# Calculating final rotational speed from angular velocity

• Anmol Dubey

#### Anmol Dubey

Homework Statement
An ice skater is spinning with a rotational speed of 1.5 rev/s. When he extends his arms and one leg, his rotational inertia increases by a factor of three. What is his final rotational speed?
Relevant Equations
Angular momentum is conserved
L = Iw
L (final) = L (initial)
I(initial)*w(initial) = I(final)*w(final)

Last edited:
What do you know about the quantities in your last relevant equation?

• Anmol Dubey
What do you know about the quantities in your last relevant equation?
Like I = mr2?
w = Δθ/Δt
I didn't get what you mean by quantities

Like I = mr2?
w = Δθ/Δt
I didn't get what you mean by quantities
No, what does the problem formulation tell you about these quantities:
I(final)
I(initial)
w(final)
w(initial)

• Anmol Dubey
No, what does the problem formulation tell you about these quantities:
I(final)
I(initial)
w(final)
w(initial)
Since L is conserved
If I(final) is increased by a factor of 3, the w(final) is decreased by a factor of 3 so that L(final) = L(initial)
I(initial)*w(initial) = I(final)*w(final)
x*9.4 rad/s = 3x * w
so w(final) = 9.4 rad/s / 3
• Thank you for helping 