A Mass Is Lying on a Flat Surface Where the Coefficient

Multiple Choice

A mass is lying on a flat surface where the coefficient of friction between the surface and the mass is $\mu$ . The mass is connected to a spring that produces a force equal to -kx, where k is the spring constant and x is the displacement from the equilibrium position. The equation of motion of the mass when it is displaced a distance x₀ is:

A) $m \ddot { x } = - k x - \mu m g$
B) $m \ddot { x } = + k x + \mu m g$
C) $m \ddot { x } = k x - \mu m g$
D) $m \ddot { x } = - k x + \mu m g$