CBSE – 9th Standard Science


Class 9 Question Bank Chapter 11 – Work and energy

Q1. What is the scientific conception of work?

Ans. According to the scientific concept work is when a force should act on an object, and the object must be displaced.

Q2. What do you mean by work done?

Ans. Work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force.

Q3. What is the unit of work?

Ans. The unit of work is newton meter (N m) or joule (J).

Q4. What do you mean by 1 joule?

Ans. Thus 1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.

Q5. What is Energy?

Ans. An object having a capability to do work is said to possess energy. The object which does the work loses energy and the object on which the work is done gains energy.

Q6. How is the energy of an object measured?

Ans. The energy possessed by an object is thus measured in terms of its capacity of doing work.

Q7. What is one KJ(kilo joule)?

Ans. 1 kJ(kilo joule) equals 1000 J(joule).

Q8. What are the types of energy?

Ans. The various types of energy are mechanical energy (potential energy + kinetic energy), heat energy, chemical energy, electrical energy and light energy.

Q9. What is Kinetic energy?

Ans. Kinetic energy is the energy possessed by an object due to its motion.

Q10. What happens to the kinetic energy with respect to speed?

Ans. The kinetic energy of an object increases with its speed.

Q11. 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.

Q12. What happens to potential energy at a height?

Ans. An object increases its energy when raised through a height.

Q13. Why an object increases its energy when it is raised?

Ans. 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.

Q14. What do you mean by Law of Conservation of energy?

Ans. According to this law, 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.

Q15. What is Mechanical energy?

Ans. The sum of kinetic energy and potential energy of an object is its total mechanical energy.

Q16. What happens during the freefall of an object?

Ans. We find that during the free fall of the object, the decrease in potential energy, at any point in its path, appears as an equal amount of increase in kinetic energy.

Q17. What is Power?

Ans. Power is defined as the rate of doing work or the rate of transfer of energy.

Q18. What is the unit of Power?

Ans. The unit of power is watt.

Q19. What is 1 watt?

Ans. 1 watt is equal to 1 joule/second.

Q20. What is the commercial unit of Energy?

Ans. The commercial unit of energy is called kilowatt hour (kW h).

Q21. How much is 1 kwh?

Ans. 1 kW h is the energy used in one hour at the rate of 1000 J s-1 (or 1 kW). 1 kW h is equal to 3.6 x 106 J.

Q22. What do you mean by 1 unit?

Ans. 1 unit means 1 kilowatt hour.

Try these:-

When do we say that work is done?

Write an expression for the work done when a force is acting on

an object in the direction of its displacement.

Define 1 J of work.

A pair of bullocks exerts a force of 140 N on a plough. The field

being ploughed is 15 m long. How much work is done in ploughing the length of the field?

An object of mass 15 kg is moving with a uniform velocity of 4 m s–1. What is the kinetic energy possessed by the object?

Find the energy possessed by an object of mass 10 kg when it is at a height of 6 m above the ground. Given, g = 9.8 m s–2.