A transverse wave propagating in a string is described by the equation y = 0.021 sin(x + 30t), where x and y are in metre and t in second. If the linear density of the vibrating string is 1.3 × 10–4 kg/m, the tension in the string is
(a) 0.21 N
(b) 0.12 N
(c) 0.64 N
(d) 2.1 N
