Question

How are kinetic energy and potential energy associated with the motion of any given object?

Answer 1

Kinetic energy

1. The amount of work done to move a body from one point to another point is called kinetic energy, i.e., the necessary work done to accelerate a body from rest is kinetic energy.
2. For a rested body, the kinetic energy is zero.
3. The energy produced in a body due to motion is kinetic energy.
4. Kinetic energy is defined by the form, $E_k=\frac{1}{2}m{v}^2$, where $m$ and $v$ are the mass and velocity of a body.

Potential energy

1. Potential energy is the energy stored within a body when it is at rest.
2. This potential energy is transferred to kinetic energy when the body will be in motion.
3. For a dynamic object, the potential energy is zero.
4. Potential energy is defined by the form, $E_p=mgh$, where $m$ is the mass of the body, $h$ is the height of the body and $g$ is the acceleration due to gravity.

Mechanical energy

1. It is the sum of kinetic and potential energy of a body.
2. Mechanical energy always remains constant.
3. So, for a body when kinetic energy decreases, potential energy increases and when potential energy decreases, kinetic energy increases.
4. 

Example

1. If we consider the example of an object dropped from a height $h$,
2. At the highest point the potential energy is maximum and kinetic energy is zero.
3. When the object reaches the lowest point, kinetic energy is maximum and potential energy is zero.
4. The graph shows the change in kinetic energy and potential energy, when an object falls from a height $h$