This is a small paragraph from my book.
The power required for the flight depends on the thrust required and flight velocity.By definition,the propulsive horsepower required is related to thrust required and flight velocity by the following equation
Pr= TrV/ 325 where
Pr is power required in hp,Tr is thrust required(total drag) in lbs and V is TAS in Knots
By inspection of this relationship,it is apparent that each pound of drag incurred at 325 knots requires one horsepower of propulsion power.
I am not able to make sense of the above statement.How would they have come to the magic figure of 325 in the denominator.Does it apply to all Jets in general.