Question

Total annual usage of energy by humankind is in the order of:
Mega Joules
Giga Joules
Terra Joules
Exa Joules

Answer 1

normally , uses of energy by A healthy human in a day = 2000 Kcal
we know,
1Kcal = 4200 Joules
so, uses of energy by humankind in a day = 2000 × 4200 Joules
= 8.4 × 10⁶ Joules

now, 1 annual = 1 year = 365 days
so, uses of energy by humankind in a year = uses of energy by humankind in a day × 365 days
= 8.4 × 10⁶ × 365 Joules
= 3066 × 10⁶ Joules
= 3.066 × 10⁹ Joules

you should know,
Kilo = 10³
mega = 10⁶
Giga = 10⁹
Terra = 10¹²
peta = 10¹⁵
exa = 10¹⁸

according to above, annual uses of energy by humankind = 3.066 Giga Joules
hence, annual uses of energy by humankind is in the order of Giga Joules