Lab issue -- Please check my projectile launcher calculations I am making a lab for a class I teach and my results aren't working out and I need another pair of eyes to see if my method is wrong (I apologize if this should go in homework, but it isn't a homework question so I thought it should go here). I have a projectile launcher. I used a force probe to find it took 7.5 N to push the launcher plug 3.5 cm or 0.035 m which gives me a spring constant of k=7.5/0.035=214. Using W=1/2kx^2 I found the KE of the projectile leaving the launcher to be KE=W=1/2(214)(0.035)^2=0.131 j. Setting KE=U I found the maximum height from 0.131=mgh where the projectile is 17 g or 0.017 kg so h=0.131/((0.017)(9.8))=0.79. When I fired the projectile my height was off by almost a factor of 2 so I think I am missing a factor of 2 somewhere. Any help would be appreciated.