Answer:
The velocity waves before rain is 10 m/s
The velocity of wave after the rope soaked up 5 kg more is 8.944 m/s
Solution:
As per the question:
Length of the rope, l = 100 m
Mass of the rope, m = 20 kg
Force due to tension in the rope, 
Frequency of vibration in the rope, f = 10 Hz
Extra mass of the rope after being soaked in rain water, m' = 5 kg
Now,
In a rope, the wave velocity is given by:
(1)
where
= mass density
Mass density before soaking, 
Mass density after being soaked, 
Initially, the velocity is given by using eqn (1):

The velocity after being soaked in rain:
