A object of mass $5.0\;g$ is projected into air using a rubber string of cross sectional area of $1;mm^2$. The length of the chord when it was unstretched is 10.0 cm. It is then stretched to 12 cm to project the object . The young's modulus of rubber is $5.0 \times 10^8 n/m^2$. The velocity of projectile is (assuming all the energy of string is transferred to projectile)

Question

$$\begin {array} {1 1} (a)\;10\;m/s \\ (b)\;20\;m/s \\ (c)\;30\;m/s \\ (d)\;40\;m/s \end {array}$$