The only given parameters are:

-Able to achieve 20mph on flat

-Can neglect wind resistance and friction.

-Person weighting 80kg.

The task is to select appropriate motor to be able to achieve that speed and the calculations must be provided.

Many assumptions can be made .

Lets assume that i want to accelerate to 20ms in 5 seconds. Newtons law:

F=m*a= 80kg *(20/5) . Thats the force i will need to accelerate to 20 mph.

Now i can calculate the torque that i need to generate using torque and force equation below:

T=F*r

T-torque

F-force

r-tire radius

Okay assuming i have calculated that torque. That will be the torque needed to achieve 20mph, but how do i know if the torque to remain constant speed at 20mph will remain the same?

What would be the other step to calculate the motor power rating