Final answer:
The magnitude of each of the two equal forces that have a resultant perpendicular to them can be found by dividing the magnitude of the resultant by the sine of 60° since they form an equilateral triangle with the resultant.
Step-by-step explanation:
The student's question relates to vector addition and the conditions for when the resultant of two forces is perpendicular to each of the forces involved. In the case where both forces make a 60° angle with the resultant, and assuming the forces have equal magnitude, we can deduce that the forces are equal in magnitude and form an equilateral triangle with the resultant. The sine rule in trigonometry or the properties of cross products in vector analysis can be utilized to calculate the magnitude of the forces. Specifically, the magnitude of each force can be calculated as the resultant divided by the sine of 60°, given that the sine of the angle between the forces and the resultant will give us the proportionality factor needed to calculate the forces.