Power

Key Stage 3

The unit of power is the Watt.

Power is how quickly energy is transferred from one store into another.

Energy Transfered is the same as Work Done, so power is also the rate of work done.

\[Power = \frac{Energy Transferred}{Time}\] \[P = \frac{E}{t}\]

\[Power = \frac{Work Done}{Time}\] \[P = \frac{W}{t}\]

Where:

P = Power

t = Time

The SI Unit of power is the watt.

Power = \(\frac{Work Done}{Time}\)

\[P = \frac{W}{t}\]

Where:

P = Power

t = Time

Power = (Current) x (Potential Difference)

\[P = IV\]

Where:

P = Power

A bow at full stretch transfers 50J of energy from its elastic potential energy store into the kinetic energy store of an arrow in 0.02 seconds. Calculate the power of this transfer correct to two significant figures.	A piano falls down a flight of stairs. In this fall 5.4kJ of energy is transferred from the gravitational potential energy store into the kinetic energy store of the piano. It take 0.80 seconds to reach the bottom of the stairs. Calculate the average power of this transfer correct to two significant figures.	A 'weight lifter' lifts a 2000N weight a distance of 1.2 metre from its original position. They do this in 0.70 seconds. Calculate the power output of the 'weight lifter' correct to two significant figures.
1. State the known quantities W = 50J t = 0.02s	1. State the known quantities W = 5.4kJ = 5400J t = 0.80s	1. State the known quantities F = 2000N d = 1.2m t = 0.70s
2. Substitute the numbers into the equation and solve. \(P = \frac{W}{t}\) \(P = \frac{50}{0.02}\) \(P = 2500W\) \(P \approx 6800W\)	2. Substitute the numbers into the equation and solve. \(P = \frac{W}{t}\) \(P = \frac{5400}{0.80}\) \(P = 6750W\)	2. Substitute the numbers into the equation and solve. \(W = \vec F \vec d\) \(W = \vec F \times \vec d\) \(W = 2000 \times 1.2\) \(W = 2400J\) \(P = \frac{W}{t}\) \(P = \frac{2400}{0.7}\) \(P = 3428.57W\) \(P /approx 3400W\)