A fighter jet flies at 680 m/s at an altitude where the speed of sound is 295 m/s. (a) Find its Mach number and classify the flight. (b) Find the half-angle of its Mach cone. Solution: (a) M = v/v_sound = 680/295 = 2.31. Since M > 1, the flight is supersonic. (b) sin(mu) = 1/M = 1/2.31 = 0.433, so mu = arcsin(0.433) = 25.7 degrees. Observers on the ground hear a sonic boom as this 25.7-degree cone sweeps past them.