A cyclist riding along a straight road continuously blows a horn of frequency 500 Hz. The sound is reflected by a high, vertical cliff standing 200 m ahead on the same road. The cyclist hears 6 beats per second between the direct sound from the horn and the sound reflected from the cliff.
Take the speed of sound in air to be 340 m s⁻¹.
(i) Calculate the speed with which the cyclist is approaching the cliff.
(ii) State whether the beat frequency will increase, decrease or remain unchanged if the cyclist continues to blow the horn while moving away from the cliff after crossing the foot of the cliff. Justify your answer briefly.