How does a radar unit determine the speed of a moving vehicle?

A radar unit determines the speed of a moving vehicle by emitting radio waves and measuring frequency shifts, which is known as the Doppler effect. When the radar emits radio waves, these waves travel through the air until they encounter a moving vehicle. If the vehicle is approaching the radar unit, the frequency of the reflected radio waves increases, and if the vehicle is moving away, the frequency decreases. The radar unit analyzes these frequency shifts to calculate the speed of the vehicle. This method is effective because it allows for real-time speed measurements and can be used across various distances and conditions, making it a reliable tool for law enforcement and traffic monitoring.

The other options do not accurately describe how radar speed detection works. Measuring engine noise would not provide a consistent or accurate speed reading, emitting light pulses pertains to laser technology rather than radar, and calculating the time taken to travel a set distance is a method used in other contexts but not specifically for how radar units operate.