Question

How long must a 400 W electrical engine work in order to produce 300 kJ of work?

Answer 1

In order to calculate the time needed, let's use the formula below:

`P=(E)/(t)`

Where P is the power in Watts, E is the energy/work in Joules and t is the time in seconds.

First, let's convert the energy from kJ to J (1 kJ = 1000 J):

`300\text{ kJ}=300000\text{ J}`

So, for P = 400, we have:

`\begin{gathered} 400=(300000)/(t) \\ t=(300000)/(400) \\ t=750\text{ s} \end{gathered}`

Therefore the time needed is 750 seconds.