Nota Physics Vol 4 l Six Chap 4( Work,Energy, Power)

WORK,ENERGY AND POWER

WORK AND ENERGY

If the force is constant

Unit of work is the Joule ( J ), where 1 J = (1 N ) ( 1 m ) = 1 Nm

If the force is not constant

Work done by Expanding or Compressing a gas

POTENTIAL ENERGY AND KINETIC ENERGY

LEARNING OUTCOMES

1. Derive and use the formula: Potential Energy ( U ) = mgh, near the surface of the Earth.

2. Derive the formula: Kinetic Energy = ½ mv 2 .

3. State and use the Work-energy theorem.

4. Apply the Principle of conservation of energy in situations involving kinetic and potential energy.

Change K.E = Work done

Gravitational Potential Energy

Elastic Potential Energy

2

0 2

1

,

keUdekeU

e

UkekeF

e

UF

UKeFW

e


From the principle of t conservation of energy

This value is known as the elastic potential energy, i.e energy stored in thespring.

Since, F = ke, then

W= ½ ke2.


Conservation of Energy

MECHANICAL ENERGY

CONSERVATION OF ENERGY

DERIVATION THE FORMULA

mghmv 22

1

Work-energy Theorem

The work done by the net force of an

object is equal to the change in the

Kinetic Energy.

PRINCIPLE OF CONSERVATION OF ENERGY

Principle of conservation of energy –

States that the energy cannot be created or destroyed but can be converted from

one form to another form of energy.

The total energy which is equal to the sum of gravitational potential energy and kinetic energy is constant.

KUKU

KUE

KUE

0

This equation shows that the gain in gravitational potential energy is equal to theLoss in kinetic energy.

UK

PROBLEMS ABOUT WORK AND ENERGY

PROBLEMS ABOUT CONSERVATION OF

ENERGY

Power and Mechanical Efficiency

LEARNING OUTCOMES

1. Derive and use the formula; P = Fv2. Use the concept of Efficiency to solve problems

Power and Mechanical Efficiency

Example:

THE END

Nota Physics Vol 4 l Six Chap 4( Work,Energy, Power)

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