1. The problem statement, all variables and given/known data At the Earth's surface, a projectile is launched straight up at a speed of 9.6 km/s. To what height will it rise? Ignore air resistance and the rotation of the Earth. 2. Relevant equations Conservation of mechanical energy [itex]K_i + U_i = K_f + U_f[/itex] 3. The attempt at a solution I am quite confident that I chose the correct formula to solve this problem; however, I have a few questions regarding the formula itself. I know that [itex]K_i[/itex] and [itex]U_i[/itex] won't be zero, because the projectile has an initial velocity and it is above the surface of the earth. Would [itex]K_f[/itex] be zero, though; because we are considering the highest point the projectile will reach, and gravity will necessary reduce its speed to zero, corresponding to the highest point. Because [itex]K_f = 0[/itex], [itex]U_f[/itex] can't equal zero, right? What would the situation be like if it was negative, how about positive?