medium difficulty5 min

Potential Energy

Potential energy is the energy possessed by a body due to its position or configuration. In this chapter, gravitational potential energy is mainly used.

In one line: Height stores energy against gravity.

Practice This Concept

Understand it

When an object is raised above a chosen reference level, work is done against gravity and energy is stored as gravitational potential energy. The value depends on mass, gravitational acceleration, and height from the reference level.

Example

Water stored in a tank on the roof has gravitational potential energy because it is at a height.

Rule to remember

PE = mgh, where m is mass in kilogram, g is gravitational acceleration in m/s², and h is vertical height in metre.

PE is measured in joule.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1A 2 kg bag is lifted 3 m.
2Taking g = 10 m/s², PE = mgh = 2 × 10 × 3 = 60 J.

Method you can reuse

Identify mass, take g as given or 9.8/10 m/s² as instructed, identify vertical height from reference level, multiply m × g × h, and write joule.

Visual tip

A vertical height diagram from reference level to object can help prevent path-length mistakes.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does a book kept on a high shelf have gravitational potential energy?

Think first, then show answer

The book has gravitational potential energy because work has been done to raise it against gravity, and it is at a height above a chosen reference level.

Common wrong answer

Using horizontal distance instead of vertical height.

Why it loses marks: Gravitational potential energy depends on height against gravity.

Don't mix this up

Students sometimes use total height from the ground even when the question gives a different reference level.

Exam tip

Read the reference level carefully. Height in mgh means vertical height from the chosen level, not distance travelled along a path.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Students are asked to calculate gravitational PE, compare PE at different heights, or explain stored energy in raised objects.

1
Enough for 1 mark
Potential energy is the energy possessed by a body due to its position or configuration. In this chapter, gravitational potential energy is mainly used.
2
Add for 2 marks
Example: Water stored in a tank on the roof has gravitational potential energy because it is at a height.
3
Add for 3 marks
When an object is raised above a chosen reference level, work is done against gravity and energy is stored as gravitational potential energy.

MCQ Quiz

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