Ok Part E, ok, when P hits the ground, Q is still moving upward. The problem then becomes like throwing a ball up in the air - the ball goes up, and then must come back to where it started. The left mass hit the ground at 1.5 seconds, so the right mass becomes a ball thrown up in the air at 1.5 seconds. It had been accelerated at a rate of 2.8 m/s^2 for 1.5 seconds, so we need to calculate its velocity. Once we know its velocity, it simply becomes a problem of determining how long the ball is in the air. (What I had before about determining velocity I believe is wrong, I don't remember the equation off the top of my head and don't want to confuse you with calculus, look the formula up yourself).