A particle is execution SHM in a straight line under the acceleration $kx$. If a periodic force of $ml$ cos $pt$ be introduced and time period of forced vibration increased to $1.5$ times then show that $$9p^2=4k$$
Here is a similar type of problem Simple Harmonic Motion under Periodic disturbing force .
But I do NOT understand how $T_2$ depends only on $p$. Thank you for your help.