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The length of an elastic string is a met...

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

A

`a- b`

B

`5b- 4a`

C

`2b- (1)/(4) a`

D

`4a- 3b`

Text Solution

Verified by Experts

The correct Answer is:
B
Since, `Delta l= (F)/(K) therefore a = L + (4)/(K), b= L + (5)/(K)`
`(1)/(K) (4-5) =a -b 1= (b-a)K`
or `K= (1)/(b-a)`
Put K in `a= L + (4)/(K)`
`L= 5a- 4b`
`c= L + (9)/(K) = 5a- 4b + 9(b-a) = 5b- 4a`
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