A platoon of soldiers is about to march across a light foot-bridge.
(i) Explain clearly why the soldiers are ordered to break step while crossing the bridge.
(ii) The bridge has a fundamental transverse oscillation frequency of 1.8Hz. The average marching rate of the platoon is two steps per second. Comment, with reason, whether the bridge is in danger of resonant vibrations in this situation.
(iii) Suggest any two structural or procedural measures that can be taken to reduce the possibility of dangerous resonance when large groups must cross such a bridge.