How to use it
- Choose how to find the work: from a force and a distance, or from the change of speed.
- For a force, enter it and the angle between the force and the direction of motion (0° when you push straight ahead).
- For a change of speed, enter the mass and the speeds before and after.
- Enter the distance and the time. Read the work in J, kJ and Wh, the average power and the force along the path.
Formulas
- Work of a constant force: W = F × d × cos θ
- Work–energy theorem: W = ½ m v₂² − ½ m v₁²
- Average power: P = W ÷ t
- Average force along the path: F = W ÷ d
- 1 kJ = 1000 J, 1 Wh = 3600 J
Worked example
Pushing a cart with 100 N straight ahead for 10 m in 5 s: W = 100 × 10 × cos 0° = 1,000 J (0.277778 Wh), P = 1,000 ÷ 5 = 200 W.
Pulling a sled with 100 N on a rope at 60° for 20 m in 10 s: only 100 × cos 60° = 50 N acts along the path, W = 50 × 20 = 1,000 J, P = 100 W.
A 1000 kg car speeds up from 0 to 20 m/s over 100 m in 10 s: W = ½ × 1000 × 20² = 200,000 J = 200 kJ, the average power is 20,000 W (20 kW) and the average net force 2,000 N.
Tips
- A force at 90° to the motion does no work. Carrying a bag along a level corridor does no work on it in the physics sense.
- The theorem gives net work. If friction also acts, the engine does more work than the change in kinetic energy.
- Use metres per second inside the formula. The calculator converts km/h and mph for you.