🔮 Calculate Kinetic Energy
What is Kinetic Energy?
Kinetic energy (KE) is the energy an object possesses due to its motion. Any object that is moving — a car, a baseball, an electron — has kinetic energy. The faster it moves or the more massive it is, the more kinetic energy it carries.
The formula KE = ½mv² tells us two important things:
- Speed matters more than mass: Because velocity is squared, doubling speed quadruples kinetic energy. This is why car crashes at 60 mph are four times more dangerous than at 30 mph.
- Mass scales linearly: Double the mass → double the KE (all else equal).
SI Units
Kinetic energy is measured in joules (J) in the SI system. 1 J = 1 kg·m²/s². For large energies use kilojoules (kJ) or megajoules (MJ).
Worked Example
A 1,200 kg car travels at 30 m/s. What is its kinetic energy?
To stop this car, the brakes must absorb exactly 540 kJ of energy as heat.
Common Mistakes
- Forgetting the ½ factor (most common error in exams)
- Using velocity in km/h instead of m/s without converting
- Squaring only part of the expression — v² applies to the whole velocity value
- Confusing kinetic energy (scalar) with momentum (vector)
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Frequently Asked Questions
What units is kinetic energy measured in?
Kinetic energy is measured in joules (J) in the SI system. 1 joule = 1 kg·m²/s². Large values may be expressed in kilojoules (kJ) or megajoules (MJ).
Why does doubling speed quadruple kinetic energy?
Because velocity is squared in KE = ½mv². If v → 2v, then v² → 4v², so KE quadruples. This is why high-speed collisions are disproportionately dangerous.
Is kinetic energy a vector or a scalar?
Kinetic energy is a scalar — it has magnitude but no direction. Momentum (p = mv) is the corresponding vector quantity.
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