def is_collade(v1, v2):
    """
    Input:
        v1,v2: velocity of train one and train two respectively in km/h

    Output:
        True if trains collade under defined circumstates, False if not
    """

    t1 = 4/v1
    s1 = t1*v2

    if s1 >= 6:
        return True
    else:
        return False