1. The problem statement, all variables and given/known data A 20.0 kg cannonball is fired from a cannon with a muzzle speed of 1000 m/s at an angle of 37.0° with the horizontal. A second ball is fired at an angle of 90.0°. (a) Use the isolated system model to find the maximum height reached by each ball. (b) What is the total mechanical energy of the ball-Earth system at the maximum height for each ball? Let y = 0 at the cannon. 2. Relevant equations 0=ΔKsys+ΔUsys Emech=Usys+Ksys 3. The attempt at a solution I understand how to do part a). The ball fired straight up has initial kinetic energy of (½)(20(1000^2)=(20)(9.8)h and h=51020m. Same idea for the second ball and h=18479m. I'm really confused about part b) though, apparently the total Mechanical energy for each ball is equal to the initial kinetic energy, which is (½)(20)(1000^2). But for the ball fired straight up I thought it would be Emech=-(½)(20)(1000^2)+(20)(9.8)(51020), which is wrong. I don't really understand how to find Emech.