Question

A bug of mass 2.2 g is sitting at the edge of a cd of radius 3.0 cm. if the cd is spinning at 280 rpm, what is the angular momentum of the bug?

Answer 1

M = 2.2 g = 2.2 x 10⁻³ kg, the mass of the bug.
r = 3.0 cm = 0.03 m, the radial distance from the center.

The angular speed is
ω = 280 rpm
    = (280 rev/min)*(2π rad/rev)*(1/60 min/s)
    = 29.3215 rad/s

The moment of inertia of the bug is
I = mr²
  = (2.2 x 10⁻³ kg)*(0.03 m)²
  = 1.98 x 10⁻⁶ kg-m²

Calculate the angular momentum of the bug.
J = Iω
  = (1.98 x 10⁻⁶ kg-m²)*(29.3215 rad/s)
  = 5.806 x 10⁻⁵ (kg-m²)/s

Answer: 5.806 x 10⁻⁵ (kg-m²)/s