What Delta Y Should Be Used to Calculate Viy in a Marshmallow Catapult?

[physics1232]

To calculate the Viy velocity for my marshmallow, what am I supposed to use for delta y? Would it be 0 because my catapult is pulled all the way to ground before I let it go, or would it be the height at which the catapult specifically flings the marshmallow?

 

[Simon Bridge]

To calculate the Viy velocity for my marshmallow, what am I supposed to use for delta y?

Depends - what does "delta y" mean?

I am guessing that "Viy" means the vertical component of the initial velocity.
It sounds like you are trying to use an equation you have written down someplace without understanding what it means instead of using physics. What does your physics tell you?