A mass of 8 kg stretches a spring 14 cm. The mass is acted on by an external force of 3sin(t/3) N (newtons) and moves in a medium that imparts a viscous force of 4 N when the speed of the mass is 8 cm/sec. If the mass is set in motion from its equilibrium position with an internal velocity of 4 cm/s, determine the position u of the mass at any time t. Use 9.8 m/s^2 as the acceleration due to gravity.

A mass of 8 kg stretches a spring 14 cm. The mass is acted on by an external force of 3sin(t/3) N (newtons) and moves in a medium that imparts a viscous force of 4 N when the speed of the mass is 8 cm/sec. If the mass is set in motion from its equilibrium position with an internal velocity of 4 cm/s, determine the position u of the mass at any time t. Use 9.8 m/s^2 as the acceleration due to gravity.