Two fly wheels $\mathrm{A}$ and $\mathrm{B}$ are mounted side by side with frictionless bearings on a common shaft. Their moments of inertia about the shaft are $5.0 \mathrm{kg} {\mathrm{m}}^2$ and $20.0 \mathrm{kg} {\mathrm{m}}^2$ respectively. Wheel $\mathrm{A}$ is made to rotate at $10$ revolution per second. Wheel B, initially stationary, is now coupled to $\mathrm{A}$ with the help of a clutch. The rotation speed of the wheels will become