A stone tied to 180cm long string at its end is making 28...

Angular velocity, $\omega = \dfrac{28 \times 2\pi}{60}rad{s}^{- 1}$.

Required centripetal acceleration is given by,

$a = {\omega}^{2}R$

$= {\left(\dfrac{56}{60} \times \dfrac{22}{7}\right)}^{2} \times 1 . 8$

$= \dfrac{( 44{)}^{2}}{225} \times 1 . 8 = \dfrac{1936}{125}$

Hence, required $x = 125$.