Thermal energy transformation is taking place.
        
             
        
        
        
We can answer the problem by Snell's Law:
Snell's law<span> (also known as </span>Snell<span>–Descartes </span>law<span> and the </span>law<span> of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.</span>
        
             
        
        
        
Explanation:
Given the conditions A,B and C when the pendulum is released, at point A the initial velocity of the pendulum is zero(0), the potential energy stored is maximum(P.E= max),
the conditions can be summarized bellow
point A
initial velocity= 0
final velocity=0
P.E= Max
K.E= 0
point B
initial velocity= maximum
final velocity=maximum
P.E=K.E
point C
initial velocity= min
final velocity=min
P.E= 0
K.E= max
 
        
             
        
        
        
Answer:
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