Question

an atomic nucleus of mass m emits a gamma ray photon of frequency v,the net loss in the interanal energy of parent nucleus is?

Answer 1

the net loss of energy by photon is equals to

E=hv
E=energy
h=Planck's constant
v=frequency

or

E=1/2.m(v)^2
E=energy
m=mass of photon
v=velocity

Hope it helps!
any doubts so comment

Answer 2

E=1/2mv^2 is your answer