coefficient(1): 1 -> x0' # initial speed
coefficient(2): -1 -> -x0 # initial length of rope already over the edge of the table
-coefficient(3): g/l # gravity constant (g) devided by the length of the rope (l)
+coefficient(3): g/l # gravity constant (g) divided by the length of the rope (l)
iintegrate (x'') -> -x':
IC: x0'