 # mechanical_ph

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physics
1. 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
2. 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?
3. 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
4. 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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