Solve the all parts of following problem:
Problem: A cannon sits 20 m from the bottom of a cliff. it shoots a cannonball at a 60 degree angle. Two and a half seconds later, the cannonball lands on the edge of the cliff.
Part I: What was the cannonball initial speed?
Part II: What is the cannonball acceleration vector at the peak of its trajectory?
Part III: How tall is the cliff?
I need help to find the cannonball acceleration vector at the peak of its trajectory.