To understand why you should brake earlier at **100 km per hour**, it is important to consider the **braking distance**. This is the distance a vehicle travels from the moment the brake is applied until it comes to a complete stop.

- **Speed**: At higher speeds, the vehicle needs more space to stop. Therefore, at 100 km per hour, the braking distance will be significantly greater than at 50 km per hour or 30 km per hour. This is because the kinetic energy of the vehicle is higher at higher speeds, which requires more time and distance to fully dissipate and stop the vehicle.

- **Defensive driving**: It is crucial to maintain an adequate safety distance and brake smoothly and in advance, especially at high speeds. This allows you to react in time to any unforeseen events and avoids sudden braking that could be dangerous.

In summary, at **100 km per hour**, it is essential to brake earlier due to the greater braking distance required, thus ensuring safe and efficient driving.