For our physics class we have to make a tennis ball launcher and we are also responsible for doing calculations to predict the distance our launcher will be able to launch the tennis ball. I have done the calculations here and can be seen in this PDF file: http://imusion.net/backup/yahoo.pdf The diagram of our launcher can be seen in here: http://imusion.net/backup/yahoo.jpg... I have looked through it but I know it is wrong. For u = 0.5kx^2 which is the first equation, x is the distance we can stretch the bungee cord which is supposed to be 1.2m and not 1.2-0.955(0.955 being the "slack " length of the cord). The problem is if I use 1.2m for x and follow through with everything else I get a ridiculous number like 500m. Which I know is not right. Just a short explanation of what else I did for the calcs. After I found the PE of our bungee cord I plugged it into E=0.5mv^2 to figure out the velocity of the ball. With E being the potential energy present in the bungee cord. After I found the velocity I used projectile motion equations to solve for time. Because of the polynomial I had to use the quadratic equation to find out the time the ball is in the air. Then afterwards I plugged it into the horizontal distance. If anyone can look through what I did and see if you can find what I did wrong I would appreciate that. I have looked through it numerous times already but I still dont' know what I'm doing wrong.