Let, Time period =T Length of simple pendulum =l Acceleration due to gravity =g ∵T=2π√
l
g
...(i) When sphere is fully filled with water, centre of mass lies at centre. Case I For, water level below centre of sphere l1>l0 ...(ii) Case II For empty sphere, $l=l_{0} ∴ From Eqs. (i), (ii) and (iii) In case I, time period increase. In case II, time period decrease.