- #1

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## Main Question or Discussion Point

p=mv then for a photon p=0*c means p=0. And also ke=1/2pv which is ke=0 and E=mc2 means E=0. please use easy words and we descriptive.

- Thread starter suchal
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- #1

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p=mv then for a photon p=0*c means p=0. And also ke=1/2pv which is ke=0 and E=mc2 means E=0. please use easy words and we descriptive.

- #2

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The universal formula which is to be used is

[tex] E^2 = \vec{p}^2 c^2 + m^2 c^4 [/tex]

where m is the rest/invariant mass which is 0 for a photon.

- #3

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See the FAQ here. Also, you might find this thread interesting.

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