Tension in the string. T = 200;
Mass of string, M = 2.50 g;
Length l = 20 m
Mass per unit length, m = M/L = 2.5/20
= 0.125 kg m-1
Velocity, v = √{T/m} = √{200/0.125}
= 40 ms-1
time taken by the disturbance to reach other end,
t = l/v = 20/40 = 0.5 s.