Answer
a) The second magnet has its N end just below the N end of the first one.
b) A third identical horizontal bar magnet should be placed with its N end to the right of the N end of the first magnet. The N ends of magnet 2 and magnet 3 both repel the N end of magnet 1 and it feels a net force of 2.1mN at an angle of $45^{\circ}$ above the horizontal and to the left.
Work Step by Step
a) The second magnet has its N end just below the N end of the first one.
b) A third identical horizontal bar magnet should be placed with its N end to the right of the N end of the first magnet. The N ends of magnet 2 and magnet 3 both repel the N end of magnet 1 and it feels a net force of 2.1mN at an angle of $45^{\circ}$ above the horizontal and to the left.
