Question

Summarize the chapter work and energy in 2 page class 9​

Answer 1

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Answer 2

Question:⤵

Summarize the chapter work and energy in two pages in notebook. Class9

Answer:⤵

Work And Energy Class 9 CBSE Notes -

Work Done

• Work done on an object is defined as the product of the magnitude of the force acting on the body and the displacement in the direction of the force. W = F.s
• If a force acting on a body causes no displacement, the work done is 0. For example, pushing a wall.

Energy

• Energy is defined as the ability to do work. Its unit is the same as that of work.
• SI unit of energy or work = Joule (Nm) or Kgm2s−2.
• Energy has different forms: Light, heat, chemical, electrical or mechanical.

Mechanical energy is the sum of:

(i) Kinetic energy (K.E)

(ii) Potential energy (P.E)

Kinetic Energy

Objects in motion possess energy and can do work. This energy is called Kinetic Energy.

F = ma.

Also W = F.s

⇒ From the 2nd equation of motion v2−u2=2as,⇒ we get s = v2−u22a ⇒Substituting equation for work done by a moving body,⇒ we get W =m.a * v2−u22a

Or

⇒ Kinetic Energy = K.E= 12 mv2 (taking initial velocity u=0)

When two identical bodies are in motion, the body with a higher velocity has more K.E.

Work-energy theorem

• The work-energy theorem states that the net work done by a moving body can be calculated by finding the change in KE.
• ⇒ W net = KE final − KE initial
• ⇒ Wnet= 12 m[v2−u2]

• Factors affecting kinetic energy

Mass

Velocity

Momentum

Potential Energy

• Energy can get stored in an object when work is done on it.
• For example, stretching a rubber string. The energy that is possessed by a body by virtue of its configuration or change in position is known as Potential Energy.

Types of Potential Energy.

• The potential energy of an object at a height.
• When an object is raised to a certain height, work is done against gravity to change its position.
• This energy is stored as Potential Energy.
• ⇒W = F.s
• ⇒F = ma
• In the case of increasing the height, F = mg
• Therefore , W (P.E) = mgh
• ⇒ ΔPE=mg(h final−h initial)

Law of Conservation of Energy

• Law of conservation of energy states that energy can neither be created nor destroyed, but can be transferred from one form to another.
• The total energy before and after the transformation remains constant.
• Total energy = KE + PE
• For example: consider a ball falling freely from a height.
• At height h, it has only PE = mgh.
• By the time it is about to hit the ground, it has a velocity and therefore has KE= 12 mv2.
• Therefore, energy gets transferred from PE to KE, while the total energy remains the same.

Power

• The rate of doing work or the rate of transfer of energy is called power.
• It is denoted by P
• ⇒ P = Wt
• SI unit is Watt (Js−1).
• Average power = Total energy consumed/Total time taken.
• The commercial unit of power is kWh i.e. energy used in 1 hour at 1000 Joules/second.
• 1kWh=3.6×106J

Explanation:⤵

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