A massless rod of length $l$ is pivoted at the upper end and two equal point masses of mass $m$ are attached to it, one at the centre of rod and one at its lower end. Then how much horizontal velocity must be provided to the lower end so that the rod just becomes horizontal?(consider only gravitational force is acting).
My question is - How to solve above question by applying mechanical energy conservation law on Centre of mass of these 2 masses rather than applying it for individual masses and equating. If we can't do it by centre of mass approach, then why so?
I asked my teacher about it and he said that you can't find out velocity for COM just like that because it's performing rotational motion.
Why is it so? What's the reason behind it?
I have taken the reference plane which passes through pivoted end.