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ENERGY
Energy is the ability to do work. Energy is a scalar quantity.
The s.I.unit of energy is joule. Energy can also be measured using other units. The units are obtained from the combination of the unit of each quantities that make up the formula the energy.
Form Of Energy:
Energy is classified into two forms:
- Potential energy
- Kinetic energy
Potential Energy:
Potential energy is the type of energy possess by any object that is at rest or a stationary object. The unit of potential energy is Joule.
potential Energy P.E = mass x height x acceleration due to gravity
Potential Energy P.E = m x h x g
Examples:
- Calculate the potential energy of a mango fruit at the top of a tree 12.3m high if the mass of the mango is 0.25 kg. ( g = 9.8 m/s² )
Solution:
Data given in the question:
Mass = 0.25kg, height = 12.3 m, g = 9.8 m/s²
Formula: P.E = m x h x g
Substitution: P.E = 0.25kg x 12.3m x 9.8m/s²
Potential Energy = 30.135 Joules
2. An object of mass 10.25kg has 26.3 J of energy at a particular height. Calculate the height. ( g = 9.8 m/s² )
Solution:
Data given in the question:
Mass = 10.25 kg, P.E = 26.3 J, g = 9.8 m/s², h = ?
Formula: P.E = m x h x g
Substitution: 26.3 = 10.25 x h x 9.8. Make h the subject of the formula.
h = 26.3 / ( 10.25 x 9.8 ).
h = 0.26 meters
Kinetic Energy K.E:
Kinetic energy is the type of energy that is process by a moving object. The unit of kinetic energy is Joule. The symbol of kinetic energy is K.E. the symbol of Joule is J.
Kinetic Energy K.E = ½ x mass x Velocity²
Kinetic Energy = ½ x m x V²
Remember that, Velocity = distance / time
therefore, K. E = ½ x mass x ( distance / time )²
Examples:
1. Calculate the K.E of a car of mass 12.5 kg if the car moves at the speed of 5 m/s.
Solution:
Data given in the question:
Mass = 12.5 kg, speed/ velocity = 5 m/s
Formula: Kinetic. Energy = ½ x m x V²
Substitution: Kinetic Energy = ½ x 12.5 x 5²
Kinetic Energy = 156.25 Joules
- The Kinetic Energy of a car is 251 J. I the mass of the car is 1.75 kg, calculate the velocity of the car.
Solution:
Data Given In The Question:
Mass = 1.75 Kg, K. E = 251 J
Formula: K.E = ½ x m x V
Substitution: 251 = ½ x 1.75 x V².
Then Make Velocity Subject Of The Formula. Then,
Velocity² = ( 251 x 2 ) / 1.75.
Velocity ² = 304 / 1.75 = 173.714
Velocity² = 173.714
Velocity = √ 173.714
Velocity = 13.180 m/s
Conservation Law Of Energy:
The conservation law of mechanical energy states that in an isolated system, the total energy of the system cannot be created nor destroyed, but can only be transformed from one form into another. Of it states that the total energy content of a system remain constant.
The conservation law of mechanical energy can be explained using the following:
- motion of object that is falling freely under the influence of gravity
2.motion of object that is undergoing simple harmonic motion