For those of you that don’t do mechanics, walk away, nothing to see here. As explained in the A-level stuff section to your top right I don’t have a maths section, so I’ll put this material here.

Basically, in mechanics, almost every paper asks a question or two about mathematical modelling, and requires a bit of common sense and awards a mark or two. I don’t have common sense, so if you’re on mutual grounds with me then you might want to know the general answers, and they are as follows:

• If it asks about how you’ve used the fact that the string is light, tensions will be the same for the two particles.

• If it asks about how you’ve used the fact that the the string is inextensible, acceleration will be the same for the two particles.

• Asking about what it means for the string to be light, mention that it has no weight.

• When asking about how a model is unrealistic or what refinements can be made for kinematics, mention air resistance or possibly the ‘spin’ of the particle (use your head).

• If it asks what it means that a beam is uniform, the weight acts at the midpoint of the beam.

• If it asks what it means for something to be a particle on a beam, mention that its weight acts precisely at that point.

• When asking about what it means for the plank or beam or whatever to be a rod, it means it’ll remain a straight line/rigid.

I think that’s correct, don’t kill me if I’m wrong. I got them from the mark schemes, and compiled them on this document:

mechanics_models.pdf |