Rotational Motion - Medium

An explosion blows a rock into three parts. Two parts go off at right angles to each other. These two are,

1\,\text{kg}

first part moving with a velocity of

12\ \text{ms}^{-1}

and

2\,\text{kg}

second part moving with a velocity of

8\ \text{ms}^{-1}

. If the third part flies off with a velocity of

4\ \text{ms}^{-1}

, its mass would be