Thank you for your response.
Obviously it can be used to calculate the energy for a change of mass taking into account momentum, but I was hoping to find applications like in nuclear fusion where the equation can be demonstrated if that makes sense.
I've been doing some research into Einstein's equation E2=(mc2)2 +(pc)2 but apart from in nuclear reactions, where you can use the simpler E=mc2 as momentum=0, I have been unable to find any applications.
Thank you in advance