Both free vortex and forced vortex can be expressed mathematically in terms of tangential velocity V at the corresponding radius r. Choose the correct combination

A

Free vortex - $$V = r \times const,$$ Forced vortex - $$V_r = const.$$

B

Free vortex - $$V^2 \times r = const,$$ Forced vortex - $$V = r \times const.$$

C

Free vortex - $$V \times r = const,$$ Forced vortex - $$V^2 = r \times const.$$

D

Free vortex - $$V \times r = const,$$ Forced vortex - $$V = r \times const.$$