given: Height = 2.5 feet OD = 2.5 feet ID/OD = .75 Specific Gravity = 1.1 will s
ID: 2021978 • Letter: G
Question
given: Height = 2.5 feetOD = 2.5 feet
ID/OD = .75
Specific Gravity = 1.1
will store 50-kwh, weigh 370 pounds, spin up to 44,000 rpm, and incur precession torque from earth rotation of 4.75 foot-pound (causing a nominal 0.6 degree tilt)."Let's see if this checks out: Their flywheel design is a thick-walled cylinder made of a composite fiber material with specific gravity = 1.1 (i.e., it is 1.1 times as dense as water.)
question is
(1)Based on the given dimensions and density, what is the mass (in kg) of this flywheel? How does this compare to the claimed 370-lb weight?
Explanation / Answer
Volume of the flywheel is volume of a 2.5 foot high cylinder with 2.5 foot diamter = 12.272 cu ft minus the volume of a 2.5 foot high cylinder with 1.875 foot diameter = 6.903 cu ft
total volume = 5.369 cu ft = 0.152 m3
which, if it were water, would have a mass of 152 kg. Since the density of this flywheel is supposedly 1.1, it should have a mass of 167.2 kg.
1 kg = 2.204 lb so 167.2 kg = 368.5 lbs, consistent within rounding and significant figures to the claimed 370 lbs.
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