(3-16)   We will use equation III-8:    

①   Mass = 2.5 kg.

when v = 0,   E = mc2  =    2.5 x (3.00 x 108 )2  =  2.25 x 1017 J.

This is quite a lot of energy: it’s equivalent to the energy released when 2.25 x 1017  / 4.18 x 109  =  54 million tonnes of TNT explode.

②  You could work it out using the full equation but the difference from the rest mass is so small it may be undetectable on your pocket calculator. So the easy way is just to work out Cormorant’s classical kinetic energy (he isn’t, sadly, quick enough to bother with the relativistic energy) and find that as a percentage of the rest energy:

Ek  =  ½ mv2  =  ½ x 2.5 x 2.02  =  5.0 J

So % increase in total energy =  5.0 x 100 / 2.25 x 1017  =  2.2 x 10-15%

Cormorant is unsure whether to be rather proud of his total energy or ashamed at his limited ability to add to it.