Physics Textbook Questions: Energy & Power

a) i) The mains filament lamp is more powerful
ii) The 10,000W electric cooker

b) 20,000,000 x 0.1 = 200,000
200,000 x 3kW = 600,000kW = 600MW

a) 5000W / 20s = 250W

b) 1W = 1J/s
12,000J / 20s = 600J/s = 600W
600W / 5000W = 12%

a) 1W = 1J/s
1500kJ (1,500,000J) / 50s = 30kJ/s = 30kW

b) 30kW / 100kW = 0.03 = 3%

a) Electricity is used to heat water, depleting the electricity store and increasing the thermal energy store. This is converted into some kinetic and mechanical energy to pump it through the shower head, gaining GPE and then swapping out the GPE for kinetic energy as it falls.

b) 12kW = 12,000W/s
4 x 20min = 80min = 4800s
4800s x 12,000W/s = (4,800,000 + 960,000) = 5,760,000W = 5.76MW