A lidar (laser radar) gun is an alternative to the standard radar gun that uses
ID: 2064807 • Letter: A
Question
A lidar (laser radar) gun is an alternative to the standard radar gun that uses the Doppler effect to catch speeders. A lidar gun uses an infrared laser and emits a precisely timed series of pulses of infrared electromagnetic waves. The time for each pulse to travel to the speeding vehicle and return to the gun is measured. In one situation a lidar gun is a stationary police car observes a difference of 1.21 x 10-7 s in round-trip travel times for two pulses that are emitted 0.430 s apart. Assuming that the speeding vehicle is approaching the police car essentially head-on, determine the speed of the vehicle.
A lidar (laser radar) gun is an alternative to the standard radar gun that uses the Doppler effect to catch speeders. A lidar gun uses an infrared laser and emits a precisely timed series of pulses of infrared electromagnetic waves. The time for each pulse to travel to the speeding vehicle and return to the gun is measured. In one situation a lidar gun is a stationary police car observes a difference of 1.21 x 10-7 s in round-trip travel times for two pulses that are emitted 0.430 s apart. Assuming that the speeding vehicle is approaching the police car essentially head-on, determine the speed of the vehicle.Explanation / Answer
We can assume the speed of light in air is close enough to its speed in a vacuum. At 3*10^8 m/s light would travel 36.3m in 1.21 x 10^7 seconds (multiplied light's speed by the time) This is the change in round trip time(to and back), so the distance the vehicle moved is 1/2 that. If the vehicle moves 18.15m in 0.430 seconds, if will be moving 18.15/0.430 = 42.2 m/s. For common vehicle speed units, multiply that by 3600 second per hour / 1000 meters per kilometer for 151.95 km/hr.
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