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#1
I am unsure on how to do this question relating to moments

A 200m bridge span is supported at both ends. The span weighs 100 tonnes. A 30tonne bus is 50m from one end of the span. Calculate the supporting force holding the bridge up at the end nearer the bus. Please give your answer to 2 significant figures.
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6 months ago
#2
(Original post by BurgerTitan00)
I am unsure on how to do this question relating to moments

A 200m bridge span is supported at both ends. The span weighs 100 tonnes. A 30tonne bus is 50m from one end of the span. Calculate the supporting force holding the bridge up at the end nearer the bus. Please give your answer to 2 significant figures.
Hi BurgerTitan00,
For this question you should use moments equations. Set A as the support closer to the bus and B as the one on the other side.
Then you should set B as a pivot and therefore: (since moments = force x perpendicular distance)
(100Tg x 100m) + (30Tg x 150m) = (Force of A x 200m)
(Also the reason why the 100 tonnes acts at a distance of 100m is because it is the centre of mass and it is assumed that the span is a uniform span) (Also T = 1x10^3 Kg and I think you need to convert in this question!)
This is the anticlockwise moments = clockwise moments. And g=9.8 as you need to use the weight of the objects, not the masses, which is confusing as it says "weighs" so you just need to be careful with that.
Now if you divide both sides by 200 you should have the Force of A which should be 710,500 N
Which is 710 kN (2sf). (Hopefully this is helps!)
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