As shown in the figure, there is a castle with a 100 meter × 100 meter site, and there is a moat of ten meters wide around it. In other words, the outside of the moat is 120 meters ×120 meters square. A feudal lord tried to pass a board to the moat and enter the castle grounds. However, the boards he brought are all 9.8 meters long and one meter wide and it’s a little short to the width of the wall.
How does he get inside the castle grounds?
(You may use as many boards as you want, but you cannot use nails or ropes to secure the plates.)