1. Aim: How do we characterize potential energy?

2. Potential Energy
Potential energy- the energy associated with an object based on its position in a force field.

3. Gravitational Potential Energy
PE = mgh The gravitational potential energy of an object is equal to the product ot the mass, the acceleration due to gravity, and the distance from the reference level. PE = potential energy M = mass H= height relative to surface Let us derive this.

4. Gravitational Potential Energy Problems
Ex. How much potential energy does Kim Kardashian, with a mass of 60.0 kg, gain when she climbs a gymnasium rope of 3.5 m? PE=mgh=(60 kg)(9.8m/s2)(3.5m)=2058 J Ex 2. You lift a 2.2 kg book from a desk which is 0.80 m high to a bookshelf that is 2.10 m high. What is the change in potential energy? ΔPE=mgΔh ΔPE=2.2kg(9.8m/s2)(1.3m)=28 J

5. Work-Energy Theorem extended
When you do work on an object, you can give the object kinetic energy and you can also give the object potential energy

6. Problem 3
A 65 kg hiker starts at an elevation of 1500 m and climbs to the top of a 2600 m peak.
What is the hiker’s change in potential energy? ΔPE=mgΔh=65kg(9.8m/s2)(1100m)=700,700J
What is the minimum work required of the hiker?
700,700 J
c) Can the actual work required for the hiker be more than this? Explain.
Yes, additional work is needed to overcome friction.

7. Graphing Gravitational Potential Energy
Which graph shows the correct relationship between gravitational potential energy and height? Graph 1

8. Mechanical Energy
Mechanical Energy is the sum of the potential energy and the kinetic energy of an object.

9. Ex 1 KE to PE or PE to KE, explain
A ball falls from a height of 2 meters in the absence of air resistance.
The potential energy decreases as the kinetic energy increases, thus potential energy is turning into kinetic energy

10. Ex 2 KE to PE or PE to KE, explain
A skier glides from location A to location B across a friction free ice.
The potential decreases and kinetic energy increases as the skier goes from A to the ground. Then the potential energy increases and the kinetic energy decreases as the skier goes from the ground to B

11. Ex 3 KE to PE or PE to KE, explain
A baseball is traveling upward towards a man in the bleachers.
The kinetic energy decreases and the potential energy increases.
Thus, kinetic energy is turning into potential energy.

12. Ex 4 KE to PE or PE to KE, explain
A bungee cord begins to exert an upward force upon a falling bungee jumper.
The kinetic energy and gravitational potential energy both decrease. (