Question

A father pulls his son, whos mass is 25 kg and who is sitting on a swing with ropes of length 3 meters, backward until the ropes make an angle of 33.6 degrees with respect to the vertical. He then releases his son from rest. What is the speed of the son at the bottom of the swinging motion? For this question i don't understand the logic behind L - Lcos33.6 degrees.

Answer 1

draw the figure. The length of the "swing" is from the piviot point to the bottome, or L. Now raise the swing to some angle theta. The hypotenuse is still L, but the downward length from the piviot to a point level with the swing is L*cosTheta.
Which with a little math and examining your diagram, the swing was raised L-LcosTheta