A/20 scale model of an automobile is tested in a wind tunnel. The test is to simulate the automobile travelling at 120 km/h in air at atmospheric pressure of 101.3

kPa and 20 °C. The wind tunnel also operates with air at the same temperature. a) At what pressure in the test section must the tunnel operate to have the same Mach. [10 marks]b) What air velocity in the wind tunnel should be used if the pressure in the wind tunnel reduced to the atmospheric pressure and temperature remains 20 °C. Explain briefly why experiment with these conditions could be a challenge. [The word limit is 50 words].