Edexcel International A Level Maths: Mechanics 1

Revision Notes

1.1.5 Modelling Assumptions

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Modelling Assumptions

What is modelling in Mechanics?

  • Mechanics uses modelling to solve problems in real life situations
  • We use assumptions to simplify real life problems in order to turn them into equations or graphs that can be solved
  • We will sometimes need to criticise or refine our assumptions to improve the model

1.1.5 Modelling Assumptions Diagram 2, downloadable Edexcel A Level Mechanics revision notes

What types of modelling assumptions are there?

  • Gravity is constant and vertical Air resistance is usually modelled as negligible and can be ignored
  • A smooth surface has no friction
  • A rough surface has a frictional force between the surface and any object that makes contact with it
  • A particle has negligible dimensions, therefore forces will all act on a particle at the same point
  • A rod or a beam should be treated as a long, rigid particle
  • A uniform object’s mass is distributed evenly
  • A light object has zero mass
  • An inextensible object cannot be stretched

Worked example

Two blocks, A and B are attached by means of a light inextensible string running over a smooth pulley. Block A has mass 0.7 kg and is accelerating along a smooth horizontal surface, block B has a mass 0.2 kg. Both A and B are modelled as particles. State how the following modelling assumptions can be used in your calculations:

a) A and B are both particles.

b) The string is light.

c) The string is inextensible.

d) The pulley is smooth.

e) The surface A is moving along is smooth.

1-1-5-worked-example-solution

Exam Tip

Make sure you fully understand the definitions of all the words in this section so that you can be clear about what your exam question is asking of you.

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