Video Lesson

Lesson objective

Dear learners,

At the end of the lesson you will be able to

• Define mechanical energy.
• State the law of conservation of mechanical energy.
• Apply the law of conservation of mechanical energy to solve problems

Brainstorming question

If you drop a ball from the top of the whiteboard, discuss the energy conversion that takes place as the ball falls down

Key Terms and Concepts

Conservation Of Mechanical Energy:

• The principle of conservation of mechanical energy is that energy can neither be created nor be destroyed but it can only be transformed from one form to the other. 
• Mechanical energy refers to the sum of potential energy and kinetic energy in an object that is used to do a particular work. 
• The principle of conservation of mechanical energy states that if an isolated subject in a system is subjected to conservative forces only, then the mechanical energy remains constant. 
• The potential energy of the system is highest when the bob reaches its maximum height, whereas the kinetic energy is zero.
• The kinetic energy is the largest at the mean position, whereas the potential energy is zero.
• The system has both kinetic and potential energy, the sum of which is constant, between these two extremes. 
• The law of conservation of mechanical energy states that in the absence of dissipative forces like air resistance and friction, the total mechanical energy of an object or system of objects remains unchanged.
• ΔME = 0
• ΔKE + ΔPE = 0
• (KE KEi) + (PE PE ) = 0
  • KE_i+ PE_i = KE_f+ PE_f

Example 6.1:

Example 6.2

For a baseball field, the distance between home plate and the center field wall is about 123m and the wall is 5m tall. If a player hits the ball at a level of 1m off the ground, an angle of 55^∘ above the horizontal, and a velocity of 40m/s, what is the total velocity of the ball as it passes over the center field wall at a height of 33m?

Neglect air resistance and assume g=10ms2

Simulation Conservation of energy

https://phet.colorado.edu/en/simulations/energy-skate-park-basics