Drag Equation
F_d=(1/2)pv^2C_dA
Now, assuming force equilibrium(I.e. constant descent velocity) yields :
v=\sqrt{2mg\over pC_DA}
Opening Shock
When a parachute is first deployed, it experiences forces greater than the Weight(mg) of the parts it is meant to support. It is important that these loads do not lead to failure of the parachute as that is bad(for obvious reasons).
There are 2 methods to calculate the maximum Opening shock force
1)The Canopy Loading Method
2)Momentum Impulse Theorem
Resources:
https://scholarworks.calstate.edu/downloads/c821gr23j