100 lb wind force at tip of a 300 ft windmill blade with a 500 rpm motor .how many HP?

You've asked the same question 3 times now. I suggest you repond to one of the two previous posts - if the info we gave before isn't helping you sufficiently, at least tell us where you're having difficulty getting the answer.

What's the blade pitch? What's the weight of the motor armature? How much load is on the generator? "Force" =100lb. How many MPH? Humidity, barometric pressure, and air density?