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P1.2 - Work & Energy
Work & Energy - OCR AS Physics
| Question | Answer |
|---|---|
| Define work done: | Work done = force x distance moved in the direction of the force |
| Define power: | Work done per second. |
| What is the principle of conservation of energy? | Energy cannot be created or destroyed. It can only be converted from one form to another. |
| How do you work out efficiency? | Useful output/total input x 100% |
| What do sankey diagrams show? | Energy input and output. |
| What does Hooke's law state? | Extension is proportional to force. |
| What is the equation for hook's law? | F = ke |
| When does hooke's law stop working? | When the load is great enough, the elastic limit. If you increase the load past the elastic limit the material will be permanently deformed. |
| What is an elastic stretch? | The material will return to it's original shape once the forces are removed. |
| What is a plastic stretch? | The material will be permanently stretched. |
| A stress causes a ...... | A stress causes a strain. |
| How do you work out the stress of an object? | Force/Area |
| How do you work out the strain of an object? | extension/original length |
| If af stress is big enough to break the material, what is it called? | The Breaking Stress. The atoms are completely separated. |
| What is elastic strain energy? | The energy stored in a stretched material. This is given by the area under a force-extension graph. |
| What equation gives the energy stored in as stretched wire? | 1/2 x Force x extension OR 1/2 x k x extension^^2 |
| How do you work out young's modulus? | Stress/Strain. It is also equal to the area under a stress/strain graph. |
| What does the stress strain graph for a ductile material look like? | It will curve. |
| What does the stress strain graph for a brittle material look like? | It is a straight line so will not curve. |
| Rubber will return to it's original length when the load is removed, what is this behaviour called? | Elastic Behaviour. |