can I have the notes of class 9 physics
work and energy
Answers
Answer:
Topics in the Chapter
• Introduction
• Work
→ Condition for work to be done
→ Conditions when work is not done
→ Unit of Work
• Negative, positive and Zeo Work
• Energy
• Forms of Energy
→ Mechanical Energy
→ Kinetic Energy
• Potential Energy
• Transformation Energy
• Law of conservation Energy
• Free fall of a Body (Energy Conservation)
• Power
→ Unit of Power
• Commercial unit of Power
• Solved Numericals
Introduction
→ The energy for the ‘life processes’ comes from food. Activities like playing, singing, reading, writing, thinking, jumping, cycling and running requires energy.
Work
→ For doing work, energy is required.
• In animals, energy is supplied by food they eat.
• In machine, energy is supplied by fuel.
Why sometimes not much work is done inspite of working hard?
→ Reading, writing, drawing, thinking,analysing are all energy consuming. But in scientific manner, no work is done in above cases.
→ Example: A man is completely exhausted in trying to push a rock (wall), but work done is zero as wall is stationary.
→ A man standing still with heavy suitcase may be tired soon but he does no work in this situation as he is stationary.
When force is applied on the wall, the wall doesn't move. Therefor, no work is done here.
• Work is said to be done when:
(i) a moving object comes to rest.
(ii) an object at rest starts moving.
(iii) velocity of an object changes.
(iv) shape of an object changes.
Scientific Conception of Work
→ Work is done when a force produces motion in a body.
→ Work is said to be done when a force is applied on a body and the body moves under the influence of force.
Condition of Work
(i) Force should be applied on the body.
(ii) Body should be displaced.
• Work is done when:
(i) A cyclist is pedaling the cycle.
(ii) A man is lifting load in upward or downward direction.
• Work is not done when:
(i) A coolie carrying some load on his head stands stationary.
(ii) A man is applying force on a big rock.
Work Done by a Fixed Force
→ Work done in moving a body is equal to the product of force and displacement of body in the direction of force.
Work = Force × Displacement
W = F × S
→ Work is a scalar quantity.
Unit of Work
→ Unit of work is Newton metre or Joule.
→ When a force of 1 Newton moves a body through a distance of 1 metre in its own direction, then the work done is 1 Joule.
1 Joule = 1 Newton × 1 metre
1 J = 1 Nm
• The amount of work done depends on the following factors:
(i) Magnitude of force: Greater the force, greater is the amount of work & vice-versa.
(ii) Displacement: Greater the displacement, greater is the amount of work & vice-versa.
Answer:
Refer to the attachment
