An underwater survey pod is stationary between two opposite rock walls, A and B, in a flooded cavern. It sends an ultrasound pulse straight towards each wall.
The echo from wall A returns after 0.085 s and the echo from wall B returns after 0.137 s. The speed of ultrasound in the water is 1460 m/s.
The pod is then moved along the line between the walls until it is midway between them.
Calculate the distance the pod moves.