A thick walled hollow sphere has outer radius \[R\]. It rolls down an inclined plane without slipping and its speed at the bottom is\[v\]. If the inclined plane is frictionless and the sphere slides down without rolling, its speed at the bottom is \[5v/4\]. What is the radius of gyration of the sphere?

• A. \[\frac{R}{\sqrt{2}}\]                
• B. \[\frac{R}{2}\]
• C. \[\frac{3R}{4}\]           
• D. \[\frac{\sqrt{3}R}{4}\]