// Ex21_2 Page:399 (2014) clc;clear; m_pi_minus = 139.6; // Mass of a pion, MeV m_p = 938.3; // Mass of a proton, MeV m_n = 939.6; // Mass of a neutron, MeV K_n = 0.6; // The kinetic energy of the neutron, MeV E_pi0 = m_p + m_pi_minus - m_n - K_n; // Mass of neutral pion, MeV E_pi0_r = sqrt(E_pi0^2 - (m_n + K_n)^2 + m_n^2); // Relativistic mass of neutral pion, MeV printf("\nThe relativistic mass of neutral pion = %5.1f MeV", E_pi0_r); // Result // The relativistic mass of neutral pion = 133.5 MeV