A metal sphere with radius $r$ is released into a tank of water. As it moves downward with speed $v$, it experiences a drag force $F$ given by $F = krv$, where $k$ is a constant. What are the SI base units of $k$?
- A$\text{kg m}^2\,\text{s}^{-1}$
- B$\text{kg m}^{-2}\,\text{s}^{-2}$
- C$\text{kg m}^{-1}\,\text{s}^{-1}$
- D$\text{kg m s}^{-2}$