For small deflections, T = 2*pi*sqrt(L / g) where T is period, L is length and g is gravity.
Setting the equations to the same period, 2*pi*sqrt(3.85 / g) = 2*pi*(L / (1/6 * g))
The equation reduces to 3.85 m = 6 * L so L = 0.642 m
chrsclrk · 7 years ago