Question

Three bodies, a ring, a solid cylinder and a solid sphere roll down the same inclined plane without slipping. They start from rest. The radii of the bodies are identical. Which of the bodies reaches the ground with maximum velocity?

• A. Ring
• B. Solid cylinder
• C. Solid sphere
• D. All reach the ground with same velocity

Answer 1

Answer: (C)

Solid sphere

Answer 2

According to conservation of mechanical energy $mgh=\frac{1}{2}mv^{2}\left(1+\frac{k^{2}}{R^{2}}\right)$ or $\quad v^{2}=\left(\frac{2 gh}{1+\frac{k^{2}}{R^{2}}}\right)$ Note : It is independent of the mass of the rolling body. For a ring, $k^{2}=R^{2}$ $v_{ring}=\sqrt{\frac{2 gh}{1+1}}=\sqrt{gh}$ For a solid cylinder, $k^{2}=\frac{R^{2}}{2}$ $V_{cylinder}=\sqrt{\frac{2 gh}{1+\frac{1}{2}}}=\sqrt{\frac{4 gh}{3}}$ For a solid sphere, $k^{2}=\frac{2}{5}R^{2}$ $v_{sphere}=\sqrt{\frac{2 gh}{1+\frac{2}{5}}}=\sqrt{\frac{10 gh}{7}}$ Among the given three bodies the solid sphere has the greatest and the ring has the least velocity at the bottom of the inclined plane.