A mass m is hooked onto the free end of a suspended coil spring and allowed to come to rest after stretching the spring a distance x = 0.4 m. At this position the spring constant k times x is equal to mg, where the acceleration of gravity is g = 10 m/s2. The mass is then given a push and it starts moving up and down. What is the angular frequency of this oscillation in units of s-1?