Find out the time both particles have the same speed?

[Fu-Kwun Hwang]

1. Click Play to view the simulation. The top one is moving with constant velocity. The lower one is de-accelerated!
2. Press initialize, then press play again after fter both particles stopped (when one of them reach one end.)

at t=4.8 second both particles have the same x coordinate again.
Question for you to think about?
 Both of them start at the same x coordinate with different initial velocity. Which one has larger initial speed? at what time both particles have the same speed?
 Can you find out the answer? How?