A mass on a spring vibrates horizontally on a smooth level surface (see the figure). Its equation of motion is x(t) = 3sin t, where t is in seconds and x in centimeters. Find the velocity at time t. equilibrium position O v(t) = 3cost O v(t) = 2cos 3t O v(t) = sin 3t O v(t) = cos 3t v(t) = 3sin 3t