A block of mass \(m\) on a frictionless horizontal surface is attached to an ideal spring. The position of the block as a function of time \(t\) is given by \(x(t) = A \cos(\omega t)\), where \(A\) is the amplitude and \(\omega\) is the angular frequency. Which of the following expressions represents the kinetic energy of the block as a function of time \(t\)?