work energy and power

1. WORK ENERGYAND POWER

2. Work
Work is said to be done only when a body undergoes displacement
under the action of a force.
Work done W=Fs joule

3. Work done against gravitational force
We have ,
W=Fs
When a body is raised through a height ‘h’
S=h
As per Newton’s Second law of motion ,
F=mg
Then, W = mgh
Work done against gravitational force is mgh.

4. Types of work
Positive work Negative work Zero work
Displacement is along
the direction of
applied force
e.g. work done by
gravity on a freely
falling body.
Displacement is
opposite to the
direction of applied
force.
e.g. work done by
friction.
Displacement is zero.
e.g. work done on
pushing a rigid wall.

5. Energy
Energy is the capacity to do work
Unit of energy is joule.
Types of energies:
Mechanical energy
Heat energy
Electrical energy etc.

6. Types of mechanical energy
Kinetic energy(K) Potential energy(U)
Energy possessed by a body by
virtue of its motion.
K=(1/2)mv2
Energy possessed by a body due
to its position.
U=mgh

7. Law of conservation of energy
Energy can neither be created nor be destroyed .
One form of energy can only be converted to another form.

8. Power
Work done per unit time or rate of doing work is power.
Power , P=W/t
Unit is J/s

9. Horse power
In the early days horses where used for pulling carts and other
purposes.
A horse power or 1 HP is the power of a horse.
1HP=746W