Q 11-13-022NEETJEE MainMedium
A $1$ kg block on a spring of force constant $100$ N/m oscillates with frequency $f$. What mass must be added so that the frequency becomes $\dfrac{f}{2}$?
Answer: (D) $3$ kg
Concept. $f \propto \dfrac{1}{\sqrt m}$.
Step 1. Halve $f$. Needs $4$ times the mass: $4$ kg in total.
Step 2. Added mass. $4 - 1 = 3$ kg.
Answer. $3$ kg (Option D).
Solution by Sreeraj P, M.Sc Physics