What is the frequency of a photon that has the same momentum as a neutron moving with a speed of 1.90 × 103 m/s?

The mass of a neutron is:

Since we know its speed, we can calculate the neutron's momentum:


The problem says the photon has the same momentum of the neutron, p.  The photon momentum is given by

where h is the Planck constant, and  is the photon wavelength. If we re-arrange the equation and we use the momentum we found before, we can calculate the photon's wavelength:


And since we know the photon travels at speed of light c, we can now calculate the photon frequency:

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