A block of metal weighing 2 kg is resting on a frictionless plane (as shown in figure). It is struck by a jet releasing water at a rate of $1 \mathrm {~kg} \mathrm {~s} ^ { - 1 }$ and at a speed of $10 \mathrm {~m} \mathrm {~s} ^ { - 1 }$. Then, the initial acceleration of the block, in $\mathrm { m } \mathrm { s } ^ { - 2 }$, will be\\
(1) 3\\
(2) 6\\
(3) 5\\
(4) 4