HOw to find curve?

Question

https://i.stack.imgur.com/FA6xX.png

I don't understand how this is wrong. I tried AF and OC. Either of those should be right, since those depict 45 angles. What's the problem?

Answer 1

You are not asked the position, you are asked about the velocity in the vertical direction. The horizontal axis of the graph is time. Since only gravity is acting in the vertical direction $v_y(t)=v_y(0)-gt$. Therefore the graph is linear in time, with a negative slope. So the answer is AE

Answer 2

Assuming $v_y$ means the vertical velocity, then it starts off positive (the cannon is shooting upwards), and decreases with time. Assuming the acceleration is constant (given by gravity), the velocity is an affine function of time. The only option that fits these is $AE$.