1. The problem statement, all variables and given/known data "A ball thrown straight up with an initial speed of 30/m/s. (a) Show the time it takes to reach its trajectory will be 3m/s (b) Show that it will reach a height of 45m" 2. Relevant equations h=ut+1/2g^2 1/2gt^2 3. The attempt at a solution Part a of the question I am fine with. Its part (b) that seems to be what got me confused. I felt the need to use the equation "h=ut+1/2g^2" due to thinking that: u=30? Initial speed in this case is 30m/s. Why can't I use it in the equation? When and what type of questions would I use h=ut+1/2g^2?? I know that to work this question out, I will need to use "1/2gt^2" I just don't understand why initial speed (u) wont be 30m/s. Also questions related to physics. How do you know when to work out -in relation to velocity or acceleration? I know the difference between the two, yet seem to get confused in exams/tests between them both? Is there a trick into isolating the questions into what they are asking rather than me assuming what they are asking?