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emoseman
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Homework Statement
A dirigible is moored to two wires. The hydrogen capacity of the craft was 200,000 m3, and together with its cabin, access spaces, and navigation surfaces it displaced 205,000 m3 of air. Its fully-loaded weight, including hydrogen gas, engines, diesel fuel, crew, 72 passengers, and 76 kg of luxury items such as caviar, was 1.95×105 kg. When the ship was safely docked, it was held down by two angled lines, each 20.6 meters long, at a height of 14.2 m above their attachment points on two mooring towers. What was the tension on each mooring line? Assume that the density of air is 1.23 kg/m3
Homework Equations
q=m/V
F=qVg
The Attempt at a Solution
Density of airship:
q = m/V = 9.5122e-1kg/m3
Force of air displaced:
qVg = 1.23 * 205000 * 9.8 = 2,471,070N
Weight of ship:
mg = 1.95e5 * 9.8 = 1,911,000N
Upward force due to bouyancy:
2,471,070N - 1,911,000N = 2,279,970N
I'm pretty confident in that so far, the next part, which is what I have a mental block all semester. I have already posted a question on the topic of force body diagrams and have had a great response, but it still isn't making sense.
This is the diagram that I've come up with for this problem:
http://img235.imageshack.us/img235/4369/fbd14122wu4.th.jpg http://g.imageshack.us/thpix.php
I have found the angle at which the two lines to be 46.4237degrees by way of cos-1(14.2/20.6).
The next part is what I'm not getting, still... The force being exerted on the wire is vertical, so am I finding the force of tension on the wire that is now the resultant ratio of the hypotenuse to the adjacent line?
Assuming that my earlier calculation for bouyant force is correct, the force I came up with is 785,824.902N. Which is wrong.
The equation I used is F = (F cos 46.4327) / 2
So, did I setup the FBD correctly?
Am I correct in that the tension of the wire is a fraction of the force because it is longer than the actual vertical force? The force is being exerted over a longer distance, therefore it is less? And the length is represented by the ratio of adjacent / hypotenuse?
Am I correct in using cosine because of the information I have available, which is what I perceive to be the adjacent side and the hypotenuse side?
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Evan
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