An engineer uses pulses of ultrasound to check the thickness of the steel wall of a pipe.
A probe on the outside of the pipe sends a pulse into the wall. The pulse reflects from the inside surface of the wall and returns to the probe.
The speed of sound in steel is 5900 m/s.
The echo returns to the probe 3.0 μs3.0\ \mu\text{s}3.0 μs after the pulse is sent.
Calculate the thickness of the wall in mm\text{mm}mm.
When the pipe was new, the wall was 12 mm thick.
Calculate the time the echo would have taken to return to the probe when the pipe was new.
The pipe must be replaced if more than a quarter of the thickness of the wall has been lost.
Determine whether this pipe must be replaced.