(a) Define simple harmonic motion. (6) The depth of water above the sea bed in a harbour can be described by simple harmonic motion as the tide comes in and goes out during the day. An anchored boat, of mass 15,000 kg, floats in the harbour, with the difference between maximum and minimum depth equal to 9 m. The time between maximum and minimum depth is 6 hours and 30 minutes. Assume all motion is vertical. (i) What is the period of the motion of the boat? (ii) Calculate the maximum net force experienced by the boat. (iii) How long after low tide is the kinetic energy of the boat at a maximum? (19) Give one other example of simple harmonic motion. (3)