A 2kg ball is attached to a ceiling by a 3 m string. The height of the room is 5.4 meters. Acceleration due to gravity is: 9.8m/s^2. What is the gravitational potential energy relative to a point at the same elevation as the ball? Answer in units of J. The way I set up the problem is: y=-(5.4-3)=-2.4 meters m=2kg g=9.8m/s^2 PE=mgy=(2)(9.8)(-2.4)=-47.04 J. however, i checked the answer in my book and it wasn't it. :( anyone can help show me what I did or/understood wrong?