Kinetic Energy of Vehicle
Energy that brakes must dissipate to stop a moving car.
Formula
Variables
Example
1500 kg at 30 m/s: KE = 675 kJ
How it works
This formula tells you how much energy a moving vehicle has because of its motion. It depends on mass and the square of speed, so doubling the speed makes the kinetic energy four times larger, which is why high-speed braking is so demanding. In a vehicle, the brakes, tyres, and sometimes the road must remove this energy and turn it mainly into heat or deformation to bring the car to rest.
When to use it
Use this when you need the energy of a moving car, truck, bike, or any other vehicle from its mass and speed. It is especially useful in braking distance estimates, crash analysis, and comparing how much harder it is to stop heavier or faster vehicles.
Worked example, step by step
A van has a mass of 1200 kg and is travelling at 20 m/s. Step 1: Write the formula: KE = 1/2 mv^2 Step 2: Substitute the values: KE = 1/2 × 1200 × 20^2 Step 3: Square the speed: 20^2 = 400 Step 4: Multiply: KE = 0.5 × 1200 × 400 Step 5: Calculate: KE = 240000 J Final answer: KE = 240 kJ
Common mistakes to avoid
- Using speed in km/h instead of m/s
- Forgetting to square the speed
- Confusing mass with weight
Did You Know?
That 675 kJ becomes heat in the brake discs — enough to boil two litres of water in one hard stop.
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