1. Two train carriages, each with a mass of 3000 kg, are at rest on a section of horizontal track. 

The connection between the carriages may be modelled as a light rod, parallel to their direction of motion along the track. 

The resistance to motion is modelled as constant force of $5800N$ for each carriage.

In order to push the carriages forward along the track, a constant force of $12500N$ in the forward direction is applied to the rearmost carriage.

Find the magnitude of their acceleration.