A stone tied to the end of a string of 1 m long is whirled in a horizontal circle with a constant speed. If the stone makes 22 revolutions in 44 sec, what is the magnitude and direction of acceleration of the stone ?

• A

  ${\mathrm{π}}^2\left(\mathrm{m}/{\mathrm{s}}^2\right)$  and direction along the tangent to the circle

• B

  ${\mathrm{π}}^2(\mathrm{m}/\mathrm{s}{)}^2$ and direction along the radius towards the centre

• C

  ${\mathrm{π}}^2/4\left(\mathrm{m}/{\mathrm{s}}^2\right)$  and direction along the radius towards the centre

• D

  ${\mathrm{π}}^2\left(\mathrm{m}/{\mathrm{s}}^2\right)$ and direction along the radius away from the centre