Physics: flywheel problem?
3. A 1.0-m radius flywheel is to be made from steel in the form of a solid disc. If the flywheel when turning at 60 rpm store as much energy as a 100-W lamp uses in one minute, how thick must the flywheel be if the density of steel is 7880 kg.m-3.
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Answers & Comments
Verified answer
Take a look at the Wiki link below. The flywheel is a cylinder, so the energy stored in it is:
1. E = m*r^2*ω^2/4
Since you know E, r, and ω, solve that one for m:
2. m = 4*E / [r^2*ω^2] = 4*100 watts*1 minute / [ (1 m)^2 * (60*2*pi/1 minute)^2 ]
Or 607.93 kg. You know the density of the material and the area; the thickness is the volume divided by the area and the volume is the mass divided by the density, so:
3. t = [ 607.93 kg / 7880 kg/m^3 ] / [ PI*(1 m)^2 ] = 2.458 centimeters
So very close to, but not quite, 1 inch thick.