Two strings of the same length 0.90m are made of the same material but have linear mass densities 0.010kgm−1 and 0.040kgm−1, respectively. They are stretched with the same tension T and vibrate in their second harmonics. If the beat frequency produced is 30Hz, find the value of T.
(a) 36N
(b) 30N
(c) 52N
(d) 23N