Hello xwrathbringerxSorry to be slow in answering - I've only just seen your question.

The velocities of the particles are the derivatives of and ; i.e. and respectively.

If they are both moving towards the origin with positive velocity, then, for each particle:

- the velocity is positive;

- the displacement is negative (because they are moving towards O).

So, sketch on a single diagram the graphs of , and find an interval for which:

Can you do it now?

Grandad