
$=2\,k$
$=2 \times 2=4\,N / m \quad m =490\,gm$
$=0.49\,kg$
$T =2 \pi \sqrt{\frac{ m }{ Keff }}=2 \pi \sqrt{\frac{0.49\,kg }{4}}$
$=2 \pi \sqrt{\frac{49}{400}}=2 \pi \frac{7}{20}=\frac{7 \pi}{10}$
No. of oscillation in the $14 \pi$ is
$N =\frac{\text { time }}{ T }=\frac{14 \pi}{7 \pi / 10}=20$

