The true statement is that different gases with the same mass and temperature always have the same average kinetic energy. This is one of the postulates of the kinetic theory of matter.
If we two objects A and B, they will have mass [tex]m_A[/tex] and [tex]m_B[/tex] and velocity [tex]v_A[/tex] and [tex]v_B[/tex] respectively. If [tex]K.E = \frac{1}{2} mv^2[/tex]. Then it follows that
[tex]\frac{1}{2}m_Av_A = \frac{1}{2} m_Bv_B[/tex]. Since the mass is the same it means the velocity of the two objects should be the same so that they have the same average kinetic energy.
