# Rotating Disk

A disk is rotating about a vertical axis in a liquid.  If the retardation due to friction of the liquid is proportional to the angular velocity, , find after seconds if the initial angular velocity was .

If the disk is rotating very rapidly, the retardation is proportional to .  Find after seconds if the initial amgular velocity was .

Source: March, Herman W., and Wolff, Henry C. (1917). Calculus. New York: McGraw-Hill. (Questions 4 & 5, p. 158)

## Author: ascklee

Dr. Lee teaches at the Wee Kim Wee School of Communication and Information at the Nanyang Technological University in Singapore. He founded The Mathematics Digital Library in 2013.