Consider question 2.
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$$$$I'm fairly confident I can answer each part of the question if we assume that the normal reaction forces are all concentrated at point C.
However, what is the justification for assuming the forces are concentrated at C in the first place? Why is this assumption reasonable, in the context of A Level modelling assumptions, and in real life?
Surely, there are 3 reaction forces- 1 going up each leg (preventing each leg from penetrating the skateboard), and 1 reaction force at C (see diagram below).
Am I right in that you can consider these three forces separately, and then prove that the model is effectively the same if all the reaction force is concentrated at C?
Thanks in advance for your help.