A mass weighing 16 pounds stretches a spring
feet. The mass is initially released from rest from a point 7feet below the equilibrium position, and the subsequent motiontakes place in a medium that offers a damping force that isnumerically equal to
the instantaneous velocity. Find the equation of motion
x(t)
if the mass is driven by an external force equal to
f(t) = 25cos(3t).
(Use
g = 32 ft/s2
for the acceleration due to gravity.)
