Answer:
The time is 16 min.
Explanation:
Given that,
Time = 120 sec
We need to calculate the moment of inertia
Using formula of moment of inertia

If the disk had twice the radius and twice the mass
The new moment of inertia


We know,
The torque is

We need to calculate the initial rotation acceleration
Using formula of acceleration

Put the value in to the formula


We need to calculate the new rotation acceleration
Using formula of acceleration

Put the value in to the formula



Rotation speed is same.
We need to calculate the time
Using formula angular velocity


Put the value into the formula



Hence, The time is 16 min.