Consider the following diagram in which an inextensible string connects two blocks passing via ring. The first block moves with a velocity of $2 \mathrm{m} {\mathrm{s}}^{-1}$and the second one moves with a velocity of $v \mathrm{m} {\mathrm{s}}^{-1}$. If the ring slides on horizontal rod then the value of $v$ is (in $\mathrm{m} {\mathrm{s}}^{-1}$)