JEE Previous Year Question

The length of a light string is 1.4 m when the tension on it is 5 N. If the tension increases to 7 N, the length of the string is 1.56 m. The original length of the string is m.

Topic: JEE PYQ

Answer: 1. Full step-by-step solution below.

Correct answer: 1

Solution

(1)
To find the original length of the string, we use the relationship between tension, elasticity constant , and the change in length of the string.
Given the equation for tension:

where is the length of the string under tension and is the original length.
When the tension is 5 N, the equation becomes:

When the tension increases to 7 N, the equation is:

By setting up a ratio from the two equations, we have:

Solving this proportion gives us the original
length :

Thus, the original length of the string is 1 meter.

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