What size motor would need to be used to move 200 lbs. with two wheels on a 1/2" dia. axle?

Not big,a vertical 3.5 hp would do it,as long as the cogs (sprockets) had the correct ratio to do it (amount of teeth) Its like this,for instance on a 10 speed,you don't have the power to peddle it in the wrong gear,down shift it,then you do it with ease,same as a car with a manual transmission (stick) my Corvette has a 427 Big block that has extreme power,it's a 4 speed and you can't start out in 4th,second you can,but 4th it'll stall.