Question

A circular disc is rotating about its natural axis
with angular velocity of 10 rads-1 A second
disc of same mass is joined to it coaxially. If
the radius of disc is half of the radius of the
first, then they together rotate with an angular
velocity of

1) 2.5 rads-1
2) 5 rads-1
3) 8 rads-1
4) 6 rads-1​

Answer 1

Explanation:

law of conservation of angular momentum

Answer 2

Answer:

3) 8 rad/sec

Explanation:

In this case angular momentum will be conserved.

Finally both the discs will rotate with same angular speed.

Linitial = Lfinal

L=Iw

(MR^2)10/2 = (MR^2)w/2 + (MR^2)w/8

w=8 rad/sec