Q 11-13-047JEE MainJEE Main 2026 (24 Jan, Shift 1)Easy
A spring of force constant $15\ \text{N/m}$ is cut into two pieces. If the ratio of their length is $1 : 3$, then the force constant of smaller piece is ______ $\text{N/m}$.
Answer: (C) 60
For a spring, $k\propto\dfrac1{\text{length}}$. The smaller piece is $\dfrac14$ of the original length:
$$k_1 = 4\times15 = 60\ \text{N/m}$$
(The other piece, $\frac34$ of the length, has $k_2 = 20$ N/m.)
Solution by Sreeraj P, M.Sc Physics