A single cylinder engine runs at 240 rpm and has a stroke of 200 mm. The reciprocating parts have a mass of 120 kg and the revolving parts are equivalent to a mass of 80 kg at a radius of 100 mm. A mass is placed opposite to the crank at a radius of 150 mm to balance the whole of the revolving mass and 2/3rd of the reciprocating mass. Determine the magnitude of the balancing mass and the resultant residual unbalance force when the crank has turned 30° from the inner dead centre. Neglect the obliquity of the connecting rod.