In this scenario, we can use the concept of relative velocity to determine the speed of the car.
The police officer's speed is given as 120 mph, and the rate at which the distance between the helicopter and the car is decreasing is given as 190 mph. We can consider the horizontal motion for simplicity.
Let's denote the speed of the car as Vc. Since the radar detects that the distance between the car and the helicopter is decreasing, the relative velocity between them is the difference between their velocities.
Relative velocity = Speed of the car - Speed of the helicopter
190 mph = Vc - 120 mph
To find the speed of the car, we rearrange the equation:
Vc = 190 mph + 120 mph
Vc = 310 mph
Therefore, the speed of the car, as detected by the radar, is 310 mph.