Figure below shows a liquid being pushed out of the tube by a piston having area of cross section $2.0 \mathrm {~cm} ^ { 2 }$. The area of cross section at the outlet is $10 \mathrm {~mm} ^ { 2 }$. If the piston is pushed at a speed of $4 \mathrm {~cm} \mathrm {~s} ^ { - 1 }$, the speed of outgoing fluid is $\_\_\_\_$ $\mathrm { cm } \mathrm {~s} ^ { - 1 }$