In a small metal mine a battery powered locomotive hauls a train of mine tubs such that:

The weight of the train of mine tubs, tonne : 3.0

The coefficient of friction between the wheels and the rails : 0.06

The coefficient of adhesion between the loco wheels and the rails : 0.2

Time required from the start to reach a speed of 1.8 m/s through constant acceleration, min : 3.0

Upward gradient to be negotiated : 1 in 20

The minimum weight of the locomotive in tonnes to meet these design requirements, is______. (round off to one decimal place)