If I have the following objects: A and B. A is a distance "Y" from the ultrasonic sense and B is a distance "x". If B is fix and A is moving, does the ultrasonic sense receive and detects A distance?
Cheap ultrasonic sensors will give you a signal when the first echo (from the closest object) is received. Hence, you'll get a reading of 'X' for object B, and probably nothing for the object A, no matter if it's moving or not.
Which makes sense, because if you keep moving in the current direction, object B is the one you should be most concerned about.