1. Chapter 5.2 Notes
Potential Energy

2. Potential Energy = PE PE = mgh
Energy that is dependent upon height is called potential energy.
Potential energy equation 1 = mass x gravity x height
Potential Energy = PE
PE = mgh

3. Potential energy equation 2 = weight x height
PE = wh

4. A ball is thrown up. At the top of the path, how fast is the ball moving?
0 m/s – Not moving
How much kinetic energy does the ball have at the top of the path?
0 – since it is not moving

5. If the ball is thrown to a height of 5 meters and the ball has a mass of 10 grams, what is the PE?
Which equation? PE = mgh or PE = wh
PE = mgh
PE = 10 g x 10 m/s2 x 5 m/s
PE = 500 J

6. If gravity is the only force causing the potential energy, than the energy is called gravitational potential energy.
A system can also have potential energy due to a spring.

7. Potential energy that is stored in a spring is called elastic potential energy.
The equilibrium of the spring is its unstretched position – where the spring has no force.

8. Equation for elastic potential energy = ½ (spring constant) (spring displacement)2
The spring constant is represented by k
The spring displacement or distance the spring is stretched is represented by x
PEelastic = ½ kx2

9. Spring constant of 180,000 and the spring is compressed
Spring constant of 180,000 and the spring is compressed .15 m, what is the elastic potential energy?
PEelastic = ½ kx2
PEelastic = ½ 180,000 x .152
PEelastic = ½ 180,000 x .0225
PEelastic = 2025 J

10. As a mass accelerates on a spring, the spring’s stored PE is converted to kinetic energy.
When the mass reaches the equilibrium position where x = 0, the Potential energy = 0 and the kinetic energy is at the maximum.

11. The mass will continue to vibrate back and forth, changing potential energy to kinetic energy until the mass stops moving.
This process with the mass vibrating right to left and back again, changing kinetic to potential and potential to kinetic is called simple harmonic motion.

12. When potential energy is converted to kinetic energy, what forces take away some of the energy?
Friction, - Energy is transformed into heat
The law of conservation of energy states that in an isolated system, energy is conserved – it cannot be created or destroyed.

13. Total energy 1 = PE + KE
Total energy 2 = mgh + ½ mv2

14. What is the total energy of a ball that has KE of 10 and PE of 10?
Which Equation; TE = KE + PE or TE = ½ mv2 +mgh?
TE = KE + PE
TE =
TE = 20

15. What is the total energy of a ball that has a mass of 250 and a height of 25 with a velocity of 40?
Which Equation; TE = KE + PE or TE = 1/2mv2 +mgh?
TE = ½mv2 +mgh
TE = ½ 250(40) (10)25
TE = ½ 250 (1600) + 250(10)25
TE=200,000+62,500 =262,500 J