Chapter-wise Notes Work, power and energy class 9

Work, power and energy

Work

Work is said to be done when a force is applied on an object and there is displacement produce in it.

work is done on the trolly

In this case, force is applied on the trolly and trolly get displace from its position, it means work is done the trolly.

 Or

work done on an object is the product of displacement and force.

 W=F.S

 Here, W is work done

F is force applied on an object

S is displacement produced in an object.

Unit of work done

It has unit Joule or  newton metre (Nm).

How to Define 1 Joule.

A  force of 1 Newton is applied on a body and 1 metre displacement is produced in a body then 1 joule of work is said to be done on the body.

 

Condition for work should be done

1.Force must be applied to a body.

2. Displacement must be produced in our body.

 

Work done by a force at an angle with  displacement

Force f is applied on a body and  theta angle between direction of displacement and force.

We know that

Cos θ = BC/AC

BC=AC Cos θ

BC =F Cos θ

Work done =Force * Displacement

 Work done=F Cos θ* S.

 Types of work done:-

1. Positive work done:- A work said to be positive when the force applied in displacement produce force is in the same direction.

2. Negative work done:- A work said to be  negative when the force applied in displacement produce force is in the opposite direction.

 

3. Zero work done:- A work said to be zero when the force applied in the direction perpendicular to displacement produced.

Energy

It is defined as the ability of a body to do a work.

Unit  it has unit Joule.

Different types of energies:-

1. Kinetic energy
2.  Potential energy
3. Chemical energy
4. Mechanical energy
5. Wind energy
6. Solar energy
7. Hydro energy etc.

Potential energy

It is defined as the energy possessed by a body due to its position, shape, size.

It has unit Joule.

 

 

Derivation

 

Kinetic energy:-

It is the energy possessed by an object due to its motion is called kinetic energy.

It has unit joule.

Mechanical energy

The sum of kinetic energy and potential energy is called mechanical energy.

Law of conservation of energy 

It states that the energy can neither be created nor be destroyed can be converted only from one form to another form.

The total energy of the system remains constant.

Kinetic energy + potential energy= constant.

 

Derivation

 

Power 

The rate at which work is done by a force is called power.

Or

The rate at which energy is transferred by a body is called power.

Or 

The rate at which energy is consumed by an electrical device is called power.

It has unit watt or joule per second.

How to Define 1 watt?

When a 1 joule of work is done at the rate of one second then the power is said to be 1 watt.

Note:-

100 watt bulb means

It can consume 100 joules of energy in one second.

 Commercial energy

The energy which can be sold or bought which cannot be drive from cattle dunk or crop Residue, please call commercial energy.

 Commercial unit of energy

 

Commercial unit of energy is kilowatt hour.

 

Conversion of one kilowatt hour in joule

Energy = Power * time

1kWh=1kW*1h

1kWh=1000W*3600 s

1kWh=3600000J

1kWh=3.6*10⁶J