JEE Main20207 Jan 2020Evening ShiftPhysicsRotational MotionActual
Mass per unit area of a circular disc of radius a depends on the distance r from its centre as σ r = A + B r . The moment of inertia of the disc about the axis, perpendicular to the plane and passing through its centre is:
Options
- A2 π a 4 A 4 + a B 5
- B2 π a 4 a A 4 + B 5
- Cπ a 4 A 4 + a B 5
- D2 π a 4 A 4 + B 5
Correct answer
A. 2 π a 4 A 4 + a B 5
Step-by-step solution
σ = A + B r ∫ d m = ∫ A + B r 2 π r d r I = ∫ d m r 2 ∫ 0 a A + B r 2 π r 3 d r = 2 π A a 4 4 + B a 5 5 = 2 π a 4 A 4 + a B 5