text: The required input data for this ? is:\nmass of object\nshape of object\nsize of object\nair density = f(altitude)\n\nI assume we are talking about the terminal velocity, which will not actually be constant, but vary with altitude.\n\nThe shape and size will determine the drag coefficient, Cd.  Cd for various shapes are found in aerodynamic texts.  The aerodynamic drag formula is\nD = Cd*(ρV²/2)*A   where ρ is the density, V the velocity, and A is the reference area the Cd is based on.\nThe driving force for the motion is simply mg, the weight of the object.  At terminal condition, D = mg, and the above eqn becomes\n\nmg = Cd*(ρV²/2)*A  --->V² = 2mg/(Cd*ρ*A)\n\nTo give you some numbers to play with, the Cd of a teardrop shaped object is in the neighborhood of 0.10 based on its cross sectional (┴ to direction of travel) area.  Air density @ 10Kft = .001758 sl/ft³ and at sea level =.00238 sl/ft³.  You can assign any mass and area you like to put in the eqn.  Area is in ft² and mg is pounds.  Velocity will be in feet /sec.\n\nGOOD LUCK!