(d) For a ring $K^{2} = r^{2}$ then $v^{2} = \sqrt{\frac{2gh}{1 + \frac{K^{2}}{r^{2}}}}$ $\therefore$ $v^{2} = \frac{2gh}{2} = gh$ $v = \sqrt{gh}$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.