What is the horizontal distance between pillar A and the centre of mass of the person when the plank starts to tip?
0.50 m0.50\text{ m}0.50 m
2.50 m2.50\text{ m}2.50 m
2.90 m2.90\text{ m}2.90 m
3.50 m3.50\text{ m}3.50 m
