At the same speed because it will slow down as it approaches the peak then speed up as it goes down again
it will be going 15m/s when it gets to the same height if we neglect air resistance and the object doesn't hit something
C, planets orbit around the sun because of gravity
A solid, liquid, or gas or plasma. Which I think it is. Check though.
Forces that are equal in size but opposite in direction and do not cause a change in an object's movement are called balanced forces.
forces that aren't equal in size and do cause a change in movement (what it seems like you're asking for) are called UNBALANCED FORCES
so answer (in case that wasn't clear, as I'm tired) : unbalanced forces
