1. The problem statement, all variables and given/known data A Cannonball is shot upward from the ground into the air at t=0 sec. With initial velocity of 50m/s. Its height above the ground in metres is given by s(t)=50t-4.9t^2 . ----What is the velocity of the cannonball when it is 100m above the ground on the way up? "says the book" Hint: set s(t) = 100 2. Relevant equations initial velocity = 50 m/s 3. The attempt at a solution I don't want the answer, I just want to know how it is worked out, because I know how to do it by trial and error. If I set s(t)=100 like the book says, then 100=50t-4.9t^2 I can't solve this equation without knowing t, am I right? Anyhow, by trial and error, i figured out t=2.73, and I think velocity at 100m = 36.5m/s... But what is the proper way to do this without using trial and error like I did? ie. The question I should ask myself first is what? 1. What is t at 100m? 2. Velocity = ? at 100m?