What is Potential Energy?

Potential energy is energy stored in an object. This energy has the potential to do work. Gravity gives potential energy to an object. This potential energy is a result of gravity pulling downwards. The gravitational constant, g, is the acceleration of an object due to gravity. This acceleration is about 9.8 meters per second on earth. The formula for potential energy due to gravity is PE = mgh. As the object gets closer to the ground, its potential energy decreases while its kinetic energy increases. The difference in potential energy is equal to the difference in kinetic energy. After one second, if the potential energy of an object fell ten units than its kinetic energy has risen ten units. Potential energy units are joules.

 

Formula:

W = Fd kg m/s2 meters Work equals force times distance,

F = ma kg m/s2 Force equals mass times acceleration,

a = g m/s2 Acceleration is g,

F = mg kg m/s2 So force equals mass times g,

W = mgd kg m/s2 meters Which means work equals mass times g times distance,

d = h meters Distance equals height,

W = mgh kg m/s2 meters Which makes work equal to mass times g times height,

W=PE Which means potential energy it the amount of work an object could do.

 

Example:

PE = mgh

PE = (20 kg)(9.8 m/s2)(10 m)

PE = (20 kg)(98 m2/s2)

PE = 1960 kg m2/s2 or 1960 joules

This block can perform 1960 joules of work.

 

 

Walk-through Discussion

    1. Put two characters on the platform of the model and one on the far end of the lever.
    2. Slide the two characters down their wire onto the end of the lever.
    3. Now lift the other character off having him follow the copper wire path.

Richard wants to know how much potential energy his cat has when it climbs to the top of the tree near his house. The tree is 15 meters high and the cat has a mass of 5 kilograms. How much potential energy does the cat have?

PE = mgh

PE = (5 kg)(9.8 m/s2)(15 meters)

PE = (5 kg)(147 m2/s2)

PE = 735 kg m2/s2 or 735 joules

What it Leads Up To

Potential energy leads up to:

 

Potential Energy

Content Worksheet

  1. Potential energy is __________ energy.
  2.  

  3. __________ is one thing that causes potential energy.
  4.  

  5. An object has potential energy if it has ___________.
  6.  

  7. ________, ________, and __________ affect the amount of potential energy in an object.
  8.  

  9. The formula for potential energy is ____________.
  10.  

  11. __________ must be shown with potential energy problems.
  12.  

  13. The change in potential energy is _________ to the opposite of the change in kinetic energy.
  14.  

  15. Gravitational acceleration is a ___________.
  16.  

  17. An object potential energy at the __________ of a fall equals an objects kinetic energy at the __________ of a fall.
  18.  

  19. Write down one real world example of potential energy.

 

Applications Worksheet

  1. John has an object suspended in the air. It has a mass of 50 kilograms and is 50 meters above the ground. How much work would the object do if it was dropped?
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  3. Mrs. Jacobs dropped an object from 10 meters. She knows it did 50 joules of work. How much did it weigh?

 

 

 

Potential Energy

Content Worksheet

Answer Key

  1. stored
  2.  

  3. gravity
  4.  

  5. height
  6.  

  7. mass; gravity; height
  8.  

  9. PE = mgh
  10.  

  11. units
  12.  

  13. equal
  14.  

  15. constant
  16.  

  17. start; end
  18.  

  19. answers will vary

 

Potential Energy

Applications Worksheet

Answer Key

  1. Solution: 24516.375 joules

PE = mgh

PE of the object is (50 kg)(9.80655 m/s2)(50 m)

PE = (2500 kg m)(9.80655 m/s2)

PE = 24516.375 kg m2/s2 or 24516.375 joules

If it was dropped it could do 24516.375 joules of work.

 

 

 

  1. Solution: .5 kilograms

PE = mgh

PE of the object is 50 joules

50 kg m2/s2 = m(9.80655 m/s2)(10 m)

Solve for m

5 kg m/s2 = (9.80655 m/s2)m

m = .5098 kg

The mass of the object was about .5 kilograms.