mechanical_ph

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1. lb force?

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

Yes
3. pressure=densityxgravityxheight

Goodmorning/Goodevening everyone I have this assignment: A weatherman carried an aneroid barometer from the ground floor to his office atop of sears tower in Chicago. On the ground level, the barometer read 30.15in Hg absolute; on top it reads 28.607in Hg absolute. Assume that the average atmospheric air density was 0.075lb/ft^3, estimate the height of the building. First I solve for the change in pressure 30.15-28.607 = 1.543inHg Then converted it to lb/ft^2 =109.165 Pressure= density x gravity x height 109.165lb/ft^2 = 0.075h 109.165/0.075 =h H= 1455ft Why is that I need to neglect or disregard gravity in this problem?

anyone?
5. Thermodynamics (enthalpy) need help

i still didnt get the part which 778 appear i know that ft-lb/BTU must appear in this conversion coz it is in imperial units but why 778? can anyone answer me briefly thx in advance
6. Thermodynamics (enthalpy) need help

you can go to this pic(link): http://imageshack.us/photo/my-images/854/scan0002fh.jpg/ In Green Circle: why is K = V^2/2k? and what is the small k? is it kinetic energy? In Red Circle: what is 778? how 778 appear in this problem? in Black circle: why is Work=pv? thx in advanced just explain even if it just one question you can answer Godbless
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