# Energy Calculations using VIt The answer for Energy in kJ = $2.5 \times 3600 \times 1 = 9000 kJ$

I do not understand what formula they are using... are they using $VIt$, where $V =12$, $t= 12.5 \times 60 \times 60$ seconds and $I$, there is no information, which means this is not the equation... can someone please explain the answer

No, they are not using the formula $E = VIt$, rather, as they have stated the energy consumption is $1.0 kJs^{-1}$, or in other words 1.0 kJ of energy is consumed each second,

So, at that rate of energy consumption, after $t = 2.5$ hours x 3600 = 9000 seconds, the total energy consumed can be considered as being:

Total energy consumption = $1.0 kJs^{-1} \times 9000s = 9000 kJ$

In general, the formula is:

Quantity per unit time x time = Total quantity

• No problem! Always good to get everything clarified and thank you for a well written and detailed question! – user8016 Oct 5 '14 at 4:38

Yes ,you are right they are using the E=VIt
The information given is it uses 1.0Kj per 1s this is the power of machine P=E/t
the equation for Power is P=VI is electronic appliances therefore they have given us the power
Therfore VI=E/t=P
So then substitute it on the formula
E=VIt
VI = P (data is P=1.0kJs-1)
There fore E = 1.0kJs-1 x (2.5 x 3600)s