WE cannot know the force ( torque) of the motor.
We can know the force at the rear wheel.
F = ma = mv/t
= 100 * 26.8 / 2.8 N
There is a problem with the second part. Constant power would require an infinite force at speed zero.
If you take constant Force then the power requirement increases with increasing speed.
Which one do you want?
Constant force means the MAXIMUM power is
F v = 100 * 26.8 / 2.8 * 26.8