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# M1 moments question watch

1. Hey!

I'm having a little trouble with this moments question from my textbook:

A non-uniform plank AB has length 5d and mass 8m. It is in equilibrim in a horizontal position resting on supports at the points P and Q where AP = 2d and AQ = 4d. A parcel of mass 6m is placed on the plank at B. The plank is on the point of tilting about Q. By modelling the plank as a rod and the parcel as a particle, calculate the distance of the centre of mass of the plank from A.

I am drawing the diagram but I do not understand where the centre of mass would be placed.
Could someone help me out?
Thanks
2. (Original post by lulu1997)
Hey!

I'm having a little trouble with this moments question from my textbook:

A non-uniform plank AB has length 5d and mass 8m. It is in equilibrim in a horizontal position resting on supports at the points P and Q where AP = 2d and AQ = 4d. A parcel of mass 6m is placed on the plank at B. The plank is on the point of tilting about Q. By modelling the plank as a rod and the parcel as a particle, calculate the distance of the centre of mass of the plank from A.

I am drawing the diagram but I do not understand where the centre of mass would be placed.
Could someone help me out?
Thanks
Assume the distance from A to the centre of mass is x.
Take moments around Q, and solve the equation

8mg(4d-x) - 6mg(d) = 0

Reaction force at P = 0 because it's on the point of tilting

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Updated: December 2, 2014
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