A light bulb is rated at 60 W. If it runs for 2 hours, how much energy does it use in kJ?

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Multiple Choice

A light bulb is rated at 60 W. If it runs for 2 hours, how much energy does it use in kJ?

Energy used equals power times time. The bulb uses 60 J each second. Running for 2 hours is 2 × 3600 = 7200 seconds. So energy = 60 J/s × 7200 s = 432,000 J, which is 432 kJ. (Alternatively, 60 W = 0.06 kW and 2 h gives 0.06 × 2 = 0.12 kWh, and 0.12 kWh = 432 kJ.)

Energy used equals power times time. The bulb uses 60 J each second. Running for 2 hours is 2 × 3600 = 7200 seconds. So energy = 60 J/s × 7200 s = 432,000 J, which is 432 kJ. (Alternatively, 60 W = 0.06 kW and 2 h gives 0.06 × 2 = 0.12 kWh, and 0.12 kWh = 432 kJ.)

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