Kinetic energy = (1/2) (mass) (speed)²
KE = (1/2) (1 kg) (30 m/s)²
KE = (1/2) (1 kg) (900 m²/s²)
KE = 450 kg-m²/s²
KE = 450 Joules
That's at the instant it leaves the thrower's hand. After that, gravity immediately begins to rob its kinetic energy, so the KE starts decreasing right away.
