The kinetic energy formula
Both factors the trolley found appear in the formula, but they do not appear in the same way.
Kinetic energy
Ek = ½ m v2
- m — the mass of the object
- v — the velocity of the object
- Ek — the kinetic energy
The units that go in
The formula gives an answer in joules only when its two inputs are in the units below. Anything else has to be converted first.
| Quantity | Symbol | Unit |
|---|---|---|
| Mass | m | kg |
| Velocity | v | m s-1 |
| Kinetic energy | Ek | J |
The velocity is squared, the mass is not
Double the mass and the kinetic energy doubles. Double the velocity and it goes up four times, because v is squared. That difference is why a small increase in speed is so much more dangerous than a small increase in load.
Square the velocity before anything else
In Ek = ½ m v2, work out v2 first, then multiply by the mass, then halve. Halving first and squaring afterwards gives the wrong answer.