Is this a lawful clause...?

[marcoma]

I have been puzzled by this clause in a contract for a college lecturer:

'You will be expected to work such hours as are reasonably necessary for the proper performance of your duties and responsibilities, inclusive of scholarly activity.'

Is this lawful? It does not define anywhere in the contract what the corporation deems as 'reasonable'. I mean if someone is contracted to work 36 hours, how is it defined in hourly terms what additional (unpaid) hours of work are reasonable?