A steel pipe has a polymer lining on its inner surface. An ultrasound transducer on the outer surface of the pipe sends a pulse normally through the steel wall and the polymer lining. The pulse reflects from the inner surface of the lining and returns along the same path to the transducer.
The steel wall is 11.8 mm thick. The speed of ultrasound is 5900 m/s in steel and 2500 m/s in the polymer.
The total time between sending the pulse and receiving the echo is 12.0 μs12.0\ \mu\mathrm{s}12.0 μs.
The lining is acceptable if its thickness is at least 9.0 mm.
Calculate the thickness of the polymer lining.
State whether the lining is acceptable. Give a reason for your answer.