Answer:
Explanation:
Given
Lowest four resonance frequencies are given with magnitude
50,100,150 and 200 Hz
The frequency of vibrating string is given by

where n=1,2,3 or ...n
L=Length of string
T=Tension
Mass per unit length
When string is clamped at mid-point
Effecting length becomes 
Thus new Frequency becomes

i.e. New frequency is double of old
so new lowest four resonant frequencies are 100,200,300 and 400 Hz
Answer: 8400 J
Explanation:
The formula referenced in the question is:
Where:
is the thermal energy
is the mass of the water sample
is the specific heat capacity of water
is the variation in temperature
Solving:
This is the thermal energy released