A 0.95-m aluminium bar is held with its length parallel to the east-west direction and dropped from a bridge. Now before the bar hits the river below, its speed is 25 m/s, and the emf induced across its length is 7.5 x 10-4 V. Assuming the horizontal component of the Earth's magnetic field at the location of the bar points directly north, (a) Decide the magnitude of the horizontal component of the Earth's magnetic field, and (b) state the number of which end of the bar is positive: 1 = east, 2 = west.