Then max velocity achievable (without taking friction into consideration) will be between

*~0.27 m/s* to

*~0.53 m/s*. It's clear that 1" wheels don't really cut it, hence let's go with 2" wheels.

*Circumference = Diameter * pi**Velocity = Circumference * RPM*

To have acceleration of

*0.25 m/s*^{2} (to be able to reach

*0.5 m/s* velocity in

*2 seconds*) each motor has to be capable of at least

*63.5 mN*m* torque.

*Force = Mass * Acceleration**Torque = Radius * Force*

You probably don't want to run motors at 100% duty cycle all the time, so to be on a safe side lets say that You want to achieve aforementioned results while running motors at 75% duty cycle. So, max motor RPM has to be at least

*~252 RPM* and stall torque has to be at least

*~85 mN*m*.

For what You want, something like

300 RPM 12V 0.39 N*m motor would be more that enough. Of course if plan on using 12V. What voltage are You planning to use?