Turn over 13 14 A seiche is a standing wave that can form on the surface of a lake in strong winds, causing flooding and erosion. (a) Early in 2020, a single-node seiche was observed on Lake Erie in the USA. A node formed at the centre of the lake. Antinodes formed at the two ends of the lake. The speed v of a seiche wave is given by v = gh where h is the mean depth of the water. Calculate the period of oscillation of the seiche. length of Lake Erie = 400 km mean depth of Lake Erie = 19 m (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Period of oscillation = ....................................................... 14 (b) Erosion causes clay particles to be washed into the lake, making the lake cloudy. The lake can remain cloudy to a depth of about 4 m for more than 6 months. One spherical clay particle has a radius of 2.5 × 10−7 m. Deduce whether this particle takes more than 6 months to fall 4 m. You should assume that the water in the lake remains still. viscosity of water = 1.0 × 10−3 kg m−1 s−1 density of water = 1000 kg m−3 density of clay = 2650 kg m−3 (6) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Turn over 15 (c) The temperature of the lake decreases with depth. Explain how this may affect the rate at which a particle falls. 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(d) In an investigation to determine the viscosity of water, a student drops a small sphere into a cylinder of water. The student uses a stopwatch to record the time it takes for the sphere to fall through the water. Assess whether the stopwatch is suitable for measuring the time in this investigation. 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(Total for Question 14 = 13 marks)