Introduction
Kinetic energy is the energy an object possesses due to its motion. It is one of the two main types of energy, the other being potential energy. In physics, the principle of conservation of energy states that energy cannot be created or destroyed but can be transformed from one form to another. This means that if you have a closed system, the total energy in that system will remain constant. Therefore, the initial energy of a system is equal to the final energy of the system. In this article, we will learn how to calculate kinetic energy using the conservation of energy principle.
Understand the Principle of Conservation of Energy
The principle of conservation of energy is a fundamental principle in physics. It states that energy cannot be created or destroyed but can be transformed from one form to another. This means that if you have a closed system, the total energy in that system will remain constant. Therefore, the initial energy of a system is equal to the final energy of the system.
Define the Variables
To calculate the kinetic energy of an object using the conservation of energy principle, you need to know the mass of the object and its initial and final velocities. The mass is represented by the letter ’m’ and the velocities are represented by ‘v1’ and ‘v2’.
Find the Initial Energy of the System
The initial energy of the system is the sum of the kinetic energy and potential energy of the object. If the object is at rest, the initial kinetic energy is zero. Therefore, the initial energy of the system is equal to the potential energy of the object, which is given by the formula PE = mgh, where ’m’ is the mass of the object, ‘g’ is the acceleration due to gravity and ‘h’ is the height of the object above the ground.
Find the Final Energy of the System
The final energy of the system is the sum of the kinetic energy and potential energy of the object at its final velocity. The potential energy of the object is still given by the formula PE = mgh. The kinetic energy of the object is given by the formula KE = (1/2)mv^2, where ’m’ is the mass of the object and ‘v’ is its final velocity.
Apply the Principle of Conservation of Energy
Since the initial energy of the system is equal to the final energy of the system, you can equate the two expressions for energy and solve for the final velocity. After solving for ‘v2’, you can then use the formula KE = (1/2)mv^2 to calculate the kinetic energy of the object.
Example Calculation
Suppose a 2kg object is dropped from a height of 10m. Using the principle of conservation of energy, calculate the kinetic energy of the object just before it hits the ground. Solution: The initial energy of the system is equal to the potential energy of the object, which is given by PE = mgh = (2)(9.81)(10) = 196.2 J. The final energy of the system is the sum of the kinetic energy and potential energy of the object just before it hits the ground. The potential energy is still 196.2 J. The final velocity of the object can be found using the equation PE + KE = Final Energy. Solving for KE, we get KE = Final Energy  PE = (1/2)mv^2, where ’m’ is the mass of the object and ‘v’ is its final velocity. After solving for ‘v’, we get v = 19.8 m/s. Finally, we can use the formula KE = (1/2)(2)(19.8^2) = 391.68 J.
Check Your Units
It is important to check your units when calculating kinetic energy using the conservation of energy principle. In the SI system, the unit of mass is kilograms (kg), the unit of velocity is meters per second (m/s) and the unit of energy is joules (J).
Practice Problems
To become proficient in calculating kinetic energy using the conservation of energy principle, it is important to practice solving different problems. Here are some practice problems to get you started:

A 1kg object is released from a height of 5m. Calculate its final velocity and kinetic energy just before it hits the ground.

A 5kg object is moving at a velocity of 10m/s. Calculate its kinetic energy.

An object of mass 3kg is moving at a velocity of 4m/s. What is its kinetic energy?
Conclusion
Calculating kinetic energy using the conservation of energy principle is a useful skill in physics. It involves understanding the principle of conservation of energy, defining the variables, finding the initial and final energies of the system, applying the principle of conservation of energy and checking your units. By following these steps and practicing with different problems, you can master this skill and solve problems involving kinetic energy with ease.