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mybrohshi5
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Homework Statement
A young physics student is standing on an initially motionless turntable with rotational inertia 0.330 kg m^2; the turntable is free to turn about a frictionless axle. He is holding a wheel of rotational inertia 0.210 kg m^2 which is spinning at 135.0 rpm about a vertical axis. When he turns the wheel upside down, student and turntable begin rotating at 65.0 rpm. Neglect the distance between the axes of the turntable and the wheel.
What is the mass of the student? Approximate the student as a cylinder of radius 0.14 m
Homework Equations
Li=Lf
Lw = angular momentum of the wheel
Lpt = angular momentum of the person and turntable
The Attempt at a Solution
Ok so the answer is 55.3 kg and i know how to get the answer but i am a little confused about one part (the part below in bold)
Li = Lw
Lf = Lpt + Lw
Li=Lf
so...
Lw = Lpt - Lw
- why is it Lpt MINUS Lw
2Lw = Lpt
2(.210)(135rev/min) = (.33 + 1/2m(.142)) * 65 rev/min
m = 55.3 kg
Thanks for any help on explaining the part i am confused about :)