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# Year 12 work, energy and power

Date post:15-Nov-2014
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• 1. Work, Energy and Power

2. Energy:
Energycanneitherbecreatednordestroyed.
It comes in manyforms:
Kinetic
Potential (gravitational, chemical, elastic)
Nuclear
Electric
Solar
3. Work and Energy:
If an object has energy, itcan do work.
Workproducesenergy.
4. Work:
Workisdonewhen a force moves an objectthroughsome distance.
No workisdonewhen the movement
isat right angles to the force.
(for instance no workisdonewalkingwith a
heavy bag at a constant heightbecausegravity
is 90 to the distance the bag moves through)
5. Work:
The work done when moving an object some distance with a force is equal to:
=

6. Kinetic Energy:
Kinetic energy is the type of energy a moving object posesses.
=122
More mass moving at the same speed has more energy.
A faster moving mass has more energy.

mass
Kinetic energy
velocity
7. Gravitational Potential:
When a mass is lifted we do work against gravity, the force applied is the size of the weight (mg) and the distance is the change in height (h).
=
=
=h

mass
Potential energy
height
gravity
8. Elastic Potential:
When we were working with springs we were applying a force to extend/compress them. We were doing work.
This work is stored in the spring as elastic potential energy ()
Note: This is the same symbol as gravitational potential so you
need to decide which one to use by identifying the context.
=122

extension
Elastic potential
Also equal to the area under a F vs. x graph.
Spring constant
9. Work and Power:
Power is defined as the amount of work done, divided by the time taken.
=
If two of the same mass are lifted to the same height, work done will be the
same. But if one mass is lifted faster than the other, that one will have
produced the greater power.
Power is measured in Watts (W)
(also Joules per second 1)

A 60 Watt lightbulbuses 60 Joules of energy per second
10. Collisions
As discussed, energycanbe "lost" in manyforms.
Kinecticenergyis not alwaysconservedin a collision, one objectmight speed up, the othermight slow down.
In an elastic collision no kineticenergyislost.
In an inelastic collision energyislost (to sound, heat, deformation etc.)
11. Elastic vs. Inelastic

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