Posted by clueless on Wednesday, November 10, 2010 at 7:10pm.
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.

PHYSICS  Damon, Wednesday, November 10, 2010 at 7:21pm
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) 
PHYSICS  clueless, Wednesday, November 10, 2010 at 7:28pm
thanks!

PHYSICS  clueless, Wednesday, November 10, 2010 at 7:35pm
If the speed of the child at the lowest position is 2.50 m/s, what is the mechanical energy lost due to friction?

PHYSICS  bobpursley, Wednesday, November 10, 2010 at 7:39pm
mechanical energy lost= PE at top1/2 m vb^2 where vb is the speed at the bottom