Energie

$E^2=m^2{c}^4+{\underset{\_}{p}}^2{c}^2$

Taylor-Entwicklung für kleine Geschwindigkeiten:

$Assumptions = c > 0 && Subscript[m, 0] >= 0 && p >= 0 && v >= 0;

Energy      := Sqrt[Subscript[m, 0]^2*c^4 + p^2*c^2];
EnergyAppox := Series[Energy, {p, 0, 5}] // Simplify;

Print["E" == EnergyAppox]

$E=c^2{m}_0+\frac{p^2}{2m_0}-\frac{p^4}{8\left(c^2{m}_0^3\right)}+O\left(p^6\right)$