Potential Energy || Work and Energy || in Hindi for Class 9

In this Science (Physics) video in Hindi for Class 9 we discussed on the potential energy of a body. We also derived the expression for the gravitational potential energy. This is a topic from Chapter 11 - 'Work and Energy' for class 9th from NCERT.

Potential energy is the energy possessed by a body due to its position / height.

Gravitational potential energy of a body of mass m situated h height from the ground is said to be mgh [here gravitational potential energy of that body at ground is considered to be zero]

When we pull the string of a bow, we do not observe any kinetic energy. But when we release the string, the arrow gets kinetic energy. But what happens to the work we do, when we pull the string. The energy is stored in the bow and this energy is known as the potential energy (more precisely, elastic potential energy).

In the above situations, the energy gets stored due to the work done on the object. The energy transferred to an object is stored as potential energy if it is not used to cause a change in the velocity or speed of the object. You transfer energy when you stretch a rubber band. The energy transferred to the band is its potential energy. You do work while winding the key of a toy car. The energy transferred to the spring inside is stored as potential energy. The potential energy possessed by the object is the energy present in it by virtue of its position or configuration.

Similarly, when we lift a body to a height, we do not observe any kinetic energy. But when we release the body, it gets kinetic energy. When we lift the body, the energy is stored as potential energy (more precisely, gravitational potential energy).

An object increases its energy when raised through a height. This is because work is done on it against gravity while it is being raised. The energy present in such an object is the gravitational potential energy. The gravitational potential energy of an object at a point above the ground is defined as the work done in raising it from the ground to that point against gravity.

Consider an object of mass, m. Let it be raised through a height, h from the ground. A force is required to do this. The minimum force required to raise the object is equal to the weight of the object, mg. The object gains energy equal to the work done on it. Let the work done on the object against gravity be W. That is,
work done, W = force × displacement
or, W = mg × h
or, W = mgh
Since work done on the object is equal to mgh, an energy equal to mgh units is gained by the object. This is the potential energy (EP) of the object.
So, Ep = mgh

It is important to note that the work done by gravity depends on the difference in vertical heights of the initial and final positions of the object and not on the path along which the object is moved.

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🔴 Click here to watch the whole playlist on Chapter 11 : 'Work and Energy' for Class 9 :

   • Work and Energy (Introduction) || in ...  

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