It's theoretically possible. You would need to know the Heats of Formation (ΔHf) of the metal hydride and the hydroxide product.  You should be able to find these numbers on the internets if you use the google. Assuming the hydride is sodium hydride (NaH), the product would be sodium hydroxide, and the energy released by the reaction NaH + ½O2 → NaOH would be approximately equal to [ΔHf(NaOH) - ΔHf(NaH)]. That number, which should be negative, represents the amount energy released by the reaction (under standard conditions), and its absolute value is the maximum amount of energy that would be possible to extract from the system. Of course, the whole hydride to wheels spinning energy transfer is not 100% efficient, so there would actually be somewhat less energy available to run the car. Exactly hwo much that value should be attenuated, I don't know. Maybe someone with an engineering background can help you out with that part.