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**Physics, Astronomy & Cosmology / Re: What are the reactions at P and Q?**

« **on:**27/08/2013 17:56:17 »

Sorry, I couldn't find a neat triangle to illustrate the support points on the drawing program! Anyway I think the diagram is pretty obvious.

You (or whoever posed the question in the first place) clearly haven't fully grasped the notion of mass and weight. The question talks rather loosely about weights in kilograms. Weight is a force, so the reaction force is calculated in the same units and there is an inherent assumption that we are talking about "kilogram force", i.e. the gravitational force mg on a 1 kg mass m. Since g was not specified, we can't assume a value, so we can't report the answer in newtons. It would be a lot less on the moon, or even on top of a mountain on earth, whereas the kilogram forces would be exactly as calculated.

You (or whoever posed the question in the first place) clearly haven't fully grasped the notion of mass and weight. The question talks rather loosely about weights in kilograms. Weight is a force, so the reaction force is calculated in the same units and there is an inherent assumption that we are talking about "kilogram force", i.e. the gravitational force mg on a 1 kg mass m. Since g was not specified, we can't assume a value, so we can't report the answer in newtons. It would be a lot less on the moon, or even on top of a mountain on earth, whereas the kilogram forces would be exactly as calculated.