The answer is destructive interference.  You have this for both C and D.  I suspect one of C or D is supposed to be constructive interference...  But destructive interference is the answer
        
             
        
        
        
Answer:
Time period for Simple pendulum, 
Explanation:
The Simple Pendulum
Consider a small bob of mass  is tied to extensible string of length
 is tied to extensible string of length  that is fixed to rigid support. The bob is oscillating in the plane about verticle.
 that is fixed to rigid support. The bob is oscillating in the plane about verticle.
        Let  is the angle made by string with vertical  during oscillation.
 is the angle made by string with vertical  during oscillation. 
Vertical component of the force on bob,  
 
Negative sign shows that its opposing the motion of bob.
Taking  as very small angle then,
 as very small angle then, 
 
    
Let  is the displacement made by bob from its mean position ,
 is the displacement made by bob from its mean position ,
then, 
so,  ........(1)
                ........(1)
Since, pendulum is in hormonic motion,
as we know, 
where  is the constant and
 is the constant and 
 .........(2)
                   .........(2)
From equation (1) and (2)


Since, 


 
        
             
        
        
        
Answer:
b. 84 minutes
Explanation:
 = Centripetal acceleration = 9.81 m/s²
 = Centripetal acceleration = 9.81 m/s²
r = Radius of Earth = 6378.1 km
v = Velocity
Centripetal acceleration is given by

Time period is given by

The time period of Earth’s rotation would be 84.43835 minutes
 
        
             
        
        
        
Answer: C) N: Electrical energy and M: Kinetic energy
Explanation:
 
        
                    
             
        
        
        
I did it last year. I thinks its A