A body of mass \( 1 \, \text{kg} \) collides head on elastically with a stationary body of mass \( 3 \, \text{kg} \). After collision, the smaller body reverses its direction of motion and moves with a speed of \( 2 \, \text{m/s} \). The initial speed of the smaller body before collision is ________ \( \text{ms}^{-1} \).
