Mass, energy and binding energyAQA A-Level Physics: Mind map

Exam questions on Mass, energy and binding energy

1. A student is analysing the helium-4 nucleus using these data: nuclear mass of helium-4 = 4.00151 u; mass of a proton = 1.00728 u; mass of a neutron = 1.00867 u; 1 u = 931.5 MeV.
   Explain why the mass of a helium-4 nucleus is less than the total mass of its separate nucleons.2 marks
2. A power station burns coal. Burning 1.0 kg of coal releases 3.0 × 10⁷ J of energy. The speed of light in a vacuum is c = 3.00 × 10⁸ m s⁻¹.
   Suggest why the mass change in a chemical reaction is never noticed, but the mass change in a nuclear reaction can be measured.2 marks
3. Average binding energy per nucleon: hydrogen-2 (deuterium) 1.1 MeV; helium-4 7.1 MeV; iron-56 8.8 MeV; uranium-235 7.6 MeV. When a uranium-235 nucleus undergoes fission, the fragments formed have an average binding energy per nucleon of 8.5 MeV. 1 MeV = 1.60 × 10⁻¹³ J.
   Explain, in terms of binding energy per nucleon, why energy is released both when light nuclei such as hydrogen-2 fuse and when heavy nuclei such as uranium-235 undergo fission.3 marks