# A Ballet Dancer Spins About a Vertical Axis at 2.5\u0001 Rad/S with His Both Arms Outstretched. with the Arms Folded, the Moment of Inertia About the Same Axis of Rotation Changes by 25%. Calculate the New Speed of Rotation in R.P.M - Physics

A ballet dancer spins about a vertical axis at 2.5Π rad/s with his both arms outstretched. With the arms folded, the moment of inertia about the same axis of rotation changes by 25%. Calculate the new speed of rotation in r.p.m.

#### Solution

ω1 = 2.5 π rad/s = 2πn1

∴ I_2 = 3/4 I_1,n_2 (r.p.m) = ?

By conservation of angular momentum,

I2ω2 = I1ω1 or I2 (2πn2) = I1 (2πn1)

The new speed of rotation in r.p.m is 100 r.p.m

Concept: Physical Significance of M.I (Moment of Inertia)
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