
$F =-\left( k _1 x+ k _2 x \right)=-\left( k _1+ k _2\right) x$
$a =\frac{ F }{ m }=-\left(\frac{ k _1+ k _2}{ m }\right) x =-\omega^2 x$
$\therefore \omega=\sqrt{\frac{ k _1+ k _2}{ m }} \Rightarrow T=\frac{2 \pi}{\omega}=2 \pi \sqrt{\frac{ m }{ k _1+ k _2}}$


where $x=$ displacement at time $t$
$\omega =$ frequency of oscillation
Which one of the following graphs shows correctly the variation $a$ with $t$ ?
Here $a=$ acceleration at time $t$
$T=$ time period