Krisken:
O.K. , with the math in front of me I am still in a void as to what is needed and that is the unknown.
Without a stated energy required it dosent help to know what energy you have.
In the formula: KE is the unknown
Mass- weight of the arrow in grains (weight in grams/7000) (I have a scale and I weigh my arrows with broadheads) Therefore this is a GIVEN.
Velocity- Speed of the arrow in fps (As shot through a chronograph in fps-this also is GIVEN).
The 450240 is a constant that is derived from the basic trajectory formula 1/2 of the Mass times velocity squared. The derivation becomes 2 X the speed of gravity (32.16) times 7000 (the weight conversion)
Plug the given values into the formula KE=Mass (VelocityXVelocity/450240) and you have only one unknown . . . the Kinetic Energy.