(b) : Moment of inertia of disc
D1 about an axis passing through its centre and normal to its plane is
I1===0.04kgm2 Initial angular velocity of
discD1,ω1=50 rad
s−1 Moment of inertia of disc
D2 about an axis passing through its centre and normal to its plane is
I2==0.02kgm2 Initial angular velocity of disc
D2,ω2=200rads−1 Total initial angular momentum of the two discs is
Li=I1ω1+I2ω2 When two discs are brought in contact face to face (one on the top of the other) and their axes of rotation coincide, the moment of inertia
I of the system is equal to the sum of their individual moment of inertia.
I=I1+I2 Let
ω be the final angular speed of the system. The final angular momentum of the system is
Lf=Iω=(I1+I2)ω According to law of conservation of angular momentum, we get
Li=Lf I1ω1+I2ω2=(I1+I2)ω ω=