Question

Question #41090

Answer 1

Time to charge the battery is 15.4 hours.

Explanation:

`2.0 MJ` is a unit of energy which is defined as power multiplied by time.

`E = P xx t`

We know that: `1MJ` of energy = `277.8Wh`

So `2.0 MJ = 2.0 xx 277.8 = 555.6Wh`

Note the is decimal is rounded off here to match the single decimal place in all the given values.

The battery charger uses `40.0W` of power, but it only supplies `90%` or `9/10` of that power to the battery.

Then: `P = 40.0 xx 9/10 = 36.0 W`

Substituting these values into the equation;

`E = P xx t`

`555.6Wh = 36.0Wt`

`t = 555.6/36.0 = 15.4h`