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# M1 question watch

1. on exam questions, when it says something remains in equilibrium, how do you know which side it goes on? e.g in this question, which side on the plank does the man (of mass 80kg) go on?
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2. it depends if he is i.i.d (uniformly and identically distributed)
3. (Original post by Phenylethanone)
how do you know if he is uniform or not?
use the formula
4. (Original post by Phenylethanone)
on exam questions, when it says something remains in equilibrium, how do you know which side it goes on? e.g in this question, which side on the plank does the man (of mass 80kg) go on?
I think this is how you would do it, I assumed that the rod was on the at the point of tilting.

5. (Original post by Phenylethanone)
on exam questions, when it says something remains in equilibrium, how do you know which side it goes on? e.g in this question, which side on the plank does the man (of mass 80kg) go on?
You don't know which side it goes on, but on the sketch it wont matter. You call the distance you want to find "x" generally, as its easiest to just find x and then finish the question there.
Draw a good diagram to help.
For these type of questions you want to Resolve forces upwards (by N2L) and the forces will balance because it remains in horizontal equilibrium, and then take moments about a point, normally about the point from which you label the distance (so in this case, A) to make calculations easier.
We know:
The distance of Centre of Mass of the rod (it is uniform) and the weight (40g) - in the question.
The reaction at each pivot - we are told to call them R
The weight of the man (80g)

Note: The rod is NOT at the point of tilting as assumed above, it hasn't told us that in the question so there is no reason to assume that. Besides, both the reactions are told to be equal (R Newtons) so if it were at the point of tilting about pivot A, then this reaction would be 0, and hence so would C, so they wouldn't be equal (a contradiction) but dont worry too much about this - just write down what you are told and apply the standard techniques..

So, it doesn't matter whether the man stands on the right or left of pivot C, just draw him at one position and label this distance from A: x. If x< 3 then he will stand on the left of C, if it turns out that 3 < x < 4 then he will be on the right, do the maths to work out which one it is! It doesn't matter too much about the sketch...

Let me know how it goes and I can help further..

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