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How to tackle questions:
- draw a diagram and mark on all of the information you have been given and allocate the unknown a symbol - in an examination annotate the one on the paper.
- Identify the 'pivot point', 'turning point' or fulcrum - the point around which the whole system turns.
- Identify all of the forces acting. If they act through the support you can ignore them (as the support will produce a reaction force that will cancel them out!) - you may have to calculate some of the forces as they may not be given to you - you may be given 'mass' instead of weight, for example.
- calculate the perpendicular distance from each of the forces to the turning point - in advanced level questions you are rarely given the correct distance!
- work out all of the clockwise moments and add them together
- work out all of the anticlockwise moments and add them together
- state the Principle of Moments
- equate the clockwise and anticlockwise moments
- find the unknown
- check that this unknown is actually the value you are asked for in the question - sometimes they ask you for a distance that requires this information before you can do the last step!
- check that you have included the corect unit in your answer and that it is to the correct number of significant figures.
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