PHYSICS
posted by clueless .
A 27.0 kg child on a 3.00 m long swing is released from rest when the swing supports make an angle of 31.0° with the vertical. Neglecting friction, find the child's speed at the lowest position.

mass is irrelevant for pendulum, cancels
Figure out how high the child is above the low point when the chains are 31 deg from vertical
h = 3 (1  cos 31)
U at top = m g h
Ke at bottom = U at to
(1/2) m v^2 = m g h
v = sqrt (2 g h) 
thanks!

If the speed of the child at the lowest position is 2.50 m/s, what is the mechanical energy lost due to friction?

mechanical energy lost= PE at top1/2 m vb^2 where vb is the speed at the bottom