A small block with mass $0\mathrm{.}390kg$ is attached to a string passing through a hole in a frictionless, horizontal surface. The block is originally revolving

in a circle with a radius of $0\mathrm{.}800m$ about the hole with a tangential speed of $4\mathrm{.}00\frac{m}{s}.$ The string is then pulled slowly from below, shortening the radius of the circle in which the block revolves. The breaking strength of the string is $30\mathrm{.}0N.$

Part A

What is the radius of the circle when the string breaks?

Express your answer with the appropriate units.