In order For this theory to be applicable the angle of displacement must have been 5 Degrees or less as the theoretical equation assumes SHM. In practice, someone Walking across the bridge would probably displace the bridge more than five Degrees, (+ its not made out of the same material + wind), so therefore our Experimental result possibly doesn’t reflect the real outcome. But it could be Used as an estimate.
The minimum Value we used for L was 0.2 because anything smaller than that would be too Fast to accurately measure. A max length of 0.7 was used as it’s the max length Of the string