(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.