6. A mass weighing 8 pounds is suspended from a spring. The mass stretches the spring feet. The entire system is immersed in a fluid offering a damping force numerically equal to 2 times the instantaneous velocity. Beginning at t = 0, an external force equal to f(t) = = 3t is impressed on the system. Find the equation of motion if the mass is initially released from rest at the equilibrium position.

6. A mass weighing 8 pounds is suspended from a spring. The mass stretches the spring feet. The entire system is immersed in a fluid offering a damping force numerically equal to 2 times the instantaneous velocity. Beginning at t = 0, an external force equal to f(t) = = 3t is impressed on the system. Find the equation of motion if the mass is initially released from rest at the equilibrium position.