Will it be going uphill or downhill?
Really, all seriousness aside, it depends on the total weight (not just the payload weight), the motion profile (how much accelerating/decelerating), the drivetrain friction (chains, belts, gearing, bearings), the rolling friction (what type of tires and what type of surface you are driving on), the efficiency of the power electronics, the wire gauges and lengths...
And what's up with the 2 wheels? Is this a Segway?