A teacher standing in a doorway 1.0 m wide blows a whistle with a frequency of 1000 Hz to summon children from the playground (Fig. 24.31). Two boys are playing on the swings 20 m away from the school building. One boy is at an angle of θo and another one 19.6o at from a line normal to the doorway. Taking the speed of sound in air to be 335 m/s, which boy may not hear the whisle? Prove your answer.