A spring of negligible mass and length l₀ hangs from a fixed point. When a mass m is attached to the free end of the spring, the length of the spring increases to l. The tension in the spring is equal to k∆x, where k is a constant and ∆x is the extension of the spring. What is k?

 

A. \(\frac{{mg}}{{{l_0}}}\)

 

B. \(\frac{{mg}}{l}\)

 

C. \(\frac{{mg}}{{l - {l_0}}}\)

 

D. \(\frac{{mg}}{{{l_0} - l}}\)