Question

Total annual usage of energy by humankind is in the order of: 
1. Mega Joules 
2. Giga Joules 
3. Terra Joules 
4. Exa Joules

Answer 1

Normally , the consumption of energy by a healthy human in a day is 2000 Kcal
we know, 
1Kcal = 4200 Joules 
so, consumption of energy by humankind in a day = 2000 × 4200 Joules 
= 8.4 × 10^⁶ Joules

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

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

So,annual consumption of energy by humankind = 3.066 Giga Joules 
Hence, annual consumption of energy by humankind is in the order of Giga Joules.