**Question:**

Einstein’s mass-energy relation emerging out of his famous theory of relativity relates mass (m) to energy (E) as E= mc2, where c is speed

of light in vacuum. At the nuclear level, the magnitudes of energy are very small. The energy at nuclear level is usually measured in MeV,

where 1 MeV = 1.6 x 10-13 J; the masses are measured in unified atomic mass unit (u) where, 1 u = 67 x 10-27 kg.

(a) Show that the energy equivalent of 1 u is 931.5 MeV.

(b) A student writes the relation as 1 u = 931.5 MeV. The teacher points out that the relation is dimensionally incorrect. Write the correct

relation.

**Solution:**

(a) Using Einstein’s mass-energy relation, the energy that is equivalent to the given mass can be calculated

1 amu = 1 u = 1.67 × 10-27 kg

Applying E = mc2

E = 931.5 MeV

b) As E = mc2

m = E/c2

Which means that 1u = 931.5 MeV/c2

The dimensionally correct relation of 1 amu = 931.5 MeV