High school physics texts covers this and is usually expressed with the following formulae:
Velocity = Initial Velocity + Acceleration * Time
Velocity * Velocity = (Initial Velocity * Initial Velocity) + 2*Acceleration*Displacement
Displacement = Initial Velocity * Time + 0.5 * Acceleration * Time*Time
In your case you want to use that 3rd formula.
Displacement = 0 (start/end position)
Initial Velocity = the yvel you specify above (units / frame)
Time = the variable you have specified as 100 frames above
Acceleration = the value you want to solve for.
So taking your values above of yvel=5 units/frame and Time=100 and Displacement = 0
0 = 5*100 + 0.5*Acceleration*100*100
rearranged gives you
-500 = 0.5*10000*Acceleration
Therefore Acceleration is
-500.0/(0.5*10000) units/frame^2
(which is -500/5000 = -0.1 units/frame^2)
EDIT - these are only for constant accelerations, like gravity in the situation you've mentioned above.
Velocity = Initial Velocity + Acceleration * Time
Velocity * Velocity = (Initial Velocity * Initial Velocity) + 2*Acceleration*Displacement
Displacement = Initial Velocity * Time + 0.5 * Acceleration * Time*Time
In your case you want to use that 3rd formula.
Displacement = 0 (start/end position)
Initial Velocity = the yvel you specify above (units / frame)
Time = the variable you have specified as 100 frames above
Acceleration = the value you want to solve for.
So taking your values above of yvel=5 units/frame and Time=100 and Displacement = 0
0 = 5*100 + 0.5*Acceleration*100*100
rearranged gives you
-500 = 0.5*10000*Acceleration
Therefore Acceleration is
-500.0/(0.5*10000) units/frame^2
(which is -500/5000 = -0.1 units/frame^2)
EDIT - these are only for constant accelerations, like gravity in the situation you've mentioned above.