A boy ties a stone of mass \( 100 \, \text{g} \) to the end of a \( 2 \, \text{m} \) long string and whirls it around in a horizontal plane. The string can withstand the maximum tension of \( 80 \, \text{N} \). If the maximum speed with which the stone can revolve is \( \frac{K}{\pi} \, \text{rev.}/\text{min} \). The value of \( K \) is : (Assume the string is massless and unstretchable)
