1. Work and Energy

2. Prior knowledge
The meaning of energy efficiency and the need for economical energy use of resources.
The relationship between force and work.
The links between kinetic energy, potential energy and work.
2821 Forces and Motion module.

3. Law of conservation of energy
“Energy cannot be created or destroyed, only transferred from one form to another.”
This hugely important in the laws of thermodynamics.

4. Meaning…
In other words there is a set amount of energy in the universe.
In a system the energy input is equal to the energy output.
Useful work done will not equal the energy input as no system can be 100% efficient.

5. Work done
Work is done when energy is transferred from one system to another.
For a constant force:
W = Fs
Where W is the work done in Joules, F is the force applied in the direction of the movement and s is the distance moved.

6. Work done = energy transferred
Work done is equal to the energy transferred to the object in question.
Work done = energy transferred

7. Kinetic Energy
This is the energy possessed by a body in motion.
Can be thought of as the work required to accelerate the mass from rest to velocity v.
Ek = ½ mv2

8. Gravitational Potential Energy
This is the work done is transferring an object of mass m through a vertical height h.
Change in gravitational potential energy
ΔEp = mgΔh

9. Q1
An object of mass 0.30 kg is thrown vertically upwards and reaches a height of 8.0 m. Calculate:
Its final PE.
The velocity with which it must be thrown, neglecting air resistance.

10. Q2
A ball of mass 0.20 kg is dropped from a height of 10 m and rebounds to a height of 7.0 m. Calculate the energy lost on impact with the floor. Ignore air resistance.

11. Q6 The energy dissipated via friction.
A block of mass 6.0 kg is projected with velocity 12 ms-1 up a rough plane inclined at 45 degrees to the horizontal. If it travels 5 m up the plane, calculate:
The energy dissipated via friction.
The frictional force (you can assume this remains constant.)