A metal coin of mass 5 g and radius 1 cm is fixed to a thin stick $AB$ of negligible mass as shown in the figure. The system is initially at rest. The constant torque, that will make the system rotate about AB at 25 rotations per second in 5 s , is close to:\\
(1) $1.6 \times 10 ^ { - 5 } \mathrm {~N} \mathrm {~m}$\\
(2) $2.0 \times 10 ^ { - 5 } \mathrm {~N} \mathrm {~m}$\\
(3) $7.9 \times 10 ^ { - 6 } \mathrm {~N} \mathrm {~m}$\\
(4) $4.0 \times 10 ^ { - 6 } \mathrm {~N} \mathrm {~m}$