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# Answer to Question #118495 in Mechanics | Relativity for Wilcox Muchineripi

Question #118495
What is the angular momentum of a figure skater spinning at 3.0 rev/s with arms in close to her body,
assuming her to be a uniform cylinder with a height of 1.5 m, a radius of 15 cm, and a mass of 48 kg ?
How much torque is required to slow her to a stop in 4.0 s, assuming she does not move her arms?
1
2020-05-28T12:00:59-0400

L=I"\\omega=1\/2 MR"2"\\omega=1\/2(48 kg)(0.15m)"2 (3.0 rev/s) (2"\\pi rad \/ 1 rev)=10 kg m^2\/s".

So, angular momentum of a figure skater spinning at 3.0 rev/s with arms in close to her body,

assuming her to be a uniform cylinder with a height of 1.5 m, a radius of 15 cm, and a mass of 48 kg is 10 kg m2/s.

If the rotational inertia does not change, then the charge in angular momentum is due to change in angular velocity.

"\\tau=\\Delta L \/ \\Delta t"=0-10 / 4 = -1.2 Nm

Negative sign indicates that torque is in opposite direction of initial angular momentum.

Torque of -1.2 Newton meters is required to slow her to a stop in 4.0 seconds.

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