Acceleration of a 5.0 kg cart pushed by a 20 N net force

Assumptions: 20 N is the net force after any opposing forces are accounted for.
Use F_net = ma, so a = F_net/m.
a = 20 N / 5.0 kg
a = 4.0 N/kg
Because 1 N/kg = 1 m/s^2, a = 4.0 m/s^2.