A 27.9 kg block (m1) is on a horizontal surface, connected to a 5.3 kg block (m2) by a massless string. The pulley is massless and frictionless. A force of 239.3 N acts on m1 at an angle of 28.9°. The coefficient of kinetic friction between m1 and the surface is 0.181. Determine the upward acceleration of m2.