Ah I now realize that my substition for t should have been 40/v0x since the required initial speed to hit the top of the cliff depends on both vertical and horizontal speed. I now got precisely 80 m/s. Thanks a lot, I feel a bit silly now.
I need a bit of help with this simple question, it's not difficult at all but I just can't see what I did wrong. I'm overlooking a crucial thing
A cannon is placed 40m away from a 37.5m high cliff.
The cannon fires a ball with an angle of 45 degrees to the horizontal.
The gravitational...