# Power

is the rate at which energy is transferred or work is done. It has units of watts (W) or joules per second (J/s). The more energy that is transferred per second, or the more work that is done per second, the greater the power rating.

## Calculating power

To calculate power, use the equation:

This is when:

• power is measured in watts (W)
• work done is measured in joules (J)
• time taken is measured in seconds (s)

### Example

A horizontal force of 50,000 N acts on a car, causing it to move a horizontal distance of 80 m in a time of 25 s. What is the power of the car?

First, find the work done on the car:

work done = force × distance

work done = 50,000 × 80

work done = 4,000,000 J

Then, find the power:

power = 4,000,000 ÷ 25

power = 160,000 W

Question

A motor applies a force of 800 N to a trolley, causing it to move 80 m in a time of 16 s. What is the power of the motor?

Work done = 800 × 80

Work done = 64,000 J

Power = 64,000 ÷ 16

Power = 4,000 W

Move on to Test