3. There are two electric drills in the shop. Drill A will transfer 25kJ of energy in 3 minutes. Whilst drill B will transfer 20kJ of energy over 4 minutes. Which drill A or B is the most powerful?

Drill A

25kJ = 25000J

3 minutes ; (3 x 60) = 180 seconds

Drill B

20kJ = 20000J

4 minutes; (4 x 60) = 240 seconds

Power drill A  = 25000/180 = 138.9W

Power drill B = 20000/240 = 83.3W

So, drill A is more powerful.

4.An electric shower has a power rating of 8kW and is used for 5 minutes, 3 times a day, for 1 week. Calculate the total energy transferred.

Power = Energy/time

Energy = Power x time

8kW = 8000W

5 minutes; (5 x 60) = 300 seconds

Total time period = 300 x 3 x 7 = 6300 seconds

Need to multiply by 3 because it is used 3 times per day, multiply by 7 as there are 7 days in one week.

Energy used = 8000W x 6300 seconds = 50400000J

or 50400kJ

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