Quick revision notes for CBSE Class 9 Science Chapter 10 Work and Energy! Get important one-liner questions and answers covering work, energy, power, kinetic and potential energy, and law of conservation of energy.
Q1. What is work in science?
Ans. Work is said to be done when a force applied on an object causes displacement.
Q2. Write the formula for work done.
Ans. Work done (W) = Force (F) × Displacement (s).
Q3. What is the SI unit of work?
Ans. The SI unit of work is joule (J).
Q4. Define 1 joule of work.
Ans. Work done is 1 joule when a force of 1 newton displaces an object by 1 meter in the direction of force.
Q5. When is the work done said to be positive?
Ans. Work is positive when force and displacement are in the same direction.
Q6. When is the work done said to be negative?
Ans. Work is negative when force and displacement are in opposite directions.
Q7. What is energy?
Ans. Energy is the capacity to do work.
Q8. What is the SI unit of energy?
Ans. The SI unit of energy is joule (J).
Q9. Name the two main types of mechanical energy.
Ans. Kinetic energy and potential energy.
Q10. What is kinetic energy?
Ans. Kinetic energy is the energy possessed by a body due to its motion.
Q11. Write the expression for kinetic energy.
Ans. Kinetic energy (Ek) = ½ mv², where m = mass, v = velocity.
Q12. What happens to the kinetic energy if the velocity is doubled?
Ans. Kinetic energy becomes four times.
Q13. What is potential energy?
Ans. Potential energy is the energy possessed by a body due to its position or configuration.
Q14. Write the expression for gravitational potential energy.
Ans. Potential energy (Ep) = mgh, where m = mass, g = acceleration due to gravity, h = height.
Q15. State the law of conservation of energy.
Ans. Energy can neither be created nor destroyed, it can only be transformed from one form to another.
Q16. What is the sum of kinetic energy and potential energy called?
Ans. It is called mechanical energy.
Q17. What is power?
Ans. Power is the rate of doing work or the rate of energy transfer.
Q18. Write the formula for power.
Ans. Power (P) = Work done (W) / Time (t).
Q19. What is the SI unit of power?
Ans. The SI unit of power is watt (W).
Q20. Define 1 watt of power.
Ans. Power is said to be 1 watt when 1 joule of work is done in 1 second.
Q21. What is 1 kilowatt (kW)?
Ans. 1 kilowatt = 1000 watts.
Q22. What is average power?
Ans. Average power is the total work done divided by the total time taken.
Q23. Give an example of energy conversion in a windmill.
Ans. In a windmill, wind energy is converted into mechanical energy.
Q24. What type of energy is stored in a stretched rubber band?
Ans. Potential energy.
Q25. What happens to the energy of a freely falling object?
Ans. Its potential energy converts into kinetic energy.
Q26. How much energy is consumed if a 500 W appliance runs for 2 hours?
Ans. Energy = Power × Time = 500 × 2 = 1000 Wh = 1 kWh.
Q27. Name a device where chemical energy is converted to electrical energy.
Ans. Battery.
Q28. How much work is done when displacement is zero?
Ans. Work done is zero.
Q29. Does a person holding a load without moving do any work scientifically?
Ans. No, because there is no displacement.
Q30. What is mechanical energy?
Ans. Mechanical energy is the sum of kinetic and potential energy of a body.
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