1. The problem statement, all variables and given/known data A diver springs upward from a board that is 3m above the water. At the instant she contacts the water her speed is 8.90 m/s and her body makes an angle of 75 degrees with respect to the horizontal surface of the water. Determine her initial velocity, both magnitude and direction. Initial velocity = V1 , Final Velocity = V2 Assuming Down as positive and up as negative Y direction X direction Dy = 3m. Dx = Unknown. Ay = 9.8 Ax = 0 v2y = Sin 75 8.90 v2x = Cos 75 8.90 v1 = unknown v1x = v2x ( since there is no accelaration ! ) 2. Relevant equations V2^2=V1^2 + 2ad 3. The attempt at a solution Since V1x = v2x , We do not need to calculate V1x since its already 2.3 ( cos 75 8.90 ) V2Y = ( Sin 75 8.90 ) = 8.60 V2y^2= V1y^2 + 2ad (8.60) = V1Y^2 + (2x9.8x3) (8.60)^2-(2x9.8x3) = V1y^2 3.89 = V1y^2 Since 3.89 is positive, it should be pointing down. But when i make a vector with y point down and x pointing to the right, after using pythagoras theorem and tan , i get the wrong degree. However, if i assume down to be as negative and up to be as positive, then my direction is correct. I have always been told by my teachers that its upto me what i take as negative and positive. I want to know why im not being able to get the answer when i take down as positive and up as negative. either way i get my Y value as positive whether i take positive down or up , so how do i know which one is right. Help will really be appreciated. Thanks.