Your potential energy and mass don't tell what your weight is.
If I walk up from the first floor to the second floor, my weight hasn't
changed even though my potential energy has increased.
Newtons 3.law: Action = Reaction
If a body exerts a force on a rope of 400 N the rope exerts a force on the body of 400N also. So the tension in the rope is 400N. See pictures below.
In fresh water sound waves travel at 1497m/s at 25 degrees, I'll assume that's the characteristics of the water.
If it's 0.01s then you need to divide the speed by 100 to get the, 14.97, however it gets there and back in that time so you need to halve it.
<u>7.485m</u>