Question 1

Why are cars rated in both hp and kW?

Accepted Answer

In Russia power is officially stated in horsepower (it sets the road tax), while Europe uses kilowatts. They are equivalent: 1 metric hp ≈ 0.7355 kW. A BMW 530i making 252 hp is 185 kW.

Question 2

Where does "horsepower" come from?

Accepted Answer

James Watt (1782) estimated that a horse could raise 33,000 pounds by one foot in one minute. Metric hp is defined as 75 kgf × 1 m/s = 735.5 W; mechanical hp is 550 ft·lb/s = 745.7 W — slightly more.

Question 3

How much power do household appliances draw?

Accepted Answer

A kettle 1,500–2,000 W, an iron 1,000–2,200 W, a microwave 800–1,200 W, a washing machine 2,000–2,500 W, a fridge 100–200 W, a TV 80–200 W, a gaming PC 500–800 W, and an LED bulb just 7–15 W.

Question 4

How does power relate to energy use?

Accepted Answer

Energy (kWh) = Power (kW) × Time (h). A 2 kW kettle on for 3 minutes uses 2 × (3/60) = 0.1 kWh. A 2.5 kW air conditioner running 8 hours a day uses 20 kWh/day, about 600 kWh over a month.

Question 5

What is reactive power?

Accepted Answer

In AC grids the apparent power (VA) combines active power (W) and reactive power (VAr). Motors and transformers "draw" reactive power without consuming it. Industry is billed for reactive power, while homes pay only for active power (the kWh on the meter).

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