P = W/t Formula – How to Calculate Power (Practice)
P = W/t — Average mechanical power
Power is the rate of doing work: P = W/t. One watt is one joule per second. For a constant force parallel to velocity, P = F v.
Guide — how to use this formula
- 1. Find work first if you are given F and d (or mgh).
- 2. Convert time to seconds (and kW to W if needed).
- 3. Compute P = W/t in watts.
- 4. Or use P = Fv when force and velocity are parallel.
Derivation
Average power is work per unit time by definition:
- Definition:
P = \frac{W}{t} - With W = F d and constant speed v = d/t:
P = \frac{Fd}{t} = Fv
Don’t label joules as watts. Convert minutes to seconds before dividing.
Examples
Example: 200 J in 4 s
P = 200/4 = 50 W.
Example: 2 minutes trap
600 J in 2 min → t = 120 s → P = 5 W (not 300 W).