A figure skater can be approximated by a uniform cylinder. If a skater has a hei

Question

A figure skater can be approximated by a uniform cylinder. If a skater has a height of 1.5 m, a radius of 15 cm, and a mass of 55 kg: What is the angular momentum of a skater rotating at 3.5 rev/see? If the skater comes to a complete stop in 5 sec, what was the torque required? Where does this torque come from? A figure skater can increase her spin rotation rate from 0.5 rev/see to 3.75 rev/sec. If her initial moment of inertia was 3.9kgm^2, what will her final moment of inertia be? How can she do this?

Explanation / Answer

given

h = 1.5 m

r = 15 cm = 0.15 m

m = 55 kg

w = 3.5 rev/s = 3.5*2*pi rad/s = 22 rad/s

a) ANgular momentum, L = I*w

= 0.5*m*r^2*w

= 0.5*55*0.15^2*22

= 13.61 kg.m^2/s

b) we know, Torque = dL/dt

= 13.61/5

= 2.72 N.m

c) The torque would come from air resistance and friction between wheels and floor.

8) Apply conservation of angular momentum

If*wf = Ii*wi

If = Ii*wi/wf

= 3.9*0.5/3.9

= 0.5 kg.m^2

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