Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

I’m writing up a worksheet for my AP Physics class to use the phet web simulation for springs.  I want them to put a weight on a spring, calculate k for the spring, stretch the spring, and calculate the energy in the spring using PE = ½ kA^2.  I was then going to have them use the stopwatch and ruler on the site to calculate the velocity at equilibrium.  With this they can use KE = ½ mv^2 to show that PE(max) = KE(max).  I thought that getting the average speed and doubling it would give the max speed but it doesn’t work.  I keep getting a speed that is 25% too large, so the KE is 33% too large.  Obviously I’m doing something wrong.  Is there some easy way to get v(max) other than to give them another formula from the book that involves k.  I want something where they can measure v on the simulation.  Any ideas?  Thx