Level 1: Is a Fully Charged Phone Heavier Than a Flat One?
The mass missing from a helium nucleus.
A helium-4 nucleus has a mass about 0.0304 u less than the total mass of 2 free protons and 2 free neutrons (1 u = 931.5 MeV/c²). Its binding energy is about:
The missing mass, the mass defect, is the energy that was released when the four nucleons bound together, and the same energy is needed to pull them apart again.
The binding energy is about 28.3 MeV. The 7.1 MeV option is the binding energy per nucleon, 28.3 divided by 4, which is a different quantity from the total the question asks for.
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