A retired Long Island teacher who prosecutors said used his authority to sexually abuse children on trips to the beach and pools was sentenced to up to five decades in prison Wednesday in what the district attorney called justice “long overdue.” Thomas Bernagozzi, 77, was slapped with a prison term of 33 1/3 years to 50 years in a case that was jumpstarted by a state law that allows child sexual abuse survivors to file civil lawsuits against their alleged tormenters. “Justice has been long