1. The problem statement, all variables and given/known data The equation E=mc^2 and its counterpart m=E/c^2 state that energy and matter are the same thing. (kinda stupid question) Does that mean that 1 joule of energy has a mass? Am I wrong in thinking this? (more to the point, does 1 unit of energy have a distinct mass) 2. Relevant equations m=E/c^2 1 joule=1kg(m/s)^2 3. The attempt at a solution m=1joule/c^2 m=1kg(m/s)^2/299792458 m/s^2 m=1kg(m/s)^2/89875517873681764(m/s)^2 m=1kg/89875517873681764 m=1.112650056053618432174089964848e-17kg so 1 joule of energy has 1.112650056053618432174089964848e-17kg of mass?