What happens to ((a)) the kinetic energy of a marble when its speed is reduced to half

Question:

What happens to $(a)$ the kinetic energy of a marble when its speed is reduced to half its initial speed and $(b)$ the energy of a photon when its speed is reduced to half its initial speed (as, for instance, when the photon travels from a medium with an index of refraction of 1 into a medium with an index of refraction of 2)?

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