1. The problem statement, all variables and given/known data A centripetal-acceleration addict rides in uniform circular motion with period T = 3.22 s and radius r = 3.00 m. At one instant his acceleration is a = (7.00 m/s2) i + (-9.00 m/s2) j. At that instant, what are the following values? (b) r X a 3. The attempt at a solution I'm really stumped on this one. I completely understand how to do cross products of a vector, but there is nothing in my text book about doing a cross product problem in uniform circular motion. I tried taking the magnitude of a and multiplying it to times r, but that wasn't right. If anyone can give me a hint as to how to start this, I would be very thankful.