Question

A thin hollow sphere of mass m is completely filled with a liquid of mass $m$. When the sphere rolls with a velocity $v$, kinetic energy of the system is (neglect friction)

• A. $\frac {1}{2} mv^2$
• B. $mv^2$
• C. $\frac {4}{3} mv^2$
• D. $\frac {4}{5} mv^2$

Answer 1

Answer: (C)

$\frac {4}{3} mv^2$

Answer 2

Total energy $= KE +$ rotational $KE$ $=\frac{1}{2}(2 m ) v^{2}+\frac{1}{3} m v^{2}$ $=\frac{4}{3} m v^{2}$