Question #41090

1 Answer
Feb 24, 2017

Answer:

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#