15.1 A string of mass 2.50 kg is under a tension of 200 N. The length of the stretched string is 20.0 m. If the transverse jerk is struck at one end of the string, how long does the disturbance take to reach the other end?

It is given in the qustion that:
Mass of the string, M=2.50 kg 
Tension in the string, T=200 N 
Length of the string, l=20.0 m  
Mass per unit length,  μ=Ml=2.5020=0.125 kg m-1
The velocity v of the transverse wave in the string:
=2000.125=1600=40 m/s
 Time taken by the disturbance to reach the other end,
 t=lv=2040=0.50 s