Vector Problem: Solving Displacement & Speed of Contact

[dreamer_asot]

Hello, my problem is attached as a picture. Could you give me some guidelines on how to approach the problem? (i know the given formulas are derived using QM (probably), and I'm not "scared" from them, i just need to know where to do a cross or a dot product, and maybe how to approach the last part of the problem - the speed of contact with the ground. This would probably mean that the vector displacement finish point will be at (a, b, 0).)

 

[Simon Bridge]

I don't see any QM in there.
You have the equation of motion along with clues to $\vec{V}$ and $\vec{A}$ - why not use this?

It may help if you pick a direction for U - if it has to be general, then $\vec{V}=U\hat{V}$ which will have zero y component (because it is "horizontal").

Notice the the y-axis is "up".