Homework Help: Math IN URGENT NEED OF FEEDBACK

Posted by Anonymous on Wednesday, April 13, 2011 at 12:08pm.

If the temperature is constant, then the atmospheric pressure P (in pounds/square inch) varies with the altitude above sea level h in accordance with the law given below where p0 is the atmospheric pressure at sea level and k is a constant.
P = p0e-kh
If the atmospheric pressure is 14.9 lb/in2 at sea level and 12.6 lb/in2 at 4000 ft, find the atmospheric pressure at an altitude of 13,000 ft. (Round your answer to two decimal places.)

For this question I got 8.65 as my answer but for some reason I keep getting it wrong. Can someone please explain what I'm doing wrong.

Math IN URGENT NEED OF FEEDBACK - bobpursley, Wednesday, April 13, 2011 at 12:26pm
12.6=14.9-k4000

k=2.3/4000

p=14.9-(2.3/4000)*13000

p=7.43PSI recheck your calcs.
Math IN URGENT NEED OF FEEDBACK - Anonymous, Wednesday, April 13, 2011 at 1:20pm
You forgot e in the calculations. I put in your number, it's not right. I'm sorry to be such a pain but I can't figure this out.
Math IN URGENT NEED OF FEEDBACK - bobpursley, Wednesday, April 13, 2011 at 1:52pm
p=14.9* e^(-kh)
12.6=14.9 * e^(-k4000) take ln of each side

ln(12.6)= ln(14.9)-k4000
.168=k*4000

k=4.19E-5

p=14.9 e^(-4.19E-5*13000)=14.9 e^(-.5447)
p=8.65 PSI
Math IN URGENT NEED OF FEEDBACK - Anonymous, Wednesday, April 13, 2011 at 2:09pm
Yeah, that's what I got too, but I keep getting the problem wrong. Don't worry about it though, I'm going to contact my professor and ask her what's going on. Thanks

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