The formula to calculate the initial velocity ( force ) for a free throw dunk is very easy , but it it is totally different than this hangtime calculator , which is valid only for vertical displacement.
Trying not to complicate things , when there is horizontal displacement too the same force applied to the ground gives different jump 'orbits' depending on the takeoff angle. It also depends on how much force you can create at that angle , its like vertical and broad jump together.
I can get some calculations and provide you with scientific valid numbers , but that would only say how much force you must apply to get there, probably useless , the horizontal jumping ability coefficient is missing.
What you can do is that :
Do your best jump from a distance you can get rim ( say the dot line , or the free throw line ). Look how many inches you are missing , those at AT LEAST how much you need to add to your vert.
Example :
You jumped from the dot line and you touched rim at 10'4''
To dunk you need 10'10'' ( forget that 10'5'' you said unless you can balm the ball like a tennisball ).
So you are missing AT LEAST 6'' to dunk from that far out.
Ill come back to this later with some calculations on that 'AT LEAST'.
Hope it helps...
