Study Materials

NCERT Solutions for Class 9th Science


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Chapter 11. Work and Energy

Text-book Questions




Work and Energy


Que. – Define 1 J of Work?

Ans. – When a force of 1 N moves a body by a distance of 1 m in its own direction is equal to 1 j . It is said to be work has been done.

Que. – What is kinetic energy?

Ans. – The energy possessed by a body by virtue of in motion is called kinetic energy.

            Kinetic Energy of a Body = ½ mv2

            Examples : - Moving objects like Bullet, Falling water, etc. 

Que – What is Power? Write it’s S.I unit.

Ans. – Power is the rate of doing Work or the rate of utilizing energy. The power of an agent may vary with time. Power is denoted by English alphabet P. And its S.I unit is Watt.

Que. – Write two conditions for work to be done.

Ans. – (a)  A force should act on an abject.

  1.  the object must be displaced.

Que. – What is work?

Ans. – When the force acts in the direction of displacement is said to be work has been done. It is equal to the product of the force and displacement.

           Work done = force ´ displacement.

Que. – S. I unit of work.

Ans. – Joule (J)

            1 KJ = 1000J

Que. – What is Potential energy?

Ans. – The Potential energy possessed by the object is the energy present in it by virtue of its position or configuration. Such a energy is called Potential energy.

            Potential energy = mgh

            Examples – Pulled rubber band, stored water on height, Pulled spring, an arrow and stretched string on bow etc.

Que.  -  Write the law of conservation of energy.

Ans. – Energy can only be converted from one form to another. It can neither be created nor destroyed. The total energy before and after the transformation remains the same. This law is valid in all situation and transformation. That is called the law of conservation of energy. r

Que. – What is mechanical energy?

Ans. -  The sum of kinetic energy and Potential energy of an object is its total Mechanical energy.

Que. – On which factors the done work on an object is depended?

Ans. – There are two factors:

  1. Value of applied force (f)
  2. Value of total displacement (s)

Que. – What is S.I Unit of commercial Energy?

Ans. – Kw/h (Kilowatt/hour )

Que. – Define 1 unit of commercial Energy.

Ans. – The consumption of electric energy by 1 kilowatt in an hour is called 1 unit.

Que – What is transformation of energy?

Ans. – When a kind of energy converts into another kind of energy is called transformation

           of energy.


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