Period of a simple pendulum with a magnet under it

[MatinSAR]

Homework Statement

The period of a simple pendulum with an iron ball is T. If we put a magnet under it, its period becomes T/2. What is F/mg equal to?(F is the force that is exerted by the magnet.)

Relevant Equations

T = 2π Square root of√L/g

Hi ...
I have answered this question and I think that F/mg equals 3.
But I've asked it from someone and he told me that F/mg is 4.
Can someone help me find out which one is correct ???

My answer :

 

[haruspex]

I'm with you.
My guess is the other solver forgot gravity still acts when the magnet is present.

 

[MatinSAR]

My guess is the other solver forgot gravity still acts when the magnet is present.

Yes he said he ignored gravity.
Thank you for your time.

 

[kuruman]

Just to be nit picking, there would be an additional force due to eddy currents induced in the iron ball as it swings past the magnet that will damp the motion.

 

[haruspex]

Just to be nit picking, there would be an additional force due to eddy currents induced in the iron ball as it swings past the magnet that will damp the motion.

Owing to a breakthrough in metallurgy, it is superconducting.

 

[MatinSAR]

Just to be nit picking, there would be an additional force due to eddy currents induced in the iron ball as it swings past the magnet that will damp the motion.

What if we ignore eddy currents ? Because if it is not omitted, the periodicity is not defined for movement.
Do you agree with F/mg=3 in this case ?

Owing to a breakthrough in metallurgy, it is superconducting.

I didn't understand ...
Can you please tell me if you disagree with my answer ...

 

[haruspex]

I didn't understand ...
Can you please tell me if you disagree with my answer ...

It was just an attempt at a humorous response to @kuruman's nitpick.
I agree with your answer.

 

[MatinSAR]

It was just an attempt at a humorous response to @kuruman's nitpick.
I agree with your answer.

I understand ...
Thanks again ...

 

[kuruman]

I too agree with your answer. I am sorry that my attempt at levity confused you.

 

[MatinSAR]

I too agree with your answer. I am sorry that my attempt at levity confused you.

I'm sorry I'm not a native speaker of English and this is why I didn't understand.
Thank you ...