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Physics hw

A non-uniform plank of wood of length 80 cm is balance on a pivot.
We know I know that the position of the centre of gravity of the plank is 30 cm from the left-hand end.
The plank is now moved and rebalance as its midpoint using a five Newton weight placed 8 cm from the right-hand end.
Calculate the weight of the plank.
Working out would be great
Next question that follows is
Calculate upward force which is now Exerted by the triangular support
(edited 2 years ago)
For Part A,

If you draw out the plank with the center of mass acting at 30cm, the pivot at 40cm and the 5N weight at 72cm then you can see that the center of mass is 10cm from the pivot and the 5N weight is 32cm from the pivot. So in order to calculate F (The weight of the plank you can do
Clockwise Moment = Anticlockwise Moment
5N x 32cm = 10F
160Ncm = 10F
16N = F
Hence the weight of the plank is 16 Newtons

For Part B,
The upwards force would need to balance the forces acting on it hence as 16 + 5 is 21, the Upwards force provided by the pivot is 21N

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