Determine the equation of motion if the spring constant is 8 lb/ft and if the weight is released 15 inches above the equilibrium with a downward velocity of 18 inches/s. (a) (t)= preview (b) find the amplitude: preview (c) find the first time that the mass attains its extreme displacement: preview seconds (d) find the first time that the object is at its equilibrium position: seconds preview ft (d) find the velocity of the object when it's its equilibrium for the first time