At this point in the trick the
skater and board have reached maximum height. The board has leveled off
and the only forces now are the mass of the board and gravity(mg)
and the mass of the rider and gravity(Mg). This indicates
that the board and rider are now moving toward the ground with an
acceleration of 9.81m/s2.
When the skater lands they
will bend their knees to help absorb the impact of the ground. At this
point we are back were we started with a net force of zero.
Forces in the Y: Mg
+ mg - FN
= 0