A mass of 100 g stretches a spring 5 cm. If the mass is set in motion from its equilibrium position with a downward velocity of 60 cm/s, and if there is no damping, determine the position u of the mass at any time t. (Use g = 9.8 m/s2 for the acceleration due to gravity. Let u(t), measured positive downward, denote the displacement in meters of the mass from its equilibrium position at time t seconds.) u(t) = When does the mass first return to its equilibrium position? t= S