Question

A metal sphere of radius r and specific heat S is rotated about an axis passing through its centre at a speed of n rotations per second. It is suddenly stopped and 50% of its energy is used in increasing its temperature. Then the rise in temperature of the sphere is –

• A. $\frac{2\pi^{2}n^{2}r^{2}}{5S}$
• B. $\frac{\pi^{2}n^{2}}{10r^{2}S}$
• C. $\frac{7}{8}$pr²n²S
• D. $\frac{5(\pi rn)^{2}}{14S}$

Answer 1

Answer: (A)

$\frac{2\pi^{2}n^{2}r^{2}}{5S}$

Answer 2

$\frac{1}{2}$ I w² = mSdT Ž I = $\frac{2}{5}$ mr²

w = 2pn