According to HowStuffWorks.com, 1 pound of thrust equals 32 feet per second, which works out at 21 mph. I'm assuming this means that 2 pounds of thrust on a 1 pound object would mean it would be:

(

*2 pounds of thrust - 1 pound of the object ) = 1 pound of thrust * 21mph = 21 mph.*

If it was 3 pounds of thrust, it would be:

*(3*

*pounds of thrust*

*- 1*

*pound of the object*

*) = 2*

*pounds of thrust*

** 21 = 42 mph.*

This seemed to make sense as a general rule, so I tried applying it to an F-15 which apparently generates around between 25,000 and 29,000 pounds of thrust per engine and the plane itself weighs around 45,000 pounds. So I take around (55,000 - 45,000) = 10,000 pounds of thrust * 21mph =

**210000 mph!**

Since we know the plane travels at 600mph and we know the weight is 45,000 pounds, does it not make sense that at 45,001 pounds of thrust the plane is moving forwards at 21mph? The original formula seems to suggest so. Would it not only then need 45,028 pounds of thrust to move at 600mph?

Where has my logic broken down? Is the formula I'm using broken? If I know the weight and pounds of thrust, is it not as straight forward to convert it to mph as I think it is? Perhaps there is just something special about twin jet engines that makes it a bad example to use?

*disclaimer - I'm bad at maths and possibly as smart as a shoe*