The radial velocity vr at any radius r, when the gap width is h, is

• A. \({v_r } = \frac{{V\;r}}{{2h}}\)
• B. \({v_r } = \frac{{V\;r}}{h}\)
• C. \({v_r } = \frac{{2Vh}}{r }\)
• D. \({v_r } = \frac{{Vh}}{r}\)