1. The problem statement, all variables and given/known data What % of PEg must be converted in KE in order to double the speed of a pendulum? So I have spent a couple of days trying to figure out this problem (it's a lab), and I can't seem to figure it out. I have asked my physics teacher about it, and he said the answer to the question is 25% of gravitational potential energy, which does not match my data. 2. Relevant equations Not sure if I need to use any equations here, but if so, PEg = KE (mgh = 1/2mv^2). 3. The attempt at a solution So the initial KE that I'm working with is 0.014 J, the PEg for that value is 2.836 J, and the velocity for that value is 0.236 m/s. If I double the velocity = 2*0.236 m/s = around 0.478 m/s (I'm using 0.478 m/s because it is the next value of my data, so it would be easier to use.) With this new velocity, the KE is 0.057 J. Therefore, I subtract 0.057 J - 0.014 J = 0.043 J. To find the percentage of 2.836 J, I divide 0.043 J/2.836 J = 0.015*100 = 1.5%, NOT 25%. 25% of 2.836 J is 0.709 J, which does not make sense with my data. I know for a fact that what I did was incorrect because if I try 1.5% with other values in my data, it does not get me to the correct values.