A boy ties a stone of mass 100 g to the end of a 2 m long string and whirls it around in a horizontal plane. The string can withstand the maximum tension of 80 N . If the maximum speed with which the stone can revolve is $\frac { K } { \pi } \mathrm { rev } \min ^ { - 1 }$. The value of $K$ is :\\
(Assume the string is massless and un-stretchable)\\
(1) 400\\
(2) 300\\
(3) 600\\
(4) 800