E= mc^2

[105907609]

Can someone explain why energy has mass? I thought it was a rule that it did not but there appears to be practice problems that state that energy does have mass.

[faith14B]

Energy only has mass if it is talking about an object having energy. The problem will explicitly say if it is a light/photon or a proton/baseball/electron/etc. For light/photon it will not have mass so do not use de broglies. For proton/baseball/electron/etc, do use de broglies to find wavelength/etc because it accounts for the mass of the object.

[Manav Patel 3L]

In the context of Einstein's theory of relativity, the relationship described suggests that energy has an equivalent mass due to mass-energy equivalence, demonstrating that energy and mass are interchangeable properties of the same entity.