I'm have trouble trying to figure out what I'm doing wrong here: The question states: A 2 kg ball is thrown upwards with a speed of 40 m/s. At what height will the ball be, when its kinetic energy is equal to its potential energy? I know that during half the trip (half the height), Potential Energy = Kinetic Energy. In order to solve for height, I use one of the kinematic equations. But here's where the problem lies, I get two different answers using different equations but can't seem to understand why. They should be equal regardless. h = hi + vit + .5at^2 h = 0m + (40m/s)(4s) + (5 m/s)(4^2) h = 240 meters or using this equation: vf^2 = vi^2 + 2ah and solving for 2 2gh = vi^2 2(10m/s)h =1600 (m/s)^2 h = 1600 (m/s)^2 / 20 h =80 meters Any idea what I'm doing wrong to get different answers?