Gravitation Question 223

Question: The length of an elastic string is [a] metre when the longitudinal tension is 4 N and [b] metre when the longitudinal tension is 5 N. The length of the string in metre when the longitudinal tension is 9 N is

Options:

A) [ab]

B) [5b4a]

C) [2a14a]

D) [4a3b]

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Answer:

Correct Answer: B

Solution:

  • Let L be the original length of the wire and K be the force constant of wire. Final length = initial length + Elongation [L=L+FK] For first condition [a=L+4K] (i) For second condition [b=L+5K] (ii) By solving equations (i) and (ii), we get [L=5a4b] and [K=1ba] Now when the longitudinal tension is 9 N, length of the string [=L+9K=5a4b+9(ba)5b4a.]


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