Explanation:
it cannot be solved. an important piece of information is missing : how far are the opposite ends of the tube apart ?
it can be 50 km, 3km, 100m or even 10m.
whatever.
the speed of the objects is only one part of the information necessary for this.
this is like asking 2 trains going from 2 train stations "against" each other. but is it Paris to Rome and from Rome to Paris, or is it Vienna Munich, or is it Bern and Basel ?
the same speed is possible in all the scenarios, just the distance, the travel times are different. they do not depend on the speed alone.
with the information here we can only calculate when the particles will come to a stop on their own ...