1. The problem statement, all variables and given/known data A 4.0X104 (or 40,000) Kg roller coaster starts from rest at point A. Neglecting friction, calculate its potential energy relative to the ground, its kinetic energy and speed at points B, C, and D. http://img189.imageshack.us/img189/6162/1234q.png [Broken] (scanned Image, if you can't see the first number its 54 m) The answers are given = Point B: Ek = 1.5x107 J Eg = 5.9x106 J V = 28 m/s Point C: Ek = 2.4x106 J Eg = 1.8x107 J V = 11 m/s Point D: Ek = 7.2x106 J Eg = 1.4x107 J V = 19 m/s 2. Relevant equations Gravitational Potential Energy = Mass X Gravity X Hight or Eg= M X g X h Kinetic Energy = 1/2 MV2 or Ek= 0.5 X M X V2 Total Energy = Gravitational Potential Energy + Kinetic Energy Or ET= Eg + Ek 3. The attempt at a solution OK so i got Point B right But the problem is point C Point A: is the Total energy so to get it Eg= 40,000 X 9.81 X 54 Ek = 0 Because its at rest Et= Eg + Ek Et = 21189600 Point B: Eg= 40,000 X 9.81 X 15 Eg= 5886000 Or 5.9x106 Which is the answer they gave us Ek= 21189600 - 5886000 Ek= 15303600 or 1.5x107 Which is also the right answer Ek= 1/2 MV2 15303600=(0.50)(40,000) V2 765.18 = V2 27.6 = V or 28 Which is the right answer Point C: Eg= 40,000 X 9.81 X 47 Eg= 18442800 or 1.8x106 Which is the right answer Ek= ET - Eg Ek= 21189600 - 18442800 Ek= 2746800 or 2.7x106 Which is WRONG because the answer is 2.4x106 What do you think???