lb force?

[mechanical_ph]

Goodmorning everyone!

 

I have this problem:

The mass of a given airplane at sea level (g=32.10 fps2) is 10 tons. Find its mass in lbm, slugs, and kg and its (gravitational) weight in lbf when it is travelling at a 50,000-ft elevation. The acceleration of gravity g decreases by 3.33 x 10-6 fps2 for each foot of elevation.

 

I already know the lbm and slugs

 

But my concern is that I can't found the answer lbf which should be 19, 850lbf

 

My solution:

 

F =ma

= 20000lbm (32.0075ft/s^2)

=640150lbm-ft/s^2

 

 

640150lbm-ft/s^2 x (1lbf/32.174lbm-ft/s^2)

 

= 19896.5lbf

But my textbook answered 19850lbf can anyone show me how the book get 19850lbf

 

Oh I get it I use 32.174 instead of 32.1 damn