The time period of free vibration of a mass hung from the end of a helical spring is 0.8 sec. When the mass is stationary, the upper end is made to move upwards with a displacement of y mm. Given that, y = 18 mm, calculate the maximum velocity of the mass.

A) 5.0 m/s
B) 7.5 m/s
C) 10.0 m/s
D) 12.5 m/s