Suppose that a 14.4 keV gamma ray could be trapped in a box with reflecting walls. (Why would this not be possible in practice?). Find the increase in mass of the box when the gamma ray is trapped inside. Compute the change in work done in lifting the box by a height h near the earth's surface. Describe quantitatively and qualitatively how this is related to the frequency shift of the gamma ray in the Pound–Rebka experiment [31].