Answer: (4)
Given parameters
The formula for the acceleration due to gravity is
\(g = frac{4pi ^{2}l}{T^{2}}\)where
l = 55cm
T = 30 sec/20
Δl = 1mm = 0.1cm
ΔT = 1/20 sec
Now to calculate percentage error in g
\(frac{triangle g}{g} times 100% = left ( frac{triangle l}{l} + frac{2triangle T}{T} right )times 100%\) \(frac{triangle g}{g} times 100% = left ( frac{0.1}{55} + frac{2left ( frac{1}{20} right )}{frac{30}{20}} right ) times 100%\) \(frac{triangle g}{g} times 100% = 6.8%\)