Physics problem?

The figure below shows a 3.2 kg mass riding on top of a 3.6 kg mass as it oscillates on a frictionless surface. The spring constant is 56 N/m and the coefficient of static friction between the two blocks is 0.56. What is the maximum oscillation amplitude for which the upper block does not slip?

Andrew Smith2017-03-18T03:59:31Z

If the acceleration exceeds g * 0.56 then the block must slip.

The total mass is 6.8 kg
kx = F = ma
-> x = ma/k
= 6.8 * 0.56g /56 m