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A simple pendulum, has a period of 5.77 seconds. When the...

A simple pendulum, has a period of 5.77 seconds. When the pendulum is shortened by 3 m, the period is 4.60 seconds. Calculate the new length of the pendulum

A.

5.23 m

B.

6.42 m

C.

4.87 m

D.

7.26 m

Correct answer is A

     Let the original length L=xm

      ;New length =( x -3 ) m

       T1 = 5.77s; T2 = 4.60s,  

       T2 α  L

       ⇒T2)=kLwhereKisconstantK=\(T21L1 = T22L2

      ⇒5.772x  = 4.602x3

      ⇒ 33.29x  = 4.602x3

      ⇒ 33.29(x-3)  = 21.16x
        
      ⇒ 33.29x - 99.87 =21.16x

      ⇒12.13x = 99.87
     
      ;x =99.8712.13  = 8.23m
    
      New length of the pendulum 
     
      =x-3 = 8.23-3
   
      =5.23m